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Clickbait-Corrected p-Value

Clickbait-Corrected p-Value

https://www.xkcd.com/2001

https://www.explainxkcd.com/wiki/index.php/2001:_Clickbait-Corrected_p-Value

[Under a heading that says Clickbait-Corrected p-Value there is a mathematical formula. Below that is the description of the two used variables and what they mean:] Clickbait-corrected p-value: P CL = P traditional ∙ click(H 1 )/click(H 0 ) H 0 : NULL hypothesis ("Chocolate has no effect on athletic performance") H 1 : Alternative hypothesis ("Chocolate boosts athletic performance") click(H): Fraction of test subjects who click on a headline announcing that H is true

Clickbait is the practice of using deceptive or hyperbolic headlines to entice readers to click on a dubious or sensationalist news story, often with the purpose of generating site traffic and ad revenue. Randall uses the scientific controversy regarding the health effects of chocolate to humans as an example, as there is widespread misinformation on the health effects of chocolate online. In fact, there are no reliable studies to confirm any health effects while no medical authority has approved any health claims regarding chocolate. Hypothesis testing in statistics is a standard method to determine whether a particular hypothesis is supported by the data. For the topic given in this comic, a researcher might compare data on athletic performance with data on chocolate consumption by those athletes to determine whether the two trend together. By convention, the "null hypothesis" (denoted H 0 ) is that there is no correlation (e.g. chocolate doesn't affect athletic performance) while the "alternate hypothesis" (H 1 ) would be that they are correlated. (If the study consists of feeding chocolate to one of two identical groups and not the other, rather than tracking what they'd be eating anyway, then the alternative hypothesis can be strengthened to be that chocolate causes improved performance.) These sets are subjected to statistical tests which return a "test statistic". From that test statistic a "p-value" is calculated. The p-value indicates the probability of observing the obtained results (or any more extreme value), when the null hypothesis is true (e.g. chocolate has no effect on athletic performance). In other words, the p-value is an indicator as to the statistical significance and consequential reliability of the results affirming the "alternate hypothesis"( not the probability that the null hypothesis is correct ). It answers the question: If there is no correlation, how likely was it that I saw a correlation at least this big? Hence, if the p-value is low enough (by convention < 0.05), the null hypothesis is rejected, and we conclude that the alternate hypothesis is supported by the data (NOT that it is "correct" or "true"). In this comic, the p-value is corrected by a factor that takes clickbait into account. This factor has the effect of increasing the p-value if H 1 is more clickbaity than H 0 , and decreases the p-value if H 0 is more clickbaity than H 1 . This suggests that whatever clickers of clickbait believe, the reverse is likely to be true. Furthermore, this factor may be interpreted as normalisation for the inherent selection bias where the p-values for more clickbaity H 1 s tend to be lower than they should be and p-values for non-clickbaity H 0 s to be higher than they should be. For example, one explanation could be that for p-values that are on the cusp of significance, researchers may be more incentivized to fudge and adjust the data to get the p-value down if the H 1 is highly sensational, since the H 1 would make the research more likely to get published and attract attention. (See also FiveThirtyEight's article on p-hacking and this Stack Exchange question about p-hacking in the wild .) P-hacking has also previously already been associated with chocolate and media sensationalism. As the statistical results now depend on people's beliefs about the hypothesis, this could appear as far from actual science as one can get. However, in a way, it is more in tune with a quote by John Arbuthnot (one of the originators of the use of p-values) attributing variation to active thought rather than chance, "from whence it follows, that it is Art, not Chance, that governs." Randall applying that quote to the thoughts of the masses brings it in line with "Art". If this correction could be somehow enforced on the scientific world, it would have the effect of keeping the popular view of scientific results more in line with reality. Often one study will be performed that shows an exciting result, and consequently be sensationalised by the media prior to further studies to verify it. This is in part due to the conflicting interest of the scientific community and the media. The clickbait correction may aid a reader in exercising caution when interpreting sensationalist scientific discoveries in news media. Additionally, there can be a problem in some areas of science where more mundane results never undergo the third-party replication studies (see replication crisis , or perhaps are even never studied in the first place. The clickbait correction factor has the opposite effect on these more mundane topics, making it easier to demonstrate effects within them with a lower statistical barrier for entry, perhaps in the hope that more will get studied, published, and exposed to the public. Technically , the comic's depiction of null and alternative hypotheses is not entirely correct. As the alternative hypothesis (H 1 ) predicts that chocolate will improve performance (i.e., a one-tailed, directional hypothesis), the null hypothesis (H 0 ) should predict that chocolate will do nothing or make performance worse. In other words, the alternative hypothesis should be true if and only if the null hypothesis is false. For example, alternatively, if the H 1 were to say that chocolate will change performance (for better or worse; i.e., a two-tailed hypothesis) then H 0 should say that chocolate will do nothing . The title text refers to Bayesian statistics , a statistical technique which involves considering (before you see the new data) how likely you think it is that the hypothesis is true. (It is worth noting that the traditional statistical analysis described above, doesn't directly say anything about how likely the hypothesis is to be *true*. It simply assesses whether the data is consistent with the null hypothesis.) Under Bayesian analysis, you begin with a prior probability , or simply just "prior", which expresses how likely you think the alternate hypothesis is. Then after seeing the new data, you apply Bayes' theorem to *update* your belief about the hypothesis, and as a result you should then consider the hypothesis to be more likely (or less likely) than you considered it before. Bayesian statistics therefore recognizes that an extraordinary claim should require more evidence to convince you than a "reasonable" claim would. (Which is, arguably, sort of, the same point being made by the Clickbait-correction.) But also that *enough* evidence, perhaps gathered step by step over time, should be sufficient to convince you even of extraordinary claims. The technique can be hard to apply in science however, because of the difficulty in agreeing upon reasonable priors. Here it's suggested that an alternative "clickbayes factor" (a pun and portmanteau of clickbait and Bayesian) could be used to approximate hard to quantify priors. [Under a heading that says Clickbait-Corrected p-Value there is a mathematical formula. Below that is the description of the two used variables and what they mean:] Clickbait-corrected p-value: P CL = P traditional ∙ click(H 1 )/click(H 0 ) H 0 : NULL hypothesis ("Chocolate has no effect on athletic performance") H 1 : Alternative hypothesis ("Chocolate boosts athletic performance") click(H): Fraction of test subjects who click on a headline announcing that H is true

LeBron James and Stephen Curry

LeBron James and Stephen Curry

https://www.xkcd.com/2002

https://www.explainxkcd.com/wiki/index.php/2002:_LeBron_James_and_Stephen_Curry

NBA Playoffs DataDive LeBron James and Stephen Curry What makes these superstars so extraordinary? [The comic consists of several plots and tables, listed here from top to bottom, left to right.] Scatter plot of Social Security number vs Free throw percentage [Social Security numbers range from 000-00-0000 to 999-99-9999. No pattern discernable, aside from points being a bit denser in the middle of the plot. Stephen Curry is marked as a point on the right edge of the plot, corresponding to a high free throw percentage.] Scatter plot of 2018 points per game vs Average teammate APGAR score [APGAR scores range from 0 to 10. Pattern suggests a somewhat positive link between the two factors. LeBron James is marked as having a lot of points, but a low teammate APGAR score of approximately 2.1.] Shot map [Legend: grey dot for all players, black dot for Stephen Curry] [A diagram of a basketball court is shown with dots placed where players have taken shots at the goal. For the all players category the dots generally cluster next to the goal basket and in front of the three point line. Stephen has 3 dots next to the basket (one is behind it), but does cluster next to the three point line. He also has several dots on the other side of the playing field, and outside it, including three in the bleachers and one in the locker room.] Sandwiches eaten during play vs Win % [Sandwiches eaten range from 0 to 4. A plot that suggests no relation between the factors because practically all dots are in the zero sandwiches column. 2018 Warriors have one dot at around 60% and 4 sandwiches.] 2018 total points [A table listing teams and their points overall and "When net is within 15° of magnetic north". The rows for the Golden State Warriors and the Cleveland Cavaliers are highlighted, the latter showing an abnormally high score in the magnetic north column.] 2018 total points Overall When net is within 15° of magnetic north Golden State Warriors 9304 330 Houston Rockets 9213 268 New Orleans Pelicans 9161 219 Toronto Raptors 9156 341 Cleveland Cavaliers 9091 1644 Denver Nuggets 9020 280 [A table at the bottom:] Stephen Curry LeBron James Have you heard of him Probably Yes President during most recent game 7 loss Obama Bush Pog collection Large Staggeringly large Career average Fed interest rate 3.42% 4.41% Name Scrabble score 22 22 Best sport Basketball Basketball Height Over 6' Over 6' Retirement year 2027 Unknown Nate Silver FiveThirtyEight total rating (devised by Nate Silver to combine all metrics into a single stat) 37.4 31.8 86.6 This comic was posted the day after the second game in the 2018 NBA Finals between the Golden State Warriors (Stephen Curry's team) and the Cleveland Cavaliers (LeBron James' team). It is the fourth consecutive time the two teams faced each other at the finals, which is unprecedented in major sports leagues in North America. The Warriors won in 2015 and 2017, the Cavaliers won in 2016. At the time of the comic, the Warriors led the current series 2-0; which they eventually won.

At the time of this comic, the 2018 NBA Finals were going on, between the Cleveland Cavaliers and the Golden State Warriors with the Warriors leading 2 games to 0 in a best of seven series. At first glance, the comic looks like an in-depth analysis of two of the star players on those teams, LeBron James and Stephen Curry . The joke is that while comprehensive, all the statistics are completely meaningless - many of them are obviously false, and many don't show any correlation, and if there is one, it's extremely unlikely there is any causal link in there. The first graph includes a nine-digit Social Security number issued for US citizens which is typically not considered a metric related to athletic ability. As Social Security numbers are essentially random numbers ( until 2011 , there was a geographic correspondence for the first three digits), the graph shows only the free throw percentage of a large number of players, artificially spread vertically. Also note that Social Security numbers are not usually made public, barring security leaks. The second graph is a graph of 2018 points per game vs teammate's APGAR score. APGAR score is used to quickly summarize the health of newborn children, with scores of 7 and above indicating an infant has generally normal health; its use to rank adult NBA players is odd, if not improper. This graph indicates LeBron's teammates have an average APGAR score of approximately 2.1. Scores of 3 and below are generally regarded as critically low and possibly requiring medical attention. Low APGAR scores can also be associated with increased risk of neurological disorders such as cerebral palsy. The joke appears to be in giving LeBron's less-than-impressive teammates a low APGAR score. The shot map shows from what position Curry's shots were scored compared to other NBA players. This references Stephen Curry's propensity to take (and make) shots from well beyond the normal distance required for 3 points. [1] The comic then takes this to hilarious extremes by showing he supposedly scored several times from outside the playing field (not a legal play), including twice from the bleachers ( definitely not a legal play), and once from the locker room (which is physically impossible due to multiple walls in between [ citation needed ] ). Next is a graph of (team) win percentage vs sandwiches eaten during play. Average win percentage seems to go down as number of sandwiches eaten goes up to 3. It does indicate that the Golden State Warriors still have quite high win rate even though they have eaten either 4 sandwiches per game, or 4 sandwiches total during games, over the course of the 2018 season (the graph is unclear on this point). Golden State Warriors seem to be an outlier as their win percentage is much higher than the one of the teams that have eaten 2-3 sandwiches. In the "2018 total points" table, the highlighted Golden State Warriors and Cleveland Cavaliers represent the teams of Stephen Curry and LeBron James respectively. Magnetic north is the south pole of the Earth's magnetic field . Certain animals use the magnetic field to navigate and align themselves (including migratory birds, bees, and foxes), but there is no evidence that humans are affected by the earth's magnetic field. This means that there should not be any correlation between orientation of a basketball court and points scored. But Cleveland Cavaliers have a much a higher percentage of goals scored when orientation is towards magnetic North than other teams, probably it is implied that LeBron James and/or his team somehow actually senses magnetic field and uses that to direct shots, but more likely explanation would be that it is just the orientation of the court during their home games. The title text is a continuation of the joke in the bottom table. FiveThirtyEight , sometimes referred to as 538, is a website that focuses on opinion poll analysis, politics, economics, and sports blogging. The table at the bottom includes more unrelated comparisons: Have You Heard of Him Although both players are well known in their native United States, elsewhere basketball is considered a minority sport. Of the 7 billion people in the world it is likely that less than 2% [ dubious ] of the total population will have heard of either player. [ citation needed ] According to Randall, LeBron James is a more well known player than Stephen Curry. President During Most Recent Game 7 Loss In the NBA, the top 16 teams qualify for a single elimination play-off to determine the season champion, with each series played as a best-of-seven series (first to win 4 games). After the fourth game, fixtures are only played as required. Most fixtures are therefore resolved before the last game. Lebron James has participated in seven playoff game 7s in his career (winning 5 of 7), and the last time his team lost a game seven was on May 18, 2008 ( George W. Bush was still President). This also highlights that James is an older athlete, yet has been fairly dominant through his career. Stephen Curry's last game 7 loss came at the hands of Lebron James in the 2016 NBA Finals ( Barack Obama was President). It is notable that both the Golden State Warriors and Cleveland Cavaliers won their respective games 7 in their Conference Finals to make it to this year's NBA Finals. Pog Collection Pogs were a fad in the 1990s. It is unclear why either would have a large collection of them, or why LeBron's collection would be even more "staggeringly large" than Curry's, besides being 4 years older than him. Career Average Fed Interest Rate The Federal Interest Rate, or federal funds rate , is an interest rate set by the United States Federal Reserve . This rate is increased or decreased periodically based on the health of the U.S. economy. As of the time of publishing, the federal interest rate was targeted at 1.75%. The rate has fluctuated from a high of around 5% to a low of near 0% (during the time of the 2008 recession ). James' career average federal interest rate is higher than Curry's, because James began his career before Curry, when interest rates were higher. Name Scrabble Score Both "lebronjames" and "stephencurry" are worth 22 points in Scrabble . However, proper names are not recognized as scorable words in Scrabble, and thus would be worth nothing. Best Sport It is claimed that their best sport is basketball. This fact should be exceedingly obvious, as they are arguably the two greatest current basketball players; considering all the work they would have dedicated to reach that point, it is extremely unlikely that they have reached an even greater level of mastery in any other sport. Height Both are listed as over 6 feet tall, which is not at all unusual for professional basketball players. Stephen Curry is 6'3" and LeBron James is 6'8", although this chart does not distinguish the exact heights. In most contexts, bucketing humans into broad height-groups would be unsurprising, but in basketball more detail is relevant. Thus, the information is accurate but uninformative --- like the rest of the data in this comic. Retirement Year In 2027, Stephen Curry will be 39 years old, which is a typical retirement age for NBA players. LeBron James's retirement age is listed as Unknown . In reality, there is no way to know when either will return, and if Curry's retirement date is just a projection or prediction, it is unclear why the same could not be done for LeBron (it could perhaps refer to James's high level of play through his mid-30s, when typical players have a decline in their performance). FiveThirtyEight Total Rating Nate Silver is a political commentator and founder of the website FiveThirtyEight , which uses and promotes statistical approaches in explaining the world. The site's two major areas of focus are in politics (especially on elections - it became famous for correctly predicting for whom 49 of 50 states would vote in the 2008 US presidential election and every US state in the 2012 election, and though it wasn't as accurate in 2016 it had given Donald Trump a larger chance of Electoral College victory than other mainstream media sources) and sports (Silver first got into statistical analysis via baseball). The presence of both sports-related and politics-related topics in the comic, however related they are (or not) with each other, seems to be a nod towards FiveThirtyEight's content. Nate Silver has a much higher 538TR than either Curry or James. As explained in the title text, the 538TR combines basketball skill (either real-life or video game basketball) with election forecasting. This could suggest that Silver is proficient at basketball, presumably the video game kind, or else that election forecasting is heavily weighted. NBA Playoffs DataDive LeBron James and Stephen Curry What makes these superstars so extraordinary? [The comic consists of several plots and tables, listed here from top to bottom, left to right.] Scatter plot of Social Security number vs Free throw percentage [Social Security numbers range from 000-00-0000 to 999-99-9999. No pattern discernable, aside from points being a bit denser in the middle of the plot. Stephen Curry is marked as a point on the right edge of the plot, corresponding to a high free throw percentage.] Scatter plot of 2018 points per game vs Average teammate APGAR score [APGAR scores range from 0 to 10. Pattern suggests a somewhat positive link between the two factors. LeBron James is marked as having a lot of points, but a low teammate APGAR score of approximately 2.1.] Shot map [Legend: grey dot for all players, black dot for Stephen Curry] [A diagram of a basketball court is shown with dots placed where players have taken shots at the goal. For the all players category the dots generally cluster next to the goal basket and in front of the three point line. Stephen has 3 dots next to the basket (one is behind it), but does cluster next to the three point line. He also has several dots on the other side of the playing field, and outside it, including three in the bleachers and one in the locker room.] Sandwiches eaten during play vs Win % [Sandwiches eaten range from 0 to 4. A plot that suggests no relation between the factors because practically all dots are in the zero sandwiches column. 2018 Warriors have one dot at around 60% and 4 sandwiches.] 2018 total points [A table listing teams and their points overall and "When net is within 15° of magnetic north". The rows for the Golden State Warriors and the Cleveland Cavaliers are highlighted, the latter showing an abnormally high score in the magnetic north column.] 2018 total points Overall When net is within 15° of magnetic north Golden State Warriors 9304 330 Houston Rockets 9213 268 New Orleans Pelicans 9161 219 Toronto Raptors 9156 341 Cleveland Cavaliers 9091 1644 Denver Nuggets 9020 280 [A table at the bottom:] Stephen Curry LeBron James Have you heard of him Probably Yes President during most recent game 7 loss Obama Bush Pog collection Large Staggeringly large Career average Fed interest rate 3.42% 4.41% Name Scrabble score 22 22 Best sport Basketball Basketball Height Over 6' Over 6' Retirement year 2027 Unknown Nate Silver FiveThirtyEight total rating (devised by Nate Silver to combine all metrics into a single stat) 37.4 31.8 86.6 This comic was posted the day after the second game in the 2018 NBA Finals between the Golden State Warriors (Stephen Curry's team) and the Cleveland Cavaliers (LeBron James' team). It is the fourth consecutive time the two teams faced each other at the finals, which is unprecedented in major sports leagues in North America. The Warriors won in 2015 and 2017, the Cavaliers won in 2016. At the time of the comic, the Warriors led the current series 2-0; which they eventually won.

Presidential Succession

Presidential Succession

https://www.xkcd.com/2003

https://www.explainxkcd.com/wiki/index.php/2003:_Presidential_Succession

A proposal for a new presidential line of succession Current politics aside, most experts agree the existing process is flawed. The Presidential Succession Act of 1947 is probably unconstitutional on several counts, and there are many practical issues with the system as well. (For more, see the surprisingly gripping Second Report of the Continuity of Government Commission , June 2009.) Proposed line of succession: President Vice president Secretary of State Secretary of Defense Secretary of Homeland Security Attorney General Five people who do not live in Washington DC, nominated at the start of the president's term and confirmed by the Senate Tom Hanks State Governors, in descending order of state population at last census Anyone who won an Oscar for playing a governor Anyone who won a Governor's award for playing someone named Oscar Kate McKinnon, if available Billboard year-end Hot 100 singles artists #1 through #10 (for groups, whoever is credited first in name, liner notes, etc) The top 5 US astronauts in descending order of total spaceflight time Serena Williams (or, if she lost her most recent match, whoever beat her) The most recent season NBA, NFL, MLB, and NHL MVPs Bull Pullman and his descendants by absolute primogeniture The entire line of succession to the British throne The current champion of the Nathan's Hot Dog Eating contest All other US citizens, chosen by a 29-round single-elimination Jousting tournament

The United States presidential line of succession is the order of people who serve as president if the current incumbent president is incapacitated, dies, resigns, or is removed from office. The Presidential Succession Act of 1947 revised the presidential order of succession to its current order. This Act, though never challenged in the courts, may not be constitutional for two reasons. First, the Act names two members of Congress as successors. There are serious questions as to whether this violates the principle of Separation of Powers. The second issue is that the Act allows for anyone skipped over for succession to later assume the office if circumstances change to allow them to hold it. This would mean that the person in question could effectively unseat a sitting President, which raises serious constitutional issues. There are also practical concerns regarding the Act. The line of succession includes all members of the Cabinet in the order that their department was established, with the oldest departments first. No consideration is given to which departments would be most relevant to the Presidency, particularly considering that this type of succession would presumably involve a serious crisis, which the new president would need to be able to address immediately. The Department of Homeland Security is in charge of the security and protection of the United States and its citizens and would probably already be privy to sensitive intelligence and briefings related to national security, but because it is the latest of the Departments to have been established (in 2003), the Secretary of Homeland Security is last in the current Presidential line of succession, behind Secretaries in much less sensitive roles, such as those of Agriculture, Housing and Urban Development, and Education. Another concern is that, by including members of Congress immediately after the Vice President, there is a serious risk that the simultaneous death of the President and Vice President could cause the Presidency to change to the opposing party, which could lead to serious political instability at the precise moment when the country is facing a national crisis. It even presents the possibility that simultaneous assassinations of the President and Vice President could function as an effective coup, shifting power to their opponents. Finally, there is the issue that, usually, everyone in the line of succession lives and works in Washington D.C. Hence, a sufficiently destructive attack or natural disaster impacting the city could realistically incapacitate all of them, leaving the USA leaderless at a time of extreme crisis. It is already established practice in the USA that everyone in this line not gather together at once. In cases where most senior government officials gather (such as the State of the Union ), at least one member of the line of succession (referred to as the "designated survivor") is secured off-site, and would assume the presidency in the unlikely event that a mass casualty event were to kill or incapacitate everyone else in the line. However, disasters impacting an entire city remain a possibility, and no provision is made for them in current law. To correct these issues, a think tank known as the Continuity of Government Commission prepared a report recommending a new line of succession, which would not include members of Congress, would reorder the cabinet secretaries so that the most suitable roles would be the first successors, and would include people who do not live or work in Washington DC. The full text of their report can be found here . A short, readable summary, including the report's recommended new line of succession, is here . The first six members of the commission's list are taken from the current line of succession, though the order is changed; they propose that after this, five new people should be appointed specifically for the purpose of assuming the presidency, if needed. Randall's list begins with these eleven people (combining the five new appointees into #7); afterwards, his list becomes increasingly comical and ridiculous. Randall's list omits members of Congress, as well as other cabinet positions, in accordance with the report's concerns about constitutionality and qualifications. However, his other additions totally ignore these issues, including people with no apparent qualifications for the office (such as actors, athletes, and competitive eaters) and people who are constitutionally ineligible for the office. The US Constitution requires that the President of the United States must be a natural-born US citizen, at least 35 years of age, and have resided in the US for at least fourteen years. Randall's list includes many people who don't meet these requirements. Most notably, he includes the entire succession to the British crown, almost none of whom meet the requirement of being natural-born citizens of the United States. It may be expected that many of the athletes, musicians and actors on this list are likely to be ineligible as well. Most professional athletes in the relevant sports are under 35 years old, particularly those at the peak of their careers (when they'd likely win MVP awards), the most popular musicians also tend to be younger than 35, and many who meet these requirements were not born US citizens (and some many not even reside in the US). However, the existing line of succession can also contain ineligible people, who would simply be skipped over for succession. For example, at the comic's publication, Elaine Chao was the Secretary of Transportation and would normally be 14th in line, but because she is a naturalized citizen of the US, rather than native-born (she was born in Taiwan) she would not qualify for the office if the line came to her. The title text mentions that ties will be broken by whoever was closest to the surface of Europa when they were born. Europa is a moon of Jupiter and one of the most likely locations in the Solar System for potential habitability . This is likely a parody of systems in which ties are broken by semi-arbitrary rules (such as the older candidate automatically winning a tie) or a randomized ones (such as ties being decided by a coin flip). The position of Europa with respect to Earth at the time of one's birth depends on enough factors that it acts as a pseudo-random tie breaker, albeit a needlessly complicated one. The presidential line of succession was first mentioned in 1933: Santa Facts Based on the comic's defined criteria for the order of succession, these are the specific individuals in that order, including only people who are otherwise eligible to be the President of United States (35 year old and natural born US citizens who lived in US for last 14 years) as of the date the comic was published . Based on the comic's defined criteria for the order of succession, these are the specific individuals in that order, including only people who are otherwise eligible to be the President of United States (35 year old and natural born US citizens who lived in US for last 14 years) as of the current date . (Last updated on 26 January 2022) A proposal for a new presidential line of succession Current politics aside, most experts agree the existing process is flawed. The Presidential Succession Act of 1947 is probably unconstitutional on several counts, and there are many practical issues with the system as well. (For more, see the surprisingly gripping Second Report of the Continuity of Government Commission , June 2009.) Proposed line of succession: President Vice president Secretary of State Secretary of Defense Secretary of Homeland Security Attorney General Five people who do not live in Washington DC, nominated at the start of the president's term and confirmed by the Senate Tom Hanks State Governors, in descending order of state population at last census Anyone who won an Oscar for playing a governor Anyone who won a Governor's award for playing someone named Oscar Kate McKinnon, if available Billboard year-end Hot 100 singles artists #1 through #10 (for groups, whoever is credited first in name, liner notes, etc) The top 5 US astronauts in descending order of total spaceflight time Serena Williams (or, if she lost her most recent match, whoever beat her) The most recent season NBA, NFL, MLB, and NHL MVPs Bull Pullman and his descendants by absolute primogeniture The entire line of succession to the British throne The current champion of the Nathan's Hot Dog Eating contest All other US citizens, chosen by a 29-round single-elimination Jousting tournament

Sun and Earth

Sun and Earth

https://www.xkcd.com/2004

https://www.explainxkcd.com/wiki/index.php/2004:_Sun_and_Earth

[The entire comic is within a panel. At the bottom of the image a curved shape depicting a small part of the Earth's surface and labeled as "Earth" is shown. At the top a similar sized shape but opposite curve is labeled as "Sun". The surface of the Sun is seething while on Earth's surface a few plants, two birds, and Cueball together with Megan are visible.] [Two arrows pointing to the Sun and the Earth with a caption applying to both of them:] Massive convective systems which occasionally blast huge plumes of heat at us without warning through mechanisms we can't directly observe and don't really understand. Cueball: What a nice day!

This is one of a number of comics which describe everyday events in unusual terms, making them sound really weird. In this case, both the Sun and the Earth are "massive convective systems [blasting] huge plumes of heat", which contrasts sharply with the daily idea of the Sun being a ball in the sky and the Earth the thing under our feet. Free convection is based on an difference in density. What is colder is typically denser, so gravity forces it downwards, displacing what is hotter (and less dense) upward (This should not be confused with forced convection , which uses fans or other devices that are not practical to build on the scale of a planet). In the sun, most of the energy to drive this process comes from nuclear fusion, specifically the fusion of hydrogen into helium. We cannot directly see inside of the earth, [ citation needed ] but its core is known to be much hotter than its surface. The magnitude of these systems gives you an idea of the size of the fluctuations you can expect. The sun is very massive, meaning the fluctuations in its convective or heat-dissipating behavior are very large. This is an instance of the Fluctuation-Dissipation theorem . These fluctuations take the form of a solar flare, as explained below. For a more thorough (but non-technical) explanation of the role of gravity and entropy in such systems, see this . The Sun produces great amounts of light and heat and blasts it towards us, which is why we can live on Earth. Since Ludwig Boltzmann pointed out the fact in 1875, people have been working on establishing exactly how such far from equilibrium systems as life might depend upon, or be formed by ( like this article ), such massive entropy gradients as between the sun and earth (or rather the sun and empty space). Main sequence stars like the sun transport energy by radiation and by convective currents of plasma , bringing the heat generated in the core of the sun to its surface. These quickly moving charged particles create a massive magnetic field, which occasionally gets concentrated into a solar prominence which can snap, causing a large amount of charged particles to get shot into space as a solar flare . If the Earth happens to be in the direction of the solar flare, we can notice all sorts of interesting and often damaging effects. Thankfully, there are lots of other directions for the sun to shoot solar flares, so they don't come by the Earth that often. The Earth's interior is also very hot. Mantle convection causes plate tectonics which is the main cause of volcanic activity (next to mantle plumes ), which essentially also consists of huge blasts of heat. This could sound like a very bad scenario, but the title text reminds us that the real scenario we live in is far worse, as we are not likely to die from a Sun blast or volcano eruption. In doing this, he indirectly points out the hard truth about our lives: that they're limited and they're short, and it is far easier to die of because of other things. In this way Randall attempts to give the reader an existential crisis; he concludes that his statement did not help to reassure himself. This comic was likely inspired by the recent eruptions of the Kīlauea and Volcán de Fuego . In contrast, solar activity is currently low, because the sunspot solar cycle is in the low end of the 11-year cycle. [The entire comic is within a panel. At the bottom of the image a curved shape depicting a small part of the Earth's surface and labeled as "Earth" is shown. At the top a similar sized shape but opposite curve is labeled as "Sun". The surface of the Sun is seething while on Earth's surface a few plants, two birds, and Cueball together with Megan are visible.] [Two arrows pointing to the Sun and the Earth with a caption applying to both of them:] Massive convective systems which occasionally blast huge plumes of heat at us without warning through mechanisms we can't directly observe and don't really understand. Cueball: What a nice day!

Attention Span

Attention Span

https://www.xkcd.com/2005

https://www.explainxkcd.com/wiki/index.php/2005:_Attention_Span

[Cueball and Megan are standing together.] Cueball: I haven't read any books in forever. I have no attention span anymore. [Zoom in on the faces of Cueball and Megan.] Megan: Didn't you literally just spend six hours obsessively reading about the theory that Thomas the Tank Engine is authoritarian propaganda depicting a post-apocalyptic fascist dystopia? [Cueball still standing there. Megan begins pacing away.] Cueball: OK Cueball: I mean I have no attention span for anything good anymore. Megan: Let's check out your bookshelf, shall we? [Cueball alone.] Cueball: What are you- Off-panel: I see a dragon holding a sword in its teeth on the cover of a book that's thicker than it is wide. Cueball: And? That's a classic! Off-panel: Just saying, I don't think this is a new development. 2005 (the comic number) is also the year of the first XKCD comic. The dragon described is very loosely similar to the legendary pokemon Zacian , whose game had been teased at the release of this comic.

People often groan about their shrinking attention span, attributing it to an increased illiteracy. This allows for fond nostalgia about the times when they were supposedly more intelligent and focused. For instance, Nicholas Carr wrote this article to compile both anecdotes (which are more abundant) and research (which is more useful) to describe this phenomenon. Cueball does the same here, but Megan retorts that he spent six hours reading over a pointless (if disturbingly plausible) theory about a banal show based off a series of bedtime stories made to entertain small children. Thomas The Tank Engine is a British children's series based off a series of books written by Wilbert Awdry. It follows the adventures of anthropomorphized train locomotives and other vehicles. Cueball qualifies his statement: he has no attention span for anything good anymore. Megan, in reply, examines Cueball’s bookshelf, finding a book that cements Cueball’s status as a nerd who reads high fantasy . Cueball protests that the book is a classic, but Megan dismisses the fact. To be fair to Cueball, many great fantasies have covers such as those in the comic (e.g. A Song of Ice and Fire , The Lord of the Rings , Randall's personal favorite Discworld ). To be fair to Megan, this book is apparently not one of them, being thicker than it is wide (like The Complete Miss Marple by Agatha Christie ), a telltale sign of needless bombast and turgid prose. Other possibilities for the dragon book are His Majesty's Dragon from the Temeraire series or Dragonsbane from the Winterlands series. If there was any doubt about Cueball’s dubious literary tastes before, Megan dispels them in the title text, refering to a novelization of the excoriated movie Surf Ninjas , a movie that is exactly what it sounds like. Signed novelizations of a movie named “Surf Ninjas” are not typical fodder for great minds. [ citation needed ] The comic contains a hyperlink to an article with the same unfortunate content Cueball has apparently finished reading prior to this comic: The Repressive, Authoritarian Soul of “Thomas the Tank Engine & Friends” . This article, the articles linked from it, further linked articles from those, links found by googling the topic, and other related web surfing on the topic could easily add up to six hours or more of reading. [Cueball and Megan are standing together.] Cueball: I haven't read any books in forever. I have no attention span anymore. [Zoom in on the faces of Cueball and Megan.] Megan: Didn't you literally just spend six hours obsessively reading about the theory that Thomas the Tank Engine is authoritarian propaganda depicting a post-apocalyptic fascist dystopia? [Cueball still standing there. Megan begins pacing away.] Cueball: OK Cueball: I mean I have no attention span for anything good anymore. Megan: Let's check out your bookshelf, shall we? [Cueball alone.] Cueball: What are you- Off-panel: I see a dragon holding a sword in its teeth on the cover of a book that's thicker than it is wide. Cueball: And? That's a classic! Off-panel: Just saying, I don't think this is a new development. 2005 (the comic number) is also the year of the first XKCD comic. The dragon described is very loosely similar to the legendary pokemon Zacian , whose game had been teased at the release of this comic.

Customer Rewards

Customer Rewards

https://www.xkcd.com/2006

https://www.explainxkcd.com/wiki/index.php/2006:_Customer_Rewards

[To the right Cueball stands in front of a sales desk, his shopping bag on the desk. Behind the desk on the left is a sales clerk wearing a peaked cap and typing on a cash register.] Sales clerk: That will be $23.03. Sales clerk: Also, I'll pay you 24 cents for your last name, 35 cents for a list of your family members, 79 cents for your cell number, and $1.20 if you hand me your phone and let me scroll through your Facebook posts. [Caption below the panel:] Loyalty cards and rewards account offers get way weirder if you think of them as separate transactions.

Many supermarkets offer customers Loyalty programs that give discounts. To join one of these programs you often need to give various personal data, such as your name, or download an app that can access your Facebook account. The supermarket gets lots of valuable marketing data to target the customer in the future. They think this will make lots of money for them, so they entice people to do this. This is why it is able to offer a discount to members of the program. Here, Cueball is at a store where the clerk is offering to give him benefits in exchange for data and to help them advertise their products. This comic imagines the exchange of data for a discount as the sales clerk offering cash at the point of sale, to emphasize how odd this exchange is. Not to mention, when flat-out asking to see someone's phone to write down their contact info and look at all their Facebook posts it sounds disturbingly like uncouth data harvesting, not too far removed from potential identity theft. The title text continues this by considering how companies will also find ways to incentivize positive viral marketing or offer services in exchange for viewing adverts. By imagining these situations as if they were cash transactions makes them seem ridiculous. All this information is used to send personalized ads which have a better chance of succeeding and earning money for the store owner. [To the right Cueball stands in front of a sales desk, his shopping bag on the desk. Behind the desk on the left is a sales clerk wearing a peaked cap and typing on a cash register.] Sales clerk: That will be $23.03. Sales clerk: Also, I'll pay you 24 cents for your last name, 35 cents for a list of your family members, 79 cents for your cell number, and $1.20 if you hand me your phone and let me scroll through your Facebook posts. [Caption below the panel:] Loyalty cards and rewards account offers get way weirder if you think of them as separate transactions.

Brookhaven RHIC

Brookhaven RHIC

https://www.xkcd.com/2007

https://www.explainxkcd.com/wiki/index.php/2007:_Brookhaven_RHIC

[A single panel contains a simplified overhead map view of the Brookhaven Relativistic Heavy Ion Collider and some of the surrounding area. The map is rotated 90°; north is to the left. The collider is located on the left hand side of the image as a yellow beam (representing the Gold ions) outlined in black. Parts of the collider are are labeled and there are light gray arrows indicating the direction of travel for the ions. At the bottom of the main accelerator ring there is a diverter that splits the ion beam and directs it towards a set of three Cash for Gold stores, passing through a more diverters along the way. Each Cash for Gold store is represented with a yellow burst and is marked with a Google maps style "store" locator pin. The following labels are written on the map.] Brookhaven Relativistic Heavy Ion Collider Gold Ion Source Accelerator Ring Diverter Gold Ion Beam [There are arrows coming from this label pointing at each store] Cash for Gold Stores [Caption below the panel:] Sadly, Brookhaven rejected my proposed experiment

The Relativistic Heavy Ion Collider is a particle accelerator designed to collide gold ions together at incredibly high speeds. This is normally done to study particle physics - the high-energy collisions allow us to learn more about how subatomic particles behave. Randall proposes that, instead of using the beam of gold ions for particle collisions, it should be diverted and sold at cash-for-gold stores to make money. In effect, the particle accelerator would be reconfigured to become an extremely complicated and expensive method to transport gold ions from the foil to the cash-for-gold stores. Randall proposed modifying part of the circular particle accelerator to add a diverter, so he can direct the gold ion beam to the three stores. It is unclear, however, how he would manage to transport the gold to the stores, as once it leaves the circular particle accelerator, parts of the beam are not in an enclosed space, and would likely collide with something. It would also cause problems once it reached the stores, as the gold ions travel at relativistic speeds. Part of the joke may be that because they are traveling at relativistic speeds, the mass of the particles being sold will be much more than the mass of the ions being supplied to the collider's input. However, it would be very difficult to sell a beam of charged particles [ citation needed ] , and the amount of gold involved is below microscopic scales. That, and the fact that he is trying to misuse the particle accelerator for his own profit, is the reason why Brookhaven rejected Randall's proposal. Also, the energy used by the particle accelerator would cost more than the revenue from selling the gold. Randall has done many comics describing impractical research proposals in the past. The title text imagines the owner of the stores complaining about the sale, not because of impracticality, but because Randall tries to sell gold ions with the entire positively-charged nucleus of the gold atom with all 79 electrons stripped from it instead of normal, electrically neutral gold atoms. This is also a pun on the word "charges", which could refer to electric charge or to criminal charges . This is an actual map of the area around Brookhaven National Laboratory , with east at the top. The cash for gold stores depicted in the comic are, from left to right: [A single panel contains a simplified overhead map view of the Brookhaven Relativistic Heavy Ion Collider and some of the surrounding area. The map is rotated 90°; north is to the left. The collider is located on the left hand side of the image as a yellow beam (representing the Gold ions) outlined in black. Parts of the collider are are labeled and there are light gray arrows indicating the direction of travel for the ions. At the bottom of the main accelerator ring there is a diverter that splits the ion beam and directs it towards a set of three Cash for Gold stores, passing through a more diverters along the way. Each Cash for Gold store is represented with a yellow burst and is marked with a Google maps style "store" locator pin. The following labels are written on the map.] Brookhaven Relativistic Heavy Ion Collider Gold Ion Source Accelerator Ring Diverter Gold Ion Beam [There are arrows coming from this label pointing at each store] Cash for Gold Stores [Caption below the panel:] Sadly, Brookhaven rejected my proposed experiment

Irony Definition

Irony Definition

https://www.xkcd.com/2008

https://www.explainxkcd.com/wiki/index.php/2008:_Irony_Definition

[Black Hat and Cueball are walking together, with Black Hat walking behind Cueball with his arms out and palms up. Cueball is visibly upset, as evidenced by the squiggle floating above his head and his balled up fists.] Black Hat: It's ironic how you know the definition of irony, yet I'm the one in this conversation who's happy.

This comic presents a snapshot of an argument between Black Hat and Cueball . Black Hat states that it's ironic how Cueball understands the definition of irony, yet Black Hat is happy while Cueball is not. Cueball is upset because Black Hat is purposely misusing the term "ironic", likely after Cueball had previously corrected him on his use of the word. Irony is a broad concept that is very often the subject of confusion and debate, especially concerning whether something is "really" irony. In this comic, Black Hat is probably referencing situational irony , which occurs when there is a sharp contrast between the expected and actual results of a situation, often in a humorous way or one that includes some sort of contradiction. For example, cane toads were introduced to Australia to control the native cane beetle, a pest to farmers. Ironically, the toads have caused massive ecological damage and become a pest themselves, and have even failed to control the cane beetles. That someone who understands what irony is would be unhappy while someone who doesn't would be happy is not an example of irony. Since Black Hat is trying to irritate Cueball, he is intentionally misusing the word "ironic". Irony can have other meanings besides situational irony. Verbal irony (which is related to sarcasm) refers to a contradiction between a statement's stated and intended meaning. Dramatic irony is a device in fiction in which the consumer of a work is aware of information that is unknown to a character in the narrative. The adjective "ironic" is often used colloquially to mean strange, interesting, unexpected, or funny based on some subversion of expectations. The use of the word in these ways is often what prompts conversations and arguments about what really is or isn't ironic. What could be going on is that Cueball was trying to correct Black Hat's misuse of the word irony, in order to make him feel bad about misusing it. However, Black Hat being the classhole he is, could have decided to take advantage of it, and misuse it again , to make Cueball angry again. In the title text Black Hat once again misuses the word ironic , this time in an even more absurd way. It is unknown what Black Hat means when he says Cueball's glaring makes him feel "ironic", as this is a totally spurious use of the word, and one which is probably not intended to actually mean anything and is only done to annoy Cueball further. [Black Hat and Cueball are walking together, with Black Hat walking behind Cueball with his arms out and palms up. Cueball is visibly upset, as evidenced by the squiggle floating above his head and his balled up fists.] Black Hat: It's ironic how you know the definition of irony, yet I'm the one in this conversation who's happy.

Hertzsprung-Russell Diagram

Hertzsprung-Russell Diagram

https://www.xkcd.com/2009

https://www.explainxkcd.com/wiki/index.php/2009:_Hertzsprung-Russell_Diagram

Expanded Hertzsprung-Russell Diagram [A scatter plot is shown, with the x-axis labeled Effective Temperature (in kelvins), and the y-axis Luminosity (watts).] [Circled items in the top left (high temperature and high luminosity):] Supergiants Giants Main sequence White dwarfs Brown dwarfs [Items shown as points and their values:] Betelgeuse: 3200 K, 1.6 × 10 31 W Vega: 10,000 K, 1.8 × 10 28 W Sun: 5800 K, 3.6 × 10 26 W Proxima Centauri: 2700 K, 2.0 × 10 23 W HD 189733 b: 2100 K, 4.8 × 10 21 W Interior of a hydrogen bomb during detonation: ~108 K, ~10 20 W Jupiter: 285 K, 1.2 × 10 18 W Venus: 330 K, 5.0 × 10 17 W Earth: 300 K, 3.0 × 10 17 W Mars: 255 K, 2.0 × 10 16 W Moon: 300 K, 1.2 × 10 16 W Nuclear Fireball: 8000 K, 2.0 × 10 14 W France: 300 K, 2.0 × 10 14 W Europa: 90 K, 3.5 × 10 14 W Lightning Bolt: 30,000 K, 30 GW Ivanpah Solar Plant Salt Tank: 1200 K, 1.2 GW Medium-sized Lava Lake: 800 K, 32 MW Cruise Ship: 325 K, 30 MW Campfire: 870 K, 7.0 kW Blue whale: 280 K, 78 kW Arc lamp: 6500 K, 150 W Lightbulb: 4800 K, 75 W LED Bulb: 5800 K, 8 W Astronomer: 310 K, 100 W

The Hertzsprung–Russell diagram is a scatterplot showing absolute luminosities of stars against its effective temperature or color. It's generally used to understand a star's age. The axes are labeled in Kelvin (degrees Celsius above absolute zero ) for effective temperature and, unlike many Hertzsprung–Russell diagrams, Watts for luminosity . While most Hertzsprung–Russell diagrams are labelled in units of solar luminosity or absolute magnitude , all three are perfectly valid measures of luminosity , which refers to the total power emitted by the star (or other body). Effective temperature refers to temperature of a blackbody with the same surface area and luminosity. This is meant to provide an estimate of the surface temperature of the object. Roughly speaking, the luminosity (i.e. total power radiated) by an object is proportional to (1) the total surface area of the object, multiplied by (2) the (absolute) temperature raised to the fourth power. So a high luminosity generally results from either a very hot or a very large object, or a combination of the two. The surface-area dependence explains why the whale and the cruise ship are more luminous than the hotter campfire. Regular Hertzsprung–Russell diagrams cover ranges of about 1,000K to 30,000K, and what is labeled on this diagram as 10 21 to 10 33 watts—i.e. the upper-left corner. Extended diagrams increase the luminosity range only to include the "Brown Dwarfs". This diagram has been extended to much lower magnitudes on both axes. The joke comes from the absurdity of a diagram meant for stars including much smaller objects, such as planets ... and astronomers. Though not included in the diagram, the title text notes that the diagram itself would probably be plotted somewhere in the lower right corner due to its (relatively) low power output and temperature. On its face this is nonsensical - the diagram itself, being mere information, possesses neither power output nor temperature - but one can read this as the power output and temperature of a typical screen displaying the diagram. Bigger screens have a higher total output (in terms of luminosity) and are thus positioned further towards the diagram's top. An "unusually big screen" would have to be something like a JumboTron or a projector for its luminosity or temperature to put it outside of the lower right corner. Expanded Hertzsprung-Russell Diagram [A scatter plot is shown, with the x-axis labeled Effective Temperature (in kelvins), and the y-axis Luminosity (watts).] [Circled items in the top left (high temperature and high luminosity):] Supergiants Giants Main sequence White dwarfs Brown dwarfs [Items shown as points and their values:] Betelgeuse: 3200 K, 1.6 × 10 31 W Vega: 10,000 K, 1.8 × 10 28 W Sun: 5800 K, 3.6 × 10 26 W Proxima Centauri: 2700 K, 2.0 × 10 23 W HD 189733 b: 2100 K, 4.8 × 10 21 W Interior of a hydrogen bomb during detonation: ~108 K, ~10 20 W Jupiter: 285 K, 1.2 × 10 18 W Venus: 330 K, 5.0 × 10 17 W Earth: 300 K, 3.0 × 10 17 W Mars: 255 K, 2.0 × 10 16 W Moon: 300 K, 1.2 × 10 16 W Nuclear Fireball: 8000 K, 2.0 × 10 14 W France: 300 K, 2.0 × 10 14 W Europa: 90 K, 3.5 × 10 14 W Lightning Bolt: 30,000 K, 30 GW Ivanpah Solar Plant Salt Tank: 1200 K, 1.2 GW Medium-sized Lava Lake: 800 K, 32 MW Cruise Ship: 325 K, 30 MW Campfire: 870 K, 7.0 kW Blue whale: 280 K, 78 kW Arc lamp: 6500 K, 150 W Lightbulb: 4800 K, 75 W LED Bulb: 5800 K, 8 W Astronomer: 310 K, 100 W

Update Notes

Update Notes

https://www.xkcd.com/2010

https://www.explainxkcd.com/wiki/index.php/2010:_Update_Notes

[There are two panels that show smartphone-esque screens with two different apps with different update notes, showing a conversation between two people. New updates are added to the top, so to follow the conversation flow one would start from the bottom and alternate between the second app and the first one.] [At the top, the status bars between the two panels are slightly different: telephone reception, WiFi strength, battery, GPS...] ["Updates" is written in uppercase at the top. The first app's icon is an "A" symbol. Next to it, there is the following information:] [The app name is a scribble] Version 3.0.1 June 22, 2018 Update Notes: v3.0.1 I'm actually off work Monday so that's perfect. v3.0 Oh, that sounds fun! What night? v2.8.31 Are you around this weekend? We're heading to the beach. v2.8.3 Hey Mike, you there? ["Updates" is written in uppercase at the top. The second app's icon consists of three stars arranged in a triangle. Next to it, there is:] [The app name is a scribble followed by two stars in parentheses] Version 7.0 June 22, 2018 Update Notes: v7.0 It peaks August 12-13 th . v6.8.16 Sorry, no, going to a wedding. But do you want to camp out for the meteor shower in August? v6.8.15 Yeah, what's up? v6.8.14 Introduced bugs and degraded performance[.] [At the bottom of each panel, there are menu icons: a star, a stack of rectangles, a bullet list, a magnifying glass and an arrow pointing down to a square] [Caption below the panels:] My friend and I both have apps we've stopped maintaining, so we just use the updates to chat. [For convenience, here are the update notes in order of release (note that the first is not part of the conversation with Mike):] "A" app (v6.8.14): Introduced bugs and degraded performance[.] "3-star" app (v2.8.3): Hey Mike, you there? A (v6.8.15): Yeah, what's up? 3-star (v.2.8.31): Are you around this weekend? We're heading to the beach. A (v6.8.16): Sorry, no, going to a wedding. But do you want to camp out for the meteor shower in August? 3-star (v3.0): Oh, that sounds fun! What night? A (v7.0): It peaks August 12-13th. 3-star (v3.0.1): I'm actually off work Monday so that's perfect.

Update notes or release notes are notes (or documents) released when software has been updated, to inform the user of any important changes to the software. In this comic, Randall and his friend are using release notes of their apps as a form of chat service, instead of actual software change information. He says this is possible because the two apps are no longer being maintained, so theoretically, there are not many people using the app who would read the update / change notes. Incidentally, one can still argue that the chat is still technically update notes, only instead of updating users on what has changed about an app, it is now giving Randall and his friend status "updates". This comic has a similar theme as 1305: Undocumented Feature both use old software forums as a chat application. This "chat service" would not be in real time, so presumably, Randall and his friend would have to be constantly checking each other's apps to see if there are updates. On the "stars" app, the last "actual" notes says "Introduced bugs and degraded performance". This is a very common change when new features are added, however, developers will normally describe what the new features are rather than just state the negative consequences. It goes in contrast with the typical change note "fixed bugs and improved performance" that usually follows. The comic also refers to a meteor shower occurring in August, most likely the Perseid meteor shower . The title text says that Randall, who is at the beach, has left his sunscreen in his car, but that the trunk (a pun with the name of the main software development branch in SVN) is unlocked, for whoever is still reading the updates for this app. This may invite the attention of thieves, who are now informed that Randall's trunk is unlocked. However they may not know what city Randall lives in, and conversely readers of the release notes could be anywhere in the world so most are probably not in a position to physically make contact with Randall's car. This comic could be seen as a subtle reference to how plain sight communication such as gang codes and steganography are used by people, possibly out of coerced necessity, to communicate information both deniably and publicly. It is likely that this often happens in real app update messages in real life. This kind of communication would more realistically allow a criminal worker to communicate with a contact point without endangering their anonymity by associating with them directly. This comic could also be poking fun at the non-descriptive updates many popular apps post in the "What's new" or change log. One example of this would be the Uber app stating "We update the app as often as possible" as a "new" feature every update. Apple recently changed AppStore guidelines [1] to require clear descriptions of new features and product changes, effectively putting an end to the problem Randall is highlighting. Realistically, even if it were permitted, this would be a rather slow form of communication, especially on platforms such as Apple’s App Store, where Randall and his friend would need to wait from a few hours to a few days for their app to be manually reviewed for each “update”. [There are two panels that show smartphone-esque screens with two different apps with different update notes, showing a conversation between two people. New updates are added to the top, so to follow the conversation flow one would start from the bottom and alternate between the second app and the first one.] [At the top, the status bars between the two panels are slightly different: telephone reception, WiFi strength, battery, GPS...] ["Updates" is written in uppercase at the top. The first app's icon is an "A" symbol. Next to it, there is the following information:] [The app name is a scribble] Version 3.0.1 June 22, 2018 Update Notes: v3.0.1 I'm actually off work Monday so that's perfect. v3.0 Oh, that sounds fun! What night? v2.8.31 Are you around this weekend? We're heading to the beach. v2.8.3 Hey Mike, you there? ["Updates" is written in uppercase at the top. The second app's icon consists of three stars arranged in a triangle. Next to it, there is:] [The app name is a scribble followed by two stars in parentheses] Version 7.0 June 22, 2018 Update Notes: v7.0 It peaks August 12-13 th . v6.8.16 Sorry, no, going to a wedding. But do you want to camp out for the meteor shower in August? v6.8.15 Yeah, what's up? v6.8.14 Introduced bugs and degraded performance[.] [At the bottom of each panel, there are menu icons: a star, a stack of rectangles, a bullet list, a magnifying glass and an arrow pointing down to a square] [Caption below the panels:] My friend and I both have apps we've stopped maintaining, so we just use the updates to chat. [For convenience, here are the update notes in order of release (note that the first is not part of the conversation with Mike):] "A" app (v6.8.14): Introduced bugs and degraded performance[.] "3-star" app (v2.8.3): Hey Mike, you there? A (v6.8.15): Yeah, what's up? 3-star (v.2.8.31): Are you around this weekend? We're heading to the beach. A (v6.8.16): Sorry, no, going to a wedding. But do you want to camp out for the meteor shower in August? 3-star (v3.0): Oh, that sounds fun! What night? A (v7.0): It peaks August 12-13th. 3-star (v3.0.1): I'm actually off work Monday so that's perfect.

Newton's Trajectories

Newton's Trajectories

https://www.xkcd.com/2011

https://www.explainxkcd.com/wiki/index.php/2011:_Newton%27s_Trajectories

[The panel shows a shaded sphere with a rocket launched from its top to the right. Several trajectories are plotted around the sphere.] [Trajectory 1 (in black) shows a successful circular orbit.] Humans slip the bonds of Earth to travel the stars [Trajectory 2 (in red) shows a ballistic arc that crashes into the sphere near the bottom.] Civilization ends in fire [Trajectory 3 (in red) shows a much shorter ballistic arc. No label.] [Caption below the panel:] In retrospect, Newton's little cannonball drawing does a surprisingly good job illustrating the range of possible futures of our species.

The comic shows the Earth, with three apparent rockets on separate trajectories. One is released with sufficient velocity to attain a stable orbit, while the other two fall towards the Earth. This is a slight modification of Newton's cannonball , a thought experiment demonstrating the planetary effects of gravity. The black rocket trajectory is typically that of a rocket delivering a payload to low earth orbit. While a satellite in orbit is still bound to earth, it represents an important step in the history of space exploration. Today, a lot of scientific research regarding the future of human spaceflight is done from low earth orbit, most notably on the ISS . The red rocket trajectories are suborbital, and more commonly associated with ICBMs . These are missiles typically equipped with nuclear warheads. Using such a weapon is likely to trigger a global nuclear war, with disastrous effects for civilization. It is worth noting that ICBMs normally use a different trajectory that goes much higher before falling down at a steeper angle. These trajectories are also different from FOBS , where missiles actually go into orbit (the black trajectory) before deorbiting and falling back on earth. Here, Newton's cannonball is used both to observe humanity’s technological future (interplanetary travel, availability of advanced technology to the masses, and constant scientific improvement; or nuclear desolation and the extinction of our species) and to underscore that argument by pointing out the inherent metaphor in the experiment: the cannonball can only escape the atmosphere by achieving high velocity (i.e. escape velocity). Similarly, Randall’s technological utopia will only deliver us from nuclear extinction if it happens quickly; otherwise, mankind will destroy itself. Of course, that threat only exists because of a triumph of technological progress, the Manhattan Project , but again, technology is a means to an end. The phrase "slip the bonds of Earth" comes from the sonnet " High Flight " written in 1941 by John Gillespie Magee Jr., an American pilot in the Second World War. Portions of this poem appear on the headstones of many interred in Arlington National Cemetery, particularly aviators and astronauts; it was also quoted in President Reagan's speech after the Challenger disaster. The title text alludes to the unfortunate film The Core , involving drilling to the center of the Earth to restart the stopped rotation of the magnetic core. The line is ostensibly aimed at the center of the Earth. Apparently, not even Newton could predict such a bold, daring and disastrous movie. Or movies. [The panel shows a shaded sphere with a rocket launched from its top to the right. Several trajectories are plotted around the sphere.] [Trajectory 1 (in black) shows a successful circular orbit.] Humans slip the bonds of Earth to travel the stars [Trajectory 2 (in red) shows a ballistic arc that crashes into the sphere near the bottom.] Civilization ends in fire [Trajectory 3 (in red) shows a much shorter ballistic arc. No label.] [Caption below the panel:] In retrospect, Newton's little cannonball drawing does a surprisingly good job illustrating the range of possible futures of our species.

Thorough Analysis

Thorough Analysis

https://www.xkcd.com/2012

https://www.explainxkcd.com/wiki/index.php/2012:_Thorough_Analysis

[The comic panel consists of the beginning of a research paper written in gray, with the last line being slightly cut at the bottom by the panels frame indicating that the text continues below.] 1. Introduction The December 1811 earthquake near New Madrid, Missouri reportedly caused church bells to ring in Charleston, South Carolina. But did it? The original bell tower has been lost, but a computer model of the church building was created from archival plans and forensic masonry analysis. Genetic testing of the timber from local trees related to those used in the bell tower shows a weakness in the [Caption below the panel:] My favorite genre of scientific papers are exhaustive 100-page treatises that answer some minor question with the obsessive thoroughness of the 9/11 Commission Report.

This comic remarks on how obsessively some scientific papers investigate some insignificant, obscure things. It gives the example of an investigation into whether an earthquake in 1811 caused church bells 600 miles away in Charleston, South Carolina to ring, which, although mildly interesting, is of minimal scientific importance. The earthquake itself is of enormous scientific interest, as an earthquake of the same magnitude in the same area today could cause enormous damage, but Charleston is not in the area considered at significant risk. An explicit comparison is made to the 9/11 Commission Report , a study that was undertaken to, broadly, answer the question of how the September 11 attacks were able to occur (and by extension, what errors in security and communication needed to be addressed to improve detection of and response to other terrorist acts). This paper describes the researchers going as far as to genetically test local trees, likely to find those most closely related to the trees used for construction, so as to measure their structural properties and extrapolate the likely structural properties of the original building. Such extrapolation might require its own study to back its validity. It is likely in real life that the small differences such research would reveal would end up being too unsubstantial to have actually warranted any searching. The title text is a continuation of this paper, which researches into the bells' shapes, and then goes on to note that the entire interview is provided in Appendix VII, indicating that this paper has a substantial amount of additional information considered distracting from the main body. The Tower of London would be a strange place to seek expertise on church bells: even its Bell Tower contains warning bells rather than church-style bells (explain xkcd's transcript with the Tower of London officials on this manner can be viewed in Appendix B). Until 2017, the nearby Whitechapel Bell Foundry would have been a much better (arguably the best possible) source of information. Whites of Appleton (in Oxfordshire) or John Taylor & Co (in Loughborough) would be current alternatives. Closer to home for the paper's author, the McShane Bell Foundry in Maryland is likely to offer far more relevant expertise certainly than the Tower of London, and may in addition be able to offer relevant insights specific to the history of bellfounding in the USA. In keeping with the meta thorough analysis theme of the original comic and this explanation, the comic starts with "The December 1811 earthquake near New Madrid, Missouri..." The town of New Madrid existed in 1811, but Missouri Territory did not exist until June 4, 1812, and the State of Missouri not until August 10, 1821. [The comic panel consists of the beginning of a research paper written in gray, with the last line being slightly cut at the bottom by the panels frame indicating that the text continues below.] 1. Introduction The December 1811 earthquake near New Madrid, Missouri reportedly caused church bells to ring in Charleston, South Carolina. But did it? The original bell tower has been lost, but a computer model of the church building was created from archival plans and forensic masonry analysis. Genetic testing of the timber from local trees related to those used in the bell tower shows a weakness in the [Caption below the panel:] My favorite genre of scientific papers are exhaustive 100-page treatises that answer some minor question with the obsessive thoroughness of the 9/11 Commission Report.

Rock

Rock

https://www.xkcd.com/2013

https://www.explainxkcd.com/wiki/index.php/2013:_Rock

[Cueball and Megan are looking at a rock that Megan is holding up in one hand.] Megan: This rock erupted from a volcano near the South Pole when the world was frozen over, just before multicellular life arose. [Zoom out reveals that Cueball and Megan are standing on the beach of a bay with hills in the background. The water surface is quite flat without any waves. Megan throws the rock which skips 5 times across the water before it sinks.] Stone: Skip Skip Skip Skip Skip Plunk [Zoom back on Cueball and Megan who are still looking in the direction she threw the stone.] Megan: Now it'll be covered in sediment that becomes a new rock layer. It will likely stay buried until it melts down, erodes away, or the earth is consumed by the sun. [Cueball and Megan still looking the same way.] Cueball: Today was a weird day in its incredibly long life. Megan: Five brief skips, then eons of darkness. Cueball: Five is a lot, though! Megan: It was a good throw. Megan throws the rock with her left hand, which supposes that she may be left-handed.

Megan either knows enough about geology to tell on sight how this particular rock formed, or has brought this rock from a collection. Alternatively she’s simply guessing. Despite admiring its formation, all she wants is to use it as a skipping stone to give it "a weird day in its life" (similar to 325: A-Minus-Minus ), and possibly confuse future geologists. Megan provides three pieces of information about the rock: It formed at the south pole, during an ice age, just before multicellular life developed. Unfortunately, due to disagreements among geologists and palaeontologists about when exactly the first multicellular life emerged it is unclear which time Megan refers to - and consequently where she is and what kind of rock she is holding. There are two possibilities: Thus — assuming that Megan has accurately identified the stone — the stone is either from Western Africa or Northern Europe and has "travelled" from there to get to her. Stone skipping is the art of throwing a flat stone across water in such a way that it bounces off the surface. Despite there being many factors attributed to successfully skipping a stone (including the attributes of the stone itself), Cueball and Megan are in agreement that skipping this particular stone five times is an above-average throw. (It is, however, far short of the world record of 88 skips set by Kurt Steiner in 2013). This comic is one of many that look at everyday things from a new, philosophical perspective. [Cueball and Megan are looking at a rock that Megan is holding up in one hand.] Megan: This rock erupted from a volcano near the South Pole when the world was frozen over, just before multicellular life arose. [Zoom out reveals that Cueball and Megan are standing on the beach of a bay with hills in the background. The water surface is quite flat without any waves. Megan throws the rock which skips 5 times across the water before it sinks.] Stone: Skip Skip Skip Skip Skip Plunk [Zoom back on Cueball and Megan who are still looking in the direction she threw the stone.] Megan: Now it'll be covered in sediment that becomes a new rock layer. It will likely stay buried until it melts down, erodes away, or the earth is consumed by the sun. [Cueball and Megan still looking the same way.] Cueball: Today was a weird day in its incredibly long life. Megan: Five brief skips, then eons of darkness. Cueball: Five is a lot, though! Megan: It was a good throw. Megan throws the rock with her left hand, which supposes that she may be left-handed.

JWST Delays

JWST Delays

https://www.xkcd.com/2014

https://www.explainxkcd.com/wiki/index.php/2014:_JWST_Delays

[Top caption, in the panel:] James Webb Space Telescope [Subtitle of top caption:] Launch Delays [There is a positive-quadrant only line graph. The x- axis is labeled 'Current Date' and the y axis is labeled 'Planned Launch Date'. The dates on both of the axes range from 1995 to 2030.] [In the graph are 15 points, starting at (1997,2007) and extending at a slope of a little less than one. The most recent one is labeled 'Now: 2021'.] [There are two lines on the graph: a red one and a dashed black one. The red one is a regression of the points on the graph. It has a slope of about ⅔. The black one is a line with a slope of one. They intersect at the point (2026,2026), marked by the label 'Late 2026'?] [Caption below the panel:] Look, at least the slope is less than one.

The James Webb Space Telescope (JWST) is a space telescope created to be the successor of the Hubble Space Telescope . The telescope has been in development since 1996, but has been plagued by numerous delays and cost overruns. This comic was likely inspired by the most recent delay announcement , which was posted on June 27, 2018. At that time, the JWST was scheduled to launch on March 30, 2021. This comic portrays the launch delays and the new predicted launch years and the times at which those predictions were made. There have been so many delays in this project that you can plot a line of best fit with a surprisingly high degree of accuracy. Randall says optimistically that the line’s slope is less than one (there is less than one year of new delay per year of elapsed time), implying, of course, that if events continue without further intervention, it will eventually be built, with a predicted date of late 2026. The title text alludes to the famous research over the universe’s accelerating expansion . The expansion had been predicted to be slowing due to gravity from everything in the universe; instead, it was found to be accelerating since about 5 billion years ago. Here, Randall looks at the apparently ever-delaying schedule and observes that the delay per time does not decrease, although the date gets nearer (which should help to schedule the launch date, as research and unknown parameters are replaced with engineering and exact predictions and measurements). However, this delay inflation contradicts Randall's usage of a linear trendline. Given the COVID-19 pandemic brought some additional delays in 2020 and 2021, the "early 2020" date was perhaps unintentionally prescient. The Wikipedia article linked above includes a table which provides the data points for the chart: [Top caption, in the panel:] James Webb Space Telescope [Subtitle of top caption:] Launch Delays [There is a positive-quadrant only line graph. The x- axis is labeled 'Current Date' and the y axis is labeled 'Planned Launch Date'. The dates on both of the axes range from 1995 to 2030.] [In the graph are 15 points, starting at (1997,2007) and extending at a slope of a little less than one. The most recent one is labeled 'Now: 2021'.] [There are two lines on the graph: a red one and a dashed black one. The red one is a regression of the points on the graph. It has a slope of about ⅔. The black one is a line with a slope of one. They intersect at the point (2026,2026), marked by the label 'Late 2026'?] [Caption below the panel:] Look, at least the slope is less than one.

New Phone Thread

New Phone Thread

https://www.xkcd.com/2015

https://www.explainxkcd.com/wiki/index.php/2015:_New_Phone_Thread

[A thread of posts by the same user is shown with a default user profile, and square and heart-shaped buttons.] Whoa, weird I'm looking at my timeline on my friends phone, and some of my posts look normal What the hell? I mean the words are correct That's exactly what I typed! ????????? I think this new phone is working really well No, it's doing it again Those are my words! Help! How do I explain? It's taking the words I type and leaving them exactly the same Forget it, I give up I'll never get a new phone. This one is perfect. What?!? Listen, if you're thinking about buying the new Mobile Pro 3, you should. It's the best phone on the market at an incredible price. [ORDER NOW button] AAAAA HELPPP I love my new phone!!!!

This comic shows the posts on an online forum by a person whose new phone is programmed to autocorrect every complaint about the phone to applaud it, à la Orwell. The phone goes so far as to change a certain complaint to a scripted customer testimonial, complete with a hyperlink to an ordering site. This is of course a highly undesirable feature [ citation needed ] . This is continued in the title text, which presumably contains several flattering compliments about the great developers and the company. "It's taking the words I type and leaving them exactly the same", "I mean the words are correct" and "some of my posts look normal" are definitely something one would not normally say. However, the auto-correct features of cell phones are so notorious for mangling people's posts, that one might express astonishment at a phone which did not change one's meaning. However the rest of the thread does not support this interpretation. The original posts may have read something like this: Whoa, weird I'm looking at my timeline on my friends phone, and some of my posts look strange What the hell? I mean the words are different That isn't what I typed!' ????????? I think this new phone isn't working properly No, it's doing it again Those aren't my words! Help! How do I explain? It's taking the words I type and changing them [from criticism to praise] Forget it, I give up I'll just get a new phone. This one is crap . {or this message may have been inserted entirely by the phone} What?!? Listen, if you're thinking about buying the new Mobile Pro 3, you shouldn't . It's the worst phone on the market , a total rip-off. DON'T BUY IT! {or this entire paragraph may be an ad inserted by the phone with no prompting} AAAAA HELPPP I hate my new phone!!!! I'm going to tell the manufacturer that their business practices are DEPLORABLE and HEINOUS and their developers are DISGUSTING and I'm going to report them to the FCC for their DESPICABLE CRIME . The posts also make sense when posts are read in the reverse order. The comic may have been inspired by a bug in Samsung Galaxy S9 and Note 8 , discovered a few days earlier – the phone sometimes sent random photos to contacts without leaving any sort of evidence. This doesn't happen with the Mobile Pro 3. [A thread of posts by the same user is shown with a default user profile, and square and heart-shaped buttons.] Whoa, weird I'm looking at my timeline on my friends phone, and some of my posts look normal What the hell? I mean the words are correct That's exactly what I typed! ????????? I think this new phone is working really well No, it's doing it again Those are my words! Help! How do I explain? It's taking the words I type and leaving them exactly the same Forget it, I give up I'll never get a new phone. This one is perfect. What?!? Listen, if you're thinking about buying the new Mobile Pro 3, you should. It's the best phone on the market at an incredible price. [ORDER NOW button] AAAAA HELPPP I love my new phone!!!!

OEIS Submissions

OEIS Submissions

https://www.xkcd.com/2016

https://www.explainxkcd.com/wiki/index.php/2016:_OEIS_Submissions

SUB[43]: All integers which do not appear in the example terms of another OEIS sequence SUB[44]: Integers in increasing order of width when printed in Helvetica SUB[45]: The digits of Chris Hemsworth's cell phone number SUB[46]: All integers, in descending order SUB[47]: The digits of the OEIS serial number for this sequence SUB[48]: 200 terabytes of nines SUB[49]: The decimal representation of the bytes in the root password to the Online Encyclopedia of Integer Sequences server [Caption below the panel:] OEIS keeps rejecting my submissions

The OEIS is the Online Encyclopedia of Integer Sequences , a listing of hundreds of thousands of sequences of integers, generally of real mathematical interest, such as prime numbers or Armstrong numbers . The OEIS normally expects submissions to be accompanied by references to scholarly articles about, or at least referencing, the sequence. They would not be interested in the personal or idiosyncratic sequences proposed by Randall, though they do have the list of subway stops on the New York City Broadway line (IRT #1) , perhaps because a NY Times article mentioned that they don't. Randall is trying to put his integer sequences on the OEIS website, including making OEIS reveal its password. sub[43] - All integers which do not appear in the example terms of another OEIS sequence Every OEIS sequence lists several example terms to demonstrate the content of said sequence. This request wants to list all integers which are not used as examples elsewhere. Any numbers used as example terms for this sequence are not counted, so this list is not self-disqualifying. It is well-defined at any given time. Like many other OEIS sequences, it has infinitely many terms (more precisely, it includes all integers except a finite number). However, it may change at any time, whenever a new sequence or a new example is added to the OEIS. If included, it would therefore have to be constantly updated. Such integers are sometimes called " uninteresting numbers " in mathematical terms, and attempts have been made to count them. The list changes, but in July 2009 it began 11630, 12067, 12407, 12887, 13258... sub[44] - Integers in increasing order of width when printed in Helvetica This sequence is not uniquely defined as it depends on the specific version of the Helvetica font used, its point size, the software used to render it (e.g. kerning algorithm), the handling of equal widths by the sorting algorithm and possibly other parameters. Also, all digits usually have the same width, with the exception of the sequence "11", which is a tiny bit narrower because a kerning pair exists in Helvetica. Without an additional tie-breaker for equal width numbers, the order is: 1 to 9 in no particular order, 11, 10 and 12 to 99 in no particular order and so on; for a particular choice of parameters the first 50 terms might be: 1, 9, 6, 2, 8, 5, 0, 7, 3, 4, 11, 61, 71, 91, 21, 51, 81, 41, 31, 19, 13, 18, 10, 12, 15, 16, 14, 17, 69, 63, 68, 79, 60, 62, 65, 73, 78, 99, 93, 98, 66, 70, 72, 75, 29, 90, 92, 95, 23, 28... Despite all of the above issues, and as a direct response to this comic, a well-defined version of this sequence was added to the OEIS . sub[45] - The digits of Chris Hemsworth's cell phone number An attempt to phish the phone number of actor Chris Hemsworth . Luckily for the OEIS there is a loophole to this request: the correct ordering of the digits isn't specified. sub[46] - All integers, in descending order To list all integers in descending order, you would have to begin at the largest integer, but there is no largest integer, so this is impossible. It is equally impossible to list all integers in ascending order, for that matter. On the other hand, A001477 is the sequence of all nonnegative integers in ascending order, as there is the smallest nonnegative integer. Also, A001057 is the sequence of all integers, but in canonical order (i.e. by increasing absolute value). sub[47] - The digits of the OEIS serial number for this sequence This sequence is only important tautologically. sub[48] - 200 terabytes of nines This submission appears to be a joke on common video game limits for, e.g., currency or ammunition, in which the maximum a player can carry is one less than a power of 10. This sequence would be entirely useless, as there is no mental effort required to conceive a list that consists only of a single repeated term, however arbitrarily large. Such a list is also incredibly wasteful; to give a comparison, this very large math proof from 2016 is also 200 terabytes, and requires a supercomputer to hold in its entirety. 200 terabytes is equal to 2 × 10 14 bytes. In UTF-8, each ASCII character, including control characters such as ␂ (start of text) and ␍ (carriage return), can be represented by a single byte. If the list is presumed to be formatted as "␂9␍9␍9 ... 9␍9␃", the first term would take up 3 bytes, and all other terms would take up 2 bytes. Assuming Randall wants the file size to be 200 terabytes minimum , the resulting list would be a minimum of 1 × 10 14 , or 100 trillion, terms long. Curiously, OEIS does in fact contain an entry that lists " all nines " which contains this proposal as a subsequence. sub[49] - The decimal representation of the bytes in the root password to the Online Encyclopedia of Integer Sequences server This would give any user the password to OEIS. Anyone can easily forecast what happens next. Perhaps the idea is to hack OEIS on the premise that accepting this sequence will force OEIS staff to populate it. sub[59] (title text) - The submission numbers for my accepted OEIS submissions in chronological order This would only be useful to Randall. If all of his submissions have been rejected, this would be an empty set. However, if this submission is accepted, the set would, by definition, include at least one number (except that this would not be known at the time of submission). Thus, as in the Russell Paradox, this set would be out of date as soon as it was accepted, since the set of accepted submission numbers would change at that point. SUB[43]: All integers which do not appear in the example terms of another OEIS sequence SUB[44]: Integers in increasing order of width when printed in Helvetica SUB[45]: The digits of Chris Hemsworth's cell phone number SUB[46]: All integers, in descending order SUB[47]: The digits of the OEIS serial number for this sequence SUB[48]: 200 terabytes of nines SUB[49]: The decimal representation of the bytes in the root password to the Online Encyclopedia of Integer Sequences server [Caption below the panel:] OEIS keeps rejecting my submissions

Stargazing 2

Stargazing 2

https://www.xkcd.com/2017

https://www.explainxkcd.com/wiki/index.php/2017:_Stargazing_2

[In a dark panel, Megan is a TV host standing in front of a group of 5 people: two Cueballs, Ponytail, Hairbun and a Megan-like woman.] Host: Welcome back to stargazing. Host: When the stars disappeared this morning, I figured I had to find a new job, but they're back! This rules! [A frame-less white panel in which the host points to the upper right with the Megan-like woman, Ponytail and Cueball looking in that direction.] Host: Those three stars form a constellation called the triangle. Host: Those three are another triangle. Host: Lotta triangles. Very important shape. [Back to a dark panel with the host now pointing to the upper left in a close-up.] Host: Those dots are planets, or "fool's stars." Without interstellar travel, they're the only ones we can realistically hope to dump trash on. Host: Speaking of space trash, that dot is a satellite. There are apps that will tell you whose fault it is. [The host is now turned right not pointing, still in a close-up.] Off-panel voice: What's that blinking one? Host: Airplane. They're full of snacks and money and stuff, but don't bother trying to catch them- they're way too high up. Host: Learned that the hard way in grad school. Host: Got a thesis out of it, at least.

This is the second comic in the Stargazing series: The first was 1644: Stargazing , two and a half years earlier. It was followed by 2274: Stargazing 3 one and a half years later. This comic continues with Megan as a TV host mixing accurate astronomical information with trivialities, as well as utterly bizarre statements. (See this section from the original Stargazing comic about the host and also the trivia , from the original comic, regarding the gender of the host). In the first panel, the host voices surprise that the stars are visible again after disappearing during daylight. The host mentions three stars in a constellation which she says is called The Triangle, likely referring to the constellation Triangulum , which is in fact just three main stars in a narrow triangle. However, this may also simply be intended to show the host's lack of knowledge of constellations, since she then goes on to point out three other stars forming a triangle and concludes that one can form lots of triangles by connecting groups of three stars. In Euclidean and non-Euclidean geometry, any set of three non-collinear points will form a triangle, so to say that there are a "lotta triangles" is both trivial and an understatement. [ citation needed ] (There are about 125 billion triangles visible in the night sky with around 9096 visible stars.) Then she points to planets, calling them dots known as "fool's stars" (like fool's gold). Planets such as Venus and Jupiter are often mistaken as stars, and the word itself is derived from the Greek, planētēs or "wanderer." She also notes that lacking interstellar transportation, humanity will likely only reach the planets within our solar system. However, she then makes the seemingly ludicrous assertion that humans will turn these planets into interplanetary landfills, which might be a comment on how humans have used the Earth. The host also notices a dot of "space trash": An artificial satellite. Since the nascent Space Age, the Earth's orbit has gradually accumulated artificial materials that include satellites, spent rockets, and space stations. There are concerns such debris accumulation will increasingly imperil current and future space projects. However, the host claims there is an app that can tell you "whose fault it is," presumably a satellite-tracking smartphone app such as SkyView which can inform you who launched a given satellite and thus whose "fault" that particular bit of space-junk might be. The host eventually goes off on a tangent when someone from the audience points out something blinking in the sky. The host says it is a plane, and tells them what is inside it. The host continues, "don't bother trying to catch that one." This could be understood as she means it's too hard to point the telescope at it properly because it is moving too fast. In the title text, however, she means this literally, revealing that at one point during her studies she apparently used the reflective mirror of a telescope to shine light directly at airplanes, which caused the Federal Aviation Administration (FAA) to close down the observatory. She claims it was worth getting shut down by the FAA because she completed her thesis for her graduate degree. "Got a thesis out of it" is a phrase typically used by a scholar after discussing a research project, as a way of indicating that it was actually the main research they had conducted as a student in graduate school. Conducting research and writing it up in a thesis is one of the major hurdles toward earning a graduate degree (masters or doctorate). In the title text, she clarifies that as she was exiting the observatory, she literally "got", as in "stole", someone else's thesis paper and multiple doctorates (presumably framed degrees), either to fraudulently claim them as her own accomplishments, or perhaps just because she wanted to steal stuff. Usually "got a thesis" is shorthand for the process of "writing a lengthy thesis paper and having it be accepted as a requirement for graduation", however in this case she simply swiped someone else's document. The revelations that she's extremely unqualified (and unethical) would explain her many bizarre statements. [In a dark panel, Megan is a TV host standing in front of a group of 5 people: two Cueballs, Ponytail, Hairbun and a Megan-like woman.] Host: Welcome back to stargazing. Host: When the stars disappeared this morning, I figured I had to find a new job, but they're back! This rules! [A frame-less white panel in which the host points to the upper right with the Megan-like woman, Ponytail and Cueball looking in that direction.] Host: Those three stars form a constellation called the triangle. Host: Those three are another triangle. Host: Lotta triangles. Very important shape. [Back to a dark panel with the host now pointing to the upper left in a close-up.] Host: Those dots are planets, or "fool's stars." Without interstellar travel, they're the only ones we can realistically hope to dump trash on. Host: Speaking of space trash, that dot is a satellite. There are apps that will tell you whose fault it is. [The host is now turned right not pointing, still in a close-up.] Off-panel voice: What's that blinking one? Host: Airplane. They're full of snacks and money and stuff, but don't bother trying to catch them- they're way too high up. Host: Learned that the hard way in grad school. Host: Got a thesis out of it, at least.

Wall Art

Wall Art

https://www.xkcd.com/2018

https://www.explainxkcd.com/wiki/index.php/2018:_Wall_Art

[White Hat and Cueball are standing together and looking at eleven framed pictures on a wall.] Cueball: Getting older is so weird. 20 years ago, I thought thumbtacked Pokémon posters made my wall look so cool. [Cueball has his hands raised up in a close-up.] Cueball: But these days I feel this compulsion to get framed oil paintings and spend hours carefully arranging them. [Return to the setting in the first frame.] White Hat: These are all oil paintings of Pokémon. Cueball: Look, I’m meeting maturity halfway. This is the only xkcd comic ever where the year when the comic was published, in the Gregorian calendar, is the same as the comic's number. This comic is numbered 2018 and was published on Wednesday, July 11, 2018.

Pokémon is a media franchise managed by The Pokémon Company, which started with the release of the first video games, Pokémon Red and Blue , for the Game Boy in 1996. Originally released in Japan as Pokémon Red and Green , the game was released in North America as Pokémon Red and Blue in 1998, 20 years ago at the time of publishing. This is another comic about getting older. Cueball mentions that he thought Pokémon posters were cool 20 years ago (when Pokémon was first released). Now that he is older, he instead has framed oil paintings, which were what wealthier older folks were displaying on their walls at the times that their teenagers were widely into Pokémon. The punchline comes when White Hat mentions that his oil paintings are just paintings of Pokémon characters, showing that Cueball hasn't completely adopted those older cultures in 20 years of maturing, but does have more money. The title text mentions that Cueball originally had "regular" oil paintings. However, these appear to have been stolen from the Louvre , a famous art museum in Paris, which houses the Mona Lisa . Thus the "grumpy and unreasonable" detectives which came to retrieve the paintings. It even suggests that Cueball had attached those valuable and expensive oil paintings on his wall by poking through them with thumbtacks. The fact that Cueball stole expensive paintings, poked them with thumbtacks, and did not realize that the detectives were trying to recover priceless artwork that rightfully belonged to the museum may demonstrate that Cueball indeed has not completely grown up. The comic repeats a common theme of poking fun at how nerds tend to not fully "get" the culture surrounding them, adopting parts but remaining completely blind to other parts. Sharing and reading jokes about this may help people who experience that pattern handle the stress of being unable to completely conform, by bonding over the commonality. [White Hat and Cueball are standing together and looking at eleven framed pictures on a wall.] Cueball: Getting older is so weird. 20 years ago, I thought thumbtacked Pokémon posters made my wall look so cool. [Cueball has his hands raised up in a close-up.] Cueball: But these days I feel this compulsion to get framed oil paintings and spend hours carefully arranging them. [Return to the setting in the first frame.] White Hat: These are all oil paintings of Pokémon. Cueball: Look, I’m meeting maturity halfway. This is the only xkcd comic ever where the year when the comic was published, in the Gregorian calendar, is the same as the comic's number. This comic is numbered 2018 and was published on Wednesday, July 11, 2018.

An Apple for a Dollar

An Apple for a Dollar

https://www.xkcd.com/2019

https://www.explainxkcd.com/wiki/index.php/2019:_An_Apple_for_a_Dollar

[Megan is at the store counter, behind which Ponytail (the cashier) is waiting.] Megan: Just this apple, thanks. Ponytail: That will be one dollar. Megan: Exactly? No tax or anything? Ponytail: That's right. [Megan stares at the apple in a frameless panel.] [Scene zooms in on Megan.] Ponytail: ...Is that a problem? Megan: It's just weird to realize that every other transaction in my life will be more complicated than this. [Scene changes focus to Ponytail behind the counter.] Megan: This is like a platonic ideal exchange. An apple for a dollar. Ponytail: I see. [Scene changes back to Megan, once again lost in profound contemplation of the apple.] Megan: Are we on a frictionless plane? Is a train leaving Chicago at 40 mph? Should I solve for something?? Ponytail: Okay, apples are $2.17 now. Megan: That's... probably better for us both.

Megan is about to buy an apple at a grocery store when she is surprised that the price is exactly one dollar. A common practice in pricing items is to deliberately make them slightly less than a round number, such as $1.99 or $1.95 instead of $2, as a psychological trick to make the item seem significantly cheaper than it really is, as "less than two dollars" sounds much less than "two dollars" even though the difference of 0.01 is minimal. Additionally, in most cases in the US, sales tax must be taken into account, as it is generally not included in the list price (although, most states do exempt food sold in grocery stores from sales taxes), so a price rarely comes out to a round value. That it came out to an exact dollar is so strange for Megan that it throws her for a loop. Buying one apple for one dollar feels to her more like a simplified, imaginary Idea of a transaction (a " Platonic Ideal ") than like something that could actually happen in real life. Megan likely shares Randall's background in engineering and math. When learning science, engineering, and math in the education system, one studies examples where every number is some round value, and all situations are simplified to the barest essentials so as to demonstrate the ideas being taught. Then, when doing real problems in the real world, one spends the rest of one's life almost never being able to use the simplified tricks demonstrated as examples in school, because when math is used to describe the natural world, nothing is ever a round number unless by design. Megan references Platonic Idealism , which is the theory attributed to Plato that abstract or non-physical Ideas represent the purest, most accurate version of reality, but we can only perceive of more flawed versions of Ideas because of our limited viewpoint (as explained in his Allegory of the Cave). Thus we can understand the concept of a perfect circle or a perfect line, even though we have never seen one, and cannot create one. Megan believes she has glimpsed a Platonic Ideal because the absolute concept of currency is it is the exact worth of something in trade. Megan is awed because, if this is true, then she is witnessing the next layer of reality, which Plato often compared to heaven. The harsh difference between being able to buy an apple for a dollar at this quaint store, and having to deal with arbitrary decimals and numbers in the rest of life could be touching on Megan's life experience of the world not being what she was prepared for, resulting in her intense response. Regardless if that is true or not, it seems the cashier is unable to figure out how to handle it (or does not want to), and raises the price to an arbitrary non-rounded value, which has the intended effect of halting Megan's outburst. The unexpected resolution of the rising tension is a source of humor in this strip. Megan's references refer to common parameters used in solving science or math questions. A Frictionless plane is a scenario from the writings of Galileo to calculate the movement of an object down an inclined plane , since his equations did not account for friction . "A train leaving Chicago at 40 mph" refers to common math questions, involving trains and solving for the distance required to overtake said train, although this problem involves the rather unrealistic assumption that the train's velocity keeps constant and doesn't need to accelerate in order to reach its speed. Like the frictionless plane, this is a common simplification that allows the problem to be solved with quite simple techniques, just like having round quantities (e.g. 1 dollar/apple) eases arithmetic problems. See also 669: Experiment . Apples themselves are commonly used as units for math problems, including problems as simple as basic arithmetic. The comic repeats a common theme in the strip of engineers and computer scientists trying to apply their technical experience to social situations. In this case, the conversation partner is "normal", and does not respond supportively, which is a common situation in the real world and a possible point of empathy with readers. -- An alternate viable reading is that the conversation partner responds extremely supportively (by cleverly removing the source of Megan's distress, rather than by questioning the validity of Megan's response). This is a possible point of wish-fulfillment for readers. It seems that according to the title text, Megan only has (or only wants to spend) one dollar, so she would not be able to buy a whole apple at the new price (0.4608 × $2.17 ≈ $1). Stores usually sell whole apples, so asking for a fraction of one is not likely to work out. [ citation needed ] There are some stores, such as Dollar Tree , that specialize in selling everything in the store for one dollar per item, which would seem to be operating at that ideal... except they usually do charge sales tax on taxable items leading many sales to not be an even multiple of a dollar. If a store were to charge one dollar per item without charging sales tax, etc. separately (i.e. building the sales tax into the price of each dollar item), they might be able to simplify some operations, such as not dealing with coin change as much, cashiers would be able to calculate the total in their heads, etc. Customers other than Megan would probably be happier. [Megan is at the store counter, behind which Ponytail (the cashier) is waiting.] Megan: Just this apple, thanks. Ponytail: That will be one dollar. Megan: Exactly? No tax or anything? Ponytail: That's right. [Megan stares at the apple in a frameless panel.] [Scene zooms in on Megan.] Ponytail: ...Is that a problem? Megan: It's just weird to realize that every other transaction in my life will be more complicated than this. [Scene changes focus to Ponytail behind the counter.] Megan: This is like a platonic ideal exchange. An apple for a dollar. Ponytail: I see. [Scene changes back to Megan, once again lost in profound contemplation of the apple.] Megan: Are we on a frictionless plane? Is a train leaving Chicago at 40 mph? Should I solve for something?? Ponytail: Okay, apples are $2.17 now. Megan: That's... probably better for us both.

Negative Results

Negative Results

https://www.xkcd.com/2020

https://www.explainxkcd.com/wiki/index.php/2020:_Negative_Results

[Cueball is sitting in an office chair at a desk typing on a laptop computer. The following message is displayed above him:] Dear Nature Magazine, I found no evidence sufficient to reject the null hypothesis in any research areas because I spent the whole week playing The Legend of Zelda: Breath of the Wild . I'll send you another update next week! [Caption below the panel:] The push to publish negative results seems kinda weird, but I'm happy to go along with it.

Recently, scientists have begun encouraging each other to publish negative results, where a study failed to find the intended effect, as a way of counteracting publication bias (where only interesting positive results get published), which results in false-positive results being published while negative results are not. Cueball misinterprets the "push to publish negative results" as meaning that he should always attempt to publish the fact that he failed to find evidence of an effect, even when he didn't even try, spending his time playing a video game instead. This plays on the unspoken assumption that scientists would only choose to submit (and journals would only accept) negative results where a study was designed and executed well enough that it should have shown an effect or at least demonstrated evidence of some kind. Besides personal preferences, The Legend of Zelda: Breath of the Wild , the most recent Legend of Zelda game at the time of publication, was likely chosen for its notable length, Nintendo nerd cred, and a relevance to Nature magazine’s subject. The average time to beat 100% of the content is over 175 hours . The title text references the practice of "pre-registration" of a study, which is one means to prevent publication bias: details of a planned study are registered with an organization before the study is conducted, so that a null result or a change in methodology cannot be hidden. The title text may be a play on words, mixing this up with registering (or booking) travel. On the other hand, it may just be playing on the absurdity of pre-registering a simple trip to the beach with a registry for scientific studies. [Cueball is sitting in an office chair at a desk typing on a laptop computer. The following message is displayed above him:] Dear Nature Magazine, I found no evidence sufficient to reject the null hypothesis in any research areas because I spent the whole week playing The Legend of Zelda: Breath of the Wild . I'll send you another update next week! [Caption below the panel:] The push to publish negative results seems kinda weird, but I'm happy to go along with it.

Software Development

Software Development

https://www.xkcd.com/2021

https://www.explainxkcd.com/wiki/index.php/2021:_Software_Development

[Cueball and Hairy are standing together and Hairy holds a power tool in his hands.] Cueball: We need to make 500 holes in that wall, so I've built this automatic drill. It uses elegant precision gears to continually adjust its torque and speed as needed. Hairy: Great, it's the perfect weight! We'll load 500 of them into the cannon we made and shoot them at the wall. [Caption below the frame:] How software development works

Software development is often characterized by graceless solutions to rudimentary problems. Cueball has built an elegant drill (function) that can adjust torque and speed as necessary automatically to fulfill his requirement of 500 holes in the wall. Hairy , in a categorically inelegant solution, loads 500 drills into a cannon and shoots them at the wall. This solution, in reality, would entail too many ludicrous safety problems to execute, but in software, the implications are only really bad code . The casual disregard for the software itself is reminiscent of the idea of cattle not pets when deploying to servers. This resembles assigning two different software teams to resolve different parts of a problem and of making the independent tools collaborate to form a fluid solution. The so-called "drill team" is given the task of making the part of the system that makes a hole in the wall. The cannon team was given the task of making the part of the system that aims what the drill team produces at the designated place on the wall and subsequently drills the hole. The drill team assumed that the aiming device would merely position their portion on the wall allowing it to make the hole, but the cannon team could not make assumptions about how the drill team would generate holes - they needed to make something that could use whatever the drill team produced to make the holes, thus making a cannon, so they could ensure their success. The title text is a joke about how often in software the best solution to a problem is general rather than specific. See for example developers using Ruby on Rails (a full web framework with support for emails, templating, and web sockets) for a simple API-only service. They only need a very small part of rails (the hole drilling part), but end up with the whole framework anyway due to design limitations. Another explanation of the title text is that software development is also often characterized by complexity and unintentional interdependence between different modules of code. It is an unending source of frustration for coders that a seemingly minor change to code can cause major changes to how the program works, including changes seemingly unrelated to the specific code that changed. A similar problem is when a line of code that “should be” unnecessary (according to the rules of the programming language) ends up being essential because the program will not work if the code is cleaned up and the line removed. A final factor is that coders often write a particular function once in the first module, and then call back to that function when necessary in subsequent modules rather than rewriting the function over and over again. In that case, the first module cannot be eliminated, even if it is no longer necessary, because then all of the calls to the original function would be null, and the rest of the modules could not work. This can happen not just within programs but across them, as much software on the internet relies on large collections of program modules in public or open source software databases. When a module goes missing it can have wide ranging effects, as seen in March of 2016. In the context of the comic, it could be that the code for the cannon was written to check if it is “loaded” before it does anything, so the drill code is still needed to get the cannon to move on its motorized base and make the holes. Or the code for the drill defines an obscure variable that is used by other code for the cannon or its base, so “removing” the drill code would cause the cannon to “crash” and not operate. [Cueball and Hairy are standing together and Hairy holds a power tool in his hands.] Cueball: We need to make 500 holes in that wall, so I've built this automatic drill. It uses elegant precision gears to continually adjust its torque and speed as needed. Hairy: Great, it's the perfect weight! We'll load 500 of them into the cannon we made and shoot them at the wall. [Caption below the frame:] How software development works

Sports Champions

Sports Champions

https://www.xkcd.com/2022

https://www.explainxkcd.com/wiki/index.php/2022:_Sports_Champions

[Two rows of people wielding sports equipment are shown, six in the upper row, five in the lower, only the last has no equipment but is standing behind a lectern with a microphone attached to it. Below each person, their name is given and the decade in which they were champions of their sport is given below their name, in brackets. Here is a list of the 11 people:] [Woman with dark hair holding a tennis racket] Margaret Court (1960s) [Cueball with a golf club] Gary Player (1970s) [Cueball with a basketball] Lonzo Ball (2020s) [Hairy on a skateboard] Jake Halfpipe (2030s) [Woman with dark hair wearing a swim cap and goggles] Sarah Goggles (2030s) [A man with a baseball cap throwing a baseball to the right] Kevin Slurve (2050s) [A woman with long black hair in a knit cap and wearing ski googles is standing on skis holding ski poles] Julia Chairlift (2050s) [Hairy holding a badminton racket bouncing a shuttlecock on it] Dwight Shuttlecock (2060s) [Hairy holding a pair of shoes in his hand] Brandon Sponsorship (2060s) [Hairbun standing next to a bicycle.] Kate Dopingscandal (2070s) [Hairy standing behind a lectern with a microphone on it.] Jebediah Disasterous Postgame PressConference (2080s) [Caption below the panel:] Fun fact: Every sport eventually produces a champion competitor named after a common element of the game.

In an example of nominative determinism , the comic lists people whose surname relates to their participation in various sports. It is presented as though it was created in the far future, reflecting on champions over the decades through to the 2080s. The first three are real sportspeople, the remainder are imaginary players of the future. The names progress from real, to fictional-but-plausible, to rare or highly unusual, to utterly implausible and impractical names. The caricatures are participating in their sport, except for Jebediah who is standing at a lectern . Margaret Court (1960s, Tennis) Margaret Court is an Australian tennis player, former world number 1, who won many competitions in the 1960s and 70s. A tennis court is the playing arena used in that sport. Gary Player (1970s, Golf) Gary Player is a South African golfer who won nine major championships between 1959 and 1978. Competitors are often known as player s, such as in The Players Championship . Lonzo Ball (2020s, Basketball) Lonzo Ball is an American professional basketball player, with the Los Angeles Lakers at the time of publishing. The 2020s decade predicts future success, as he began playing professionally in 2017 and the comic was published in 2018. Basketball is, of course, a ball game . Jake Halfpipe (2030s, Skateboarding) A halfpipe is a structure used in extreme sports such as skateboarding and snowboarding. Sarah Goggles (2030s, Swimming) Goggles are protective eyewear used in many sports, such as swimming or skiing. Kevin Slurve (2050s, Baseball) A slurve is a baseball throwing technique, a portmanteau of sl ider and c urve . Julia Chairlift (2050s, Skiing) A chairlift is an aerial machine often used to transport winter sports participants up mountains. Dwight Shuttlecock (2060s, Badminton) A shuttlecock is a projectile used in the sport of badminton. Brandon Sponsorship (2060s, Unclear) Sporting professionals are often sponsored by corporations. Brandon is holding a pair of shoes, which are probably a branded sponsorship item. Possible pun on "brand on sponsorship", i.e. a sponsored player. Kate Dopingscandal (2070s, Cycling) There have been many doping scandals in the world of cycling. Doping refers to the "use of physiological substances or abnormal methods to obtain an artificial increase in performance." (See: 1173: Steroids .) Jebediah Disasterous Postgame-PressConference (2080s, Unspecified) At the end of sporting events - i.e. post-game - there is often a press conference where the competitors discuss the result. Sometimes, these live interviews are a disaster. Randall has chosen to spell his name as "Disasterous", rather than the more conventional "Disastrous". Title Text: Usain Bolt (2010s) and Derek Legs (2090s, Sprinting) From the title text, Usain Bolt is a retired world record sprinter . He was a solid contender for this list since he can bolt down the track. However the fictional Derek Legs is selected, either as an even faster sprinter, or because “legs” more clearly and unambiguously relates to running than “bolt” does. [Two rows of people wielding sports equipment are shown, six in the upper row, five in the lower, only the last has no equipment but is standing behind a lectern with a microphone attached to it. Below each person, their name is given and the decade in which they were champions of their sport is given below their name, in brackets. Here is a list of the 11 people:] [Woman with dark hair holding a tennis racket] Margaret Court (1960s) [Cueball with a golf club] Gary Player (1970s) [Cueball with a basketball] Lonzo Ball (2020s) [Hairy on a skateboard] Jake Halfpipe (2030s) [Woman with dark hair wearing a swim cap and goggles] Sarah Goggles (2030s) [A man with a baseball cap throwing a baseball to the right] Kevin Slurve (2050s) [A woman with long black hair in a knit cap and wearing ski googles is standing on skis holding ski poles] Julia Chairlift (2050s) [Hairy holding a badminton racket bouncing a shuttlecock on it] Dwight Shuttlecock (2060s) [Hairy holding a pair of shoes in his hand] Brandon Sponsorship (2060s) [Hairbun standing next to a bicycle.] Kate Dopingscandal (2070s) [Hairy standing behind a lectern with a microphone on it.] Jebediah Disasterous Postgame PressConference (2080s) [Caption below the panel:] Fun fact: Every sport eventually produces a champion competitor named after a common element of the game.

Y-Axis

Y-Axis

https://www.xkcd.com/2023

https://www.explainxkcd.com/wiki/index.php/2023:_Y-Axis

[Graph within a frame. The x-axis is unlabeled, with, in addition to the vertical line representing the y-axis, six straight vertical grid lines, evenly spaced, each corresponding to one of the six data points of the line plot. The y-axis has eleven grid lines, including the x-axis, which are evenly spaced where they intersect the y-axis. Only the lines for 0% (the x-axis), 50% (the line starting halfway up the graph), and 100% (the top of the graph) are labeled. Except for the x-axis and the top line, these "horizontal" grid lines are not straight: they start out horizontally, but by the time they have met the first vertical line, representing the first data point, they have diverged significantly from their original positions. The lines representing 20% to 90% curve upwards and then back to horizontal, so that the eight lines representing y-axis values from 20%-90% are, after the first data point, squeezed into the top 10% of the area of the graph. From this point onwards, the line representing 20% is horizontally even with the label for the 90% line, and the 30%-90% lines are evenly spaced between the 20% line and the 100% line at the top of the graph. Similarly, the 10% line curves downwards and then back to horizontal by the first data point, continuing horizontally from there at a level of approximately 2% of the total height of the graph. The data points are at approximately 30%, 35%, 20%, 33%, 30%, and 80% of the total height of the graph, and are all between the lines which begin at 10% and 20% of the height of the y-axis.] [Caption below the frame:] People have wised up to the "Carefully Chosen Y-Axis Range" trick, so we misleading graph makers have had to get creative.

The comic itself makes a poke at recent trends where the y range for a given dataset is exaggerated, so that a dataset that varies very little in its y-values is exaggerated by constricting the y-axis of the graph to range from just barely below the minimum y-value to just barely above the maximum y-value. This spreads out the y-values so very small differences appear larger and more significant than they really are. The graph shows an attempt to mislead readers by manipulating the y-axis scale of the graph in a creative manner: The y-axis labels at the left side of the graph are normally spaced; however, the thin, gray gridlines marking each 10% increment are wavy, not straight, and they bunch up before reaching the first data point, resulting in a distorted effective y-axis for the rest of the graph. All the data points lie between the 10% and 20% gridlines, but a casual reader may not notice this and think that the graph uses the full 0% to 100% range. The title text refers to the Semi-log plot , where one of the two axes is plotted on a logarithmic scale. The title text takes this to a further extreme with the semi-semi-log, where the y-axis labels are only interpreted as logarithmic on the left half of the graph. (For example, on the left half of the graph "3" would be interpreted as 10^3, or 1000, but on the right half it would be interpreted as 3) [Graph within a frame. The x-axis is unlabeled, with, in addition to the vertical line representing the y-axis, six straight vertical grid lines, evenly spaced, each corresponding to one of the six data points of the line plot. The y-axis has eleven grid lines, including the x-axis, which are evenly spaced where they intersect the y-axis. Only the lines for 0% (the x-axis), 50% (the line starting halfway up the graph), and 100% (the top of the graph) are labeled. Except for the x-axis and the top line, these "horizontal" grid lines are not straight: they start out horizontally, but by the time they have met the first vertical line, representing the first data point, they have diverged significantly from their original positions. The lines representing 20% to 90% curve upwards and then back to horizontal, so that the eight lines representing y-axis values from 20%-90% are, after the first data point, squeezed into the top 10% of the area of the graph. From this point onwards, the line representing 20% is horizontally even with the label for the 90% line, and the 30%-90% lines are evenly spaced between the 20% line and the 100% line at the top of the graph. Similarly, the 10% line curves downwards and then back to horizontal by the first data point, continuing horizontally from there at a level of approximately 2% of the total height of the graph. The data points are at approximately 30%, 35%, 20%, 33%, 30%, and 80% of the total height of the graph, and are all between the lines which begin at 10% and 20% of the height of the y-axis.] [Caption below the frame:] People have wised up to the "Carefully Chosen Y-Axis Range" trick, so we misleading graph makers have had to get creative.

Light Hacks

Light Hacks

https://www.xkcd.com/2024

https://www.explainxkcd.com/wiki/index.php/2024:_Light_Hacks

[Megan walks to the right, holding a sheet of paper and a light bulb] Megan: I discovered a cool life hack - you can put a white sheet behind a lightbulb to reflect more light. Off-panel voice: I'm ... not sure that's a life hack. [Megan stops, and positions the light bulb between two sheets of paper] Megan: And you can put a sheet in front to diffuse the light. Off-panel voice: So you've invented the lampshade. Megan: Life hacks! Megan: Freeman Dyson suggested that advanced civilizations would build spherical shells that surrounded their bulbs, redirecting 100% of their energy. Off-panel voice: Yes, they have those at IKEA. Megan: Well, they might. Infrared surveys are inconclusive. Off-panel voice: You know you can just check their website. Megan: Ooh, great life hack! Off-panel voice: No!

" Life hacking " is the practice of using common everyday items in novel ways to increase the convenience or enjoyment of daily activities. This comic pokes fun at the many blogs and video channels that purport to cover life hacking tips, but merely point out obvious or intended uses for products or well known techniques as low effort clickbait. Megan tells someone off panel, possibly Cueball , that, by using sheets of paper, she can reflect and diffuse the light coming from a lightbulb. She refers to her discovery as a life hack, while Cueball sarcastically points out that all she has done is reinvent the lampshade, to which Megan again refers to as a life hack. A Dyson sphere is a hypothetical energy-collecting megastructure encompassing a star, and collecting a large percent of its energy in the process. It is named after the physicist and mathematician Freeman Dyson . The joke here is that Dyson spheres are generally not intended for lightbulbs, yet using them in this way is suggested by Megan as a life hack, poking fun at the fact that life hacks make things more complicated instead of convenient. Freeman Dyson argued that Dyson spheres, if they existed, could be found by infrared surveys, as large objects that would emit infrared radiation. IKEA pendant lampshades are spherical shells that surround the bulb. Megan claims studies have tried to use infrared surveys to find Dyson spheres at Ikea locations, without success. When Cueball tells her the easier way, searching for it online, she eagerly refers to his method as another life hack, much to Cueball's annoyance. The title text creates a different sort of confusion of the term lifehack, with another sort of popular clickbait videos. Described activity, if done, would be considered a prank - depriving the distractible civilization of their sunlight and energy source, rather than bringing any benefit to the builders of the smaller sphere. [Megan walks to the right, holding a sheet of paper and a light bulb] Megan: I discovered a cool life hack - you can put a white sheet behind a lightbulb to reflect more light. Off-panel voice: I'm ... not sure that's a life hack. [Megan stops, and positions the light bulb between two sheets of paper] Megan: And you can put a sheet in front to diffuse the light. Off-panel voice: So you've invented the lampshade. Megan: Life hacks! Megan: Freeman Dyson suggested that advanced civilizations would build spherical shells that surrounded their bulbs, redirecting 100% of their energy. Off-panel voice: Yes, they have those at IKEA. Megan: Well, they might. Infrared surveys are inconclusive. Off-panel voice: You know you can just check their website. Megan: Ooh, great life hack! Off-panel voice: No!

Peer Review

Peer Review

https://www.xkcd.com/2025

https://www.explainxkcd.com/wiki/index.php/2025:_Peer_Review

[Ponytail is sitting in a office chair at a desk reading from a laptop. Above her the text from the screen is shown in a frame with a zigzag arrow pointing to the laptop.] RE: Economics Journal Submission We have received your manuscript "The Bizarre Economics of Academic Publishing: Why Volunteer Peer Reviewers Should Rise Up and Demand Payment from For-Profit Journals." We have elected not to send it out for review.

When a researcher wants to publish their findings, they send it to an academic journal. The editor of the journal is another researcher (usually a college professor), who gets paid nothing or a minimal honorarium for editing the journal. The editor chooses a few (usually three) peer reviewers who are other researchers familiar enough with the study's subfield to judge the study's quality fairly and accurately, and sends it out to them for review. These peer reviewers do not get paid for the work of reviewing the manuscript and offering a detailed critique of every part of the study, from literature review to methodology to conclusions drawn from the results. If the peer reviewers and editor agree that the study was well-conducted and the paper well-written (or just needs minor revisions), it is accepted and published in the journal. The researcher is not paid for getting their paper published in the journal. In short, nobody in the process is paid for their work except the journal publisher, who charges other researchers, libraries and individuals for access to the fruit of these people's free labor. This is commonly referred to as a " paywall ". This system relies upon researchers to be employed by either companies or universities in positions which require them to publish in order to remain employed or achieve promotions or pay raises. In universities, only postdocs and tenure-track or tenured professors are paid in a way that figures in their research time as well as their teaching time, which means that anyone not in one of those positions (lecturers, educators, adjunct instructors) is not paid for any research they might be doing and publishing, nor are those who are conducting research but cannot get a tenure-track job due to universities replacing tenure lines with non-tenure-track positions. Charging for access to these works has raised controversy in recent years, due to concerns that this may lead to information silos . Ponytail seems to be presenting papers concluding that this flow of currency is not equitable. Unfortunately, the journal she has submitted these findings to has opted not to review or publish them, likely because they have a financial interest that conflicts with the publishing of her findings, since sending her paper to review would reach her target audience of voluntary peer reviewers and could potentially incite them to go on strike and demand payment for their work. Furthermore, the comic contains the joke that Ponytail is doing exactly what she is dis-encouraging in the paper: publishing it in a journal, which probably does not pay their reviewers and possibly locks the papers behind a paywall. However, as this is how science works at the moment, she is obliged to do so in order to reach her audience. The title text refers to a Twitter post that went viral. Researcher Dr. Holly Witteman informs the public that you could just ask many researchers for a PDF copy of their academic paper and that they would be delighted to do so free of charge. (This hearkens back to the days of snailmail, when researchers would distribute printed copies, "reprints", of their work for, at most, the price of a self-addressed stamped envelope.) She has additionally written an article on the situation and how to get papers for free. Pre-print repositories, such as arXiv , are online databases for researchers to publish drafts of their research for quick distribution to willing reviewers, sidestepping the lengthy and often arduous reviewing process as conducted by many research journals. These databases are free to access by researchers and the general public, and often papers will remain on these sites long after their journal publication, making them a convenient way to get to papers locked behind a paywall. However, the pre-print versions of the papers will often lack peer review, and as such may contain a higher occurrence of errors. There are also sites which collect and re-publish papers for free, such as Sci-Hub , which attempts to provide all published papers free of charge globally. Links to Sci-Hub can go dead after being widely published; as of 4/5/22, this link is active. In the title text, the publisher refuses to publish a paper that describes ways to get around the paywall restrictions that make up their bottom line. In this refusal they even acknowledged that the author has tried to trick them, maybe by using one of those very long titles filled with incomprehensible jargon that is almost impossible to read, and remember to the end. So they finish the refusal by adding a "but nice try". [Ponytail is sitting in a office chair at a desk reading from a laptop. Above her the text from the screen is shown in a frame with a zigzag arrow pointing to the laptop.] RE: Economics Journal Submission We have received your manuscript "The Bizarre Economics of Academic Publishing: Why Volunteer Peer Reviewers Should Rise Up and Demand Payment from For-Profit Journals." We have elected not to send it out for review.

Heat Index

Heat Index

https://www.xkcd.com/2026

https://www.explainxkcd.com/wiki/index.php/2026:_Heat_Index

[A flowchart is shown beneath its title:] How to Calculate the "Heat Index": [There are four boxes with arrows between. The first rectangular box is at the top, and an arrow points straight down:] Measure the Temperature [From there an arrow goes straight down to a decision diamond:] Does it look hot enough? [Two arrow goes out from the diamond. One goes straight down to another rectangular box. Both the arrow and the box has labels:] No Add a few degrees [From the bottom box an arrow goes back to the diamond. The other arrow from the diamond goes right to a final box with no arrows. Again both the arrow and the box has labels:] Yes Done

Heat index, like wind chill, is a way to combine multiple factors, in this case temperature and humidity, to get a single number indicating what the air "feels like." This page gives a table, a formula, and lots more explanation. Human skin does not directly detect temperature - only the rate of heat gain or loss. This is why a piece of metal feels cooler than a piece of plastic or wood at the same exact temperature (below body temperature, above it is the other way around) - the metal conducts heat away from the higher body temperature at a higher rate than a good insulator does. So in warm weather, it's not just the temperature that matters for comfort. The humidity and wind speed also factor into it. When humidity is high, sweat evaporation is less effective at cooling us off than in a "dry heat" with low humidity. Hence, meteorologists use a combination of temperature and humidity to come up with the "heat index" value...and a combination of temperature and wind speed to produce a "wind chill" number. Neither scale is particularly scientific in terms of measuring how people feel - but both are a more accurate representation of comfort levels than temperature alone. The joke here is that these numbers seem entirely subjectively chosen - and in a sense, they really are, although they are calculated from an actual formula (a multivariate fit to a mathematical model of the human body - with nine terms!) and not by guesswork as the flow chart implies. The title text suggests another way it is calculated: In general the effective temperature is calculated based on the conductivity of heat based on humidity. This is a legitimate method of determining how hot something feels because the heat conductance of water is higher than dry air and humans perceive more heat when the humidity is higher. But humans also tend to exaggerate and so Randall implies to add still a bunch more to satisfy the subjective sentiment. [A flowchart is shown beneath its title:] How to Calculate the "Heat Index": [There are four boxes with arrows between. The first rectangular box is at the top, and an arrow points straight down:] Measure the Temperature [From there an arrow goes straight down to a decision diamond:] Does it look hot enough? [Two arrow goes out from the diamond. One goes straight down to another rectangular box. Both the arrow and the box has labels:] No Add a few degrees [From the bottom box an arrow goes back to the diamond. The other arrow from the diamond goes right to a final box with no arrows. Again both the arrow and the box has labels:] Yes Done

Lightning Distance

Lightning Distance

https://www.xkcd.com/2027

https://www.explainxkcd.com/wiki/index.php/2027:_Lightning_Distance

[Cueball and Megan stand on either side of a window, observing a bolt of lightning in a dark sky.] Cueball: What's that trick for telling how many miles away lightning is? Megan: Just count the seconds between the visible flash and the radio wave burst, then multiply by 5 billion.

The usual trick for determining the distance to a lightning flash is to count the seconds from when you see the flash until when you hear thunder , and divide by five to get miles (or three to get kilometers). This works because the transmission of light is essentially instantaneous over the relevant distances, while the speed of sound is 331.2 m/s (1,087 ft/s, 1,192 km/h, or 741 mph, varying a bit based on temperature), or about 1/5 mile per second (1/3 kilometer per second). This comic subverts the usual trick by having Megan describe a highly impractical alternative method. Megan's method is based on the fact that the speed of electromagnetic radiation, which includes light and radio waves, is not truly fixed and varies by wavelength in a refractive medium (consider the classic case of visible light in a prism). The electromagnetic radiation emitted by lightning on Earth also has to travel through air, which changes its speed in a fashion which depends on its frequency. Lightning is most visibly observable in the near-infrared visible spectrum around a wavelength of 777 nm . The refractive index (n) of air at 15˚C for a wavelength of 777 nm is 1.0002752 , which equates to a speed of light of 299,709,978 m/s given the relation n=c/v, where c=speed of light in a vacuum and v=the velocity of light in the medium. Terrestrial lightning generates very-low-frequency radio waves ranging in frequency from 1 kHz to 30 kHz known as whistlers from bouncing off the ionosphere, and wider-band emissions known as sferics . Much of this would exist in the very low frequency category of radio waves, for which literature values of refractive index is harder to determine. Using the formula given in this paper , the refractive index for radio waves in similar conditions is 1.000315, which equates to a speed of light of 299698.0 km/s (or 186223.7 miles/s). This means that to get the distance in kilometers, the time difference between flash and radio burst should instead be multiplied by 13.6 billion (or 8.45 billion for miles). Using a setup similar to that used for passive radar , it would theoretically be possible to use this effect to determine the distance to a source of extremely short bursts of visible light and radio waves, although one might have to compensate for the tiny effect time with tricks involving phase detection or receiver harmonics. Large inaccuracies may propagate from the inconsistency of air pressure, temperature, electron density, humidity in the atmosphere, even local temperature of the receiver, which may need to be taken into account. The joke is that it is impractical for people who haven't spent time with radio engineering, because they haven't heard of measuring such small time intervals (on the scale of 0.1 nanoseconds per kilometer or mile) and because they don't know how to detect radiation outside the visible spectrum, which can be done with a $20 radio dongle. An upconverter may be needed to measure the low-frequency details, and possibly building one's own loop antenna to pick them up in the first place. It would be difficult to use such a "rule of thumb" for somebody not already exposed to either the amateur software-defined-radio scene or professional hardware. Although lightning lasts about 60 to 70 microseconds , during which time the signals we receive would rise and fall somewhat erratically, a software-defined radio can sample the phase and strength of the signal in detail during this time and provide a record of it for comparison with a recording at a different frequency. A more expensive radio would make life easier, as a sampling rate of at least a few GHz would allow for the time discrepancy to be measured directly using the onset of the signal, rather than possibly inferred from phase differences at different frequencies. For the purpose of the joke, the "5 billion" value used in the comic is a fair estimate which also references the original rule of 5 seconds per mile nicely, though the result can have a huge margin of error depending on actual conditions (temperature, humidity, etc.), as the title text suggests ("the index of radio refraction does have a lot of variation"). The title text suggests another method of calculating the distance to lightning. Since the absorption of light is also different in different wavelengths, it would be possible to calculate the difference by comparing the brightness instead of relative delay. This would, however, require the knowledge of the emission spectrum of lightning and attenuation ratios of different wavelengths (which would both vary across conditions). [Cueball and Megan stand on either side of a window, observing a bolt of lightning in a dark sky.] Cueball: What's that trick for telling how many miles away lightning is? Megan: Just count the seconds between the visible flash and the radio wave burst, then multiply by 5 billion.

Complex Numbers

Complex Numbers

https://www.xkcd.com/2028

https://www.explainxkcd.com/wiki/index.php/2028:_Complex_Numbers

[Cueball (the student) is raising his hand and writing with his other hand. He is sitting down at a desk, which has a piece of paper on it.] Cueball: Does any of this really have to do with the square root of -1? Or do mathematicians just think they're too cool for regular vectors? [Miss Lenhart (the teacher) is standing in front of a whiteboard.] Miss Lenhart: Complex numbers aren't just vectors. They're a profound extension of real numbers, laying the foundation for the fundamental theorem of algebra and the entire field of complex analysis. [Miss Lenhart is standing slightly to the right in a blank frame.] Miss Lenhart: And we're too cool for regular vectors. Cueball (off-screen): I knew it!

The complex numbers can be thought of as pairs of real numbers with rules for addition and multiplication. As such, they can be modeled as two-dimensional vectors , with standard vector addition and an interesting rule for multiplication. The justification for this rule is to consider a complex number as an expression of the form , where , i.e. i is the square root of negative 1. Applying the common rules of algebra and the definition of i yields rules for addition and multiplication above. Regular two-dimensional vectors are pairs of values, with the same rule for addition, and no rule for multiplication. The usual way to introduce complex numbers is by starting with i and deducing the rules for addition and multiplication, but Cueball is correct to say that some uses of complex numbers could be modeled with vectors alone, without consideration of the square root of a negative number. The teacher, Miss Lenhart , counters that to ignore the natural construction of the complex numbers would hide the relevance of the fundamental theorem of algebra (Every polynomial of degree n has exactly n roots, when counted according to multiplicity) and much of complex analysis (calculus with complex numbers; the study of analytic and meromorphic functions), but she also agrees that mathematicians are too cool for "regular vectors." Just because the complex numbers can be interpreted through vector space, however, that doesn't mean that they are just vectors, any more than being able to construct the natural numbers from set logic mean that natural numbers are really just sets. In mathematics, a group is the pairing of a binary operation (say, multiplication) with the set of numbers that operation can be used on (say, the real numbers), such that you can describe the properties of the operation by its corresponding group. An Abelian group is one where the operation is commutative, that is, where the terms of the operation can be exchanged: The title text argues that the "link" between algebra and geometry in "algebreic [sic] geometry" and "geometric algebra" is the operation in an Abelian group, such that both of those fields are equivalent. Algebraic geometry and geometric algebra are mostly unrelated areas of study in mathematics. Algebraic geometry studies the properties of sets of zeros of polynomials. It runs relatively deep. Its tools were used for example in Andrew Wiles' celebrated proof of Fermat's Last Theorem. For its part, a geometric algebra (a Clifford algebra with some specific properties) is a construct allowing one to do algebraic manipulation of geometric objects (e.g., vectors, planes, spheres, etc.) in an arbitrary space that has a resultant geometric interpretation (e.g., rotation, displacement, etc.). The algebra of quaternions, which is often used to handle rotations in 3D computer graphics, is an example of geometric algebra, as is the algebra of complex numbers. Meta-Abelian groups (often contracted to metabelian groups) is a class of groups that are not quite abelian, but close to being so. Randall's joke in the title text is a wordplay combining the concepts of (meta-)abelian groups and change in the order of word orders with the general idea of "meta". This comic is similar to the earlier Miss Lenhart comic 1724: Proofs . [Cueball (the student) is raising his hand and writing with his other hand. He is sitting down at a desk, which has a piece of paper on it.] Cueball: Does any of this really have to do with the square root of -1? Or do mathematicians just think they're too cool for regular vectors? [Miss Lenhart (the teacher) is standing in front of a whiteboard.] Miss Lenhart: Complex numbers aren't just vectors. They're a profound extension of real numbers, laying the foundation for the fundamental theorem of algebra and the entire field of complex analysis. [Miss Lenhart is standing slightly to the right in a blank frame.] Miss Lenhart: And we're too cool for regular vectors. Cueball (off-screen): I knew it!

Disaster Movie

Disaster Movie

https://www.xkcd.com/2029

https://www.explainxkcd.com/wiki/index.php/2029:_Disaster_Movie

[A fraction of an office with two desks is shown. On the right Cueball sits behind a computer while in the middle Ponytail talks into a radio device with a small antenna. On the left Megan runs into the scene holding something like a tablet computer in her hand.] Megan: The lava is entering the sea, and new rifts are opening to the north! Ponytail: Get a GIS survey team in the air! We need to revise our coastline shapefiles! [Caption below the frame:] I want to make a disaster movie that just shows scientists rushing to update all their data sets.

Disaster movies are a sub-genre of movies, which resolve around a disaster, such as a natural disaster, worldwide disease pandemic or an attack. Typically, the plot of a disaster movie is how the main characters escape the disaster, avert its climax or deal with the aftermath of the disaster. Here, Randall has subverted this plot device by showing Ponytail call for a GIS survey team to map out the result of the disaster. Instead of panicking for survival, the scientists are rushing to update their data sets. "Lava entering the sea, and new rifts opening to the north" may be a reference to the 2018 lower Puna eruption , a volcanic event on the island of Hawaii . Due to this eruption event, lava did enter the Pacific Ocean. As of the time of publishing, this event was still occurring. GIS ("geographic information system") is a computer system that stores and analyses spatial and geographic data, and by extension, the profession of experts who use computers to make maps and perform spatial analysis. Presumably, a "GIS survey team" would go above the affected area in a helicopter, mapping the coastline changes caused by the natural disaster. A "GIS survey team" presumably means a team of geographic surveyors. However, surveying is usually carried out on the ground, and surveying is not usually considered part of GIS. Also, these days, satellite imagery is usually used for this purpose, as there are several companies that can provide imagery refreshed as often as every day. Finally, a "GIS survey team" would most likely be one of many companies that provides these kinds of services, not "scientists", as suggested in the caption. An example of this is an ArcGIS map of the mentioned 2018 lower Puna eruption. A Shapefile is a proprietary data format for spatial data which remains in widespread use, despite being created in the early 90s, and based on an even older database format. Amongst non-GIS people "shapefile" is often used synonymously with "geographic data", regardless of the actual file format. "Our coastline shapefiles" then means "our geographic data for the coastlines", although such data would most likely be stored in a database, not a Shapefile. The situation described (scrambling to update geographical datasets in the advent of natural disaster) is actually a common occurrence these days. The Humanitarian OpenStreetMap Team 's Disaster Response unit does almost exactly this: When there is a natural disaster in a location that lacks high quality GIS data (common in much of the developing world), a team of volunteers across the world mobilises to update and improve OpenStreetMap. They use the latest available satellite imagery, usually donated free for the purpose. Disaster response teams then use the GIS data in OpenStreetMap to create maps and plan their response. The title text refers to the fact that most GIS datasets are not published in "real time", but, rather in updates every 3 months or less often. This is due to the many manual steps still present in many GIS publishing and consuming workflows, which preclude more frequent schedules. Thus, there is not as much of a rush to do their updates, and the need is not as urgent as the proposed film would show. Randall claims the urgency was exaggerated for dramatic effect, humorously disregarding the fact that neither version of this scene would be dramatic to a typical moviegoer. [A fraction of an office with two desks is shown. On the right Cueball sits behind a computer while in the middle Ponytail talks into a radio device with a small antenna. On the left Megan runs into the scene holding something like a tablet computer in her hand.] Megan: The lava is entering the sea, and new rifts are opening to the north! Ponytail: Get a GIS survey team in the air! We need to revise our coastline shapefiles! [Caption below the frame:] I want to make a disaster movie that just shows scientists rushing to update all their data sets.

Voting Software

Voting Software

https://www.xkcd.com/2030

https://www.explainxkcd.com/wiki/index.php/2030:_Voting_Software

[A Megan-like woman, with bushy hair, is holding a handheld microphone and interviewing Hairbun and Cueball, standing in a line] [Heading above the panel]: Asking aircraft designers about airplane safety: Hairbun: Nothing is ever foolproof, but modern airliners are incredibly resilient. Flying is the safest way to travel. [In a frameless panel, Hairy is holding a handheld microphone and interviewing Cueball] [Heading above the panel]: Asking building engineers about elevator safety: Cueball: Elevators are protected by multiple tried-and-tested failsafe mechanisms. They're nearly incapable of falling. [Ponytail is holding a handheld microphone and interviewing Megan and Cueball, standing in a line] [Heading above the panel]: Asking software engineers about computerized voting: Megan: That's terrifying . [Zoomed in on Ponytail, Megan and Cueball's faces] Ponytail: Wait, really? Megan: Don't trust voting software and don't listen to anyone who tells you it's safe. Ponytail: Why? Megan: I don't quite know how to put this, but our entire field is bad at what we do, and if you rely on us, everyone will die. [Zoomed back out, showing Ponytail, Megan and Cueball standing in a line] Ponytail: They say they've fixed it with something called "blockchain." Megan: AAAAA!!! Cueball: Whatever they sold you, don't touch it. Megan: Bury it in the desert. Cueball: Wear gloves.

This comic is a commentary on voting machines specifically, and more generally the contrast between what experts will trust and what the average user will trust. The first two panels of this comic involve a reporter talking to professional mechanical engineers, asking about the given safety of the products/solutions that each of their fields help to produce (airplanes from aircraft designers in panel 1, elevators from building engineers in panel 2). While the two inventions selected are relatively new when compared to how long humans have existed, the two fields mentioned have existed for multiple human generations, giving enough time to find flaws in their products/solutions and solve said flaws to the point that they can be considered safe for the general public to use. The comic from panel 3 onwards contrasts this with computer engineers Megan and Cueball , both agreeing that their given field (computer science/software development/software engineering) does not have the overall consistent competency that other fields have (or at least appear to have). Indeed, at least anecdotally there are very few ethical and security restrictions for what developers can/cannot do, and relatively minor consequences when catastrophes arise from poor decisions. When the reporter follows the interview up with a mention of blockchain technology, Megan and Cueball reflexively tell the reporter to avoid any voting system using the technology at all costs. Blockchain is a relatively new technology that is intended to solve some computer security issues by making it difficult to doctor old data. However, in the process of solving the old computer security issues, it has introduced new computer security issues that have not yet been ironed out; for instance, it doesn't solve input fraud issues, only data-doctoring fraud, so if a program caused the voting machine to record a vote for candidate B whenever a vote for candidate A was cast (such a program could be uploaded to the voting machines through USB, or through the internet which the voting machine must be connected to for blockchain), blockchain would not prevent it. Blockchain has also had a large number of high-profile scams, thefts, and implementations with critical security holes. Thus, Megan and Cueball may not trust this blockchain solution because of this history. The title text confirms the comic's stance by implicitly saying that any digital voting systems are to not be used under any circumstances. It may also highlight that anyone working in the field is vulnerable to corruption, or at least that the field is far from maturity. Humorously the title text says digital voting systems should still be developed, but mostly to keep the people who want to use them occupied, rather than allowing them to actually publish their work in the real world where it can cause serious harm. Computer systems, operating primarily in a digital domain, fail differently from most traditional areas of engineering, which operate in analog (or continuous) domains. A small error in an analog part often gives a result which is close to the desired properties (it almost fits, it works most of the time). By contrast, a small error in a digital system (just one bit being changed) can easily make the system function in radically different ways (if not just crash entirely). So not only is software engineering younger than other areas of engineering, but the domain is much less forgiving. Even small errors/variations produce catastrophe down the line. This fear of computerized voting is a result of a fundamental difference between computer security and other types of safety measures: Most engineers only have to deal with wear and tear, and very rarely have to guard against sabotage. In contrast, in cryptography there is always somebody trying to undo what you've built. Not only that, but new advances in cryptography tend to point out vulnerabilities with previous versions, making them not only obsolete, but dangerously so. For these reasons, it is especially important to make sure that whoever is selling you the security method is both competent and non-malicious, but because crypto software is highly technical and often confidential/proprietary, it can be hard to verify this if you're not an expert in the field (which you won't be, if you're buying it). These issues are especially pertinent to voting machines , which store incredibly sensitive information but are often catastrophically outdated due to lack of funding. There are also major issues with electronic voting in general; for example, this video from Computerphile raises issues of malware infections, transferring the votes to the election authorities without having them intercepted, and needing to trust both the machine's software and central counting system to present an accurate account of the votes. Furthermore, the people purchasing them, the politicians, are generally not known for their technical understanding -- or their impartiality. Interestingly, this comic was posted a day before DEF CON 2018, and it was shown there that the voting systems that will be used across America for the mid-term vote in November are, in many cases, extremely insecure. The topic of voting machines has been covered before in 463: Voting Machines , where the use of anti-virus software on the machines has been discussed. The way blockchain works is that several computers have data being inputted into them. With each tick, they all share their current states with each other, and encrypt and hash it. That state then becomes a 'block' in the chain. They then share states, including that block as part of the state, then hash and encrypt it, and then it becomes a 'block' in the chain. Each 'block' is included in the cryptographic hash of all following blocks, so if a change is made to any given block, all blocks after that block must be changed. Due to the distributed nature, if changes are made to any chain, it can be compared against the other chains, and so long as the majority say that the changes didn't happen, it's reverted and removed. This is really great at preventing post-facto data changes. With blockchain you can somewhat guarantee that no one comes in after the election and changes the votes on the machines. (Unless they're handling the blockchain in a stupid fashion, for example without the distribution.) What you cannot do is prevent someone from installing a program on the machine that makes it think that there's a voter when it's idle, and makes it start registering the correct sequence of actions to signify a vote while idle. Also, the security issues that Blockchain solves could also be solved via write-once memory, which would be more secure and more difficult to doctor. Most computer security specialists are more worried about programs that randomly deliberately misreport a vote, than people changing the votes after they're already recorded, so blockchain would solve an issue that most computer security specialists are less worried about, while causing new issues (the perpetual internet connection among them). [A Megan-like woman, with bushy hair, is holding a handheld microphone and interviewing Hairbun and Cueball, standing in a line] [Heading above the panel]: Asking aircraft designers about airplane safety: Hairbun: Nothing is ever foolproof, but modern airliners are incredibly resilient. Flying is the safest way to travel. [In a frameless panel, Hairy is holding a handheld microphone and interviewing Cueball] [Heading above the panel]: Asking building engineers about elevator safety: Cueball: Elevators are protected by multiple tried-and-tested failsafe mechanisms. They're nearly incapable of falling. [Ponytail is holding a handheld microphone and interviewing Megan and Cueball, standing in a line] [Heading above the panel]: Asking software engineers about computerized voting: Megan: That's terrifying . [Zoomed in on Ponytail, Megan and Cueball's faces] Ponytail: Wait, really? Megan: Don't trust voting software and don't listen to anyone who tells you it's safe. Ponytail: Why? Megan: I don't quite know how to put this, but our entire field is bad at what we do, and if you rely on us, everyone will die. [Zoomed back out, showing Ponytail, Megan and Cueball standing in a line] Ponytail: They say they've fixed it with something called "blockchain." Megan: AAAAA!!! Cueball: Whatever they sold you, don't touch it. Megan: Bury it in the desert. Cueball: Wear gloves.

Pie Charts

Pie Charts

https://www.xkcd.com/2031

https://www.explainxkcd.com/wiki/index.php/2031:_Pie_Charts

[Two colored circles are shown. The circle on the right is warped and bent in shape and shows some shadows from the middle to the outer edges, like a round piece of cloth with wrinkles going out from the center.] [The left pie chart:] Wrong: 45% (red) 15% (blue) 30% (yellow) 40% (green) [The right warped and bent pie chart with shadows:] Right: 45% (red) 15% (blue) 30% (yellow) 40% (green) [Caption below the frame:] How to make a pie chart if your percentages don't add up to 100

Pie Charts graph proportions as "slices" of a circle, like a pie that you cut into slices. The circle, or Pie, represents the whole sum of the slices, or 100% of the data. As such, if the data represented by the slices is expressed as percentages, the total of all the slices, by definition, must total 100%. This comic introduces a new technique for getting around that rule by "warping" the circle to allow more than 100% of the data to exist in the graph. Thus the total amount of 130% is represented with a shape presumably 30% larger in area than the circle. The resulting warped circle is then actually part of a hyperbolic plane , while a normal circle is part of a flat plane. Of course, it doesn't matter if the geometric shape is a circle or a hyperbolic plane: A changed graphic doesn't magically solve the misrepresentation of percentages. At best, it serves to highlight the methodical error. Regarding doctored statistics: If the same numbers were presented as absolute values instead of percentages, the error would still remain but would be less obvious, especially if you omit the total count of the sample ( Of all people asked, 40 selected green as favorite color, 45 selected red, 30 yellow and 15 blue. This statement omits that you surveyed only 100 people and several of them named several colors, and readers will assume a larger sample.) Percentages that add up to more than 100% are often a sign that a math error has occurred, whether a typo somewhere or a sloppy case of taking numbers from different sources. However, they can arise naturally in cases where each item can belong to more than one group, such as approval voting (40% of the people like green 45% like red etc., however there may be some that like both green and red). In such cases, a more accurate depiction would have some form of overlap of the pie pieces, not a warping of the space which they occupy, or a completely different representation, such as a bar chart. Minor cases can also occur if the percentages of the pieces have been rounded for readability - summing the rounded numbers can result in them adding to 99% or 101%. Percentages don't need to add up to 100% to be correct. For example, if ten people wear blue t-shirts and ten wear red t-shirts, then 50% of them wear each color for a total of 100%. Now if one of each joins the group, 55% of the original population wears each color, for a total of 110%, as the total population risen by 10%. That said, this change should be represented by something like a bar graph, not by pie chart. If percentages are represented by a pie chart, the assumption is that the total should be 100%, independently of the math behind it. In this case, the right image appears to be what happens when you cut the pie chart segments out of fabric, stitch them together, and let the resultant fabric flop around a bit. The title text presents an alternative if shading is not possible, namely to excuse the percentage inaccuracy with scientists discussing curvature of space. [Two colored circles are shown. The circle on the right is warped and bent in shape and shows some shadows from the middle to the outer edges, like a round piece of cloth with wrinkles going out from the center.] [The left pie chart:] Wrong: 45% (red) 15% (blue) 30% (yellow) 40% (green) [The right warped and bent pie chart with shadows:] Right: 45% (red) 15% (blue) 30% (yellow) 40% (green) [Caption below the frame:] How to make a pie chart if your percentages don't add up to 100

Word Puzzles

Word Puzzles

https://www.xkcd.com/2032

https://www.explainxkcd.com/wiki/index.php/2032:_Word_Puzzles

[Cueball and Megan standing together. He makes some gestures with his hand and some musical notes are above him while Megan holds her fist before her mouth.] Cueball: Parts of this aria were composed by Brian Eno's Opera Star au pair at the start of his post-live era. Megan (thinking): ...parts...start...eno...aria... [Caption below the frame:] My hobby: Messing with word game enthusiasts by using words that make them sure there's a puzzle to solve

This is another comic in the " My Hobby " series, where Randall presents his hobby of fooling other people. This particular hobby seems to be a case of Nerd Sniping . Cueball knows that Megan is a word game enthusiast and - while both are probably at a party - he presents a complex sentence rather than just doing small talk. And he is successful as we can see that she is just thinking about the proper solution to that puzzle where probably none exists. The dialog, caption, and title text contain many words that appear frequently in crossword puzzle answers because they fit well with intersecting words, in part because they have a high density of vowels. Some of the terms (parts of, start of) are also commonly used in cryptic crossword clues to indicate that nearby words should be combined or split to create an answer. Brian Eno is an English musician, composer, record producer, singer, writer, and visual artist. He is best known for his pioneering work in ambient music and contributions to rock, pop, electronic, and generative music. He was born on 15 May 1948, and is still an active artist. But live concerts by him were rare and may not happen ever again. However, the aria was not written by himself but by his au pair who is also an opera star. And this happened after Eno ended his live career. The title text goes further on this puzzle and asserts that Lance Ito was playing the aria solo on an oboe at the fictive Ohio's AirAsia Arena . Ito is well known as the judge in the O. J. Simpson murder case. The kind of puzzle that Megan thinks she is solving is called a "Cryptic" or cryptic crossword , which has markedly different rules than ordinary crosswords. If Cueball's statement had been "Part of this aria is an Indian garment" the answer would have been "sari", because a part of the phrase "this aria" is the sequence "sari", which in turn is an Indian garment. Cueball's actual statement contains quite a few familiar cryptic puzzle triggers. The word "composed" can be a hint of a preceding or following anagram, in this case of "this aria" or of "by Brian" or of even longer adjacent strings. Although "opera star" could be a famous singer, say "Caruso", it might also be the name of an opera followed by the name of an astronomical star. "Au pair" could be any of its ordinary meanings, say "nanny", but might also be "earrings" (because Au is the chemical symbol for gold, and a gold pair could be earrings). The word "start" is often a hint to take just the beginning of a word, so "the start" would be "t", or "start of his" would be "h" or "hi". The New York Times runs a cryptic crossword as its "second Sunday puzzle" every other month or so, and there are other regular cryptic crossword venues. There are various guides on the web for solving cryptics, such as this one at The Atlantic: Puzzler Instructions . [Cueball and Megan standing together. He makes some gestures with his hand and some musical notes are above him while Megan holds her fist before her mouth.] Cueball: Parts of this aria were composed by Brian Eno's Opera Star au pair at the start of his post-live era. Megan (thinking): ...parts...start...eno...aria... [Caption below the frame:] My hobby: Messing with word game enthusiasts by using words that make them sure there's a puzzle to solve

Repair or Replace

Repair or Replace

https://www.xkcd.com/2033

https://www.explainxkcd.com/wiki/index.php/2033:_Repair_or_Replace

[Cueball is sitting in a car parked to the left of Hairy, who thus stands in front of it while pointing behind him towards a big black hole.] Cueball: My engine's making a weird noise. Can you take a look? Hairy: Sure, just pop the hood. Cueball: Oh, the hood latch is also broken. Hairy: OK, just pull up to that big pit and push the car in. We'll go get a new one. [Caption below the frame:] I'm sure the economics make sense, but it still freaks me out how quick companies are to replace computing devices instead of trying to fix them.

This comic compares the repair of cars with that of computers or other similar electronic devices. The question Repair or Replace? comes up more frequently with electronics than with cars, hence the title of the comic, and the humor derived. Cueball is in his car. He says that there is a weird sound and asks if the car mechanic Hairy will take a look. Hairy asks him to open the car's hood , exposing the engine, to further identify the cause of the problem. Cueball then says that his hood latch, the lever used to open the hood, is also broken. The solution, according to Hairy, is then to discard the car, and "replace" it with a new car. In reality, fixing the latch on the hood is a simple task for a skilled mechanic and would not justify writing-off the car. When a car is malfunctioning, the usual response is to attempt to repair it. A car is designed so that many of the parts can be replaced or adjusted. Even in the case of a product recall where the manufacturer recalls the vehicles, it is usually only a single malfunctioning part that needs to be replaced and the rest of the car is left alone to return to the customer. It would be extremely inefficient for a car dealership or mechanic to simply "replace" the entire car when there is a problem with it (although many insurers will provide a temporary replacement "courtesy car" while the car is being repaired). However, right around the time this comic was published, Subaru just instituted a recall of a few hundred vehicles that it says it will replace the entire car (rather than a single malfunctioning part), as seen here , and this could be the inspiration for this comic. By contrast, when a computer or electronic device is malfunctioning, it is often judged to be more expensive to repair than to replace, and the usual action is to purchase a new device. It is generally possible to replace each part of a desktop or laptop computer, but harder to do so for more integrated devices such as tablets, and almost impossible to repair individual components with faulty or damaged integrated circuits. Even where replacing a component is relatively easy (needing little more than a set of screwdrivers), the cost of replacement parts and labor can be a significant proportion of the cost of a completely new device, particularly where a user is not technically confident and pays a repair shop to fit new components. Also, the length of the technology "upgrade cycle" - typically around 3-5 years - is roughly the mean failure time of a device's components. Thus, users may already be considering a new purchase when their device breaks. Thus, Randall notes in this comic that while it does make sense for electronic devices, the "solution" of replacing an object instead of attempting to repair seems absurd for any other object. The title text refers to data stored on a computer or electronic device. Before replacing the device, it is recommended backup all your personal files, so that you have future access to them, and to remove them for security. Randall likens this to having your friends and family exit the vehicle, or making backup friends and family before the vehicle is thrown away. The economics Cars are much more expensive than computers or other electronic devices, and become obsolete less quickly. The point at which it becomes cheaper to purchase a new computer or phone rather than repair an old one comes much more quickly. Cars are mostly valuable for their macroscopic features and functions, whereas electronics deliver value mostly with microscopic circuitry. While we can mass produce integrated circuit devices efficiently, the equipment is massively complex and expensive, so it's only practical on an industrial scale. Repairing an individual switch or data line in an individual chip might take a team of experts and a state of the art lab with electron microscopes etc. - millions of times the per unit cost once assembly lines are running Also, although the comic implies that replaced electronics are discarded (like a car pushed into a pit), sometimes they are sent off to be repaired or refurbished elsewhere. This provides a better experience for the customer (they get a working device right away instead of waiting for repair) and is more efficient for the company (a consolidated repair facility can have the experience and equipment to repair a device much more quickly than at a retail location). This assumes that the customer asked the manufacturer for a replacement, and did not throw it away themselves before purchasing a new one. Electronics Repair Although most corporations find it more profitable to have consumers replace their electronics, there are many resources that are more geared towards repair. Free Geek offers free technology to volunteers in exchange for their work in repairing broken items. More locations across the world are listed near the bottom of their resources page. Alternatively, hackerspaces are present in many large cities, and often at the larger ones there are people who would be happy to assist somebody trying to learn to repair their electronics. On one's own, most problems with electronics can be fixed with some persistence, googling, purchasing of a few tools, and carefully watching youtube videos. [Cueball is sitting in a car parked to the left of Hairy, who thus stands in front of it while pointing behind him towards a big black hole.] Cueball: My engine's making a weird noise. Can you take a look? Hairy: Sure, just pop the hood. Cueball: Oh, the hood latch is also broken. Hairy: OK, just pull up to that big pit and push the car in. We'll go get a new one. [Caption below the frame:] I'm sure the economics make sense, but it still freaks me out how quick companies are to replace computing devices instead of trying to fix them.

Equations

Equations

https://www.xkcd.com/2034

https://www.explainxkcd.com/wiki/index.php/2034:_Equations

[Nine equations are listed, three in the top row and two in each of the next three rows. Below each equation there are labels:] E=K 0 t+1/2 ρvt 2 All kinematics equations K n =∑ ∞ i=0 ∑ ∞ π=0 (n-π)(i-e π-∞ ) [K sub n = the summation from i = 0 to infinity of the sum from pi = 0 to infinity of (n - pi) * (i-e^(pi-infinity))] All number theory equations ∂/∂t ∇⋅ρ=8/23 (∯ ρ ds dt ⋅ ρ ∂/∂∇) All fluid dynamics equations |ψ x,y 〉=A(ψ)A(|x〉⊗|y〉) All quantum mechanics equations CH 4 +OH+HEAT→H 2 O+CH 2 +H 2 EAT All chemistry equations SU(2)U(1)×SU(U(2)) All quantum gravity equations S g =(-1)/(2ε̄) ið(̂ ξ 0 ⨢ p ε ρ v abc ⋅η 0 )̂ f̵ a 0 λ( ξ ) ψ(0 a ) All gauge theory equations H(t)+Ω+G⋅Λ ... [There is a brace linking the three cases together.] ... > 0 (Hubble model) ... = 0 (Flat sphere model) ... < 0 (Bright dark matter model) All cosmology equations Ĥ - u̧ 0 = 0 All truly deep physics equations

This comic gives a set of mock equations. To anyone not familiar with the field in question they look pretty similar to what you might find in research papers or on the relevant Wikipedia pages. Most of the jokes are related to the symbols or "look" of most equations in the given field. The comic makes jokes about the fields of kinematics, number theory, fluid dynamics, quantum mechanics, chemistry, quantum gravity, gauge theory, cosmology, and physics equations. Of course, all of the equations listed are not real equations ( and H 2 EAT are clearly jokes and making a mockery of the given field). As always, Randall is just having a laugh. All kinematics equations Most kinematics equations tend to make heavy use of constants, addition, powers, and multiplication. This specific equation resembles the actual kinematics equation d = vt + 1/2at^2, but replaces a (acceleration) with v (velocity) times (density) and replaces velocity with "K 0 ", which is not a term used in kinematics. All number theory equations Randall jokes about how number theory often involves the use of summations. The use of π as an integer variable in the double summation is a joke, as π is essentially always used for the well-known constant 3.14159..., not a variable. The use of i as a summation variable is common, though it can also be confused with the imaginary unit √-1. The constants e , i , and π , as well as the theoretical upper bound , often appear in number theory equations. All fluid dynamics equations Fluid dynamics equations often involve copious integrals, especially those over closed contours as done here, which are often the main telling factors of those equations to an outsider. The time derivative and gradient operator are common in fluid dynamics, mostly via the Navier-Stokes equation, and the fluid density is one of the functions of central importance. The fraction 8/23 is a comically weird choice, but various unexpected fractions do pop up in fluid dynamics. The ds and dt go with the double contour integral (s is probably distance, t is time), but the derivative with respect to at the end is very much not allowed. All quantum mechanics equations Quantum mechanics often involves some of the foreign-looking symbols listed, including bra-ket notation , the tensor product , and the Greek letter Psi for a quantum state. Specifically, the left side of the equation is a ket state labeled Psi that depends on x and y (probably positions), while the right-hand side may be an operator A that depends on the state Psi (it is very unusual to have such a dependence) acting on what looks like another copy of that operator which depends on the outer product of states labeled by x and y (again strange). A charitable interpretation could be that the second A is the eigenfunction A of the operator A. Normally this is clearly indicated by giving the operator a “hat” (^ symbol) or making the eigenfunction into a ket eigenstate, but since the equation is intentionally nonsense both A’s are left ambiguous. Also note that the bra-ket math is inconsistent here, as the left side is a ket, but the right side is just two A’s, which are either operators or functions but are definitely not kets. All chemistry equations Chemistry equations use formulas of chemical compounds to describe a chemical reaction. Such equations show the starting chemicals on the left side and the resulting products on the right side, as displayed. Sometimes such an equation might optionally indicate that an activation energy is required, for the reaction to take place in a sensible timeframe, e.g. by heating. A reaction requiring heating is usually indicated by a Greek capital letter Delta ( Δ ) or a specified temperature above the reaction arrow, however this comic uses the "+ HEAT" term on the left side instead. The joke is that Randall interprets "HEAT" to be another chemical, which reacts with Hydrogen (H) to H 2 EAT, which is nonsensical, as heat is transferred energy here, not added matter. Regardless of this, Randall gets the stoichiometry of this equation correct, with the same number of all types of 'atoms' on each side of the equation. All quantum gravity equations Quantum gravity uses mathematical groups denoted by uppercase letters, as shown. SU(2) , U(1) , and U(2) are all well-studied groups, though 'SU(U(2))' makes no sense. The lack of relator means this expression isn't an equation. All gauge theory equations Gauge theory is a subset of field theory. Most gauge theory equations appear to have many strange-looking constants and variables with odd labels. However, almost none of the symbols used here are found or applicable to gauge theory. All cosmology equations Cosmology is the science of the development and ultimate fate of the universe. The joke here may be pertaining to the different models accepted in the field of cosmology. H is the Hubble parameter , Ω is the universal density parameter , G is the gravitational constant , and Λ is the cosmological constant . All truly deep physics equations The joke about the "truly deep physics equations" is that most of the universal physics equations are simple, almost exceedingly so. In general, many of these equations are types of conservation law equations, which reflect some of the basic truths of the universe. A hallmark of conservation laws is that the total amount of some physical value does not change, and so one side of the equation is zero, as shown in the example. One example is Einstein's E = mc² , which shows conservation of mass-energy. Noether's theorem shows that conservation laws have a one-to-one correspondence with a symmetry of nature, making these equations truly 'deep'. The title text is referencing the fact that the electric and magnetic fields are often explained to physics students using an analogy with fluid dynamics, as well as the fact that they do share some similarities (only in terms of mathematical description as three-dimensional vector fields) with fluids. The permittivity constant (represented with ε 0 ) and the permeability constant (represented with μ 0 ) are coefficients that relate the amount of charge required to cause a specific amount of electric flux in a vacuum and the ability of vacuum to support the formation of magnetic fields, respectively. They appear frequently in Maxwell's equations (the equations that define the electric and magnetic fields in classical mechanics), so Randall is making the joke that any surface integral with them in it automatically is an electromagnetism equation. [Nine equations are listed, three in the top row and two in each of the next three rows. Below each equation there are labels:] E=K 0 t+1/2 ρvt 2 All kinematics equations K n =∑ ∞ i=0 ∑ ∞ π=0 (n-π)(i-e π-∞ ) [K sub n = the summation from i = 0 to infinity of the sum from pi = 0 to infinity of (n - pi) * (i-e^(pi-infinity))] All number theory equations ∂/∂t ∇⋅ρ=8/23 (∯ ρ ds dt ⋅ ρ ∂/∂∇) All fluid dynamics equations |ψ x,y 〉=A(ψ)A(|x〉⊗|y〉) All quantum mechanics equations CH 4 +OH+HEAT→H 2 O+CH 2 +H 2 EAT All chemistry equations SU(2)U(1)×SU(U(2)) All quantum gravity equations S g =(-1)/(2ε̄) ið(̂ ξ 0 ⨢ p ε ρ v abc ⋅η 0 )̂ f̵ a 0 λ( ξ ) ψ(0 a ) All gauge theory equations H(t)+Ω+G⋅Λ ... [There is a brace linking the three cases together.] ... > 0 (Hubble model) ... = 0 (Flat sphere model) ... < 0 (Bright dark matter model) All cosmology equations Ĥ - u̧ 0 = 0 All truly deep physics equations

Dark Matter Candidates

Dark Matter Candidates

https://www.xkcd.com/2035

https://www.explainxkcd.com/wiki/index.php/2035:_Dark_Matter_Candidates

Dark matter candidates: [A line graph is shown and labeled at left quarter in eV and further to the right in g together with some prefixes.] [The labels read:] µeV, meV, eV, keV, MeV, GeV, TeV, 10 -18 kg, ng, µg, mg, g, kg, TON, 10 6 kg, 10 12 kg, 10 18 kg, 10 24 kg, 10 30 kg [All items are shown in bars ranging between two approximately values:] < 1 µeV - 10 meV: Axion 1 eV - 10 keV: Sterile neutrino 0.5 MeV (exactly): Electrons painted with space camouflage 10 GeV - 10 TeV: Neutralino 100 TeV - 10 -17 kg: Q-ball 1 ng - 100 ng: Pollen 0.1 mg - 1 mg: No-See-Ums 10 -1 g (exactly): Bees 10 g - 100 g: 8-balls 100 kg - TON: Space cows TON - 10 9 kg: Obelisks, monoliths, pyramids 10 9 kg - 10 33 kg: Black holes ruled out by: 10 9 kg - 10 13 kg: Gamma rays 10 13 kg - 10 17 kg: GRB lensing 10 15 kg - 10 22 kg: Neutron star data 10 21 kg - 10 30 kg: Micro lensing 10 24 kg - 10 30 kg: Solar system stability 10 30 kg - 10 33 kg: Buzzkill astronomers 10 33 kg - >10 36 kg: Maybe those orbit lines on space diagrams are real and very heavy

Dark matter is a hypothetical, invisible form of matter used by the vast majority of astronomers to explain the far too high apparent mass of objects at large scales in our universe. In galaxies, stars are orbiting faster than the gravitational force of the sum of the masses of visible matter in the galaxy could cause, and entire galaxies are observed moving much faster around each other than their visible masses could explain. In galactic collisions, the mass can appear to separate from the visible matter, as if the mass doesn't collide but the visible matter does. A small handful of galaxies have been observed to not have this property, suggesting that it is a thing that a galaxy can have more or less of and is separable from. At scales of our solar system, those effects are too small and can't be measured. The most plausible explanation for all of these phenomena is that there is some "dark matter" that has gravity, but is otherwise undetectable. In cosmology, dark matter is estimated to account for 85% of the total matter in the universe. This comic gives a set of possibilities for what dark matter could possibly be, charted by mass from smallest (given in electronvolts ) to largest (given in kilograms). Masses in the range 10 −15 to 10 −3 kg are given in grams together with appropriate prefixes, while the ton takes the place of 10 3 kg. Only massive objects ranging from subatomic particles up to super massive ones are covered in this comic. There are also alternative hypotheses trying to modify general relativity with no need of additional matter. The problem is that these theories can't explain all different observations at once. Nonetheless dark matter is a mystery because no serious candidate has been found yet. The joke in this comic is that the range of the mass of the possible particles and objects stretch over 81 powers of ten, with explanations suggested by astronomers covering only some portions of that range. Randall fills the gaps with highly absurd suggestions. An axion is a hypothetical elementary particle postulated in 1977 to resolve the strong CP problem in quantum chromodynamics , a theory of the strong force between quarks and gluons which form hadrons like protons or neutrons . If axions exist within a specific range of mass they might be a component of dark matter. The advantage of this particle is that it's based on a theory which could be proved or also disproved by measurements in the future. Other theories, not mentioned in this comic, like the weakly interacting massive particles (WIMPs) are much more vague. Sterile neutrinos are hypothetical particles interacting only via gravity. It's an actual candidate for dark matter. The well known neutrinos are also charged under the weak interaction and can be detected by experiments. Electrons are fundamental particles which compose the outer layers of atoms. A large number of electrons in the galaxy would be relatively easy to detect, as they not only interact with light (which dark matter does not appear to), but also have a strong electric charge. Presumably, space camouflage is a positively-charged coating which prevents electrons from interacting with light. (Needless to say, this is not an actual candidate for dark matter.) The mass of an electron is about 0.5 MeV which fits well into the graph. A neutralino is a hypothetical particle from supersymmetry and is also a current candidate for dark matter. But there is not evidence whether or not supersymmetry is correct and none of the predicted particles have been found yet. In theoretical physics, a Q-ball is a stable group of particles. It's an actual candidate for dark matter. (In billiards, a cue ball is the white (or yellow) ball hit with the cue in normal play. In addition, Cueball is the name explainxkcd uses for the most common xkcd character.) Pollen is a joke candidate, though people with seasonal allergies may suspect that the universe is genuinely made up entirely of pollen in the springtime. No-See-Ums are a family (Ceratopogonidae) of small flies, 1–4 mm long, that can pass through most window screens. Another joke candidate, because dark matter is invisible and the name "no-see-ums" implies that the flies are invisible. Insects of the clade Anthophila are major pollinators of flowering plants. In recent years bees have been disappearing at an alarming rate; Doctor Who explained that they are in fact aliens leaving Earth prior to a Dalek invasion. In pool, the 8-ball is a black ball numbered 8. It's a pun with Q-ball/cue ball. Unless undetected aliens have discovered billiards and become addicted to it, 8-balls are found only on Earth and are, hence, unlikely dark matter candidates. The 8-ball is also a popular unit of sale for black market pharmaceuticals like cocaine, where it stands for ⅛ ounce (3.5 g). This doesn't make sense as a dark matter candidate either – unless dark matter is hard to detect because it's illegal & trying to avoid the cops. Cows are bovines extensively farmed on Earth for milk and meat. [ citation needed ] Although there is folklore concerning cows achieving circum-lunar orbits , not to mention their appearance on a beloved space western TV show , as Muppet cow Natalie in the Sesame Street News Flash (and others less-remembered ), they have yet to be found elsewhere in the Universe. In the television show "Too Close for Comfort", one of the characters is the cartoonist of a comic strip called "Cosmic Cow". Spherical cows (and especially those in a vacuum, as they would essentially be if in space) have also been used (humorously) by physicists needing to simplify some source of mass in a given problem. While those human constructions are huge on a human scale, they're negligible at universe-scale. It would take a large number of such constructions, distributed through space, to replicate the effects of dark matter; while a scenario could be envisioned where enough such constructs existed, with properties and distribution allowing them to match observations, this is obviously not a likely explanation. They often show up in fiction and pseudo-scientific literature as alien artifacts generating immense unknown power out of nowhere, with the most famous and influential example being the three monoliths from 2001: A Space Odyssey (with the largest having a mass of about 500,000 tonnes). Black holes are known to occur in sizes of a few solar masses (about 10 30 -10 31 kg) as remnants of the core of former big stars, as well as in quite large sizes at the centers of galaxies (millions or even billions of solar masses). But recent gravitational wave detections indicate that black holes at 50 or 100 solar masses also exist, though their origin is still not understood. Randall doesn't mention this but some astronomers hope that these could fill at least a part of the gap. While black holes are widely reported to be ruled out as a candidate for dark matter for various reasons Randall has listed, such constraints are based on "monochromatic" mass distributions -- meaning that all such black holes are assumed to have the same mass -- which is considered physically implausible for populations of merging bodies which are known to have vastly different masses. See: Primordial Black Holes as Dark Matter (2017) and Primordial black hole constraints for extended mass functions (2017) (That this is a common practice in cosmology may be part of the reference to "buzzkill" astronomers.) He rules out all black holes in the range of approximately 10 10 kg to 10 33 kg even when below some gaps at the bars appear. Except the last item, all range below the mass of the sun (2x10 30 kg) while the smallest known black hole is about four solar masses. Not covered by this comic are massive astrophysical compact halo objects (MACHOs) composed of hard to detect dim objects like black holes, neutron stars, brown dwarfs, and other objects composed of normal baryonic matter. Nevertheless observations have shown that the total amount of baryonic matter in our universe on large scales is much smaller than it would be needed to explain all the measured gravitational effects. Diagrams of our solar system (or any planetary system) often show lines representing the elliptical paths the planet takes around its sun. These lines don't show real objects, though. Astronomers just draw them on pictures of the solar system to show where the planets move. If you draw a line on a map to give someone directions, that line isn't an object in real life; it's just on the map. If these lines were real, they would be huge (Earth's would be 940 million km long (2π AU) and Neptune's would be 28 billion kilometers long). Powers of Ten (1977) gives a good sense of just how large these orbit lines need to be in order to be visible in space diagrams. If these orbit lines were also very dense, they would have a huge mass and could possibly account for the missing 85% of the mass in the universe. But they would also constantly be impaling the planets, including the Earth, which would probably be a problem. [ citation needed ] Their mass would also affect planetary motions in ways which we would detect. A related worry about space travel was expressed in previous centuries; it was thought that the planets were embedded within crystal shells (spheres or Platonic solids), and a rocket into space could smash the shells and send planets plummeting to Earth. Another joke candidate. The title text refers to the fact that space is just vast emptiness where a little bit of dirt could be overlooked. Actually the mean density of detectable matter in the universe, according to NASA, is equivalent to roughly 1 proton per 4 cubic meters . And because this matter is mostly located in galaxies -- and inside there in stars and clouds -- the space between is even more empty. For comparison, one gram of hydrogen consists of 6.022 × 10 23 atoms . Like at home wiping with a cleaning cloth in which we can see the dirt that wasn't clearly visible on the surface we have wiped, Randall believes that some few atoms more per cubic meter could stay undetected in the same way. This isn't true because in the space between galaxies astronomers can detect matter as it spreads over thousands or millions cubic light years. Atoms can't hide; there is always radiation. Dark matter candidates: [A line graph is shown and labeled at left quarter in eV and further to the right in g together with some prefixes.] [The labels read:] µeV, meV, eV, keV, MeV, GeV, TeV, 10 -18 kg, ng, µg, mg, g, kg, TON, 10 6 kg, 10 12 kg, 10 18 kg, 10 24 kg, 10 30 kg [All items are shown in bars ranging between two approximately values:] < 1 µeV - 10 meV: Axion 1 eV - 10 keV: Sterile neutrino 0.5 MeV (exactly): Electrons painted with space camouflage 10 GeV - 10 TeV: Neutralino 100 TeV - 10 -17 kg: Q-ball 1 ng - 100 ng: Pollen 0.1 mg - 1 mg: No-See-Ums 10 -1 g (exactly): Bees 10 g - 100 g: 8-balls 100 kg - TON: Space cows TON - 10 9 kg: Obelisks, monoliths, pyramids 10 9 kg - 10 33 kg: Black holes ruled out by: 10 9 kg - 10 13 kg: Gamma rays 10 13 kg - 10 17 kg: GRB lensing 10 15 kg - 10 22 kg: Neutron star data 10 21 kg - 10 30 kg: Micro lensing 10 24 kg - 10 30 kg: Solar system stability 10 30 kg - 10 33 kg: Buzzkill astronomers 10 33 kg - >10 36 kg: Maybe those orbit lines on space diagrams are real and very heavy

Edgelord

Edgelord

https://www.xkcd.com/2036

https://www.explainxkcd.com/wiki/index.php/2036:_Edgelord

[Cueball is talking to White Hat, who is balling his fist and has small lines above his head to indicate annoyance.] Cueball: So, I hear you're a real edgelord. White Hat: No! [Caption below the frame:] How to annoy a graph theory Ph.D.

"Edgelord" is modern slang describing a brash provocateur on social media; often in a satirical way that if taken literally would be found disturbing or insensitive. The term derives from the word "edgy", which is used to describe things which are designed to be provocative. "Edgy" and "edgelord" are quite derogatory, carrying further implications of being style over substance, or only having appeal with rambunctious teenagers. In mathematics, graph theory is the study of graphs, mathematical structures made up of nodes (points) which are connected by edges (or lines). This comic plays on the fact that graphs have edges. Calling someone with a Graph Theory Ph.D. an 'edgelord' (a master of edges) is somewhat analogous to calling an engineering student a 'forcelord', an astronomy PhD a ' starlord ', or a pharmacologist a ' druglord '. In reply, White Hat shouts "No", and is also clenching his fists in anger, which is ironic, because he seems to be on edge. Because "edgelord" is perceived as an insult by socially aware adults, Cueball is actually provoking White Hat, making Cueball an edgelord in this interaction. Similar situational humor is also found in 2008: Irony Definition . The title text makes the same joke, except that the title would be hyperedgelord instead of edgelord. A hypergraph is a generalization of a graph in which each edge may have more than two endpoints. The term "hyper edge" could easily be considered stereotypically "edgy." [Cueball is talking to White Hat, who is balling his fist and has small lines above his head to indicate annoyance.] Cueball: So, I hear you're a real edgelord. White Hat: No! [Caption below the frame:] How to annoy a graph theory Ph.D.

Supreme Court Bracket

Supreme Court Bracket

https://www.xkcd.com/2037

https://www.explainxkcd.com/wiki/index.php/2037:_Supreme_Court_Bracket

[A tournament bracket tree is shown with 16 participants each on the left and right side. From both sides toward the middle the brackets reduce to eight, then four, two, and one line where the latter join to a rectangle in the middle.] [Left side:] Marbury - Madison McCulloch - Maryland Gibbons - Ogden Near - Minnesota NLRB - Jones & Laughlin Brown - Board of Education Gideon - Wainwright Griswold - Connecticut [Right side:] Miranda - Arizona Loving - Virginia Roe - Wade United States - Nixon Bush - Gore Lawrence - Texas Massachusetts - EPA Obergefell - Hodges [Caption below the frame:] Now that we've finished the round of 32, the Supreme Court will be moving on to the Sweet 16.

The Supreme Court of the United States is the highest federal court of the United States. A tournament bracket is a tree diagram that represents the series of games played during a knockout tournament. US Supreme Court cases are typically titled as Petitioner versus Respondent. To spoof this, Randall has put sixteen famous Supreme Court cases into a tournament bracket, as though they were games in the first round of a single-elimination tournament, and that the winners of the 16 listed court cases will somehow file against each other and then again until the final winner is selected. This is similar to college basketball's March Madness , complete with a ranking bracket. "Sweet 16" in the context of a tournament refers to the stage in a tournament where 16 competitors remain. This comic's concept is thus a word play on "court" (court of law v. basketball court). The phrase "Supreme Court Bracket" also sounds similar to "Supreme Court Docket", which is the official schedule of cases that the Supreme Court will adjudicate (as all of these cases have been). The cases are: The case Marbury v. Madison declared a provision of the Judiciary Act of 1789 unconstitutional, thus preventing several late-term appointments by outgoing President John Adams from being seated under incoming President Thomas Jefferson . More importantly, the ruling established the principle of judicial review by which the Supreme Court can overturn, on the basis of unconstitutionality, laws passed by Congress and signed into law by the President . For this reason it is considered the single most important decision in American constitutional law. The case McCulloch v. Maryland established a broad interpretation of the "necessary and proper" clause, specifically finding that Congress could incorporate a Bank of the United States because the purpose was to help carry out Congress' explicit powers under Article I, section 8. The case Gibbons v. Ogden established that interstate commerce is regulated by the U.S. Congress according to the U.S. Constitution, that interstate navigation is fundamental to interstate commerce, and that therefore the power to regulate interstate navigation in this way rests with the U.S. Congress, not with any state legislature. On 01 March 1824, the US Supreme Court decided in favor of Thomas Gibbons in his appeal of a case brought against him by Aaron Ogden in an attempt to prevent Gibbons from operating steamboats to transport goods and passengers between New York City, New York and Elizabethtown, New Jersey. The US Supreme Court decision reversed a prior injunction against Gibbons issued by a New York State court deciding that Ogden held exclusive navigational rights by way of having licensed them from two men to whom the New York State Legislature had granted the navigation rights in several acts between 1798 and 1807. The case Near v. Minnesota is a landmark United States Supreme Court decision that found that prior restraints on publication violate freedom of the press as protected under the First Amendment to the United States Constitution , a principle that was applied to free speech generally in subsequent jurisprudence. The Court ruled that a Minnesota law that targeted publishers of "malicious" or "scandalous" newspapers violated the First Amendment to the United States Constitution. Noteworthy it was later a key precedent in New York Times Co. v. United States (1971), in which the court ruled against the Nixon administration's attempt to enjoin publication of the Pentagon Papers. National Labor Relations Board v Jones & Laughlin Steel Corporation was a US labor law case. It declared that the National Labor Relations Act of 1935 was constitutional. It effectively preserved the New Deal , which was being pursued by US President Roosevelt in reaction to the Great Depression . Previous Supreme Court cases, unlike NLRB v. Jones & Laughlin , had invalidated New Deal statutes. The case Brown v. Board of Education the Court declared state laws establishing separate public schools for black and white students to be unconstitutional. It stated that "separate educational facilities are inherently unequal." This ruling paved the way for the Civil Rights Movement . However, the decision did not spell out any sort of method for ending racial segregation in schools, and the Court's second decision in Brown II only ordered states to desegregate "with all deliberate speed." In the case Gideon v. Wainwright the Supreme Court unanimously ruled that states are required under the Sixth Amendment to the U.S. Constitution to provide an attorney or lawyer to defendants in criminal cases who are unable to afford their own attorneys. In the case Griswold v. Connecticut (1965), the Court ruled that a statute barring birth control to prevent pregnancy, also known as contraception, was unconstitutional, at least in its application to married couples, as there was an implicit right to privacy in the "penumbras" and "emanations" of other constitutional provisions. This ruling was used as precedent in Eisenstadt v. Baird (1972), which extended the right to unmarried couples, and in Roe v. Wade and Lawrence v. Texas (see below). In Miranda v. Arizona , it was ruled that inculpatory and exculpatory statements would not be accepted in court if a defendant was not informed of their rights under the Fifth Amendment. The "Miranda Rights" warning ("You have the right to remain silent", etc.) is now used across the US. In Loving v. Virginia the Supreme Court ruled that state laws prohibiting interracial marriage were unconstitutional, and were struck down. This decision was well ahead of public opinion; a Gallup poll (cited by Think Progress ) conducted the following year showed only 20% in favor. This case was cited as precedent in Obergefell v. Hodges, listed below. In Roe v. Wade , the Supreme Court ruled that a woman's right to privacy, balanced against the state's interest in limiting abortions , allowed women to undergo abortions in the first and second trimesters and allowed states the right to forbid third-trimester abortions. In United States v. Nixon , the Supreme Court unanimously ruled that then-President Richard Nixon 's refusal to hand over certain tape recordings during his impeachment process was unconstitutional. This case placed limits on the power of executive privilege. In Bush v. Gore , the Supreme Court decided the highly contested 2000 presidential election between George W. Bush and Al Gore, arguing in a 5-4 decision that the recount required by Florida state law could not be carried out before the December 12 deadline required by the United States Code. As such, the statewide recount was stopped, and the now-official initial count (which favored Bush) propelled Bush to the presidency. Lawrence v. Texas ruled that sodomy laws were unconstitutional, making same-sex sexual activity legal in all US states and territories. It explicitly overturned another Supreme Court decision, Bowers v. Hardwick , a case which had previously ruled such laws to be constitutional. In Massachusetts v. EPA , Massachusetts and 11 other states sued the EPA for not regulating carbon dioxide and other greenhouse gases, saying that contrary to the claims of the EPA at that point in time, greenhouse gases are pollutants. In a 5-4 decision, the Supreme Court ruled in favor of the petitioners, forcing the EPA to start placing regulations on greenhouse gases. In Obergefell v. Hodges , the Supreme Court ruled 5-4 that the right to marriage is protected for same-sex couples by the Fourteenth Amendment. With the results given above, the "Sweet 16" of the bracket given would be as follows: The title text refers to a practice of filling out a March Madness bracket, predicting a winner for each game up to the championship. A bracket is "busted" when the result of a game is not as predicted; because future matchups depend on previous results, the whole bracket is worthless at that point. Randall "had Massachusetts v. Connecticut in the final", predicting both parties would win all previous rounds and advance to the final game/case. Because Connecticut lost its first-round case to Griswold, his bracket is busted in the first round. In the second part of the title text, Randall writes: "I had Massachusetts v. Connecticut in the final, probably in a case over who gets to annex Rhode Island." In fact, there actually was a Supreme Court case Massachusetts v. Connecticut (summary at Justia.com , full text at Google Scholar ) dealing with water rights on the Connecticut River, which flows between the two states. Rhode Island is a smaller state that borders both Massachusetts and Connecticut (and no other state), hence the joke about "who gets to annex Rhode Island." In an actual March Madness bracket, "Massachusetts" and "Connecticut" refer to the basketball teams from the University of Massachusetts and the University of Connecticut. So it is possible that a "Massachusetts v. Connecticut" matchup could occur in the basketball championship as well. Occasionally, cases with the same names (if not the same defendants) have occurred in the United States. [A tournament bracket tree is shown with 16 participants each on the left and right side. From both sides toward the middle the brackets reduce to eight, then four, two, and one line where the latter join to a rectangle in the middle.] [Left side:] Marbury - Madison McCulloch - Maryland Gibbons - Ogden Near - Minnesota NLRB - Jones & Laughlin Brown - Board of Education Gideon - Wainwright Griswold - Connecticut [Right side:] Miranda - Arizona Loving - Virginia Roe - Wade United States - Nixon Bush - Gore Lawrence - Texas Massachusetts - EPA Obergefell - Hodges [Caption below the frame:] Now that we've finished the round of 32, the Supreme Court will be moving on to the Sweet 16.

Hazard Symbol

Hazard Symbol

https://www.xkcd.com/2038

https://www.explainxkcd.com/wiki/index.php/2038:_Hazard_Symbol

[The comic shows symbols, drawn in black on top of a yellow background.] [One large symbol embeds four others and it's composed of the outline of three overlapping and outwards narrowing rings arranged by 120 degrees.] [The symbol at the center shows at the same orientation three blades with a small stepped circle in the middle.] [Inside the ring on top is a symbol of a backwards falling human with a small line depicting the ground.] [The ring on the right below the center contains a circle with radiant alternating smaller and longer lines around. One more longer line points toward the center of the image.] [Embedded into the left lower ring is a bolt with an arrow pointing left downwards.] [Caption below:] It's important to know the international warning symbol for radioactive high-voltage laser-emitting biohazards that coat the floor and make it slippery.

Hazard symbols are often required to indicate certain threats to human health. These symbols are typically black symbols on yellow backgrounds, a contrast typically associated with danger even in nature, a phenomenon known as aposematism . However, these symbols also need to be easy to interpret. Therefore, they have simple, recognizable shapes that are internationally uniform and intended to be well-understood. This comic inverts this latter expectation, by combining multiple hazard symbols into one, creating something that is unique, and very hard to understand. In practice, if such an object were to be labelled, the five hazard symbols would be separated, each in their own triangle. The hazard symbols are biohazard ☣, radiation ☢, slip and fall hazard symbol, laser hazard, and high voltage symbol ⚡︎. Another ridiculous aspect of this comic is how these hazards interact with each other, and their attendant risks. Radioactive waste is usually a show-stopper on its own, but bio hazards, lasers, and high-voltage situations usually scare people more than slippery floors. This is probably a joke on how some hazard symbols are worse than others. Some of these would also cancel each other out: both high voltage and lasers have a tendency to harm microorganisms that might be bio-hazards. Most radioactive substances are solid, thus they are hard to slip on. While they do form compounds which could potentially be liquid and therefore slippery, many of these would kill the pathogens. For example, Uranium hexafluoride is a powerful oxidizer that would destroy most germs. Biohazard and radioactivity could be combined as radioactive isotopes of Hydrogen, Carbon and Oxygen can be substituted for their stable counterparts, and high voltage electricity can be applied to anything. However laser hazard and slipping hazard seem to be mutually exclusive as the former applies to devices and the latter to substances. One possibly "solution" could be a room sized gas discharge tube filled with a radioactive biohazard that partly condenses and makes the floor slippery. The title text refers to another unsafe subversion of expectations, in this case, against the NFPA 704 "fire diamond". These are the colourful diamond-shaped symbols often found on the back of tankers, but they are also necessary inclusions on materials safety datasheets. These symbols give numeric indication of the hazardous nature of the material, in three different respects (flammability, health, and reactivity), in addition to providing space for an extra warning on the bottom, typically in the form of one or more letters. Using an emoji instead of numbers and letters would defeat the purpose of the fire diamond, as it would only give a qualitative indication of the danger ("very dangerous"), and additionally, could be very easily mistaken for a 0 (meaning safe). Note, Material Safety Data Sheets have been deprecated in favor of SDS (Safety Data Sheets) in order to come into compliance with the GHS (Globally Harmonized System) . 😰 is described by Emojipedia as " Anxious Face With Sweat ". As an additional joke, using this symbol in the fire diamond could be an expression of how awful this mysterious substance is. [The comic shows symbols, drawn in black on top of a yellow background.] [One large symbol embeds four others and it's composed of the outline of three overlapping and outwards narrowing rings arranged by 120 degrees.] [The symbol at the center shows at the same orientation three blades with a small stepped circle in the middle.] [Inside the ring on top is a symbol of a backwards falling human with a small line depicting the ground.] [The ring on the right below the center contains a circle with radiant alternating smaller and longer lines around. One more longer line points toward the center of the image.] [Embedded into the left lower ring is a bolt with an arrow pointing left downwards.] [Caption below:] It's important to know the international warning symbol for radioactive high-voltage laser-emitting biohazards that coat the floor and make it slippery.

Begging the Question

Begging the Question

https://www.xkcd.com/2039

https://www.explainxkcd.com/wiki/index.php/2039:_Begging_the_Question

[Ponytail and White Hat standing next to each other talking. White Hat has raised his hand while Cueball stands behind him.] Ponytail: That food made me nauseous. White Hat: No, the food was nauseous. It made you nauseated . Cueball: Come on, you're just begging the question. [Caption below the frame:] I annoy people on all sides by using "beg the question" to mean "fight a losing battle against changing usage".

This comic makes fun of the constant battle between those who maintain a prescriptive view of language and those who have a descriptive view . In the prescriptive view, language has fixed rules and fixed usage, and any usage that does not adhere to established rules is incorrect. In the descriptive view however, language is malleable and any usage can be correct if it is common and understood by most people. The comic specifically calls out two phrases which are commonly misused in the prescriptive sense, and whose meanings have changed in modern usage in the descriptive sense: Nauseous Nauseous in its supposedly 'proper' form means "causing nausea ", while nauseated means affected with nausea. Prescriptively speaking, it is only correct to use the word "nauseous" to describe the food item since that was the cause of Ponytail's nausea. Saying "the food made her nauseous" would be interpreted, by a prescriptivist, as meaning the food somehow caused her (her body, her appearance, etc.) to become so disgusting that she now causes other people to feel nausea. As White Hat states, the proper phrasing is that the "the food was nauseous", and it "made [her] nauseated". Both historically and in modern usage, however, "nauseous" is a valid synonym of "nauseated". It is difficult, if not impossible, to cite an era of history when most people would not understand "she is nauseous" to mean she does not feel well. Begging the question Begging the question originally referred to a logical fallacy where an argument assumed its conclusion. The phrase first meant to question (beg) the original question. In modern usage, it has come to mean to "raise a question or point that has not been dealt with". This is often a point of contention for prescriptivists. However, as the caption explains, Cueball has an entirely different meaning for this phrase that he created himself: "fight a losing battle against changing usage". This is actually a meta-meaning, as that is actually the common activity of prescriptivists who complain about incorrect usage; it's a losing battle, because language change is inevitable and unstoppable. And specifically, trying to preserve the original meaning of "begging the question" is a losing battle. Ponytail might recognize that her exposure to nauseous food has both nauseated her and caused her to become nauseous to Cueball. The question is not merely begged, it is missed. The title text also plays on another word commonly argued over by prescriptivists. "Enormity" in its classical usage means either extreme wickedness or a monstrous offense or evil, though it is more commonly used in modern writing as a synonym for enormousness (i.e. largeness in size). The title text exploits the lexical ambiguity that this creates. [Ponytail and White Hat standing next to each other talking. White Hat has raised his hand while Cueball stands behind him.] Ponytail: That food made me nauseous. White Hat: No, the food was nauseous. It made you nauseated . Cueball: Come on, you're just begging the question. [Caption below the frame:] I annoy people on all sides by using "beg the question" to mean "fight a losing battle against changing usage".

Sibling-in-Law

Sibling-in-Law

https://www.xkcd.com/2040

https://www.explainxkcd.com/wiki/index.php/2040:_Sibling-in-Law

[A single layer of a family tree with 15 people depicted as sticky figures side by side is shown. They are connected alternated either by a bracket on top or a short line between them. The four outermost figures on each side are faded out in gray.] [In the middle is Cueball and from below an arrow points at him:] Me [To the left Ponytail is connected by a bracket and the arrow below says:] Sibling [To the right of Cueball Megan is shown connected by a small line, an arrow below her reads:] Spouse [Further to the left and the right the next figures have an arrow below with the nested text:] Siblings-in-law [The next connected figures on both sides are drawn with two other wider arrows embedding this statement:] Also siblings-in-law, I think? [All remaining figures left and right have similar arrows below and the text is:] Possible additional siblings-in-law??? [Caption below the frame:] People complain that “<X> th cousin <Y> times removed” is hard to understand, but to me the most confusing one is sibling-in-law, because it chains across both sibling and marriage links and I don't really know where it stops.

This comic shows the complicated way that English refers to sibling-in-law family relationships. As shown in the comic, your sibling's spouse would be called your "sibling-in-law" (brother-in-law for male, sister-in-law for female). However, your spouse's sibling is also called the same way. The confusion lies with your siblings-in-law's siblings. Randall says they may be "also siblings-in-law, I think?" and further relations are also "possible additional siblings-in-law". According to Wikipedia, "sibling-in-law is one's spouse's sibling, or one's sibling's spouse, or one's spouse's sibling's spouse"; therefore Randall would be correct with the "also siblings-in-law" on the right (his 'spouse's sibling's spouse') but would be incorrect regarding the one on the left (his 'sibling's spouse's sibling' would not generally be considering a sibling-in-law). Wiktionary lists a more restrictive definition: siblings-in-law are either "the sibling of one's spouse" or "the spouse of one's sibling". This definition includes only those whom Randall calls siblings-in-law, and none of those he calls "also siblings-in-law, I think?". The spouse of the sibling of one's spouse or the sibling of the spouse of one's sibling are to be referred as co-siblings-in-law. If anything, this shows that the definition of a sibling-in-law is loose, justifying the "I think ?" sentence of the comic. Many families also use the term "out-law" to jokingly refer to the distant sibling+spouses which Randall seems uncertain about. The caption compares "sibling-in-law" to "<X>th cousin <Y> times removed". This family relationship, for example, 1st cousin once removed , is used to describe your 1st cousin's child or the first cousin of one of your parents. The "once removed" indicates that the family relative is one generation above or below yours. The title text describes a scenario in a traditional wedding in most English-speaking regions. Prior to the wedding being completed, the officiant will provide a final opportunity for anyone in the audience to speak a reason to object to the wedding. This intended for reasons why they cannot lawfully be wed -- such as that one of the participants is already married to someone else or is too young to marry, that the couple are so closely related that the marriage would be incestuous, or that the marriage license is expired -- or other serious emergencies -- such as evidence of infidelity (sexual or otherwise) that might change one of the participants' minds about their continued commitment to their spouse-to-be. In movies and fiction, this is usually a dramatic moment used for the climax of a critical scene. Regardless, it is an incredibly serious objection to raise, and should not be done so lightly. However, the title text describes a confusing and mundane scenario where the only reason the speaker is objecting to the wedding is because they're unsure whether the marriage would make one of the participants their brother-in-law and thus wouldn't know what to call the groom after the wedding. In order to avoid their own confusion, they attempted to stop the wedding altogether. The officiator rightly ruled that this objection was neither just cause to object nor a reason that the wedding would be unlawful, and is therefore no reason the couple should be prevented from their own chance at wedded bliss. Since the title text begins with a FYI (for your information) it is implied that Randall has actually tried to stop a wedding using that reason and has been overruled, and thus he wishes to help others avoid that socially-awkward experience. [A single layer of a family tree with 15 people depicted as sticky figures side by side is shown. They are connected alternated either by a bracket on top or a short line between them. The four outermost figures on each side are faded out in gray.] [In the middle is Cueball and from below an arrow points at him:] Me [To the left Ponytail is connected by a bracket and the arrow below says:] Sibling [To the right of Cueball Megan is shown connected by a small line, an arrow below her reads:] Spouse [Further to the left and the right the next figures have an arrow below with the nested text:] Siblings-in-law [The next connected figures on both sides are drawn with two other wider arrows embedding this statement:] Also siblings-in-law, I think? [All remaining figures left and right have similar arrows below and the text is:] Possible additional siblings-in-law??? [Caption below the frame:] People complain that “<X> th cousin <Y> times removed” is hard to understand, but to me the most confusing one is sibling-in-law, because it chains across both sibling and marriage links and I don't really know where it stops.

Frontiers

Frontiers

https://www.xkcd.com/2041

https://www.explainxkcd.com/wiki/index.php/2041:_Frontiers

[In a single framed picture a hand drawn rhombiod is shown. At the inside a few small arrows pointing to the four sides. The text in the middle reads:] Human achievement so far [Text above the top left side:] Space [Text above the top right side:] The oceans [Text below the bottom left side:] The human mind [Text below the bottom right side:] Alaska [Caption below the frame:] Final remaining “frontiers,” according to popular usage

This comic refers to four remaining “final frontiers” of human discovery, according to popular usage—perhaps analyzed using an Internet search engine. It seems to imply that other fields of research aren’t a challenge anymore. Outer space is so vast in size that it’s impossible for humans to discover even just the stars in our galaxy within a lifetime. Space travel is also very difficult and expensive. The oceans are very deep [ citation needed ] . The vast majority of the deeper oceans hasn’t been visited by humans, and there is still much we don’t know about the living beings in the deep sea. The human mind is not only very complex, but also often seems irrational, which makes it harder to investigate. Its relation to the brain is also somewhat mysterious: philosophy of mind is split on whether the mind is ultimately material (materialism) or immaterial (dualism/idealism). Further, certain philosophical systems have trouble explaining its relation to the body, in what is termed the mind–body problem . Alaska is the state of largest area in the U.S., and also the most sparsely populated. Many places in Alaska have only been partially explored to this day. Randall was probably inspired by the TV series Alaska: The Last Frontier , which plays off of the state’s official nickname of “The Last Frontier”. The humor from this comic comes from the fact that Alaska seems comparably of less important than the other “Final Frontiers”. It is not as hard or expensive to explore as the ocean bottom and outer space, and it is much smaller. While one's own human mind is much more easily accessible than the other three locations, its nature is a substantial frontier in human knowledge. Furthermore, minds other than one’s own are very hard to access. The title text refers to the movie Star Trek V: The Final Frontier , released in 1989. “Final frontier” is a recurring motif in the Star Trek franchise (coming from the opening narration for Star Trek: The Original Series ), and is used to describe the exploration of outer space, which remains a notable frontier to humans, both in real life and within Star Trek . Randall , however, jokingly posits that the frontier to be explored is the film itself, and assumes that, because this movie has been out for a while—nearly thirty years—it ought to be fully and comprehensively explored by now. [In a single framed picture a hand drawn rhombiod is shown. At the inside a few small arrows pointing to the four sides. The text in the middle reads:] Human achievement so far [Text above the top left side:] Space [Text above the top right side:] The oceans [Text below the bottom left side:] The human mind [Text below the bottom right side:] Alaska [Caption below the frame:] Final remaining “frontiers,” according to popular usage

Rolle's Theorem

Rolle's Theorem

https://www.xkcd.com/2042

https://www.explainxkcd.com/wiki/index.php/2042:_Rolle%27s_Theorem

[A single framed picture shows a colored x-y-graph with a text above:] Rolle's Theorem From Wikipedia, the free encyclopedia Rolle's theorem states that any real, differentiable function that has the same value at two different points must have at least one "stationary point" between them where the slope is zero. [The graph shows a sine like curve in blue intersecting the x-axis at points "a" and "b" marked in red while in the middle a point "c" has a vertical dashed green line to the apex and on top also in green f'(c)=0 is drawn with a horizontal tangent line.] [Caption below the frame:] Every now and then, I feel like the math equivalent of the clueless art museum visitor squinting at a painting and saying "c'mon, my kid could make that."

In mathematics, a differentiable function is a function that is "smooth" everywhere, without any sudden breaks or pointy "kinks" or similar. The derivative of such a function is a new function that represents the "slope" or "rate of change" of the original. The function in this comic curves up from point (a) until a point above (c), smoothly turns around, and then curves down from (c) to (b). As a result, the derivative of this function is positive from (a) to (c), and then is negative from (c) to (b). At (c) itself, the function is "flat": the more one zooms in, the more horizontal it looks. The function is moving neither up nor down, so the derivative is neither positive nor negative, but zero. This is what f'(c) = 0 means, as f' is a common notation for the derivative of the function f in differential calculus . A theorem in mathematics is a statement that has been proven from former accepted statements, like other theorems or axioms . This comic references Rolle's theorem . The theorem essentially states that, if a smoothly changing function has the same output at two different inputs, then it must have one or more turning points in between, as the derivative is zero at each one. As a special case, should the function remain flat between the two inputs, then its derivative is actually zero for every point between the inputs. To Randall , this is obvious. However, the proof of this theorem is not as obvious as the result. The seeming triviality of the theorem, coupled with the honour bestowed on the theorem namer, leads Randall to make a comparison to attendees of art museums who look at abstract art pieces and perceive only an apparent technical simplicity in the work. Such a visitor might exclaim "My child could paint that!". However, such works of art typically are seen as having value from attributes other than the painterly difficulty in achieving the piece. For example, an artist's work in this style may be lauded for its visionary qualities, or the emotions expressed through the choice of colours or textures. One such artist is Jackson Pollock . The 'clueless' visitor does not see these aspects and believes their child could imitate the piece. Randall suggests he experiences a similar feeling looking at Rolle's Theorem and noting only the obvious correctness without acknowledging the complicated nature of the proof, or other hidden aspects of the theorem. In the title text, Randall mentions a line together with a coplanar circle. This simply means that both those two-dimensional objects must lay in the same plane in a higher, three-or-more-dimensional space. And by this means, every line drawn through the center of a circle is just a diameter which divides it into two equal parts. Even if this fact is trivial, Proclus says that the first man who proved it was Thales . Auctioning of naming rights , also noted in the title text, refers to the practice of naming entertainment venues for companies which pay for the privilege, such as any of the three Red Bull Arenas or Quicken Loans Arena . Furthermore, "Rolle's" sounds like "Rolls", a common abbreviation for the Rolls Royce brand implying possible sponsorship by the British car manufacturer. The naming of mathematical theorems (along with lemmas, equations, laws, methods, etc.) is not always straightforward and often results in misleading names . Randall implies that there are many seemingly easy theorems like this. For instance the Dirichlet's box principle, also known as the Pigeonhole principle , that states that if you have more objects than containers, you're going to have to put at least two objects in one container. [A single framed picture shows a colored x-y-graph with a text above:] Rolle's Theorem From Wikipedia, the free encyclopedia Rolle's theorem states that any real, differentiable function that has the same value at two different points must have at least one "stationary point" between them where the slope is zero. [The graph shows a sine like curve in blue intersecting the x-axis at points "a" and "b" marked in red while in the middle a point "c" has a vertical dashed green line to the apex and on top also in green f'(c)=0 is drawn with a horizontal tangent line.] [Caption below the frame:] Every now and then, I feel like the math equivalent of the clueless art museum visitor squinting at a painting and saying "c'mon, my kid could make that."

Boathouses and Houseboats

Boathouses and Houseboats

https://www.xkcd.com/2043

https://www.explainxkcd.com/wiki/index.php/2043:_Boathouses_and_Houseboats

[A chart with three rows and three columns is shown, both with the same heading "car", "house", and "boat". On the top left a text with the word "this" two times embedded in a bubble and an arrow respectively pointing to the row and column heading reads:] A this that holds this [Most entries have the common word in black, but crossed out in red with another word below also in red. Two entries remain in green.] A Car that holds a Car: Tow truck Carcar A House that holds a Car: Garage Carhouse A Boat that holds a Car: Car ferry Carboat A Car that holds a House: Mobile home Housecar A House that holds a House: Apartment Househouse A Boat that holds a House: Houseboat (green text) A Car that holds a Boat: Boat trailer Boatcar A House that holds a Boat: Boathouse (green text) A Boat that holds a Boat: Lifeboat Boatboat [Caption below the frame:] I really like the words for "boathouse" and "houseboat" and think we should apply that scheme more consistently. The first version of the comic image used a different wording to indicate which word held the other. The column word holds the row. The original wording can be seen here .

Most English compound nouns can be constructed recursively. In many cases they are written open or spaced like "piano player" (a player of a piano.) But closed forms like "wallpaper" (paper for a wall) are not less common. Randall is engaging in creative linguistics again. This time he is humorously suggesting to use a consistent naming scheme for things holding other things, the same way we call a boat holding a house a houseboat. He is extending this to all combinations boats, houses and cars. This would, however, be somewhat impractical, as these names do not include why one thing is on an other, and are also sometimes ambiguous: a carcar can be a tow truck as much as a car carrier, and a househouse can be either an apartment (house in a house) or an apartment building (house containing houses). Additionally, he is somewhat inconsistent in some parts of the chart. While the chart is supposed to show examples of neologistic compound words <x><y> that refer to a <y> that holds an <x>, rather than a <y> in an <x>. However, Randall's examples sometimes are those of the latter example. He proposes to call lifeboats, which are boats held by other boats, "boatboat", instead of using that to refer to boats holding other boats, such as floating drydocks. Additionally, it is established naval practice to refer to a boat which is carried by another vessel as a "ship's boat", and call any vessel that carries a boat a "ship". In other words, according to usual naval terminology, a "boatboat" is a contradiction in terms; it is either a "boatship", synonymous with ship and hence redundant, or a "shipboat", the ship's boat. "Apartment" is a similar case: an apartment is a house in a house, while a house that holds a house is an apartment building or apartment complex. (However, in the title text, Randall points out an <x><y> could also refer to a <y> in an <x>, similar to the lifeboat and apartment examples. Nevertheless, "lifeboat" and "apartment" do not fit with the rest of the items of the chart and disobey the rule annotated in the corner.) In the title text: "Truck food" is in some areas a common term for the meals offered by " food trucks" . Car phones were a feature in automobiles throughout the late 1960s, 1970s and 1980s, serving as the predecessors to mobile phones, although they were permanently installed into a car and not removable. Bananaphone , a song by Raffi Cavoukian, is also mentioned. [A chart with three rows and three columns is shown, both with the same heading "car", "house", and "boat". On the top left a text with the word "this" two times embedded in a bubble and an arrow respectively pointing to the row and column heading reads:] A this that holds this [Most entries have the common word in black, but crossed out in red with another word below also in red. Two entries remain in green.] A Car that holds a Car: Tow truck Carcar A House that holds a Car: Garage Carhouse A Boat that holds a Car: Car ferry Carboat A Car that holds a House: Mobile home Housecar A House that holds a House: Apartment Househouse A Boat that holds a House: Houseboat (green text) A Car that holds a Boat: Boat trailer Boatcar A House that holds a Boat: Boathouse (green text) A Boat that holds a Boat: Lifeboat Boatboat [Caption below the frame:] I really like the words for "boathouse" and "houseboat" and think we should apply that scheme more consistently. The first version of the comic image used a different wording to indicate which word held the other. The column word holds the row. The original wording can be seen here .

Sandboxing Cycle

Sandboxing Cycle

https://www.xkcd.com/2044

https://www.explainxkcd.com/wiki/index.php/2044:_Sandboxing_Cycle

[The comic consists of four panels arranged in a circle around the center. Black arrows connecting them clockwise in an infinite loop. All panels show the same 14 tiny circles and three different rings embedding some of the circles while other circles are outside. A few circles and rings are connected by lines but there is no connection between them all.] [The panel at top left shows this configuration but with a few circles in red.] "I wish these parts could communicate more easily." [Clockwise the next panel on the right shows new lines in green connecting nearly all remaining also now green circles and the lower most circle has a dashed green line to the outside.] "Ohh, this new technology makes it easy to create arbitrary connections, integrating everything!" [At the third panel to the bottom right all green parts are now in black and even more connections are established. Parts of these and some others are now highlighted in red.] "Uh-oh, there are so many connections it's creating bugs and security holes!" [At the fourth panel to the bottom left all red parts are now in black, showing a complex structure. Four green rings separate the structure with only green connections between them and to the outside.] "Ohh, this new technology makes it easy to enclose arbitrary things in secure sandboxes!" [The arrow above the fourth panel connects it to the first and the circle continues from the beginning.]

A sandbox or sandpit is a playground where children can play safe without interfering the world outside. By this meaning the term was adopted by others like the sand table in military uses, or as a Wikipedia Sandbox , a playground for inexperienced editors to test their additions, and in computer security (sandbox) which Randall probably references at this comic. Software is getting more and more complex, and in an effort to reduce programming work and security vulnerabilities, large applications are composed of multiple programs. Getting these mostly self-contained programs to work with each other can be tricky, since requirements can vary a lot between different applications, requiring a rather general interface or API for communication. The more open such interfaces are, the higher the risk of unintended side effects, like vulnerabilities and overly permissive data access which could be exploited by hackers. At the top left panel it could be a software collection whose parts are not yet fully connected to each other; the parts of the system which are as yet unconnected are shown in red, symbolizing a problem. A simple example is a typical office suite used for documents, presentations, spreadsheets, charts, databases, and more. In the early days those separate applications weren't much connected together, copy and paste was one of the most important features; which suggests the applications haven't yet been fully developed. However, software is never fully developed, improvements can always be made. The next panel uses some "new technology" (in green, representing a solution) to interconnect those parts not only internal but also to the world outside at the internet. In the simple office suite example this means a document can now use a spreadsheet directly by using just a simple connection to another file. If that spreadsheet is changed the document uses this new content without any need of copying it manually. But this leads to the third panel, with undesired connections shown in red. The undesired connections mean that problems in specific applications may spread to other applications because nobody can oversee everything in a large environment. It even may destroy the original document in the office suite example or allow malicious users to exploit security holes. The fourth panel shows (in green, representing a solution) a method applied to this problem known as sandboxing. This is a security mechanism for separating running programs without risking harm to others. This can tighten up sloppy security. A direct consequence of restricted communication is that the programs now again can't connect easily to each other, resulting in a situation very similar like in the first panel and restarting the "sandboxing cycle." The point made by this comic is that it is often difficult to easily use a system without lowering security in that system; a dilemma that can be found both in the office suite example above or the social media example below. The dilemma is again stated in the title text: Randall wants both ease of use and high security. In practice, a tradeoff has to be made. [The comic consists of four panels arranged in a circle around the center. Black arrows connecting them clockwise in an infinite loop. All panels show the same 14 tiny circles and three different rings embedding some of the circles while other circles are outside. A few circles and rings are connected by lines but there is no connection between them all.] [The panel at top left shows this configuration but with a few circles in red.] "I wish these parts could communicate more easily." [Clockwise the next panel on the right shows new lines in green connecting nearly all remaining also now green circles and the lower most circle has a dashed green line to the outside.] "Ohh, this new technology makes it easy to create arbitrary connections, integrating everything!" [At the third panel to the bottom right all green parts are now in black and even more connections are established. Parts of these and some others are now highlighted in red.] "Uh-oh, there are so many connections it's creating bugs and security holes!" [At the fourth panel to the bottom left all red parts are now in black, showing a complex structure. Four green rings separate the structure with only green connections between them and to the outside.] "Ohh, this new technology makes it easy to enclose arbitrary things in secure sandboxes!" [The arrow above the fourth panel connects it to the first and the circle continues from the beginning.]

Social Media Announcement

Social Media Announcement

https://www.xkcd.com/2045

https://www.explainxkcd.com/wiki/index.php/2045:_Social_Media_Announcement

[Cueball sitting in front of a laptop typing.] Why I'm Quitting Facebook, Joining LinkedIn, Deleting My LinkedIn, Rejoining Facebook, Quitting Twitter, Getting Locked Out of Facebook, Moving to Mastodon, and Lobbying Microsoft to Take Over Mastodon and Merge It With LinkedIn: A Manifesto. In the original version of this comic, Cueball misspelled "Mastodon" as "Mastadon".

In 2018, especially after Facebook privacy abuses were revealed in the Cambridge Analytica scandal , many individuals began seeking alternatives. The #deletefacebook hashtag peaked around April 2018, and in some communities, this type of "why I'm leaving Facebook" announcements were popular. Randall parodies this mentality with Cueball, who wants to think he is making a point about standing by his values, values he assumes other people share. However the overly-long title of his manifesto is too specific to apply to anyone but himself, and also reveal a few embarrassing confessions that probably have nothing to do with his values (such as losing his Facebook password). Mastodon is a distributed, federated social network with microblogging features similar to Twitter . "Federated" means that there is one app hosted in many places, so users can choose a host that meets their needs, but everyone can still talk to each other, similar to email. Near the peak of #deletefacebook, mastodon became trending as a twitter alternative with less nazis . Wil Wheaton famously moved to Mastodon from Twitter, but was ultimately disappointed by the experience , because while Mastodon's community is generally less toxic, it does not yet have the tools to handle the kind of targeted harassment that a celebrity might face. Microsoft has been buying up professional-themed social media platforms lately, such as LinkedIn and GitHub , intending to integrate them more fluidly with their enterprise software suite. Mastodon seems an unlikely target for an acquisition, since its decentralized nature means that one corporate entity can't control it, and the culture there is decidedly unprofessional as of this comic. The title text presents an alternative approach by moving most social activities to the cloud-based proprietary team collaboration platform Slack . After making his first workspace in Slack he suggests that he wishes to avoid the people invited, so he creates a second account and a new workspace. This also didn't last long and he stops interacting on social media entirely and reverted to simple texting, probably sending old fashioned SMS-messages to others or just writing texts on paper no one reads. [Cueball sitting in front of a laptop typing.] Why I'm Quitting Facebook, Joining LinkedIn, Deleting My LinkedIn, Rejoining Facebook, Quitting Twitter, Getting Locked Out of Facebook, Moving to Mastodon, and Lobbying Microsoft to Take Over Mastodon and Merge It With LinkedIn: A Manifesto. In the original version of this comic, Cueball misspelled "Mastodon" as "Mastadon".

Trum-

Trum-

https://www.xkcd.com/2046

https://www.explainxkcd.com/wiki/index.php/2046:_Trum-

[Cueball and Megan walking together while talking.] Megan: It's pretty weird that we've had two totally unrelated presidents whose last names start with "T-R-U-M-" . Cueball: Oh, sure, that's definitely the weirdest thing about the presidency right now. Megan: It's less weird than every other fact . But still weird. Cueball: True.

The President of the United States , at the time when this comic was published, is Donald Trump and he shares the first letters of his surname with Harry S. Truman , who was US President between 1945 and 1953. Megan notes that both of these presidents' last names start with "T-R-U-M", but she also states that they are not much related. There were several presidents of the US who even have the exact same last name. For example, John Adams and his son John Quincy Adams , and the more recent father and son George H. W. Bush and George W. Bush . Similarly Theodore Roosevelt and Franklin Delano Roosevelt are 5th cousins. Grandfather and grandson William Henry Harrison and Benjamin Harrison also share a last name. And there are the two most distantly related presidents with the same surname, both Andrew Johnson and Lyndon B. Johnson have the last name of Johnson (7 letters), although the shared last name is coincidental, given they do not share any relatives with the name Johnson. Besides T-R-U-M- and the cases of identical names, the longest common surname prefix is H-A-R (3 letters), shared by William Henry (or Benjamin) H-A-R-rison and Warren Gamaliel H-A-R-ding. (The next longest common surname prefixes are B-U-, shared by James B-U-chanan and George (H.) W. Bush; and C-L-, shared by Grover Cleveland and Bill Clinton.) The longest common suffix (not counting identical names) is also 4 for I-S-O-N for James Madison and the two Harrison presidents. (It is an interesting fact that the name HARRISON contains both the second-longest common prefix and the longest common suffix among non-identical president surnames.) The joke is that the matching of those few letters is the least weird thing. Trump's presidency is commonly considered weird in ways too varied to concisely list in this article, and both Megan and Cueball seem to agree on this. The title text lists "absurd" last names that could start with the same letters as other presidents: Bill Eisenhamper, Amy Forb, Ethan Obample, and Abigail Washingtoast. These would refer to Dwight D. Eisenh ower , Gerald For d , Barack Obam a , and George Washingto n . [Cueball and Megan walking together while talking.] Megan: It's pretty weird that we've had two totally unrelated presidents whose last names start with "T-R-U-M-" . Cueball: Oh, sure, that's definitely the weirdest thing about the presidency right now. Megan: It's less weird than every other fact . But still weird. Cueball: True.

Beverages

Beverages

https://www.xkcd.com/2047

https://www.explainxkcd.com/wiki/index.php/2047:_Beverages

[Inside a single frame, liquid pouring out of a glass through mouth, the esophagus, and to the stomach is shown. However the surrounding bodies like the organs or the glass are not pictured, are only defined by the shape of the liquid, and must be imagined. Further two small parts within or near the invisible stomach with no visible connection to the rest are also wetted.] [Caption below the frame:] It freaks me out to imagine what a beverage is shaped like when I’m in the middle of drinking it.

It is frequently stated that liquids take the shape of their container. While being poured, though, what that "shape" is is open to interpretation. The comic shows the "shape" of a liquid being "poured" down someone's throat (in the process of drinking) and highlights how unsettling this may look without any visible guidance for its flow. While the flow of the beverage wets every parts downwards, it looks as if the stomach is only partially filled, because the process of drinking is still underway and the glass is still half full, and because the contents of the glass would not be enough to fill the stomach in any case. Therefore the shape of the liquid in the stomach area would not correspond to the full shape of the stomach, and there could be additional blobs of liquid where it might have splashed and detached from the main liquid mass, such as depicted by the two little disconnected pieces to the right of the stomach area. The title text expands on this, encouraging the reader to think of the liquid travelling through the entire human digestive tract and to consider that it will eventually dilute through the entire human body ("shaped like me"), with what doesn't leaving the body to pass through the water treatment process ("some pipes and tanks"), and that finally most particles from any ingested liquid will mix with all water on Earth ("all of Earth's oceans"). But by the time a beverage is diluted enough to take the shape of Earth's oceans, the molecules will be so dispersed that the beverage effectively becomes invisible. Note: A barium swallow is a medical procedure that actually studies the shape of a liquid when it is being swallowed, to diagnose problems in the esophagus and other structures. [Inside a single frame, liquid pouring out of a glass through mouth, the esophagus, and to the stomach is shown. However the surrounding bodies like the organs or the glass are not pictured, are only defined by the shape of the liquid, and must be imagined. Further two small parts within or near the invisible stomach with no visible connection to the rest are also wetted.] [Caption below the frame:] It freaks me out to imagine what a beverage is shaped like when I’m in the middle of drinking it.

Curve-Fitting

Curve-Fitting

https://www.xkcd.com/2048

https://www.explainxkcd.com/wiki/index.php/2048:_Curve-Fitting

Curve-Fitting Methods and the messages they send [In a single frame twelve scatter plots with unlabeled x- and y-axes are shown. Each plot consists of the same data-set of approximately thirty points located all over the plot but slightly more distributed around the diagonal. Every plot shows in red a different fitting method which is labeled on top in gray.] [The first plot shows a line starting at the left bottom above the x-axis rising towards the points to the right.] Linear "Hey, I did a regression." [The second plot shows a curve falling slightly down and then rising up to the right.] Quadratic "I wanted a curved line, so I made one with math." [At the third plot the curve starts near the left bottom and increases more and more less to the right.] Logarithmic "Look, it's tapering off!" [The fourth plot shows a curve starting near the left bottom and increases more and more steeper towards the right.] Exponential "Look, it's growing uncontrollably!" [The fifth plot uses a fitting to match many points. It starts at the left bottom, increases, then decreases, then rapidly increasing again, and finally reaching a plateau.] LOESS "I'm sophisticated, not like those bumbling polynomial people." [The sixth plot simply shows a line above but parallel to the x-axis.] Linear, no slope "I'm making a scatter plot but I don't want to." [At plot #7 starts at a plateau above the x-axis, then increases, and finally reaches a higher plateau.] Logistic "I need to connect these two lines, but my first idea didn't have enough Math." [Plot #8 shows two red lines embedding most points and the area between is painted as a red shadow.] Confidence interval "Listen, science is hard. But I'm a serious person doing my best." [Plot #9 shows two not connected lines, one at the lower left half, and one higher at the right. Both have smaller curved lines in light red above and below.] Piecewise "I have a theory, and this is the only data I could find." [The plot at the left bottom shows a line connecting all points from left to right, resulting in a curve going many times up and down.] Connecting lines "I clicked 'Smooth Lines' in Excel." [The next to last plot shows a echelon form, connecting a few real and some imaginary points.] Ad-Hoc filter "I had an idea for how to clean up the data. What do you think?" [The last plot shows a wave with increasing peak values. Finally the plot of the wave is continued beyond the x- and y-axis borders.] House of Cards "As you can see, this model smoothly fits the- wait no no don't extend it AAAAAA!! "

An illustration of several plots of the same data with curves fitted to the points, paired with conclusions that you might draw about the person who made them. These data, when plotted on an X/Y graph, appear to have a general upward trend, but the data is far too noisy, with too few data points, to clearly suggest any specific growth pattern. In such a case, many different mathematical and statistical models could be presented as roughly fitting the data, but none of them fits well enough to compellingly represent the data. When modeling such a problem statistically, much of the work of a data scientist or statistician is knowing which fitting method is most appropriate for the data in question. Here we see various hypothetical scientists or statisticians each applying their own interpretations to the exact same data, and the comic mocks each of them for their various personal biases or other assorted excuses. In general, the researcher will specify the form of an equation for the line to be drawn, and an algorithm will produce the actual line. Nonetheless scientists work much more seriously on the reliability of their assumptions by giving a value for the standard deviation represented by the Greek letter sigma σ or the Latin letter s as a measure to quantify the amount of variation of the data points against the presented best fit . If the σ-value isn't good enough an interpretation based on a specific fit wouldn't be accepted by the science community. Since Randall gives no hint about the nature of the used data set - same in each graph - any fitting presented doesn't make any sense. The graphs could represent a star map, the votes for the latest elected presidents, or your recent invoices on power consumption. This comic just exaggerates various methods on interpreting data, but without the knowledge of the matter in the background nothing makes any sense. Linear regression is the most basic form of regression; it tries to find the straight line that best approximates the data. As it's the simplest, most widely taught form of regression, and in general differentiable functions are locally well approximated by a straight line, it's usually the first and most trivial attempt of fit. The picture to the right shows how totally different data sets can result in the same line. It's obvious that some more basics about the nature of the data must be used to understand if this simple line really does make sense. The comment below the graph "Hey, I did a regression." refers to the fact that this is just the easiest way of fitting data into a curve. Quadratic fit (i.e. fitting a parabola through the data) is the lowest grade polynomial that can be used to fit data through a curved line; if the data exhibits clearly "curved" behavior (or if the experimenter feels that its growth should be more than linear), a parabola is often the first, easiest, stab at fitting the data. The comment below the graph "I wanted a curved line, so I made one with math." suggests that a quadratic regression is used when straight lines no longer satisfy the researcher, but they still want to use simple math expression. Quadratic correlations like this are mathematically valid and one of the simplest kind of curve in math, but this curve doesn't appear to satisfy the data any better than does simple, linear regression. A logarithmic curve grows slower on higher values, but still grows without bound to infinity rather than approaching a horizontal asymptote . The small b in the formula represents the base which is in most cases e , 10, or 2. If the data presumably does approach a horizontal asymptote then this fit isn't an effective method to explain the nature of the data. The comment below the graph "Look, it's tapering off!" builds up the impression that the data diminishes while under this fit it's still growing to infinity, only much slower than a linear regression does. An exponential curve , on the contrary, is typical of a phenomenon whose growth gets rapidly faster and faster - a common case is a process that generates stuff that contributes to the process itself; think bacteria growth or compound interest. The logarithmic and exponential interpretations could very easily be fudged or engineered by a researcher with an agenda (such as by taking a misleading subset or even outright lying about the regression), which the comic mocks by juxtaposing them side-by-side on the same set of data. The comment below the graph "Look, it's growing uncontrollably!" gives an other frivolous statement suggesting something like chaos. Also this even faster growth is well defined and has no asymptote at both axes. A LOESS fit doesn't use a single formula to fit all the data, but approximates data points locally using different polynomials for each "zone" (weighting data points differently as they get further from it) and patching them together. As it has many more degrees of freedom compared to a single polynomial, it generally "fits better" to any data set, although it is generally impossible to derive any strong, "clean" mathematical correlation from it - it is just a nice smooth line that approximates the data points well, with a good degree of rejection from outliers. The comment below the graph "I'm sophisticated, not like those bumbling polynomial people." emphasises this more complicated interpretation, but without a simple mathematical description it's not very helpful to find informative interpretations of the underlying data. Also known as a constant function, since the function takes on the same (constant) value c for all values of x . The value of c can be determined simply by taking the average of the y -values in the data. Apparently, the person making this line figured out pretty early on that their data analysis was turning into a scatter plot, and wanted to escape their personal stigma of scatter plots by drawing an obviously false regression line on top of it. Alternatively, they were hoping the data would be flat, and are trying to pretend that there's no real trend to the data by drawing a horizontal trend line. The comment below the graph "I'm making a scatter plot but I don't want to." is probably done by a student who isn't happy with their choice of field of study. The logistic regression is taken when a variable can take binary results such as "0" and "1" or "old" and "young". The curve provides a smooth, S-shaped transition curve between two flat intervals (like "0" and "1"). The comment below the graph "I need to connect these two lines, but my first idea didn't have enough math." implies the experimenter just wants to find a mathematically-respectable way to link two flat lines. Not a type of curve fitting, but a method of depicting the predictive power of a curve. Providing a confidence interval over the graph shows the uncertainty of the acquired data, thus acknowledging the uncertain results of the experiment, and showing the will not to "cheat" with "easy" regression curves. The comment below the graph "Listen, science is hard. But I'm a serious person doing my best." is just an honest statement about this uncertainty. Mapping different curves to different segments of the data. This is a legitimate strategy, but the different segments should be meaningful, such as if they were pulled from different populations. This kind of fit would arise naturally in a study based on a regression discontinuity design. For instance, if students who score below a certain cutoff must take remedial classes, the line for outcomes of those below the cutoff would reasonably be separate from the one for outcomes above the cutoff; the distance between the end of the two lines could be considered the effect of the treatment, under certain assumptions. This kind of study design is used to investigate causal theories, where mere correlation in observational data is not enough to prove anything. Thus, the associated text would be appropriate; there is a theory, and data that might prove the theory is hard to find. One notable time this is used is when a researcher studying housing economics is trying to identify housing submarkets. The assumption is that if two proposed markets are truly different, they will be better described using two different regression functions than if one were to be used. The additional curved lines visible in the graph are the kind of confidence intervals you'd get from a simple OLS regression if the standard assumptions were valid. In the case of two separate regressions, it would be surprising if all those assumptions (that is, i.i.d. Normal residuals around an underlying perfectly-linear function) were in fact valid for each part, especially if the slopes are not equal. A classical example in physics are the different theories to explain the black body radiation at the end of the 19th century. The Wien approximation was good for small wavelengths while the Rayleigh–Jeans law worked for the larger scales (large wavelength means low frequency and thus low energy.) But there was a gap in the middle which was filled by the Planck's law in 1900. The comment below the graph "I have a theory, and this is the only data I could find." is a bit ambiguous because there are many data points ignored. Without an explanation why only a subset of the data is used this isn't a useful interpretation at all. As a matter of fact, with the extra degrees of freedom offered by the piecewise regression, it could indicate that the researcher is trying to fit the data to confirm their theory, rather than building their theory off of the data. This is often used to smooth gaps in measurements. A simple example is the weather temperature which is often measured in distinct intervals. When the intervals are high enough it's safe to assume that the temperature didn't change that much between them and connecting the data points by lines doesn't distort the real situation in many cases. The comment below the graph "I clicked 'Smooth Lines' in Excel ." refers to the well known spreadsheet application from Microsoft Office . Like other spreadsheet applications it has the feature to visualize data from a table into a graph by many ways. "Smooth Lines" is a setting meant for use on a line graph , a graph in which one axis represents time; as it simply joins up every point rather than finding a sensible line, it is not suitable for regression. Drawing a bunch of different lines by hand, keeping in only the data points perceived as "good". Not really useful except for marketing purposes. The comment below the graph "I had an idea for how to clean up the data. What do you think?" admits that in fact the data is whitewashed and tightly focused to a result the presenter wants to show. Not a real method, but a common consequence of misapplication of statistical methods: a curve can be generated that fits the data extremely well, but immediately becomes absurd as soon as one glances outside the training data sample range, and your analysis comes crashing down "like a house of cards". This is a type of overfitting . In other words, the model may do quite well for (approximately) interpolating between values in the sample range, but not extend at all well to extrapolating values outside that range. Note: Exact polynomial fitting, a fit which gives the unique th degree polynomial through points, often display this kind of behaviour. The comment below the graph "As you can see, this model smoothly fits the- wait no no don't extend it AAAAAA!!" refers to a curve which fits the data points relatively well within the graph's boundaries, but beyond those bounds fails to match at all. The name is also a potential reference to the TV show House of Cards . The plot in House of Cards began with a premise of a rise to power in the United States government, but as it continued into more seasons the premise was taken to an extreme, introducing more and more ridiculous plot points ("WAIT NO, NO, DON'T EXTEND IT!"). Cauchy-Lorentz is a continuous probability distribution which does not have an expected value or a defined variance. This means that the law of large numbers does not hold and that estimating e.g. the sample mean will diverge (be all over the place) the more data points you have. Hence very troublesome (mathematically alarming). Since so many different models can fit this data set at first glance, Randall may be making a point about how if a data set is sufficiently messy, you can read any trend you want into it, and the trend that is chosen may say more about the researcher than about the data. This is a similar sentiment to 1725: Linear Regression , which also pokes fun at dubious trend lines on scatterplots. A brief Google search reveals that Augustin-Louis Cauchy originally worked as a junior engineer in a managerial position. Upon his acceptance to the Académie des Sciences in March 1816, many of his peers expressed outrage. Despite his early work in "mere" engineering, Cauchy is widely regarded as one of the founding influences in the rigorous study of calculus & accompanying proofs. Notably, his later work included theoretical physics, and Lorentz was also a well-known physicist. Therefore, the title-text may be referring back to 793: Physicists . Alternately, the title-text could be implying that the person who applied the Cauchy-Lorentz curve-fitting method may not be well qualified to the task assigned. Curve-Fitting Methods and the messages they send [In a single frame twelve scatter plots with unlabeled x- and y-axes are shown. Each plot consists of the same data-set of approximately thirty points located all over the plot but slightly more distributed around the diagonal. Every plot shows in red a different fitting method which is labeled on top in gray.] [The first plot shows a line starting at the left bottom above the x-axis rising towards the points to the right.] Linear "Hey, I did a regression." [The second plot shows a curve falling slightly down and then rising up to the right.] Quadratic "I wanted a curved line, so I made one with math." [At the third plot the curve starts near the left bottom and increases more and more less to the right.] Logarithmic "Look, it's tapering off!" [The fourth plot shows a curve starting near the left bottom and increases more and more steeper towards the right.] Exponential "Look, it's growing uncontrollably!" [The fifth plot uses a fitting to match many points. It starts at the left bottom, increases, then decreases, then rapidly increasing again, and finally reaching a plateau.] LOESS "I'm sophisticated, not like those bumbling polynomial people." [The sixth plot simply shows a line above but parallel to the x-axis.] Linear, no slope "I'm making a scatter plot but I don't want to." [At plot #7 starts at a plateau above the x-axis, then increases, and finally reaches a higher plateau.] Logistic "I need to connect these two lines, but my first idea didn't have enough Math." [Plot #8 shows two red lines embedding most points and the area between is painted as a red shadow.] Confidence interval "Listen, science is hard. But I'm a serious person doing my best." [Plot #9 shows two not connected lines, one at the lower left half, and one higher at the right. Both have smaller curved lines in light red above and below.] Piecewise "I have a theory, and this is the only data I could find." [The plot at the left bottom shows a line connecting all points from left to right, resulting in a curve going many times up and down.] Connecting lines "I clicked 'Smooth Lines' in Excel." [The next to last plot shows a echelon form, connecting a few real and some imaginary points.] Ad-Hoc filter "I had an idea for how to clean up the data. What do you think?" [The last plot shows a wave with increasing peak values. Finally the plot of the wave is continued beyond the x- and y-axis borders.] House of Cards "As you can see, this model smoothly fits the- wait no no don't extend it AAAAAA!! "

Unfulfilling Toys

Unfulfilling Toys

https://www.xkcd.com/2049

https://www.explainxkcd.com/wiki/index.php/2049:_Unfulfilling_Toys

[The comic presents toys in six different frames.] [Cueball slaps his wrist with a strap-like item in his hand.] Smack Rigid slap bracelet [Cueball jumps on top of a pouch full of air connected via a hose to an air propelled rocket. The pouch does not budge and the rocket remains connected to its base.] Sealed stomp rocket [Ponytail holds a water gun and makes use of its hand-operated pump system.] Pump pump pump Pump Click Pump-only SuperSoaker [Megan pulls an item apart between her hands. The middle section breaks into many pieces on the ground and liquid is falling from the end parts.] Pop Glass glow stick [Cueball holds a figurine sitting on top of a hand-held device and pulls a string connected to it.] Spin Wingless sky dancer [Megan holds a yo-yo until the yo-yo falls from the string and starts rolling on the ground.] Roll No-strings-attached yo-yo [Caption below the frames:] My least successful product line was probably "deeply unfulfilling versions of classic toys."

This comic lists and illustrates six different classic toys that are missing a key piece or attribute that makes them work and/or that makes them unique or fun. Slap bracelets are flexible curved strips of spring steel that roll up and become a bracelet when you slap them against your wrist. This function operates on the same principle and basic design as the rolled band of metal inside a tape measure. A rigid one would not twist and would be deeply frustrating and potentially painful. A stomp rocket has a rubber pouch full of air, connected via a hose to a vertical cylinder contained snugly within the base of an air-propelled rocket. By stomping on the pouch, the air is forced out the top end of the cylinder, launching the rocket into the air. By sealing the air channel, the rocket would stay on the cylinder and the person would just be bounced into the air by the pouch — acting like the world's smallest bouncy house — or the pouch will burst, rendering the toy even more useless. A Super Soaker ™ is a brand of water gun that works by first pumping air into the gun, thereby introducing pressurized air above the water, then releasing the water using the gun's trigger – the extra pressure from the pumped air makes the water go much further than a traditional water gun which relies upon the pressure generated from a single pump of the trigger itself. In Randall 's version, the water cannot be released, so the fun part of the water gun – getting to spray your friends – isn't available. In a classic glow stick , made of flexible plastic, one must first bend it enough to break the glass cylinder inside. This allows the chemicals inside to mix and begin glowing within the plastic tube. If the entire tube were made of actual glass, however, it would not only shatter into many sharp glass pieces but would also cover the hands of the unfortunate user with a mixture of mild but not harmless chemicals. Also, depending on this contraption's construction and/or luck, the chemicals either won't mix and not glow at all, defeating the purpose of the glow stick, or stain your hands, clothes, and surroundings with a glowing liquid, which would be rather unfortunate. In the original toy , a doll or figure with folded-up wings sits on top of a hand-held device with a wrapped string or other mechanism that lets it spin the doll very fast. As the doll spins, centrifugal force causes the wings to unfold and provide lift, and the doll rises up in the air and flies, spinning, sometimes going quite high. Without the wings, the doll will spin but otherwise remain flightless. In a traditional yo-yo , one attaches a string to their finger and the other end of the string is looped around the shaft of the yo-yo, in such a way that it will hold the yo-yo but the yo-yo can still spin. In this case, the string is presumably included but not attached to the yo-yo, so when the yo-yo reaches the end of its string it will fall off, instead of coming back to the person or spinning at the end of the string. Nonetheless off-string yo-yoing technique exists that has been a division of the World Yo-Yo Contest since 2003. The division specifies that the string is tied to one finger but not the yo-yo. It was popularized by yo-yo player Jon Gates. It differs from the manipulation of a Diabolo because the string is tied to one finger instead of being tied to two sticks. The return is accomplished with a twist of the string called a bind. Diabolos don't return. A good example is here at this video titled "Crazy Stringless Yoyo Tricks!" . Note that the phrase "no strings attached" is an idiom and usually refers to something being available without special conditions or restrictions, a favor being done with nothing expected in return, or a relationship intended to be very casual. In this case, it is literal rather than an idiom, in that the string that is normally attached to the yo-yo is literally not attached. In order to build the magnetic Rubik's Cube , you would need to embed magnets in the inward-facing sides of each cube. This actually can be achieved by using a checkered pattern for the polarity of each piece, a single piece uses the same polarity at all its connecting sides while the immediate neighbor is configured in the opposite. This video shows the principle and even a working 5x5x5 magnetic cube. Because such a cube doesn't fall apart Randall had to remove it from his "deeply unfulfilling versions of classic toys." It is also worth noting that although Randall said that there were 27 small magnetic cubes, only 26 small 'cubes' (or 'cubelets') appear in a traditional Rubik's cube, of three main types. There is no center block in a traditional Rubik's cube, instead there is a pivoting armature connecting the six face-centres (with just a single flat face) together while allowing their individual rotation, each of which can keep the 12 edge-centres (two externally-flat faces) rotatably-anchored to at least one face at a time by a form of dovetailed tab on those edge pieces and, similarly, those hold the eight corners (with three outer faces) in place even as they follow a single face's rotation primarily held by the two most currently relevent of the adjacent edges. It might also refer to various square-shaped neodymium magnet-based toys, like this one or this one , which although they can be taken easily apart, they are successful and very fulfilling products on their own. [The comic presents toys in six different frames.] [Cueball slaps his wrist with a strap-like item in his hand.] Smack Rigid slap bracelet [Cueball jumps on top of a pouch full of air connected via a hose to an air propelled rocket. The pouch does not budge and the rocket remains connected to its base.] Sealed stomp rocket [Ponytail holds a water gun and makes use of its hand-operated pump system.] Pump pump pump Pump Click Pump-only SuperSoaker [Megan pulls an item apart between her hands. The middle section breaks into many pieces on the ground and liquid is falling from the end parts.] Pop Glass glow stick [Cueball holds a figurine sitting on top of a hand-held device and pulls a string connected to it.] Spin Wingless sky dancer [Megan holds a yo-yo until the yo-yo falls from the string and starts rolling on the ground.] Roll No-strings-attached yo-yo [Caption below the frames:] My least successful product line was probably "deeply unfulfilling versions of classic toys."

6/6 Time

6/6 Time

https://www.xkcd.com/2050

https://www.explainxkcd.com/wiki/index.php/2050:_6/6_Time

[Cueball and White Hat are walking to the right. Cueball has his hands up in an explaining position.] Cueball: Under my time system, the sun rises at 6 am and it sets at 6 pm, as it should . Cueball: The length of the second is different each day and night, and the current time shifts with your latitude and longitude. Cueball: Today is one of the two days each year when my clocks run at the same speed as everyone else's. [Caption below the frame:] Time standards are so unfixably messy and complicated that at this point my impulse is just to try to make them worse.

Cueball suggests a regional time system similar to that used in many societies prior to the invention of mechanical time keeping , such as Japan during the Edo period or the Roman Empire , where the day is separated into two parts based on night and day and then subdivided by hour, minute, and second to give season-variable lengths for each. This method is also named temporal hour , and still in use in the Jewish religion time table. Midpoints in time such as noon and midnight vary on the longitude from east and west, while the length of day and night depends on the latitude . The first problem is solved today by using time zones in which at noon the sun is in most cases at or close to the zenith and sunrise/sunset happens at different times. The second issue is attributed to the tilt of Earth's axis and the curvature of its surface; in summer days are longer than nights and vice versa in winter. In the polar regions, there are very long days (and nights) and by Cueball's suggestion the entire months-long polar day would last only 12 of the newly defined "hours". The caption lays out the punchline in which Randall has very strong feelings and opinions on how standards of time should be measured (his feelings on Daylight Savings Time have been well-documented in other comics), but as bad as he believes the official standards are he also recognizes that his own rules would not be popular with other people. After coming to recognize this he has made a hobby or game out of making the worst possible system of measuring time and sharing it with other people. The caption, though vague, can also be assumed to relate to the gradual deviation of certain regions from the Coordinated Universal Time (UTC) zones with " Daylight Saving Time " that is observed inconsistently and smaller regions opting for awkward fractional increments of deviation from Coordinated Universal Time. The title text refers to Einstein's special theory of relativity which postulates that the speed of light is the same for all observers, regardless of the motion of the light source (or the observers). An observer at high speed measures the same speed of light as an observer with no motion, measured from the same light source. In classical physics, the speed of the moving observer would be added up, but in special relativity, this isn't true. Instead, the time runs slower for the moving observer. Additionally to this time dilation , there is also a length contraction , without which the geometry wouldn't work. "Today is one of the two days each year when my clocks run at the same speed as everyone else's" refers to the autumnal and vernal equinoxes when day and night are the same lengths, therefore causing his clocks to match the world. The comic was released one day after that year's September equinox, which would be the autumnal equinox for Randall. [Cueball and White Hat are walking to the right. Cueball has his hands up in an explaining position.] Cueball: Under my time system, the sun rises at 6 am and it sets at 6 pm, as it should . Cueball: The length of the second is different each day and night, and the current time shifts with your latitude and longitude. Cueball: Today is one of the two days each year when my clocks run at the same speed as everyone else's. [Caption below the frame:] Time standards are so unfixably messy and complicated that at this point my impulse is just to try to make them worse.

Bad Opinions

Bad Opinions

https://www.xkcd.com/2051

https://www.explainxkcd.com/wiki/index.php/2051:_Bad_Opinions

[Cueball sits at a laptop.] Offscreen voice: What are you doing? Cueball: I just thought of a bad opinion someone could have, and now I'm searching to see if anyone does so I can be mad at them. Offscreen voice: Sounds like you have a healthy relationship with the internet. Cueball: Hey, at least I'm not this guy I just found!

Cueball is imagining bad opinions, searching them up on the Internet, and becoming angry with the people holding said opinions. An offscreen character, upon learning about this, sarcastically remarks that this indicates a "healthy relationship with the internet." Of course, if Cueball wasn't thinking of all these bad opinions, they most likely wouldn't have come to his attention, and he wouldn't have an opportunity to be mad about them. The fact that Cueball is the cause of his own agitation is the joke of (or perhaps, the sad part of) the comic. Cueball misses the offscreen character's point and remarks that he's not as bad as some person he has discovered, presumably through the aforementioned method of searching for bad opinions he thinks up. In title text he goes further, where he can't find an opinion he imagined on the internet, but still wants to discredit it, just because he is so infuriated by just being able to imagine it. This is similar to straw man fallacy , where someone attempts to discredit an opponent by misrepresenting their argument, rather than addressing their real point. Ironically, the comic itself could potentially be considered an example of this kind of behavior. It is possible that Randall imagined the absurd person and behavior depicted in the comic, and wrote a comic satirizing it, without knowing if such a person actually exists. The unhealthy conversation habits enabled by the Interblag has been a regular theme in xkcd. In fact, this is a rather obvious callback to one of the most popular xkcd comics, 386: Duty Calls , wherein Cueball is actively seeking to discredit and correct people who are "wrong" on the internet. This is later done in 2071: Indirect Detection . Perhaps due to the inherent combination of disconnection and intense focus involved in use of the internet, it's pretty common for people to get into arguments online. Cueball has followed the trend of finding social success online by dedicating more time and energy to arguing pedantic points than his opponents. He's done this to such a great degree that he is now actively seeking possible arguments, even when the situations do not arise on their own. The end result is that his life has needlessly more stress, his interpersonal habits are those of contradiction and conflict, he makes unnecessary enemies, and he is always looking at a computer screen instead of his real world friends. [Cueball sits at a laptop.] Offscreen voice: What are you doing? Cueball: I just thought of a bad opinion someone could have, and now I'm searching to see if anyone does so I can be mad at them. Offscreen voice: Sounds like you have a healthy relationship with the internet. Cueball: Hey, at least I'm not this guy I just found!

Stanislav Petrov Day

Stanislav Petrov Day

https://www.xkcd.com/2052

https://www.explainxkcd.com/wiki/index.php/2052:_Stanislav_Petrov_Day

[Megan is looking at her phone while Cueball stands in front of her.] Megan: Hey, Wednesday was Stanislav Petrov Day. We missed it. Cueball: Oh, shoot! Cueball: I got a calendar alert for it, but I assumed it was a false alarm.

Stanislav Yevgrafovich Petrov was a lieutenant colonel of the Soviet Air Defence Forces who became known as "the man who single-handedly saved the world from nuclear war " for his role in the 1983 Soviet nuclear false alarm incident . The incident was unknown to the public until it was revealed shortly before the dissolution of the Soviet Union in 1991. On 26 September 1983, during the Cold War , the satellite-based early-warning system of the Soviet Union reported the launch of multiple intercontinental ballistic missiles from the United States . At the time, tensions with the U.S. were on edge, and high officials of the Soviet Union, including General Secretary Yuri Andropov , were thought to be highly suspicious of a U.S. attack. Petrov checked ground-based radars which had not detected a launch, noted that the warning system had detected only 1-5 missiles instead of the hundreds that would have been expected in the event of a first strike , and chose to mark the system alert as a false alarm. This decision is seen as having prevented a retaliatory nuclear attack, which would have probably resulted in immediate escalation of the Cold War stalemate to a full-scale nuclear war and the deaths of hundreds of millions of people. Investigation of the satellite warning system later confirmed that the system had indeed malfunctioned. While it is highly probable that if Petrov had reported this incident to his superiors they would have come to the same conclusion, it was a point in time when many people feared that the Cold War might become hot. Andropov, the new Soviet leader, was considered weak by the US president Ronald Reagan , and the Western countries were deploying new missile installation in Europe to counter existing missiles in the Eastern Bloc. This fear of nuclear war meant that at this time the peace movement in most western countries reached one of its highest levels. In this comic Cueball reacts to his alert on Stanislav Petrov Day as if it was a false alarm. This is of course a pun since what we celebrate is that Stanislav treated an alert as a false alarm. Also his first comment "Oh shoot" could have been the reaction of Stanislav if he had not assumed it was a false alarm. In real life, many alerts reach everybody on their mobile devices, often causing them to be ignored without deeper knowledge about the issue behind. This was however not the point in this comic. The title text presents a much less important false alarm where one of them, probably Cueball (or perhaps Randall ), was thinking about giving a gift to the other one in the form of an alarm clock that alerts randomly in the middle of the night. That particular alarm is one where she or he can just breathe a sigh of relief and go back to sleep because it's not a real alarm and is perfectly safe to ignore. However if this keeps going off when it’s not supposed to, then when you are actually supposed to wake up you may very well end up assuming that it’s another false alarm, and thus will sleep late anyway, completely defeating the point of the alarm. Also when a real alarm is supposed to wake you up in the middle of the night, you will have been trained to ignore alarms. This is all part of the joke. On the 2007 anniversary, Eliezer Yudkowsky wrote a blog post for LessWrong suggesting that "Wherever you are, whatever you're doing, take a minute to not destroy the world." Not destroying the world has since evolved into an annual tradition. There is a website for the holiday, with several variations of a ritual involving lighting and snuffing candles. The intended mood is that of a somber holiday, somewhere between Thanksgiving and a funeral. However, there are also more lighthearted takes . A "hardcore mode" would be just like the normal holiday, but "During said ceremony, unveil a large red button. If anybody presses the button, the ceremony is over. Go home. Do not speak." Alternatively, "you use a website connected to *another* house where people are also celebrating Petrov Day. If anyone in one house presses the button, the other house receives a launch alarm. They have 60 seconds to respond. At the end of 60 seconds, their party is over, and they must go home silently. The website has some chance of giving you a false alarm." The website can be found here with instructions on how to use it here . Stanislav Petrov himself died in 2017, but in 2018 the Future of Life Institute decided to award his surviving family a $50,000 prize for his contributions. However, in the words of MIT Professor Max Tegmark, who presented the award, the fact that Petrov's son couldn't "get a visa to visit the city his dad saved from nuclear annihilation is emblematic of how frosty US-Russian relations have gotten, which increases the risk of accidental nuclear war.” [Megan is looking at her phone while Cueball stands in front of her.] Megan: Hey, Wednesday was Stanislav Petrov Day. We missed it. Cueball: Oh, shoot! Cueball: I got a calendar alert for it, but I assumed it was a false alarm.

Incoming Calls

Incoming Calls

https://www.xkcd.com/2053

https://www.explainxkcd.com/wiki/index.php/2053:_Incoming_Calls

[A line graph shows the portions of phone calls by type over time beginning slightly before 1990 until today.] Incoming personal calls over time or: why I finally stopped picking up for unknown numbers [The x-axis is labeled with years beginning at 1990 in five-year segments up to NOW (2018). The y-axis shows a relative distribution of callers.] [The calls are (from top to down):] Appointment reminders, misc. (small growing all over time) Family (larger in the beginning, constant with some fluctuations since 2000) Friends (growing from 1995 to 2005, then decreasing but intersected with "that one friend who hates texting", after that decreasing) Legal telemarketers (peak in the beginning, decreasing over time) Auto insurance scammers (a big peak between 2005 and 2012) Other scammers (beginning in 2010, replacing the auto insurance, increasing until today) Political (starting in 2002 and increasing since then) Wrong numbers (constant up to 2000 and then decreasing to nearly today)

This comic shows a graph (a 100% stacked area chart) of incoming phone calls over time to Randall since he was older than six years. Not covered are major modern ways to communicate like SMS , talking on Facebook , or other messaging apps. Wrong numbers used to be a small but significant portion of the phone calls that Randall received and remained fairly steady until the late 1990s, when they began a gradual and accelerating decline, eventually tapering off to nearly none in 2015. This is likely due to the rise of cellphones and programmable land-line phones, which contain their own address books and only require the caller to enter the number once, greatly reducing the chances of accidentally entering a wrong number in general and eliminating the possibility entirely for anyone with whom you have taken the time to save their number. Appointment reminders and miscellaneous similar calls have steadily increased with time, likely due to a combination of Randall's increasing responsibilities as he ages, and thus the number of appointments and legitimate businesses who need to contact him, and the increased use by businesses of automated reminder systems. The appointments section seems to be slightly tapering off, possibly for the rise of using other means, such as SMS, for reminders. The proportion of family members started slowly decreasing until 1998 where it remained almost constant until roughly 2008-2009. Possible reasons for the decline is that Randall's family has been passing away from old age, or that Randall has ceased contact with them; a possible reason for the increase thereafter is Randall's meeting of his current wife, thus gaining in-laws. A note to keep in mind though is that the graph represents the relative percentage of calls, not the absolute number; therefore, a third possibility is simply that the number of calls hadn't changed, but rather the volume of phone calls from everyone else has gone up. Likewise, the increase in phone calls from family might simply be due to the number of phone calls from everyone else going down while family calls have remained constant. Additionally, as mentioned below, phone communication may be be decreasing due to the rise of other communication mediums. The proportion of friends who call Randall rapidly increased in the 1990s and began to overtake family, likely due to a combination of gaining new friends over time and old friends growing into teenage years owning a cell phone roughly starting in the 2000s. At that time the Internet wasn't a primary method of communication especially when away from home, thus phone calls were the main way to connect with friends when apart. Over time, Randall's friends and family have been less likely to make phone calls to him, likely as phone calls have been succeeded by other methods of communication. This is supported by an entry for "that one friend who hates texting" which has grown to encompass pretty much the entire "Friends" category; presumably all his friends EXCEPT that "one friend" do all their communicating with Randall by text or other chat services. Additionally, although there was a large percentage of phone calls from legal telemarketers in the 1990s, this percentage has significantly dropped, perhaps due to the National Do Not Call Registry in the United States, which prohibits telemarketing/automatic dialing to those on the list. Political advertisements are exempt from this list. Instead, there has been a rise in phone calls from scammers and political advertisements. Telemarketers may target calls based on victims' age or other publicly available statistics. The rise and fall of auto insurance scammers may indicate targeting people in their early twenties. It could also be tied to other events, such as the purchase of an automobile. There have also been various reports online about the commonality of this scam in and around 2013, ( [1] ) indicating this may have been a particularly challenging problem during this period. The title text refers to a common scamming tactic in which a robocaller , typically one named "Emily," will claim to be having trouble with their headset and say "Can you hear me now?" The trick is either to keep you on the line while taking a second or two to connect you to a real person to get scammed, or to get a recording of you saying "yes" for potential fraudulent use (or both). [A line graph shows the portions of phone calls by type over time beginning slightly before 1990 until today.] Incoming personal calls over time or: why I finally stopped picking up for unknown numbers [The x-axis is labeled with years beginning at 1990 in five-year segments up to NOW (2018). The y-axis shows a relative distribution of callers.] [The calls are (from top to down):] Appointment reminders, misc. (small growing all over time) Family (larger in the beginning, constant with some fluctuations since 2000) Friends (growing from 1995 to 2005, then decreasing but intersected with "that one friend who hates texting", after that decreasing) Legal telemarketers (peak in the beginning, decreasing over time) Auto insurance scammers (a big peak between 2005 and 2012) Other scammers (beginning in 2010, replacing the auto insurance, increasing until today) Political (starting in 2002 and increasing since then) Wrong numbers (constant up to 2000 and then decreasing to nearly today)

Data Pipeline

Data Pipeline

https://www.xkcd.com/2054

https://www.explainxkcd.com/wiki/index.php/2054:_Data_Pipeline

[Cueball is standing with an open laptop, showing it to Ponytail and White Hat.] Cueball: Check it out - I made a full automated data pipeline that collects and processes all the information we need. [Ponytail is looking down at Cueball's laptop.] Ponytail: Is it a giant house of cards built from random scripts that will all completely collapse the moment any input does anything weird? [Borderless beat panel] [Cueball looks at his laptop.] Cueball: It... might not be. Ponytail: I guess that's someth- Cueball: Whoops, just collapsed. Hang on, I can patch it.

In the first panel Cueball shows Ponytail and White Hat a Data Pipeline he has constructed that, as he puts it, 'collects and processes all the data we need'. This implies that the three are running some sort of project that requires data processing. Ponytail assumes that this data pipeline is an unstable mess of scripts that will cease to function correctly should any unexpected input be received. Cueball tries to claim it isn't, but his hesitation (including using the word "might") essentially states that this is very likely, although he seems to hope that it might not be. Ponytail then seems impressed and expresses this to him. She, however, gets interrupted by Cueball who tells her that the system just malfunctioned and collapsed. He, however, states that he can fix it, making it seem like this cycle of patching and collapsing could repeat infinitely, or until all problems have been patched. Knowing Cueball's code, though, it seems more likely he can't patch it. In the title text, Ponytail or White Hat proceeds to question how such an important system can run on such a small computer. However, Cueball makes it worse by saying he uses his phone due to the better connection. While this might give the pipeline more uptime, it also means its system resources are far more limited. This comic can be logically connected to the Code Quality series ( 1513: Code Quality , 1695: Code Quality 2 and 1833: Code Quality 3 ), similarly showing Cueball having a coding ineptitude and Ponytail's exasperation with it, though this Cueball shows a higher level of competence by having produced something useful, albeit fragile. However, Ponytail doesn't see the actual code in this case, and there's no issues with or comments on coding syntax like in the Code Quality series. Cueball's hesitant response in this comic has some similarities to 410: Math Paper . [Cueball is standing with an open laptop, showing it to Ponytail and White Hat.] Cueball: Check it out - I made a full automated data pipeline that collects and processes all the information we need. [Ponytail is looking down at Cueball's laptop.] Ponytail: Is it a giant house of cards built from random scripts that will all completely collapse the moment any input does anything weird? [Borderless beat panel] [Cueball looks at his laptop.] Cueball: It... might not be. Ponytail: I guess that's someth- Cueball: Whoops, just collapsed. Hang on, I can patch it.

Bluetooth

Bluetooth

https://www.xkcd.com/2055

https://www.explainxkcd.com/wiki/index.php/2055:_Bluetooth

[Cueball and White Hat are talking, Cueball is holding a cell phone and wireless headphones.] Cueball: I haven’t used a wireless/bluetooth thingy in like ten years. Is audio stuff still a nightmare? White Hat: Nah, it’s great now. [Zoom in on White Hat, who is holding his palm out. Cueball is off-screen.] White Hat: You tap devices together twice to link them and they flash in sync. (It pairs using accelerometer timing and sound.) Tap them three times to disconnect. White Hat: You can pair multiple inputs and outputs and it handles it smoothly. Cueball (off screen): Nice! White Hat: It just works. Sound comes from where you expect. Cueball (off screen): Wonderful. [Zoom out to White Hat and Cueball facing each other.] White Hat: Haha, just kidding, it’s a nightmare. Cueball: Noooooo! White Hat: When I connect to my car, music starts blasting from my headphones while the car repeatedly plays a “New connection!” chime. Cueball: This is not what Josiah Bluetooth intended! Though it has been around since 2001, Bluetooth has been a well known technology for use with wireless speakers and headphones since smartphones became popular in the early 2010s. Bluetooth was the subject of particularly wide public attention in 2016 when Apple announced the removal of the 3.5 mm headphone jack in their then-latest smartphone, the iPhone 7 . Apple believes the future of audio lies in Bluetooth earphones, but some others argue that the technology is not advanced enough to replace wired earphones. The debate continues as other companies have followed suit in removing headphone jacks in favor of Bluetooth devices.

Bluetooth is a technology invented in the mid 1990s and intended for devices to connect wirelessly over a relatively short range for the purpose of transmitting information and/or audio. For example, a headset that connects via Bluetooth could be connected to a computer that's also Bluetooth-enabled, and then whatever would normally come out of the computer's speakers would come out the headset's ear pieces instead, and whatever was spoken into the headset's microphone would be transmitted to the computer's audio input system as if coming in through the computer's microphone. For this to work, the two devices need to be paired, which means they need to know the unique identification number of the other device and have been given permission to communicate with it, as well as knowing what kind of data exchanges are both possible and allowed. Pairing is not always a smooth process, especially given the somewhat limited methods some of these devices have for user interaction. For example, headsets typically don't have screens and user interfaces that make it easy to select what computer or other device you want them to connect to, so you're often confronted by blinking lights and/or sounds to make it through the pairing process, with each device having its own method for initiating or accepting a pairing request. Cueball is talking to White Hat about Bluetooth and wireless connectivity. He asks if it has become easier to stream audio via Bluetooth since he last used it. White Hat then jests that it has become an easy-to-use and streamlined service, where connecting devices is easy, and he gives some examples of how easy it is to use. Cueball is excited about this, until White Hat reveals that he was lying and that Bluetooth is still as hard to use as ever. Cueball then invokes the name of "Josiah Bluetooth", a fictitious person implied to have invented the eponymous Bluetooth. "Josiah" is an old-timey name and suggests the amusing idea that in the 1700s or 1800s a hardy inventor named Josiah Bluetooth came up with the idea for wireless audio. (Note that while there is no "Josiah Bluetooth" person, there is a " Josiah " Bluetooth ceramic speaker.) This comic also references the common problem of audio playing through the wrong device when Bluetooth is activated. The title text is another misdirection joke because while the first part of the sentence is true (Bluetooth was indeed named after a tenth-century Viking king), it goes on to make the silly claim that King Harald himself developed a wireless charging standard. This is a reference to the Qi wireless power transfer standard that, like Bluetooth, is a well-branded industry standard with a catchy name and wide adoption that also does not work quite as well as promised even 10 years after its first release. (It could also be a reference to Medieval Vikings charging into battle, which is, by most accounts, usually a fairly wireless affair [ citation needed ] (assuming one discounts chainmail armor). In this case, the standard could be a pun as a standard also denotes a royal or military flag.) Specifically, the Viking king referenced in the title text, Harald “Bluetooth” Gormsson , usually called Harald Bluetooth, was a ruler of Denmark and Norway who died in 985 or 986. Jim Kardach of Intel named the Bluetooth protocol after him, apparently as he united the various Norse tribes of Denmark into a single kingdom just as Bluetooth unites communication protocols. The Bluetooth logo unites the two Norse runes corresponding to "H" and "B" for Harald Bluetooth. [Cueball and White Hat are talking, Cueball is holding a cell phone and wireless headphones.] Cueball: I haven’t used a wireless/bluetooth thingy in like ten years. Is audio stuff still a nightmare? White Hat: Nah, it’s great now. [Zoom in on White Hat, who is holding his palm out. Cueball is off-screen.] White Hat: You tap devices together twice to link them and they flash in sync. (It pairs using accelerometer timing and sound.) Tap them three times to disconnect. White Hat: You can pair multiple inputs and outputs and it handles it smoothly. Cueball (off screen): Nice! White Hat: It just works. Sound comes from where you expect. Cueball (off screen): Wonderful. [Zoom out to White Hat and Cueball facing each other.] White Hat: Haha, just kidding, it’s a nightmare. Cueball: Noooooo! White Hat: When I connect to my car, music starts blasting from my headphones while the car repeatedly plays a “New connection!” chime. Cueball: This is not what Josiah Bluetooth intended! Though it has been around since 2001, Bluetooth has been a well known technology for use with wireless speakers and headphones since smartphones became popular in the early 2010s. Bluetooth was the subject of particularly wide public attention in 2016 when Apple announced the removal of the 3.5 mm headphone jack in their then-latest smartphone, the iPhone 7 . Apple believes the future of audio lies in Bluetooth earphones, but some others argue that the technology is not advanced enough to replace wired earphones. The debate continues as other companies have followed suit in removing headphone jacks in favor of Bluetooth devices.

Horror Movies

Horror Movies

https://www.xkcd.com/2056

https://www.explainxkcd.com/wiki/index.php/2056:_Horror_Movies

[White Hat and Cueball are standing together and talking. White Hat points at Cueball who has raised his arms.] White Hat: Wanna see a horror movie? Cueball: Sure! I love watching terrible things happen to people and feeling afraid! [Caption below the frame:] I know everyone's into what they're into, but I have never understood horror movies. In early issues, Randall frequently referenced his fear of velociraptors based on watching Jurassic Park as a kid.

This comic is the first in the Horror Movies series, which was followed by 2076: Horror Movies 2 a month later. Horror movies are a genre of movie or film which attempt to elicit the emotional response of fear in the viewer. Some enjoy that type of movie because it allows them to experience and release that emotion, perhaps as a form of catharsis or release. Others take a more detached view and enjoy watching bad things happen to other people, perhaps deriving humor or enjoyment out of a situation that they are glad not to be in themselves. White Hat suggest to Cueball that they see a horror movie, and Cueball appears excited and states Sure! I love watching terrible things happen to people and feeling afraid! This is basically the idea about seeing horror movies, so people who like them might make a statement like this if they say they enjoy them. As the caption speaks against horror movies, it's most likely that Cueball is being sarcastic. Randall comments on this in the caption below the panel saying that he simply does not understand why people would want to watch a movie whose themes and intended emotions are steeped in such negativity. While he fully admits he is criticizing from a position of ignorance (and tries his best not to think less of horror movie fans) he still cannot wrap his head around them. In the title text a conversation between Randall and a friend goes on, as the friend double checks that his favorite movie of all time is Jurassic Park . This movie could be considered a "horror" film as there are elements of fear and terror, especially when the dinosaurs that Randall loves so much are chasing and eating humans. However, this movie type is usually placed in the adventure or science fiction genre. Randall agrees that he likes it, but instead of claiming that Jurassic Park isn't a horror film, replies by saying that he likes dinosaurs and actually wants there to be an island full of them. He then continues by giving an example of an alternative premise for Jurassic Park which maintains the horror aspect of the film by removing the dinosaurs and adding serial killers instead, and that type of movie wouldn't appeal to Randall. An amusement park about "Serial killers in creepy masks" refers to the movie trope from the Scream , Halloween and the Friday the 13th series of films, among others. The friend then states that such an idea would be really great for a horror movie. While Randall may not agree, he could see the humor in watching Jeff Goldblum (who portrays Ian Malcolm in Jurassic Park), in the scene where his attempts to prevent the "brilliant" idea of breeding serial killers as an amusement park attractions from coming to fruition, fails! This of course also fails in the case with Dinosaurs in the original movie, but how could Jeff fail to convince people about the bad idea in breeding human serial killers for an amusment park? It is that scene, and only that, Randall would like to watch from that alternative movie. [White Hat and Cueball are standing together and talking. White Hat points at Cueball who has raised his arms.] White Hat: Wanna see a horror movie? Cueball: Sure! I love watching terrible things happen to people and feeling afraid! [Caption below the frame:] I know everyone's into what they're into, but I have never understood horror movies. In early issues, Randall frequently referenced his fear of velociraptors based on watching Jurassic Park as a kid.

Internal Monologues

Internal Monologues

https://www.xkcd.com/2057

https://www.explainxkcd.com/wiki/index.php/2057:_Internal_Monologues

[Beneath a two line caption are five characters shown, with their thoughts inside thought bubbles. Below them are labels giving their respective fields of science.] Internal Monologues from various fields Botany Megan: I can't get over the fact that trees are made of air. Physics Cueball [looking at a phone in his hand]: It's so weird that I can feel the Earth and my phone being pulled together. Computer security Blondie: I wonder if today will be the day everyone gets hacked and it all finally collapses. Graphic design Hairy: I wonder how that store ended up with the Law & Order font for their sign. Medicine Ponytail: We're all acting normal even though we're full of blood and bones and poop.

This comic explores some seemingly strange perspectives that academics or professionals might have due to their deeper knowledge and understanding of the fields that they study. Many seemingly mundane phenomena can actually be quite weird or counterintuitive if you understand how they really work. The five people featured in this comic, all from different disciplines, are all aware of certain facts about reality that seem so strange even they have trouble believing they are true; yet, undeniably, they are. Four of the five people are pondering things that they happen to find very interesting but that aren't too concerning to an everyday person, whereas what Blondie is pondering could have widespread or even global effects on our way of life. In the title text, Blondie amends her thought, since she actually knows an even more concerning truth: we've already all been hacked, and we just don't know it yet. Below, the people's thoughts are explained in detail. Botany Much of the mass of trees is extracted from the air. An Australian ABC program explains that " Trees are made from air ". More precisely: The bulk of the mass of a tree is composed of cellulose and water. Cellulose is a polysaccharide, a large molecule consisting of many glucose molecules (C 6 H 12 O 6 ) bonded together. Plants make those glucose molecules through photosynthesis: they make them by combining water (H 2 O) and carbon dioxide molecules (CO 2 ) using the energy from sunlight, releasing oxygen in the process (O 2 ). Plants get the carbon dioxide from the atmosphere, and arguably the water also as it usually comes from rain which is condensed water vapor. The main photosynthesis balance is given by the formula : 6 CO 2 + 6 H 2 O -> C 6 H 12 O 6 + 6 O 2 Physics Gravity is the weakest of the four fundamental forces in physics but also to humans the most preeminent one. In everyday experience, most people tend to think of gravity merely as a pervasive downward force, but as a physicist, Cueball is more aware that in fact, all gravitational forces are mutual; any pair of objects will exert a gravitational force on each other, regardless of how big they are. Therefore, he is correct in saying that his phone and the Earth are being "pulled together", and finds it remarkable that he is able to sense this interaction between two objects of such an disparate size even when the gravitational pull of the phone is hard to detect. Computer Security Anyone well versed in computer security understands just how insecure the systems that we depend on actually are. In the title text it is noted that possibly all our systems are already hacked, and we just haven't found out yet. Since malicious hackers do their work covertly, a successful hack often isn't discovered until days, weeks, or even years later if at all. By that time they may have successfully hacked many other systems using the same techniques and/or exploiting the same widely unknown or un-patched security flaws. Some high profile hacks recently discovered at the time of this posting include a 50-million user hack of Facebook and Google+ announcing they are shutting down the consumer side of Google+ , in part due to a security flaw that was discovered and patched months ago. Graphic Design Graphic designers recognize fonts and design elements, and see how they come together. In this comic, the graphic designer wonders how the Law & Order font was chosen for a particular storefront's sign. Law & Order is a police procedural TV series created by Dick Wolf in 1990, which has had various spinoffs. The font used for the title sequence of Law & Order is called Friz Quadrata , and is also the font used for the signage of the New York Police Department headquarters. Medicine Doctors are well versed in human anatomy , and are likely to think about what is inside of people more than the average person would. And most people would actually like not to think about all the blood and bones we are all carrying around with us. Not to mention the poop or the contents of our stomach that could be considered vomit or the pee etc. Most people do not think about that the person next to them is actually a skeleton packed in meat and animated by electricity... But Ponytail does, because she is being exposed to this fact all the time through her study of medicine. [Beneath a two line caption are five characters shown, with their thoughts inside thought bubbles. Below them are labels giving their respective fields of science.] Internal Monologues from various fields Botany Megan: I can't get over the fact that trees are made of air. Physics Cueball [looking at a phone in his hand]: It's so weird that I can feel the Earth and my phone being pulled together. Computer security Blondie: I wonder if today will be the day everyone gets hacked and it all finally collapses. Graphic design Hairy: I wonder how that store ended up with the Law & Order font for their sign. Medicine Ponytail: We're all acting normal even though we're full of blood and bones and poop.

Rock Wall

Rock Wall

https://www.xkcd.com/2058

https://www.explainxkcd.com/wiki/index.php/2058:_Rock_Wall

[Ponytail is gesturing towards Megan with her hand, while talking to her.] Ponytail: I live next to a wall of rock 20 miles thick. There's no way around or over it. I'm trapped on this side forever. Ponytail: I study the stuff on the other side. [Caption below the frame:] Mantle geology seems like the most frustrating field.

Mantle geologists study that part of the planet that's below the top " crust " of the planet. The top layer of the planet, which is several dozen miles thick, is the only layer we've been able to explore, by digging tunnels , spelunking , etc. The only way to study the mantle and other inner layers of the earth are through non-visual, non-tactile, indirect methods, and by analyzing old samples of the mantle that have made their way to the surface. In this comic, Ponytail , talking to Megan , is describing her job as a mantle geologist as that of living on one side of a thick wall that is, and likely always will be, impossible to get around, but she has to study what is on the other side of the wall. In this case the wall is horizontal rather than vertical, the wall being the earth's crust, and makes a complete sphere, so the only way to get past the wall would be to go through. It is theoretically possible to go through, but as of the comic's posting, humanity is far from doing so. (The deepest hole dug as of at that time, as measured by true vertical depth , is the Kola Borehole , which only goes down to 12,262 metres out of the estimated 35,000 meters needed to get through at that location.) In the title text Randall states that he doesn't trust mantle/core geologists. Because if they got the chance he believes they would not hesitate (even the duration of a heartbeat) to strip away Earth's crust to study the mantle or even worse the core directly. Of course if they only did this locally to look at the mantle it would not shatter the Earth although that local area may become a volcano. But if they actually peeled the entire outer layer away, we humans would have no place to live, as the mantle is really hot and would melt easily (producing magmas and therefore lavas when magma’s exposed to surface, see title text of 1405: Meteor to be more confused). However, after a while all these erupted lavas would solidify and become a new crust. Humanity needs to withstand just some millennia of active worldwide volcanism. If they somehow exposed the core even locally something weird would be bound to happen. [ citation needed ] But Randall is afraid that their craving to get around that 20 mile wall would prevent the researchers from even hesitating if they did get that chance. Fortunately, we can study planetary cores in the solar system without stripping Earth's surface by visiting an asteroid which is thought to be the exposed iron core of a protoplanet. The Psyche mission is scheduled to launch in 2022 and arrive at 16 Psyche in 2026. This comics seems to be a spin-off from the previous comic 2057: Internal Monologues , where Randall tried to find some interesting monologues from scientist from different research fields. Maybe he did not find an internal monologue he liked for geologists, but ended up with this idea instead. Thinking about the core or mantle, lava and magma seems to be something Randall does a lot, and thus he must have some ideas about how a geologist would , as in 913: Core . [Ponytail is gesturing towards Megan with her hand, while talking to her.] Ponytail: I live next to a wall of rock 20 miles thick. There's no way around or over it. I'm trapped on this side forever. Ponytail: I study the stuff on the other side. [Caption below the frame:] Mantle geology seems like the most frustrating field.

Modified Bayes' Theorem

Modified Bayes' Theorem

https://www.xkcd.com/2059

https://www.explainxkcd.com/wiki/index.php/2059:_Modified_Bayes%27_Theorem

[The comic shows a formula with a header in gray on top:] Modified Bayes' theorem: [The formula:] P(H|X) = P(H) × (1 + P(C) × ( P(X|H)/P(X) - 1 )) [Variables and functions are described also in gray:] H: Hypothesis X: Observation P(H): Prior probability that H is true P(X): Prior probability of observing X P(C): Probability that you're using Bayesian statistics correctly

Bayes' Theorem is an equation in statistics that gives the probability of a given hypothesis accounting not only for a single experiment or observation but also for your existing knowledge about the hypothesis, i.e. its prior probability. Randall's modified form of the equation also purports to account for the probability that you are indeed applying Bayes' Theorem itself correctly by including that as a term in the equation. Bayes' theorem is: P(H | X) is the probability that H , the hypothesis, is true given observation X . This is called the posterior probability . P(X | H) is the probability that observation X will appear given the truth of hypothesis H . This term is often called the likelihood . P(H) is the probability that hypothesis H is true before any observations. This is called the prior , or belief . P(X) is the probability of the observation X regardless of any hypothesis might have produced it. This term is called the marginal likelihood . The purpose of Bayesian inference is to discover something we want to know (how likely is it that our explanation is correct given the evidence we've seen) by mathematically expressing it in terms of things we can find out: how likely are our observations, how likely is our hypothesis a priori , and how likely are we to see the observations we've seen assuming our hypothesis is true. A Bayesian learning system will iterate over available observations, each time using the likelihood of new observations to update its priors (beliefs) with the hope that, after seeing enough data points, the prior and posterior will converge to a single model. The probability always has a value between zero and one, the latter value represents a 100% probability. Both extremes would be: It is a linear-interpolated weighted average of the belief from before the calculation and the belief after applying the theorem correctly. This goes smoothly from not believing the calculation at all up to be fully convinced to it. Bayesian statistics is often contrasted with "frequentist" statistics. For a frequentist, probability is defined as the limit of the relative frequency after a large number of trials. So to a frequentist the notion of "Probability that you are using Bayesian Statistics correctly" is meaningless: One cannot do repeated trials, even in principle. A Bayesian considers probability to be a quantification of personal belief, and so concepts such as "Probability that you are using Bayesian Statistics correctly" is meaningful. However since the value of such subjective prior probablities cannot be independently determined, the value of P(H|X) cannot be objectively found. The title text suggests that an additional term should be added for the probability that the Modified Bayes Theorem is correct. But that's this equation, so it would make the formula self-referential, unless we call the result the Modified Modified Bayes Theorem. It could also result in an infinite regress -- needing another term for the probability that the version with the probability added is correct, and another term for that version, and so on. If the modifications have a limit, then a Modified ω Bayes Theorem would be the result, but then another term for whether it's correct is needed, leading to the Modified ω+1 Bayes Theorem, and so on through every ordinal number . Modified theories are often suggested in science when the measurements doesn't fit the original theory. An example is the Modified Newtonian dynamics theory, among many others, in which some physicists try to explain dark matter with not much success. [The comic shows a formula with a header in gray on top:] Modified Bayes' theorem: [The formula:] P(H|X) = P(H) × (1 + P(C) × ( P(X|H)/P(X) - 1 )) [Variables and functions are described also in gray:] H: Hypothesis X: Observation P(H): Prior probability that H is true P(X): Prior probability of observing X P(C): Probability that you're using Bayesian statistics correctly

Hygrometer

Hygrometer

https://www.xkcd.com/2060

https://www.explainxkcd.com/wiki/index.php/2060:_Hygrometer

[Megan and Cueball are walking and talking. Cueball is holding his phone with one hand, looking at it.] Megan: ...A hygrometer is a device for measuring— Cueball: I want one! Ooh, found one for $7.99 with free shipping! I'm buying it. Megan: —Humidity. Cueball: Oh, cool! [Caption below the frame:] For some reason, I feel a powerful compulsion to own any device whose name ends in "-ometer."

Here, Megan is talking to Cueball about hygrometers . But before she can even finish explaining what it does, Cueball has looked up, found, and purchased the product. A hygrometer is an instrument for measuring the amount of water vapor in the atmosphere, or the amount of water in solids such as soil or wood. It seems Randall (or Cueball) loves being able to measure things and therefore finds instruments or measurement tools that end in -ometer very interesting, and wishes to own all of them. Many measuring instruments use the suffix -meter which is derived from the Greek noun μέτρον for "measure". The character "o" always belongs to the first term, but it also belongs to old Greek words like Thermo -meter, micro -meter, or even hygro -meter. Other measurement devices such as speedometer use an English word with an "o" appended to mimic the Greek-derived terms, purportedly for easier marketing. Because themes in science often based on Greek terminology that ending at the first part appears often. Nonetheless, Randall believes that this "o" belongs to the general term for measuring devices. In the title text, Randall states he is working on assembling a combination of usually unrelated measuring instruments, for a purpose that is neither stated in the comic nor easy to guess. The list consists of: Finally, he mentions an ometerometer , a concatenation of -ometer with itself, which would be a device for measuring devices. It has been included in a humorous list of Other Types of Ometers from 2007, where it was described as measuring the measuring capacities of other measuring devices. [Megan and Cueball are walking and talking. Cueball is holding his phone with one hand, looking at it.] Megan: ...A hygrometer is a device for measuring— Cueball: I want one! Ooh, found one for $7.99 with free shipping! I'm buying it. Megan: —Humidity. Cueball: Oh, cool! [Caption below the frame:] For some reason, I feel a powerful compulsion to own any device whose name ends in "-ometer."

Tectonics Game

Tectonics Game

https://www.xkcd.com/2061

https://www.explainxkcd.com/wiki/index.php/2061:_Tectonics_Game

[Cueball is standing behind Ponytail, who is sitting on the floor playing a video game on a TV which displays a diagram of tectonic plates.] Cueball: What game is that? Ponytail: Tectonics! Ponytail: You steer chunks of crust around, rifting, subducting, and building and eroding mountains. [A view of the game screen is shown. It includes a large cross-section of the Earth with smaller charts around it.] Ponytail (narrating): You try to keep your climate stable and your biosphere rich. Ponytail (narrating): Avoid making large igneous provinces! They're the worst . [Cueball holds his hand out in a frameless panel.] Cueball: Cool! Cueball: Can I try? Ponytail (off-panel): Sure! [Cueball plays the game while Ponytail watches.] Cueball: ...How do I unpause? Ponytail: It's not paused. Cueball: ... Ponytail: Continents can only move a few inches per year. [Cueball has stopped playing and holds the controller in one hand. Ponytail points at the screen that shows an achievement page with no completed achievements, but a progress bar halfway done for an achievement with the number 1 and a mountain.] Cueball: It's real-time? Ponytail: Just 400 millennia to go until your first mountain achievement!

This comic is to show similarity to many simulation games , which have various niche popularity. Similar to Maxis' Spore , the game in question allows you to terraform entire worlds. However, in a typical Randall twist, unlike most simulation games, you could not speed up the progress of time to make world-changing endeavours occur in a matter of seconds. The game operates in real time, which means most of the user time-frame will be spent idly watching nearly non-moving continents, drifting at the real speed of continental drift, a couple of inches a year, which makes for very slow gameplay. Thus several hundred millennia of play time is needed to reach a game achievement of forming a kilometre high mountain. Many computer games simulate to one degree or another real items and tasks, but often simplify them to fit into a game format -- to make them more exciting, to make them quicker, to advance a particular plot line or quest, etc. For example, a game about farming might allow you to grow corn, but whereas in real life corn takes about 90 days to germinate from seed and grow to maturity, in a game the growth might be instantaneous or measured by minutes, rather than by days/weeks/months. The comic may thus be a jab at how our lives already are real time MMORPG . In this game, especially, one would expect such shortcuts, given the extreme time frames required for geological events to be manifested. The joke is that this game is so realistic that it's played in "real-time", which means for every second or hour or eon something would take in real life, in the game it would take the same second or hour or eon to happen. Playing such a game where the events take longer than the person would be alive would likely be unsatisfying. [ citation needed ] A mildly less extreme example of a simulation game being played in real-time would be the Desert Bus video game where you have to drive a bus from Tucson, Arizona , to Las Vegas, Nevada , in real time at a maximum speed of 45 MPH. The trip requires eight hours of continuous play to complete, at which point you score one point with the option to continue playing for additional points at the rate of one point per successful eight hour trip. The action consists almost entirely of just keeping the bus from veering off the road. It cannot be paused or sped up, and failure requires a tow back to the starting point at the same 45 MPH speed. The frames show some elements of gameplay. The first frame shows a destructive plate margin in which an oceanic plate (grey) is being subducted under a continental plate (brown with a person standing on it) while sediments between the plates are compressed to form mountains. Clockwise from top left, the second frame shows a cross section through the planet and various statistics about the planet (CO 2 levels of 840 ppm, solar irradiation of 1184 W/m 2 and heat-flow through the crust of 91 mW/m 2 ). Solar irradiation and heat-flow are similar to the Earth, but CO2 levels are raised. Bottom right displays several stats titled L T , L M , L A and L L , and bottom left is a view of the planet showing the proportion covered by ice (3%), land (31%) and water (66%). It seems that the raised CO2 levels have reduced the amount of ice compared to the Earth. The final panel shows some of the achievements that can be unlocked, the first is 1 km mountain and the last achievement of the first row is 10 km mountain. Below that seem to be achievements in the formation of an atoll. Large igneous provinces are suspected to be related to extinction level events and rapid climate changes in real life. Thus, they 'are the worst' in this game. In the title text type A3 V stars are mentioned which are white main sequence stars at mass from 1.4 to 2.1 times the mass of the Sun. Thus they have a shorter lifespan than the Sun, hundreds of millions of years, compared to the 10 billion years lifespan of the Sun. By starting the game now with an A3 V star, there would be plenty of time to complete the game before the real Sun would go to a Red Giant destroying the Earth. [Cueball is standing behind Ponytail, who is sitting on the floor playing a video game on a TV which displays a diagram of tectonic plates.] Cueball: What game is that? Ponytail: Tectonics! Ponytail: You steer chunks of crust around, rifting, subducting, and building and eroding mountains. [A view of the game screen is shown. It includes a large cross-section of the Earth with smaller charts around it.] Ponytail (narrating): You try to keep your climate stable and your biosphere rich. Ponytail (narrating): Avoid making large igneous provinces! They're the worst . [Cueball holds his hand out in a frameless panel.] Cueball: Cool! Cueball: Can I try? Ponytail (off-panel): Sure! [Cueball plays the game while Ponytail watches.] Cueball: ...How do I unpause? Ponytail: It's not paused. Cueball: ... Ponytail: Continents can only move a few inches per year. [Cueball has stopped playing and holds the controller in one hand. Ponytail points at the screen that shows an achievement page with no completed achievements, but a progress bar halfway done for an achievement with the number 1 and a mountain.] Cueball: It's real-time? Ponytail: Just 400 millennia to go until your first mountain achievement!

Barnard's Star

Barnard's Star

https://www.xkcd.com/2062

https://www.explainxkcd.com/wiki/index.php/2062:_Barnard%27s_Star

[A black sky is shown with a yellow spot near the bottom, left of the center. Three smaller red spots at the diagonal from top left to bottom right indicate a moving star over time. Above these red spots lines are connected to a text that starts and ends with many A s, first growing, and at the end getting smaller:] ...AAAAHHi Sun! I was here billions of years before you formed and will shine for trillions of years after you dieEEEEEEAAA... [Caption below the frame:] Sometimes, I wonder what Barnard's Star is saying to the Sun as it performs its 20,000-year-long high-speed flyby.

Barnard's Star is a very-low-mass red dwarf about 6 light-years away from Earth in the constellation of Ophiuchus . It is the fourth-nearest known individual star to the Sun after the three components of the Alpha Centauri system; it is the closest star to Earth in the Northern Hemisphere. It is a red dwarf with a mass of 0.144 Solar masses, a diameter one fifth that of the Sun, and it is 7–12 billion years old. Because of this low mass the gravitational pressure in the core is much lower and thus the fusion rate is far smaller than in the core of the Sun. In fact this star is so dim that, even though it's one of the nearest, it can't be seen by the naked eye. The low fusion rate also means that the lifespan of small stars is much longer. While huge stars might last a few hundred million years, and the Sun about 10 billion years, a small red dwarf has a lifespan of about a trillion years. Barnard's Star is the star with the greatest proper motion in the sky. Proper motion is motion in the sky other than that caused by Earth's rotation or orbit. Barnard's star is both very close to the sun (as these things go) and moving now at a speed of more than 140 km/s toward the Sun. It will make its closest approach to the Sun in approximately 10,000 years, at a distance of about 3.75 light-years. The image on the right shows different stars near the Sun over 100,000 years and it can be seen that none of them are getting closer than 3 light-years. This is a safe distance to our Solar System and the stars will not influence the orbits of the planets or smaller bodies. It's also obvious that much closer approaches never have happened since the Solar System formed 4.5 billion years ago because otherwise the nearly circular orbits of the planets in the same plane wouldn't be possible. Closer encounters have happened in the past by mostly small stars like Scholz's Star which actually passed through the Oort cloud at a distance of 0.82 light-years about 70,000 years ago, and at least one estimate suggests that a star is expected to pass through the Oort Cloud every 100,000 years or so. This distance is still too far away to influence the orbits of the planets, but those encounters cause comets perturbed from the Oort cloud to the inner Solar System roughly 2 million years later. The comic shows the sizes and the distances not in a proper scale. If the Sun was 1.4 cm (1.4 Mio km in real) in diameter, Barnard's Star would be less than 3 mm at a distance of 356 km. Even Jupiter wouldn't fit into this picture -- at ten times smaller than the Sun, it would be a few pixels, but at a distance of 7.8 m to the Sun and all the other planets would fit into a circle less than 100 meters in diameter. The distances to others stars are far beyond human imagination and at its closest distance a message still takes 3.75 years from Barnard's Star to the Sun. In regards to "20,000-year-long high-speed flyby", the joke here is suggesting Barnard's Star would need to scream out the maleficent, trolling statement as quickly as possible due to 20,000 years being such a small segment of time relative to the lifespan of the star (and our Sun, for that matter). The title text emphasizes that this close approach will not be any hazard to the Solar System, but someone is envious of the long lifetime of Barnard's Star or annoyed by its unpleasant behavior (yelling at the sun for 20,000 years would be a minuscule amount of time for the stars, but for humans it would be a vast length of time, and would get annoying very quickly). [A black sky is shown with a yellow spot near the bottom, left of the center. Three smaller red spots at the diagonal from top left to bottom right indicate a moving star over time. Above these red spots lines are connected to a text that starts and ends with many A s, first growing, and at the end getting smaller:] ...AAAAHHi Sun! I was here billions of years before you formed and will shine for trillions of years after you dieEEEEEEAAA... [Caption below the frame:] Sometimes, I wonder what Barnard's Star is saying to the Sun as it performs its 20,000-year-long high-speed flyby.

Carnot Cycle

Carnot Cycle

https://www.xkcd.com/2063

https://www.explainxkcd.com/wiki/index.php/2063:_Carnot_Cycle

[A cartesian plot in the first quadrant with axes labeled "P" on the vertical axis and "V" on the horizontal axis, with a rhombus-shaped set of four points with arrows between them.] [Caption above the graph:] The four stages of the Carnot Cycle [The first line starts at the top-left point and goes right and slightly downwards to the next point. The label is:] 1. Isometric Expansion When heated, the gas becomes larger due to increasing volume [The next line starts at the last point and goes downwards and a little to the right.] 2. Isotonic Expansion The gas expands further due to dark energy while percent milkfat remains constant [The next line starts at this last point and goes to the left and slightly upwards.] 3. Isopropyl Compression While inflation is held constant, the gas contracts due to tightening interest rates [The last line goes upwards and slightly to the left, returning to the first point.] 4. Decline and Fall The gas diminishes and goes into the west while remaining Galadriel, completing the cycle

This comic shows a Pressure–volume diagram which is used in this case for a Carnot cycle , a theoretical thermodynamic cycle covered in most thermodynamics classes which looks a lot like the figure drawn. The most common example of a (suboptimal) Carnot cycle is the vapor compression cycle used in refrigerators . However in this case, Randall has replaced the labels of the 4 stages of the real Carnot cycle with new ones. Pressure–volume diagrams were first developed to understand the efficiency of steam engines and plot the change of pressure p with respect to volume V for a specific process. The process forms a cycle and the amount of energy involved can be estimated by the area under the curve on the chart. The Carnot cycle describes the ideal efficiency that such an engine can achieve during the conversion of heat into work, or vice versa like in a refrigeration system. The real steps are called (explained in short): An isothermal process is a change of a system, in which the temperature remains constant. In this diagram the volume increases (expansion) or decreases (compression). The term isentropic describes a lossless process where no heat leaves the gas, here the increased volume only causes a further decrease in pressure; it is also called an adiabatic process and is the thing which warms air when you compress it quickly. Isentropic means "doesn't cause the heat death of the universe", which is a rare thing. The prefix iso- is derived from the Ancient Greek word ísos which translates to equal and used widely in modern days in science like here to indicate a process at the same temperature (-thermal) which is not shown in the graph. The prefix is- to the term entropy is used because isoentropic sounds stupid. In the comic, the cycle also has two phases of expansion followed by two phases of contraction (or "decline"), but the names of steps one to three are replaced with other words beginning with the prefix "iso-" meaning same or equal, and the factors that are held constant are absurd. Each step in this comic is explained below: 1. Isometric expansion. When heated, the gas becomes larger due to increasing volume Isometric (literally "equal dimensions") can refer to a property or process that is symmetrical in all dimensions (i.e. the gas is expanding radially) or to a type of thermodynamic process where volume is held constant but temperature is free to vary, the exact opposite of the first step in the real Carnot cycle. Additionally, the comic text uses a circular argument (become larger due to increasing volume). In mathematics, an isometric mapping (between metric spaces) is a map that keeps all the distances intact. If we measure the distance the same way throughout the cycle, then isometric expansion (or for that matter, isometric compression) is not really an expansion (or a compression). 2. Isotonic expansion. The gas expands further due to dark energy while percent milkfat remains constant. Isotonic is a descriptor commonly associated with sports drinks (and not thermodynamics), which contain similar concentrations of salt and sugar as in the human body. Dark energy is hypothesized to be a cause for the expansion of the universe, which obviously isn't relevant to thermodynamics.(Yet.) The density of milk depends on milkfat and solids-non-fat, which includes lactose. Fortified milk has increased solids-non-fat but the same percentage of milkfat, resulting in increased calories and an increased density. So the fortification of milk results in increased calories, possibly referred to as dark energy, and a contraction, as less space is needed for 1 kg of milk. However, this explanation does not match the expansion suggested in the comic. Later Randall again combined dark energy (and also dark matter) with milkfat in 2216: Percent Milkfat . 3. Isopropyl compression. While inflation is held constant, the gas contracts due to tightening interest rates. Isopropyl alcohol is commonly used for cleaning. Inflation and contraction could refer to changes in gas volume, but the reference to interest rates puts them in the context of macroeconomics . Raising ("tightening") interest rates tends to reduce inflation and/or "contract" the economy. High interest rates are a feature of the third stage (recession) of the Juglar cycle . In economics (and other sciences) to better understand model parameter relations, some parameter may be held constant in theory. This could refer to the Fisher equation . Holding one parameter constant is also done in the Carnot cycle (for a physical parameter): not only in theory but also in practice! (In free market economies the inflation cannot be directly held constant). But inflation may also refer to dark energy mentioned at the isotonic expansion section above. Inflation in cosmology is a theory of the exponential expansion of space in the early universe, an effect associated with the "accelerating universe" and for which findings the 2011 Nobel Prize in Physics was given. The National Geographic blog entry Nobel Prize in Physics 2011 – The Accelerating Universe explains that "...Today, most physicists, influenced by inflation, would ... call it dark energy." 4. Decline and fall. The gas diminishes and goes into the West while remaining Galadriel, completing the cycle. Galadriel is a character in The Lord of the Rings . She is one of the leading elves , a race that in the time of the book is said to be dwindling (in number and importance) in Middle Earth and migrating westward to Valinor . Galadriel is one of the last elves to leave, after successfully resisting temptation to take the One Ring and become an all-powerful queen who dominates Middle-earth, instead saying "I will diminish, and go into the West, and remain Galadriel." The title may be a reference to Edward Gibbon 's 18th century masterpiece The History of the Decline and Fall of the Roman Empire , or to the novel Decline and Fall by Evelyn Waugh (which is itself a reference to Gibbon's book). This stage is present in the cycle because in the real cycle, at this stage, volume of the gas decreases without exchange of heat. It is the last stage after which the gas has its original value of variables, thus completing the cycle. The title text refers to Richard Wagner and J.R.R Tolkien . Wagner's Ring Cycle consists of four operas. Tolkien wrote The Lord of the Rings , which some have suggested was inspired by Wagner's Ring. Their works are known as literary cycles . [A cartesian plot in the first quadrant with axes labeled "P" on the vertical axis and "V" on the horizontal axis, with a rhombus-shaped set of four points with arrows between them.] [Caption above the graph:] The four stages of the Carnot Cycle [The first line starts at the top-left point and goes right and slightly downwards to the next point. The label is:] 1. Isometric Expansion When heated, the gas becomes larger due to increasing volume [The next line starts at the last point and goes downwards and a little to the right.] 2. Isotonic Expansion The gas expands further due to dark energy while percent milkfat remains constant [The next line starts at this last point and goes to the left and slightly upwards.] 3. Isopropyl Compression While inflation is held constant, the gas contracts due to tightening interest rates [The last line goes upwards and slightly to the left, returning to the first point.] 4. Decline and Fall The gas diminishes and goes into the west while remaining Galadriel, completing the cycle

I'm a Car

I'm a Car

https://www.xkcd.com/2064

https://www.explainxkcd.com/wiki/index.php/2064:_I%27m_a_Car

[The bottom right rear end of a car is shown with a bumper sticker next to the unreadable license plate.] I'm a car and I vote

This comic was released eleven days before the United States midterm elections on Tuesday, November 6, 2018 and even the header text at the top of the xkcd page had changed a few days before by showing a link to vote.org to help US citizens to register and finding their polling places. Randall uses a neutral way to encourage people to use the right to rule their governmental representatives. Before the presidential election, 2016 , however, he chose the Democrats as shown in the comic 1756: I'm With Her (see more here ). This comic shows a car with a bumper sticker , which is generally a thin rectangle piece of plastic with a message on one side and adhesive on the other side in order to stick to a car. This allows the owner of the car to display a message they want to present to whoever is driving behind them or in their vicinity. Bumper stickers are usually used to express a viewpoint, whether personal or political, held by the owner or driver of the car. This comic makes literal the ones that include or allude to the personal pronoun "I" and its variations, i.e. first person singular statements. Of course the intent is that "I" is referring to the person who put the bumper sticker on the car, but as the sticker is attached to the car the more literal interpretation is that "I" is referring to the car. So the humor is derived by the notion that the car itself is making these statements. (On an even more meta level, the comic could be interpreted as saying that the person who wrote the words in the comic, i.e. Randall , is saying that he is a car.) The bumper sticker on the car in the comic is a variation of a sticker used to both encourage people to vote, as well as express their political position: "I'm a ___, and I vote" (where the blank is traditionally filled in with "Union Worker", "Catholic", "Senior Citizen", "Gun Owner" or some other demographic or organizational membership). However here it is attributed to an automobile which is not capable of voting [ citation needed ] . The comic could be an indirect reference to the growing "intelligence" of self-driving cars , such that one day they might have the intellect to communicate, vote, and engage in other self-motivated activities. See ‘ Sally ’ by Isaac Asimov . It may also relate to security concerns around increasing use of electronic voting mechanisms - the joke being that the car is able to abuse the interfaces to such systems either to vote on behalf of its owner or as its own entity. Though voting might not be one's biggest concern if their "intelligent" car got dragged into a bot net... The title text seems to be another typical message on a bumper sticker, saying that the driver is a "Proud Parent Of An Honor Student". However, this sticker is a bit longer, since it continues to state that "the person driving me is proud, too". Thus once again it is the car who is the proud parent. And thus maybe it is a car that is the honor student? Another thought is that this may be a reference to the 1965-66 TV sitcom My Mother The Car . [The bottom right rear end of a car is shown with a bumper sticker next to the unreadable license plate.] I'm a car and I vote

Who Sends the First Text?

Who Sends the First Text?

https://www.xkcd.com/2065

https://www.explainxkcd.com/wiki/index.php/2065:_Who_Sends_the_First_Text%3F

Who sends the first text more often? [A line graph with a segmented bar underneath shows a 50/50 marker in the middle while the left end is labeled "I text first 100% of the time" whereas the right end is labeled "They text first 100% of the time".] [The bar below is divided into five sections:] [A small part at the left, and a next, slightly larger part. The text below points to the second part:] People who I think of as friends but secretly worry that they're just politely putting up with me [Below this a text is shown for the first part:] ... definitely just politely putting up with me [In the middle is a big part:] Friends [To the right the parts are symmetric, the first is larger:] That really nice friend who keeps inviting me to things even though I flake constantly [The last small bar at the right:] Automated alerts and political campaigns

Text messaging is a back-and-forth communication via SMS between two users. In this comic, Randall shows a line graph of "who sends the first text more often?" This is meant to show who Randall initiates conversations with, and who initiates conversations with him. Maintaining a friendship or relationship (whether intimate, friendship, casual, or business) typically requires communication; often that communication takes place when two individuals are not in the same location by means of an exchange of text messages. A normal balanced relationship typically involves both parties involved to have an approximately equal interest in making conversations happen, as measured in this case by "who sends the first text". The person who desires that a particular communication take place typically will send a text message, and once the other person responds the conversation happens, and the relationship progresses. If neither person initiates, the relationship will likely suffer. While this graph shows the majority of his relationships involve friends whereby both sides are prone to initiating conversations, the graph also shows some groups that are a little more at the extremes, some where Randall texts a lot but they typically don't initiate text conversations to him, and some where others text him a lot but he rarely initiates text conversations with them. On the left side of the graph are people with whom Randall initiates conversations with "100% of the time". On the right side of the graph are those who initiate conversations with Randall. The chart is separated into 5 blocks. The two blocks on the left are those who may be, or definitely are, "just politely putting up with [Randall]". This is implied that they may not be close friends with Randall, but Randall still wants to be friends with them. Their reluctance to initiate conversation with Randall is shown by the fact that Randall usually sends the first text to them. The largest block, in the middle, is "friends". These friends range from Randall initiating a lot, to them initiating a lot. There is a healthy range of who initiates first. The next block to the right is for "that really nice friend who keeps inviting me to things even though I flake constantly". This means that Randall promises to go to events that this friend invites him to, but does not always follow through. This friend is still persistent in inviting Randall. Additionally, Randall could be less close to this person, based on him not categorizing this person under "friends". The final block is "automated alerts and political campaigns". Randall would certainly not be likely to initiate "conversation" with automated systems, and would be very unlikely to initiate conversations with political campaigns. The fact that the bar is not purely 100% suggests that he has on rare occasion sent the first text to such recipients, perhaps for a campaign he believes in, or to request to be added to an automated alert system (i.e. opt-in). The fact that it includes political campaigns is a reference to the incessant texts being sent to Americans about the upcoming midterms. In the title text, Randall wishes that he would know the percentage of "who sends the first text more often", for each person that he texts. But he is also wary of the potential implications of finding out this information. (Many old school messenger like pidgin offer such statistics through plugins though) Who sends the first text more often? [A line graph with a segmented bar underneath shows a 50/50 marker in the middle while the left end is labeled "I text first 100% of the time" whereas the right end is labeled "They text first 100% of the time".] [The bar below is divided into five sections:] [A small part at the left, and a next, slightly larger part. The text below points to the second part:] People who I think of as friends but secretly worry that they're just politely putting up with me [Below this a text is shown for the first part:] ... definitely just politely putting up with me [In the middle is a big part:] Friends [To the right the parts are symmetric, the first is larger:] That really nice friend who keeps inviting me to things even though I flake constantly [The last small bar at the right:] Automated alerts and political campaigns

Ballot Selfies

Ballot Selfies

https://www.xkcd.com/2066

https://www.explainxkcd.com/wiki/index.php/2066:_Ballot_Selfies

[Megan, Ponytail, Cueball, White Hat, and Hairbun are standing in a line with Hairbun in front. All are facing forward to the right except Cueball, who is looking to his left at Ponytail. Megan holds a phone in her hand while Ponytail carries an easel under her left arm and a paintbrush in her right hand.] Ponytail: Ballot selfies are illegal in this state, so to immortalize my vote I'm doing an oil painting in the voting booth.

This comic was published six days prior to the 2018 United States general elections , also called midterm elections , because they happen halfway between two presidential elections, two years before and after. At the time, the xkcd header still provided a link to vote.org , a website that helps US citizens with essential voting issues, like how to register or how to find their polling locations. It is the first of three consecutive comics that deal with this election. In the United States, " ballot selfies " refers to the practice of taking a picture of oneself with a completed ballot. These have been illegal in many states, due to laws passed to prevent vote selling. Without proof of how a vote was cast, if someone bribed (or even violently coerced) a voter to vote for candidate A, the voter could just vote 'B' and the coercer would be unable to tell whether they voted as instructed. This is at the heart of the concept of "a secret ballot". But if ballot-selfies or other proof-of-vote mechanisms are permitted then the evil-doer can demand verification that the voter did what they were coerced to do - and this jeopardizes the idea of a truly free and fair election. However, the "secret ballot" principle is not universally valued nor enforced. Some voting machines produce a paper receipt showing the choices the voter made - and many jurisdictions permit use of a postal ballot - so there are plenty of other ways to circumvent the law in those places. So the ban on ballot selfies is harder to justify unless those other lines of coercion are also ruled out. On the other hand, the desire to take and distribute ballot selfies often comes from an excitement in participating in the voting process and the desire to share that excitement in the hopes of encouraging others to vote, and anything that helps get more people to the polls is generally considered to be a good thing. In addition, the law is incredibly difficult to enforce -- there is little way to prevent somebody from photographing their ballot and privately showing this photo to somebody else -- and the practice of enforcing it (i.e. searching for possible photographic devices all together) would make the local government incredibly unpopular. Lastly, voters storing evidence of their votes could be useful to prevent voting fraud performed by the state. This dual threat/benefit has led some states to explicitly legalize ballot selfies, other states to specifically disallow them and even levy steep financial penalties, while the rest are still debating or ignoring the issue . As Ponytail is aware of this law, she believes she has identified a solution wherein she will make an oil painting of her voting rather than taking a photograph . A painting being more of an artistic endeavor that doesn't have to faithfully record all aspects of the image, it may well be valid both on grounds of freedom of speech as well as not being a verbatim record of her vote - thereby preserving the secrecy of the ballot. Of course, making a painting of her vote may lead to additional problems. If she intends to paint the portrait herself, of herself (i.e. a self-portrait ) casting her vote, it would be very difficult and time consuming to attempt to do that, especially without a mirror, which she apparently doesn't have with her and which is generally not standard issue in voting booths. [ citation needed ] She could also try to recruit someone else to do the painting, not knowing the level of their artistic talent, however, usually only the person casting the vote is allowed in the booth, and they are expected to close the curtain or otherwise ensure no outside person, like the painter, can view the vote casting act. It would also require her to stay in the booth longer than most voters. While Hairbun and White Hat are simply standing in line, Megan can be seen using a mobile phone. The comic might also be a reference to the existing ban of cameras in US courtrooms , which lead US newspapers to widely adopt cartoons as a replacement. In many US states, changes to state law can be made through the initiative and referendum process, which can be initiated and pursued by any citizen. The title text refers to the legality of taking a ballot selfie whilst voting against the law against ballot selfies. [Megan, Ponytail, Cueball, White Hat, and Hairbun are standing in a line with Hairbun in front. All are facing forward to the right except Cueball, who is looking to his left at Ponytail. Megan holds a phone in her hand while Ponytail carries an easel under her left arm and a paintbrush in her right hand.] Ponytail: Ballot selfies are illegal in this state, so to immortalize my vote I'm doing an oil painting in the voting booth.

Challengers

https://www.xkcd.com/2067

https://www.explainxkcd.com/wiki/index.php/2067:_Challengers

[A loading screen appears shortly before the large picture has rendered. We can see an American flag in an oval badge with the text:] I voted [And beneath a text saying:] Loading... 2018 Midterm Challengers The bigger the candidate's name, the higher the office and the better their chances of success. [In a frame a zoomable map shows all US-States (Alaska and Hawaii are shown in the left lower corner.) The candidates are shown colored mainly in red and blue at different sizes. Each state has many landmarks shown in gray. There are also many comics embedded into the picture.] By Randall Munroe, Kelsey Harris, and Max Goodman Landmarks from Wikipedia. Success odds estimated from district voting history, special election results, and seat ratings. Thank you to Dailykos Elections for their spreadsheets, shapefiles, election ratings, and advice, and to @davidshor, @charlotteeffect, and @thedlcc for additional candidate data. Map of interesting features on the comic ( Red X : comic strip, Green X : independent candidate, Blue X : xkcd landmark)

Regarding the midterm elections held in the United States on November 6, 2018, this comic shows probably all challengers, which are candidates running against the current office-holder, as well as those running in open seats where a change of the major party from the previous election could occur. It is the second of three consecutive comics that deal with this election. Randall states on top that "The bigger the candidate's name is," While an office can be subclassified by order from state down to county, the guesses on better chances to success can be only based on surveys before the elections. All names provide an indirect link to the first Google Search result on that specific person and position. As common, Democratic candidates are shown in blue text, Republican candidates in red, and independent candidates are in green. The landmarks shown in gray are essentially links to Wikipedia pages containing coordinates pointing to the US in their body (both visible on the site and hidden in the wiki source) that point to places in the US. If they contain more than one coordinate then the first one is used, for example the List of the major 3000-meter summits of the United States page is shown in Alaska, and the xkcd page is linked near Boston, Massachusetts. This list seems to be auto-generated from a Wikipedia dump made possibly before 2017. There doesn't seem to be any other criteria as the list also contains orphaned wikipedia pages that only contain hidden coordinates in their sources pointing to the US, for example this one . Wikipedia pages containing these coordinates can be easily enumerated on the site in blocks of 500 at a time. Since the map is large there's also a loading screen present that can be seen while the map is loading. There are a total of nine comics embedded into the map at various locations. They are showed when zooming into the map at the appropriate section. Location: Lubbock, Texas [Black Hat and Cueball are talking.] Black Hat: Starting on November 7th, we're going to blanket the airwaves with attack ads. Cueball: Isn't the election on November 6th? Black Hat: Yeah, the advertising rates go way down after that. Attack ads are campaign advertising that usually attack the opponents' campaign instead of promoting one's own. The comic also refers to the fact that media outlets usually spike their advertising prices during the campaign, and it becomes cheaper afterwards. However there's usually no point in advertising afterwards for a campaign as the polling has already taken place. This may also be a callback to 1130: Poll Watching . Lubbock was the place where some attack ads were shown few months before the election. Texas is also notable as in 2008 during the Democratic Party primary Hillary Clinton started running attack ads aimed at Barack Obama, who later became President, causing controversy. Location: Weed, California [Cueball is holding a piece of paper and talking to Megan.] Cueball: Question #1 voids all 2018 ballot measures except itself. Cueball: Question #2 retroactively lowers the threshold for passing ballot measures to 5%. Cueball: Question #3 requires a re-vote on all failed ballot measures a day later. Cueball: Question #4 requires a re-vote on all passed ballot measures a day later. Cueball: Question #5 bans those annoying phone scammers, but also says that if an odd number of ballot measures pass, Christmas is canceled. Cueball: Question #6 makes a "yes" count as a "no" on odd-numbered ballot measures. Cueball: Question #7 does nothing but counts as a ballot measure passing. Cueball: Question #8 says that- Megan: I'm leaving these all blank and voting against whoever approves ballot measures. Ballot measures are proposed laws that are approved and rejected by voters. In California, apart from the elections to Congressional and state offices, there will be also be 12 extra propositions for the voters in this election. Sometimes propositions also include changing how voting should be done in subsequent elections. There are people who believe proposals on US ballots are asked in a very convoluted way, and could be made simpler. In this comic a lot of the proposals sound complex and self-referential as well, therefore Megan just says that she doesn't wish to vote to any of them, and would actually like to ban people creating ballot papers like this. Not voting might also refer to the scenario where people believe none of the choices during an election are good, and instead vote to no-one or deface their ballot papers in protest. The name of the town chosen, Weed, California, may be a pun on how marijuana is legal in California. Location: Bellingham, Washington [Cueball holds a presentation to a group of people including White Hat and Hairbun sitting at an office desk. The presentation shows a map of a district.] Cueball: Under my new Carlymandering plan, we'll create five red districts, five blue districts, and one district which contains only Carly Rae Jepsen. Hairbun: That seems fair. This refers to gerrymandering , a tactic used to re-shape voting district boundaries to make sure one candidate prevails over the other. "Carlymandering" is a malamanteau which combines gerrymandering with Carly Rae Jepsen , a Canadian singer, whose single " Party for One " was released the day before the comic's publication. Although the song is about partying (e.g. going out) alone, [ citation needed ] the joke is that it could also mean a one-person political party, and she would have a full gerrymandered district to herself. Jepsen lives in Vancouver, which is just on the other side of the US border in Canada. The comic is placed in Whatcom County, which is notable for Point Roberts , a peninsula which, although part of Washington state, is actually an exclave of the US, as it's surrounded by sea on three sides, and has its only land border with Vancouver to the north. The comic might refer to the fact that Jepsen could solely live in this exclave. However, since she is not a US citizen, she can neither vote nor be elected in US elections. Location: Washington, DC [Cueball is standing in the middle of Washington, DC] Cueball: I can see my House from here! Comic is probably referencing the White House , the residence of the President, located in Washington, DC. This could also refer to the Capitol Building , the home of the House of Representatives , also located in Washington, DC. Location: Primm, Nevada [A group of five people are standing] Blondie: Remember: The only poll that counts is the one on Election Day. And the ones that help campaigns allocate resources. And the ones that drive media coverage and the ones that inform us all about what our fellow members of the public believe. And the ones that... The word "poll" has two distinct meanings in regards to elections -- the place where you go to cast your official vote is called a poll, as are the unofficial surveys done to try to gauge how people are likely to vote. During campaign there is usually polling done by survey companies to determine each candidate's chances of winning. This comic refers to the fact that often the candidate that is behind in the unofficial polls tells their electorate that these polls don't matter, as they are just surveys and not the actual final result. This is usually to encourage their voter base that it's still worth voting for them. The joke here is that Blondie doesn't finish here but tells the electorate that other polls are actually also important. Nevada is one of the states where there is only a slim difference between the candidates based on polls hence the need for each candidate to rally their supporters and make sure everyone is voting. Location: Chadron, Nebraska [Megan is standing at a podium with her arm raised] Megan: If elected, I vow to find and punish the voters responsible. Often candidates make promises of things they will do when they are elected. Vowing to find and punishing people responsible for a certain action, oftentimes criminals, is also common. However, certain performance artists aside, these two things are generally not conflated, as they are here, to ludicrous effect. Putting this comic into Nebraska might refer to the fact that in 2016 Nebraska voted to repeal the death penalty ban , allowing the reinstatement of the death penalty, also called capital punishment, in the state. Location: Storm Lake, Iowa Cueball: The midterms are so stressful. Megan: I just hope J.D. Scholten wins. Cueball: Why? Megan: Google Steve King. [Cueball looking at his phone] Cueball: Yikes. J.D. Scholten is a Democratic candidate for Iowa's 4th Congressional District. Steve King is a Republican representative who has stirred controversy due his endorsement of candidates, in other countries, who were members of parties with white supremacist ties, and he has explicitly and frequently stated concern with the American society being destroyed by "other people's babies" . King would go on to win re-election by a narrow margin. Location: Richmond, Virginia [Cueball is holding a sign that says: Abigail Spanberger for Congress] Abigail Spanberger was a candidate running for Congress in Virginia's 7th district, which includes Richmond. Based on polls she had a chance to beat her opponent, and she then became the first Democrat in her district after 50 years of Republican control, beating out Republican incumbent David Brat by 2 percentage points. Cueball probably was trying to encourage people to vote for her on election day. Location: Saint Louis, Missouri [Two people next to the Gateway Arch are talking] Cueball: Ah, Saint Louis. Home of America's largest... Whatever that thing is. Saint Louis, Missouri is the location of the Gateway Arch , the largest arch in the United States. (It's also one of the most recognizable arches in Saint Louis, according to 1368: One Of The .) Since in this comic they are next to the side of the arch, it is possible its sheer size stops them from determining what it is, although they should probably know. An alternate interpretation is that they are baffled by the existence of a giant, seemingly-useless steel arch, and do not know what to refer to it as. The area surrounding the Arch was known as Jefferson National Expansion Memorial until February 2018, when it was renamed to Gateway Arch National Park. The title text shows the hint that the reader can zoom in and move over all 50 states to reveal details which can't be seen in the overall view. Furthermore Randall calls on Americans to vote: he requests that people take an active part in the elections to change that picture. [A loading screen appears shortly before the large picture has rendered. We can see an American flag in an oval badge with the text:] I voted [And beneath a text saying:] Loading... 2018 Midterm Challengers The bigger the candidate's name, the higher the office and the better their chances of success. [In a frame a zoomable map shows all US-States (Alaska and Hawaii are shown in the left lower corner.) The candidates are shown colored mainly in red and blue at different sizes. Each state has many landmarks shown in gray. There are also many comics embedded into the picture.] By Randall Munroe, Kelsey Harris, and Max Goodman Landmarks from Wikipedia. Success odds estimated from district voting history, special election results, and seat ratings. Thank you to Dailykos Elections for their spreadsheets, shapefiles, election ratings, and advice, and to @davidshor, @charlotteeffect, and @thedlcc for additional candidate data. Map of interesting features on the comic ( Red X : comic strip, Green X : independent candidate, Blue X : xkcd landmark)

Election Night

Election Night

https://www.xkcd.com/2068

https://www.explainxkcd.com/wiki/index.php/2068:_Election_Night

[Megan and Cueball face each other while talking on the left of the panel] Megan: Ugh, I'm just going to hide out for election night. We'll know the results the next day anyway. The drama is so unnecessary. Cueball: Yeah. The internet and the 24-hour news have turned elections into a continuous, inescapable media onslaught. [A man in a top hat appears on the right side of the panel with a "Poof"] [Panel with just the man in a top hat, holding a newspaper] Man in a top hat: Hi! I'm a time traveler from 1896. Let me tell you about our election night coverage. Man in a top hat: *Ahem* Man in a top hat: From the Chicago Tribune [Zoom in on the head of the man in a top hat] Man in a top hat: "Once every hour from the roof of the Great Northern Hotel a series of bombs, which will ascend for several thousand feet, will be fired. Two colors will be used, blue and red." Man in a top hat: "Blue to indicate McKinley's election, red to indicate Bryan's election." Man in a top hat: "The bombardment of the skies will commence at 7 o'clock and will be repeated hourly." [Grey citation]: Chicago Tribune, Oct 30th & Nov 1st, 1896 [Megan and Cueball on the left looking at the man in the top hat on the right] Megan: Yeah, well, we have a needle, though. Man in a top hat: A needle. Megan: It jiggles! Man in a top hat: Sounds awful. Cueball: Listen, you had to be there.

This is the third comic in a row that deals with elections in the United States; the trio has been published in the week before the US midterm elections held on November 6, 2018 and it compares media coverage on election results in 1896 and 2018. During this time the Header text of xkcd was also changed three times, including on the release days of both this and the previous comic, to help people go and vote. See more in the trivia section . While elections and voting have been a public staple for generations, election coverage by the media can result in voter fatigue . While voter fatigue is considered a major criticism of things like first past the post voting systems, media outlets will also contribute. The time traveler from 1896, wearing a top hat (the typical hat used at that time), presents Megan and Cueball a method how the latest news --over the night-- is published to the public. No broadcasting television or even radio existed then and most newspapers, reaching the readers on the next morning, were printed in the evening before the election results were certain. For the election referenced in this clipping , Republican candidate William McKinley (assigned the color Blue) won in a close race against Democrat-Populist candidate William J. Bryan (assigned the color Red). Here, Randall is taking a unique opportunity to point out that unlike our recollection of history (which is usually modified by the misinformation effect , where we perceive the past as being easier and find a source to blame for the election night jitters) that in fact, in the past, a bombardment of fireworks every hour was used to convey the hour-by-hour play of the election night, a significantly more jarring effect that couldn't even be turned off. We have progressed, in some ways, to a more opt-in system, rather than the opt-out system of the past, where you had to leave Chicago to avoid the news. The part about the "jiggling needle" may be a reference to the New York Times' 2016 presidential election results webpage, which displayed a "needle" it used to forecast the results of the presidential election between then-candidates Donald Trump and Hillary Clinton. The position of the needle was initially set based on pre-election polls, pointing heavily toward Hillary Clinton, but as election results from around the country -- and from individual counties within states -- started coming in it changed to reflect those results. Especially near the beginning, before a lot of real election data had come in, results reported from small counties could dramatically swing the needle to one side or the other when coming from heavily Democratic or Republican districts, then swing again when another county reported. Only when a significant amount of data had come in did the needle settle down and move more incrementally. The title text explains that in 1896 even blind people were taken care of, as enormous megaphones were installed to convey the news equally unavoidably to those who couldn't (or didn't want to) see the color bombs. This is in fact true but was intended for those in the colosseum, not all of Chicago. [Megan and Cueball face each other while talking on the left of the panel] Megan: Ugh, I'm just going to hide out for election night. We'll know the results the next day anyway. The drama is so unnecessary. Cueball: Yeah. The internet and the 24-hour news have turned elections into a continuous, inescapable media onslaught. [A man in a top hat appears on the right side of the panel with a "Poof"] [Panel with just the man in a top hat, holding a newspaper] Man in a top hat: Hi! I'm a time traveler from 1896. Let me tell you about our election night coverage. Man in a top hat: *Ahem* Man in a top hat: From the Chicago Tribune [Zoom in on the head of the man in a top hat] Man in a top hat: "Once every hour from the roof of the Great Northern Hotel a series of bombs, which will ascend for several thousand feet, will be fired. Two colors will be used, blue and red." Man in a top hat: "Blue to indicate McKinley's election, red to indicate Bryan's election." Man in a top hat: "The bombardment of the skies will commence at 7 o'clock and will be repeated hourly." [Grey citation]: Chicago Tribune, Oct 30th & Nov 1st, 1896 [Megan and Cueball on the left looking at the man in the top hat on the right] Megan: Yeah, well, we have a needle, though. Man in a top hat: A needle. Megan: It jiggles! Man in a top hat: Sounds awful. Cueball: Listen, you had to be there.

Wishlist

Wishlist

https://www.xkcd.com/2069

https://www.explainxkcd.com/wiki/index.php/2069:_Wishlist

[In a frame a bullet-list is shown:] Mario/Luigi hybrid The SkiFree monster Siri Ellie from Up Zordon Clippy The Sarlaac The InstallShield Wizard Mr. Clean Comet Cursor Beto O'Rourke The Monopoly boot Lot's wife D.B. Cooper The Blair Witch Mavis Beacon [Caption below the frame:] Super Smash Brothers never did end up adding anyone from my wishlist.

Super Smash Brothers (also titled as Super Smash Bros. and usually shortened to Smash ) is a crossover fighting game series published by Nintendo , with the core roster of playable characters originating from Nintendo's own intellectual properties such as Super Mario and The Legend of Zelda . At the time this comic was published, there were 77 playable characters in total across the 5 games in the series. Starting with the third game, Super Smash Bros. Brawl , characters from third-party franchises (non-Nintendo) have been made available, though most of them had at least made major appearances on a Nintendo system at some point. This comic is a parody of various fans' wishes for the roster of Super Smash Bros. Ultimate , which was announced in 2018 along with multiple trailers revealing new characters to appear in the roster. In the November 1st trailer it was stated every new character in the launch version of the game had been announced, though with five more characters coming in 2019 as downloadable content . Throughout the series fans have suggested new characters to add; however, developer acquiescence to these requests is rare, with only six characters out of 77 ( King Dedede , Steve, Sonic the Hedgehog , Ryu , Bayonetta , and Ridley ) having been added this way. On November 3rd, 2018, the developer studio Sora Ltd. made a statement on Twitter telling fans that the as-yet unrevealed DLC characters for Ultimate were already chosen and that they were not accepting further requests; all remaining characters would then be gradually released over the next three years, culminating in Sora 's reveal in October 2021. This comic lists 16 "characters" that Randall supposedly wishes were made available in Super Smash Bros. , ranging from plausible playable characters, to the absurd. Mario / Luigi hybrid Mario and Luigi are characters in the Super Mario series, one of Nintendo's flagship franchises. They are both playable characters in the Super Smash Bros. series. A hybrid of these two characters would be quite interesting, even though such a concept does not exist within the Super Mario series. When considering how Mario and Luigi have evolved throughout the Smash series, one could argue that Dr. Mario is a hybrid of these two in terms of moveset. The SkiFree monster SkiFree is a computer game for Windows released in 1991. The player controls a skier trying to avoid obstacles. After the end of a full run, a white furry monster appears, and tries to catch the player. The SkiFree monster was a subject of the 667: SkiFree comic. Unlike most of the characters on this list, the SkiFree monster at least has had an appearance on a Nintendo system, as the game had a Game Boy Color port as part of the "The Best of Entertainment Pack" in 2001. Siri Siri is the name given to Apple's personal virtual assistant for iOS, macOS, and its other operating systems. Siri is generally a voice without a visual representation, so it is unclear how Siri would be a playable character in Super Smash Bros. Ellie from Up Ellie is one of the characters in Up , a 2009 Pixar film. In the beginning of the film, Ellie passes away, leaving her husband Carl alone, and leading him to start his adventure in Paradise Falls. While there was a tie-in video game based on the movie released in the same year for multiple systems (including the Wii and Nintendo DS), Ellie was not playable in it. Zordon Zordon is a fictional character from the Power Rangers franchise who serves as the mentor for the earlier Ranger teams. While he is technically trapped in another dimension, he is usually depicted as a blurry head in a tube. He occasionally has lightning powers, and had a robot sidekick (Alpha 5) who might be able to move him around. Alas, he is currently dead, having used his life energy to remove all evil from the galaxy at that time. While there have been many Power Rangers video games over the years, including on Nintendo platforms, Zordon would be an unlikely character not only due to his lack of extremities, but also due to the fact that the Power Rangers franchise is primarily built on stock footage of the Japanese Super Sentai series. Clippy Clippit, commonly nicknamed Clippy , was one of the Office Assistants for Microsoft Office (versions 1997 to 2003). It was an user interface with the purpose to assist users. Clippy (and the other Office Assistants) was negatively received by users, and was eventually removed in Office 2007. The Sarlaac [sic] The Sarlacc is an alien monster that lived in Tatooine in the Star Wars universe. It is most prominently shown in the film Return of the Jedi , when the main heroes are sentenced to death by being dropped into the Sarlacc's mouth. Notably, the Sarlacc is a large, stationary creature embedded in the ground (essentially, a pit). This could be a reference to the Piranha Plant being confirmed as a DLC character, as Piranha Plants are typically stationary and embedded in the ground, and also have their big, toothy mouth as a primary feature. While the Sarlacc was featured in 1994's Super Star Wars: Return of the Jedi for the Super Nintendo Entertainment System , its lack of mobility would make it a poor choice for a character. InstallShield Wizard A wizard is a type of UI that simplifies configuration of an app or process by guiding the user through a number of screens in sequence. A user makes one decision on each screen, and the overall process puts less cognitive load on the user. InstallShield is a proprietary software tool for creating installer applications (or software packages) for Microsoft Windows. When the created package is being installed, the installer application can be shown in form of a 'standard Windows Wizard' dialog. Depending on the creativity of the user creating the package, the Wizard can display images while different stages of the installer are being executed. There are known instances of The InstallShield Wizard showing a wizard-like character images. Also, the standard wording of the installer text shown to the user ('software-to-be-installed is preparing the InstallShield Wizard, which will guide you through the program setup process') suggests that the Wizard is a 'real character'. Mr. Clean Mr. Clean is a brand and mascot for Procter & Gamble used for all-purpose cleaners and melamine foam cleaners. Comet Cursor Comet Cursor was Windows software that allowed users or websites to customise the mouse cursor. It was often installed with minimal user interaction and was accused of tracking users and being "spyware". Beto O'Rourke Beto O'Rourke is an American politician and businessman serving as the U.S. Representative for Texas's 16th congressional district since 2013. He was the nominee of the Democratic Party in the 2018 Texas U.S. Senate election (which was held the day before this comic appeared), running against Republican incumbent Ted Cruz. O'Rourke received much media attention leading up to the election, with many considering the election abnormally competitive. He ultimately did lose against Ted Cruz. While not a video game character, it is more than possible to create a Mii Fighter based on Beto O'Rourke in the game. However, the game does not come with a Beto O'Rourke Mii, and Nintendo has not created an official Mii of Beto O'Rourke. [ citation needed ] The Monopoly boot The "boot" is one of the classic pewter tokens from the board game Monopoly . Despite the absurdity of the request, the boot appeared in the 1999 Monopoly video game adaptation for the Nintendo 64. In 2017, the boot token was retired from the standard version of Monopoly . Lot's wife Lot and his wife are characters from the book of Genesis in the Bible. According to the book of Genesis, Lot and his family had to flee the city of Sodom , which was being judged by God for its wickedness. They were commanded to flee and not look back at the city. However, Lot's wife looked back at the city and was turned into a pillar of salt. It is unclear which version of Lot's wife Randall wishes to be playable in the game. D.B. Cooper D.B. Cooper is the name popularly used to refer to an unidentified man who hijacked a Boeing 727 aircraft on November 24, 1971. He extorted $200,000 in ransom and parachuted out of the plane. His identity and whereabouts have never been discovered. D.B. Cooper was a subject of the 1400: D.B. Cooper comic. As mentioned above, an enterprising player could easily make a Mii Fighter based on D.B. Cooper, though no such Mii has been provided by Nintendo. The Blair Witch The Blair Witch is the titular character of the The Blair Witch Project , a 1999 "found footage" supernatural horror film. The film became one of the most successful independent films of all time. The witch is never actually shown in the film, making it difficult to turn into a character in the game. Mavis Beacon Mavis Beacon is a fictional character and the mascot of the Mavis Beacon Teaches Typing software series. The title text refers to two US Supreme Court Associate Justices who were considered as additions to Smash . Ruth Bader Ginsburg was appointed by Bill Clinton; Elena Kagan was appointed by Barack Obama. Both are considered to be on the "liberal" wing of the court, but Ginsburg’s forceful dissenting opinions may explain why she would have been a more popular character for Super Smash Bros. Additionally, Ginsburg has been parodied on Saturday Night Live , adding to her popularity: [1] [In a frame a bullet-list is shown:] Mario/Luigi hybrid The SkiFree monster Siri Ellie from Up Zordon Clippy The Sarlaac The InstallShield Wizard Mr. Clean Comet Cursor Beto O'Rourke The Monopoly boot Lot's wife D.B. Cooper The Blair Witch Mavis Beacon [Caption below the frame:] Super Smash Brothers never did end up adding anyone from my wishlist.

Trig Identities

Trig Identities

https://www.xkcd.com/2070

https://www.explainxkcd.com/wiki/index.php/2070:_Trig_Identities

[Inside a single frame comic a right-angled triangle is shown. The shorter sides are labeled "a" and "b" and the hypotenuse has a "c". All angles are marked: the right angle by a square and the two others by arcs. One arc (enclosed by "a" and "c") is labeled by the Greek symbol theta (θ).] [Supposed trigonometric functions of the marked angle θ are shown:] sin θ = b/c cos θ = a/c tan θ = b/a cot θ = a/b sec θ = c/a csc θ = c/b cin θ = b/s cas θ = o/c tab θ = b²/n​a bot θ = a/c → boat θ = a²/c → stoat θ = a²/c · s​t/b tan θ ( = b/a = b/a · c/c = b/c · c/a = sin θ sec θ ) = insect θ² (tan θ)² = b²/a² ( → t²n²a⁴ = b²/θ² → a​t²b​a(n​a)² = b³/θ² from physics: distance = 1/2 a​t² → ) distance2banana = b³/θ² [Caption below the frame:] Key trigonometric identities

This comic shows several real trigonometric identities at the first two lines and further below some identities "derived" by applying algebraic methods to the letters in the trigonometric function names, which is obviously nonsense. The first line are the known trigonometric functions: sine, cosine and tangent, and the second line contains the reciprocals of the trigonometric functions from the first line: cosecant, secant, and cotangent. The following identities are made up and are increasing in absurdity. The comic reflects on the confusion one gets when working more intensely with these identities, since there are a lot of hidden dependencies between them. You can also check how they are related through the various Trigonometry Formulas . The third and fourth line is made by treating the trigonometric function as a product of variables rather than a function and then using the above identities to create words. e.g. sin = b/c -> cin = b/s (this could also be a reference to the C++ cin). The second to last line performs some algebra on the individual letters of (tan θ)² = b²/a² as a setup to the last line. The last line takes the formula distance = 1/2 a​t² "from physics" and plugs it into the equation of the previous line, doing some algebra to replace a​t² with distance2 and expanding (na)² into nana to get the final equation, distance2banana = b³/θ². This is valid algebra only if the trigonometric operators are taken as variable products rather than operators, but this is a common misconception encountered when people first learn trigonometry. The distance equation is the distance a constantly accelerating object initially at rest moves in a given length of time t, most often used to find how far an object dropped from rest will fall under the influence of gravity in a given amount of time (or how long it will take to fall a given distance). There are a few formulas that have mistakes if you simply make algebraic manipulations to the six standard trigonometric functions. The title text is an anagram . Due to the commutative property of multiplication (which states that order does not affect the product), these equations are equivalent if treated as individual variables as earlier. Another layer of absurdity is added in that the variable Theta is spelled out and broken into its letters, which are then treated as individual variables. (The arctangent referred to here is the inverse tangent, a one-sided inverse to the tangent function. You would not normally write , since the theta in the comic refers to an angle, and the arctangent has an angle as its value rather than as its argument ; however, using theta here is merely unconventional, not forbidden.) The arctangent generally produces theta, the meaning of it being taken on theta being poorly understood. Randall here elucidates, via tongue-in-cheek algebraic proof, that taking a second arctangent of theta produces magical effects. The formula s=1/2 a​t² gives the distance a uniform accelerating object reaches over time. The second formula belongs to astronomy and the third law of Kepler in which the square of the orbital period of a planet is directly proportional to the cube of the semi-major axis of its orbit , meaning the fraction of b 3 and t 2 is a constant (banana). But using the angle θ as an argument leads to Richard Feynman , who did many famous Lectures on Physics and his lost lecture about the Motion of Planets Around the Sun from 1964 in which he only used geometry, based on the orbital ellipse, a circle around, and matching right-angled triangles to illustrate this law from Kepler. For deeper understanding why it really does work there is a nice presentation at the "Journal of Symbolic Geometry": Feynman Says: “Newton implies Kepler, No Calculus Needed! (Brian Beckman, 2006)” Some have tried to argue there are mathematical justifications for the errors in some of the formulas, by stating (without proof) that you could prove that valid solutions to the original six trig identities (where letters are taken to be variables multiplied together) can be manipulated to show that solutions must have a=o and s=t. These proofs are incorrect and can be shown easily with a counterexample. If you make the following assignments of variables like o=s=1/2 and set c=e=2 while leaving the other variables set to 1 (a=b=i=n=t=θ=1). This variable assignment will simultaneously satisfy all six original trig identities: ; ; ; ; ; . However in this valid assignment, we have since and we have as . This demonstrates that you can not make a valid algebraic derivation of or without additional assumptions beyond the six given trigonometric identities. [Inside a single frame comic a right-angled triangle is shown. The shorter sides are labeled "a" and "b" and the hypotenuse has a "c". All angles are marked: the right angle by a square and the two others by arcs. One arc (enclosed by "a" and "c") is labeled by the Greek symbol theta (θ).] [Supposed trigonometric functions of the marked angle θ are shown:] sin θ = b/c cos θ = a/c tan θ = b/a cot θ = a/b sec θ = c/a csc θ = c/b cin θ = b/s cas θ = o/c tab θ = b²/n​a bot θ = a/c → boat θ = a²/c → stoat θ = a²/c · s​t/b tan θ ( = b/a = b/a · c/c = b/c · c/a = sin θ sec θ ) = insect θ² (tan θ)² = b²/a² ( → t²n²a⁴ = b²/θ² → a​t²b​a(n​a)² = b³/θ² from physics: distance = 1/2 a​t² → ) distance2banana = b³/θ² [Caption below the frame:] Key trigonometric identities

Indirect Detection

Indirect Detection

https://www.xkcd.com/2071

https://www.explainxkcd.com/wiki/index.php/2071:_Indirect_Detection

[A single social media post is shown. On the top left is a portrait of a spiky-haired face, the text right aside is not readable. The post is:] Everyone on here needs to stop laughing about how "adopting pets from a shelter is for losers" and "those animals should all be hunted for sport instead." It's reprehensible on so many levels! First of all... [Caption below the frame:] Sometimes, one of my friends posts an angry response to some terrible opinion I've never heard before, and it's a weird indirect way to learn how awful their other friends must be.

This comic shows an angry social media post by one of Randall's spiky-haired friends, objecting to the views of unknown third parties, which appear to be a cartoonishly and unrealistically evil take on the proper treatment of abandoned animals. This could perhaps be in part a callback to 2051: Bad Opinions , in which Cueball is looking to post a response to an absurd or inflammatory opinion that currently may or may not actually exist anywhere on the internet. Sometimes when posting something on social media, such as Facebook, that post can be seen by all the people you have designated as your "friends." In this case the original comment was intended to be read by the people holding these views, people who are not direct friends of Randall's and whose posts he therefore could not see, but because it was posted by his direct friend he could read that response and was able to imagine what it was those other people were saying. Knowing a little about what these other mystery people are saying, through direct quotes from within his friend's comment, and having to fill in the rest by his imagination, he reflects on how weird it is to learn that people who hold such views exist in such an indirect manner. The title text is a pun comparing the shadows of Plato's cave to the practice of " throwing shade " (slang for throwing insults, usually subtly), and "the wall" could have a double meaning of both the wall of the cave and the term for someone's social media page. Plato's Cave is an allegorical tale taking place in a hypothetical cave. The cave contains lifelong prisoners who are chained such that they may only look at one wall. A fire burns, and the goings-on are cast as shadows upon this wall. Lacking a more complete or direct source of information, the cave occupants can only guess about the world by interpreting these shadows as a view of the world itself, and therefore base their other beliefs about the world upon the transitory appearances of these shadows. In this way, Plato's Cave serves as an allegory for our limited understanding of phenomena that occur primarily or entirely outside direct perception by our natural senses. It also offers imagery of how our perceptions and beliefs can be so restricted by what our information channels provide to us, which are now controlled by hidden computer algorithms and marketing teams. In the same way one might make incorrect assumptions about the makeup and chemical properties of air if one's information on the subject were gathered entirely from watching wind blow through leaves, the hypothetical occupants of Plato's Cave may reasonably be expected to produce wildly inaccurate theories about the outside world, a world they experience only as a kind of shadowplay. To be more specific, if one sees only a reaction (shadow) to an unseen post, one might become polarized against an imagined horrible thing, like if there were a large percentage of people who supported killing pet animals from shelters for sport, when in fact it is only the shadow which you have observed anything about, rather than the object that cast it. [A single social media post is shown. On the top left is a portrait of a spiky-haired face, the text right aside is not readable. The post is:] Everyone on here needs to stop laughing about how "adopting pets from a shelter is for losers" and "those animals should all be hunted for sport instead." It's reprehensible on so many levels! First of all... [Caption below the frame:] Sometimes, one of my friends posts an angry response to some terrible opinion I've never heard before, and it's a weird indirect way to learn how awful their other friends must be.

Evaluating Tech Things

Evaluating Tech Things

https://www.xkcd.com/2072

https://www.explainxkcd.com/wiki/index.php/2072:_Evaluating_Tech_Things

[Megan and Cueball talking.] Megan: Sooner or later, someone is going to fly a drone into a tornado and post the footage to YouTube. [Zoom in on Cueball imagining a semicircular dial with a moving pointer currently fixed vertically in the mid value. The left-most value indicating his opinion to be "This raises big questions about technology and society" and the right-most being "Haha, cool!"] [Panel with just Cueball and the imaginary dial above his head, the pointer having shifted a small amout to the right.] [Same panel with Cueball, his right hand pensively on his chin, the pointer having shifted an equally small amount to the left of the mid value.] [Panel with Cueball, Megan and the imaginary dial above, the pointer now all the way to the right.] Cueball: Haha, cool!

Many things are possible today thanks to technology, and while often the "wow factor"—how cool it is that we can do that—kicks in right away, there can also be deep potential longer term consequences for humanity. Things like atomic fission , the Internet , CRISPR technology, are amazing things we have learned how to do, but they also have the potential, in some cases already realized, of massively affecting human life (e.g. nuclear annihilation, instant wide-scale communication, elective genetic engineering), both for the better and for the worse. Here Cueball , upon hearing of a cool idea he hadn't thought of before, mentally measures it on a scale to decide if he can be excited about it, or should be worried about how it might affect humanity. After weighing it out, he decides it's just plain cool and it will not adversely affect humanity at all. In the comic, it appears this mental decision took awhile, judging by the multiple panels showing him thinking, ambivalently rubbing his chin as the dial oscillates left and right, before he gives his response. The title text refers to this mental weighing also being known as the Black Mirror – Mythbusters scale. Black Mirror and Mythbusters are both TV shows that explore science and technology. Black Mirror , on the one end of the scale, explores the unintended and often dire consequences of many of our more influential technologies—the horrible stuff that can happen—whereas Mythbusters , on the other end of the scale, explores the fun side of technology to see what kinds of cool things can or cannot be done. Worrying about the effect that technology has on our lives is a theme that has been explored before, in 1215: Insight . [Megan and Cueball talking.] Megan: Sooner or later, someone is going to fly a drone into a tornado and post the footage to YouTube. [Zoom in on Cueball imagining a semicircular dial with a moving pointer currently fixed vertically in the mid value. The left-most value indicating his opinion to be "This raises big questions about technology and society" and the right-most being "Haha, cool!"] [Panel with just Cueball and the imaginary dial above his head, the pointer having shifted a small amout to the right.] [Same panel with Cueball, his right hand pensively on his chin, the pointer having shifted an equally small amount to the left of the mid value.] [Panel with Cueball, Megan and the imaginary dial above, the pointer now all the way to the right.] Cueball: Haha, cool!

Kilogram

Kilogram

https://www.xkcd.com/2073

https://www.explainxkcd.com/wiki/index.php/2073:_Kilogram

[Black Hat talking to Ponytail, Cueball, and Megan while all stand in a row. Megan's hands are raised emphatically.] Black Hat: To end many years of confusion, the International Committee for Weights and Measures has just voted to redefine the kilogram. Black Hat: As of next May, it will equal exactly one pound. Ponytail: Oh, cool. Cueball: That does make things simpler. Megan: No!! To further expand on this, the classic definitions of all our various units of time, length, mass, and temperature are based on phenomena that are neither convenient to measure precisely nor in fact consistently reproducible. The duration of an Earth day and year vary unpredictably, the circumference of the Earth varies, the International Prototype Kilogram gains or loses mass any time it is handled (and in fact just sitting there it and its reference copies diverge from each other), and the value of baseline temperatures such as the freezing point of water depend on which isotopes of hydrogen are in the water molecules. Nevertheless, there really are constants of nature. For example, one of them is ‘ c ’, the speed of light in a vacuum. The expressed value of c depends on your choice of the unit of distance and the unit of time, but it’s a constant in those units. Now just suppose we all had a reproducible way to define a specific unit of time, which just for fun we call a ‘second’. You might not know the length of a ‘metre’, but if I told you that measured in metres per second the universal constant value of c is exactly 299792458 metres per second, then I would have fixed the length of a metre to be exactly the distance light travels in a vacuum in 1/299792458 seconds. And in fact this is what the international body responsible for defining our SI units has done. One second is defined to be a specific number of periods of the radiation emitted in a certain transition of a cesium 133 atom. The specific number was set in the year 1967, so as to match a previous astronomical standard called ephemeris time to the limit of human measuring ability at the time. The 1967 definition didn’t change the actual duration of a second, but it did make its measurement forever reproducible. In 1983 the value of c was fixed to the value noted above. Prior to that it had been measured with respect to existing definitions of a metre, and had to be expressed with a measure of uncertainty. For example in 1973 a team at the US National Bureau of Standards refined c to 299,792,457.4 m/s ± 1 m/s. But from 1983 onwards, with an exact integer value for c that is quite close to that Bureau measurement, the length of a metre is now fixed with no plus/minus uncertainty. Furthermore, both the second and the metre match their predecessor definitions for all intents and purposes. Similar redefinitions of units of mass and of temperature in terms of universal constants have been agreed to, mass with regard to the Planck constant h , and temperature with regard to the Boltzmann constant k . The constants h and k had previously been measured quantities, complete with uncertainties. The SI body fixed both of them to exact values, resulting in exact, no-uncertainty values for a kilogram of mass and a kelvin of thermodynamic temperature. As with the second and the metre, these new definitions match their predecessor definitions for all intents and purposes. To expand on this even further, three additional universal constants that were previously measured and that had uncertainty values have been assigned fixed values, resulting in exact definitions of three corresponding units of measurement without affecting their applicability. Fixing the unit of elementary charge, e , serves to define the unit of electric current, the Ampere. Fixing the unit of luminous efficacy K cd serves to define the unit of luminous intensity, the candela. And fixing the Avogadro constant N A serves to define the unit of amount of substance, the mole. A Wikipedia article about redefining the SI units of measure in terms of newly fixed values of things taken to be universal constants is 2019 redefinition of the SI base units . Additionally, it might be worth noting the pound has multiple different types and definitions. The most common definition today is the international avoirdupois pound (lb), which is defined (discarding the semantics) as a unit of mass equal to 0.45359237 kilograms. However the pound is commonly used as to describe force, defined as the force an avoirdupois pound exerts on the Earth (lbf). These definitions however are identical in practical terms, such that an item with 0.45359237 kilograms of mass exerts one avoirdupois pound of force on the Earth. In the SI, the derived unit of force is the newton.

Standard units such as the kilogram, metre, and second are redefined from time to time as measurement technologies improve. These redefinitions are generally done to improve the precision to which the various units can be known or reproduced, without changing their actual value. The joke here is that redefining the kilogram to equal one pound sounds like an incredible idea to Americans who never use the kilogram. It would not only fail to improve on its precision, but would also significantly change the value of what a kilogram is, making all things already measured for science and in the rest of the world impossible to correctly understand the mass of. On the day of this comic, the General Conference on Weights and Measures (which Randall confuses with the International Committee for Weights and Measures ) voted to redefine the kilogram by fixing it to the value of Planck's Constant . This is measured using a Kibble balance , which involves passing a measured current through an electromagnet to exert a force to balance 1 kg. The change took effect on May 20, 2019, when the platinum cylinder International Prototype Kilogram that defines the unit was retired. This means that the mass of a kilogram is no longer tied to a physical object, but to the fundamental properties of the universe. By fixing the value of Planck constant to 6.62607015×10 -34 kg⋅m 2 ⋅s −1 , the kilogram is defined in terms of the second and the speed of light via the metre. The previous method of confirming that a kilogram is accurate is to use physical metal weights measuring exactly one kilogram, periodically transporting them around the world to an official weight lab to confirm they still weigh the same. Over time these physical objects have changed very slightly in their mass making them unreliable in the long run -- thus running into the issue that a kilogram did not stay a constant measure of mass. Note that these weights and comparisons are so precise that a fingerprint on one of the weights could throw them off. The new method of confirming that a kilogram is accurate relies upon an extremely precise knowledge of local gravitational effects & an absence (or counteraction) of electromagnetic interference. On a traditional scale, two units of equal weight will balance, regardless of local gravitational levels; whereas the new method requires that the gravitational force be determined precisely for every site, meaning an additional measurement has to take place. This involves a high-precision gravimeter such as the FG5 absolute gravimeter. In this comic, Black Hat announces that the kilogram has been redefined as equal to one pound . Ponytail and Cueball seem to think this makes things simpler, but Megan is alarmed. The metric system of measurement is the one used by most of the world and is the standard system used in science. Redefining the kilogram to be equal to the pound would be very disruptive and outrage supporters of the metric system. Redefining the kilogram as being a completely different size from before will create a lot of confusion, since now when people read a mass in kilograms they need to work out whether it was written in old kilograms or new (pound-sized) kilograms. The pound is officially defined as 0.45359237 kilograms, or less than half a kilogram. This makes defining a kilogram as one pound even more impossible as they are then stuck in a loop, as 0.45359237 kilograms must have the same mass as 1 kilogram, meaning the value of the kilogram would be equal to zero. The title text continues the joke by saying that the metre has been defined as exactly three feet. The yard, the closest US measurement to the metre, is three feet. However, a metre is about 9 centimetres (~3.55 inches) longer than a yard. As with the pound, the metric system is used to define the yard as it is officially defined as 0.9144 metres. This joke recreates the comic in the real world, with Randall playing as Black Hat, and the reader responding. Those who fall for the claim will either be excited that things are simpler, or devastated at what the result will be. [Black Hat talking to Ponytail, Cueball, and Megan while all stand in a row. Megan's hands are raised emphatically.] Black Hat: To end many years of confusion, the International Committee for Weights and Measures has just voted to redefine the kilogram. Black Hat: As of next May, it will equal exactly one pound. Ponytail: Oh, cool. Cueball: That does make things simpler. Megan: No!! To further expand on this, the classic definitions of all our various units of time, length, mass, and temperature are based on phenomena that are neither convenient to measure precisely nor in fact consistently reproducible. The duration of an Earth day and year vary unpredictably, the circumference of the Earth varies, the International Prototype Kilogram gains or loses mass any time it is handled (and in fact just sitting there it and its reference copies diverge from each other), and the value of baseline temperatures such as the freezing point of water depend on which isotopes of hydrogen are in the water molecules. Nevertheless, there really are constants of nature. For example, one of them is ‘ c ’, the speed of light in a vacuum. The expressed value of c depends on your choice of the unit of distance and the unit of time, but it’s a constant in those units. Now just suppose we all had a reproducible way to define a specific unit of time, which just for fun we call a ‘second’. You might not know the length of a ‘metre’, but if I told you that measured in metres per second the universal constant value of c is exactly 299792458 metres per second, then I would have fixed the length of a metre to be exactly the distance light travels in a vacuum in 1/299792458 seconds. And in fact this is what the international body responsible for defining our SI units has done. One second is defined to be a specific number of periods of the radiation emitted in a certain transition of a cesium 133 atom. The specific number was set in the year 1967, so as to match a previous astronomical standard called ephemeris time to the limit of human measuring ability at the time. The 1967 definition didn’t change the actual duration of a second, but it did make its measurement forever reproducible. In 1983 the value of c was fixed to the value noted above. Prior to that it had been measured with respect to existing definitions of a metre, and had to be expressed with a measure of uncertainty. For example in 1973 a team at the US National Bureau of Standards refined c to 299,792,457.4 m/s ± 1 m/s. But from 1983 onwards, with an exact integer value for c that is quite close to that Bureau measurement, the length of a metre is now fixed with no plus/minus uncertainty. Furthermore, both the second and the metre match their predecessor definitions for all intents and purposes. Similar redefinitions of units of mass and of temperature in terms of universal constants have been agreed to, mass with regard to the Planck constant h , and temperature with regard to the Boltzmann constant k . The constants h and k had previously been measured quantities, complete with uncertainties. The SI body fixed both of them to exact values, resulting in exact, no-uncertainty values for a kilogram of mass and a kelvin of thermodynamic temperature. As with the second and the metre, these new definitions match their predecessor definitions for all intents and purposes. To expand on this even further, three additional universal constants that were previously measured and that had uncertainty values have been assigned fixed values, resulting in exact definitions of three corresponding units of measurement without affecting their applicability. Fixing the unit of elementary charge, e , serves to define the unit of electric current, the Ampere. Fixing the unit of luminous efficacy K cd serves to define the unit of luminous intensity, the candela. And fixing the Avogadro constant N A serves to define the unit of amount of substance, the mole. A Wikipedia article about redefining the SI units of measure in terms of newly fixed values of things taken to be universal constants is 2019 redefinition of the SI base units . Additionally, it might be worth noting the pound has multiple different types and definitions. The most common definition today is the international avoirdupois pound (lb), which is defined (discarding the semantics) as a unit of mass equal to 0.45359237 kilograms. However the pound is commonly used as to describe force, defined as the force an avoirdupois pound exerts on the Earth (lbf). These definitions however are identical in practical terms, such that an item with 0.45359237 kilograms of mass exerts one avoirdupois pound of force on the Earth. In the SI, the derived unit of force is the newton.

Airplanes and Spaceships

Airplanes and Spaceships

https://www.xkcd.com/2074

https://www.explainxkcd.com/wiki/index.php/2074:_Airplanes_and_Spaceships

[A timeline is shown with three dots on it. Each dot has a label beneath the dot, and the two intervals between the dots are also labeled, with lines indicating which dots are belonging to that label.] Dot 1 December 17, 1903 First human airplane flight Dot 2 April 12, 1961 First human spaceflight Dot 3 Today Interval 1-2 57 years 4 months Interval 2-3 57 years 7 months [Caption beneath the frame:] Spaceships are now older than airplanes were when we flew our first spaceships.

This comic is pointing out that more time has elapsed since the first spaceship flight, than previously elapsed between the first airplane flight and the first spaceship flight. (This was at the time of release of this comic on November 19th of 2018, a month before the 115th anniversary for the first airplane flight). Airplanes and spaceships are often considered to be related vehicles, under the term aerospace, with degrees in aerospace fields often having aeronautics (airplanes) or astronautics (spaceships) tracks. The jump in technology and performance between the first airplane and the first spaceship was enormous: the Wright Flyer had a max speed of 30 mph (48 km/h), and the first flights reached only about 30 feet (9 m) above ground, with distances of only 120 to 850 feet (260 m). In comparison the Vostok 1 mission of Yuri Gagarin reached orbital velocity of 17,500 mph (28,000 km/h), a minimum altitude of 91 miles (480,480 ft; 146 km), and traveled once around the earth (about 25,000 miles or 40,000 km). This represents an increase in performance of between about 600 and 150,000 times. By contrast, an equal amount of time has passed between the first spaceflight and the publish date of this comic, but aeronautical performance has not improved much at all. Although the Apollo mission broke speed and altitude records, and later space missions extended the distance traveled in a single flight by sustaining Earth orbit for longer, the overall technology and performance is not much different than that used during the first space mission. It is one of the typical takes by Randall to try to make people feel old . Flight seemed old news when the Apollo mission started, so people who lived through the space race, will now feel very old since they were alive back when the space race is new, and that is now old news. This take is also used in the title text. The title text refers to the 2003 film The Core . In this film, there is an instability in the Earth's magnetic field, so a team of scientists attempt to drill to the center of the Earth and set off nuclear explosions to restart the rotation of the Earth's core. To do this, they travel in a vehicle made of "Unobtainium" that can withstand the heat and pressure within the Earth's crust. Randall is sad to report that there is little progress being made on creating this vehicle. Incidentally, The Core is a film which represents science and engineering wrong in many, many aspects. There is a long list of flaws . For instance, if a material is resistant to the extreme heat and pressure of the Earth's core, then the significantly cooler and less forceful techniques of human metallurgy would certainly not be able to work that material at all, let alone craft it into a functional hull for a vehicle. Randall makes sure to mention that the movie is from 2003, so 15 years old. Many people are surprised when realizing that a movie they saw "recently" is now so old that children born that year no longer need their parents guidance when watching it. The Core was already used as the main plot starter in 673: The Sun back in 2009, and earlier in 2018 it was mentioned in the title text of 2011: Newton's Trajectories . That Randall has a great interest in the Earths cores is shown in several comics, and may explain why he continues to return to the movie, even though he probably (taken from his comics mentioning it) thinks is a bad movie. See a recent comic here, 2058: Rock Wall and of course 913: Core . [A timeline is shown with three dots on it. Each dot has a label beneath the dot, and the two intervals between the dots are also labeled, with lines indicating which dots are belonging to that label.] Dot 1 December 17, 1903 First human airplane flight Dot 2 April 12, 1961 First human spaceflight Dot 3 Today Interval 1-2 57 years 4 months Interval 2-3 57 years 7 months [Caption beneath the frame:] Spaceships are now older than airplanes were when we flew our first spaceships.

Update Your Address

Update Your Address

https://www.xkcd.com/2075

https://www.explainxkcd.com/wiki/index.php/2075:_Update_Your_Address

[Cueball is standing and talking on a phone.] Voice: Do you still live at 342 River St? Cueball: No, I moved last year. [Cueball is standing behind a counter with Hairy, whose hands are on a keyboard.] Hairy: Is 21 Ash Tree Lane still a good address? Cueball: What? That's my childhood home. How is that even in your system? [Cueball is talking on a phone again in a borderless panel.] Voice: The address we have is 205 Second St #2. Cueball: I... think that's where my parents lived before I was born!? [Cueball stands behind another counter with Ponytail and a tablet.] Ponytail: Are you still living in... "The Austro-Hungarian Empire?" Cueball: You know what, sure. Ponytail: Austria-Hungary dissolved in 1918. Cueball: Well, I come from a long line of people who hate updating stuff.

In this comic, Cueball is facing several instances where entities asking or confirming his address find that the address they possess is incorrect - each address is progressively more outdated. In the final comic, Cueball gives up and confirms that yes, he is still living in a country that hasn't existed for over a century. Inaccurate addresses may be a common problem for someone who has moved constantly in their lifetime. Alternatively, Cueball and his family do not find it important to update addresses for those particular businesses / entities. Austria-Hungary was a European empire that existed between 1867 and 1918, dissolving during World War I . It is possible that Cueball's ancestors hail from the Austro-Hungarian Empire, though it would be even more absurd for that to be used as an address, given that the polity ended a century ago, whereas the earliest programmable computer was created 20 years after the country was dissolved and personal/small business computers approximately 40 years after that. Ash Tree Lane refers to House of Leaves , a postmodern novel from 2000 in which one of many nested plots involves a house on Ash Tree Lane that is bigger on the inside than on the outside, and in fact contains a labyrinth with a minotaur . The book, and Ash Tree Lane specifically, have previously been referenced in 472: House of Pancakes , 827: My Business Idea , and 886: Craigslist Apartments . The title text treats bank accounts (and the PIN codes needed to access them) as though they were physical heirlooms passed down generation to generation. The patent for PIN codes was submitted in May 1966, and the first public use of a PIN code was in 1967, when Barclays used them to process cheques at automated teller machines . It would be unusual for Cueball to inherit both an active bank account and the PIN associated with it -- when a person with a bank account dies, the bank usually closes the account altogether and transfers the money to a separate account of whoever is named the beneficiary. Treating the account number and/or its PIN as though they were physical heirlooms plays into the joke of them not changing through the years (due to the perceived difficulty of updating them). [Cueball is standing and talking on a phone.] Voice: Do you still live at 342 River St? Cueball: No, I moved last year. [Cueball is standing behind a counter with Hairy, whose hands are on a keyboard.] Hairy: Is 21 Ash Tree Lane still a good address? Cueball: What? That's my childhood home. How is that even in your system? [Cueball is talking on a phone again in a borderless panel.] Voice: The address we have is 205 Second St #2. Cueball: I... think that's where my parents lived before I was born!? [Cueball stands behind another counter with Ponytail and a tablet.] Ponytail: Are you still living in... "The Austro-Hungarian Empire?" Cueball: You know what, sure. Ponytail: Austria-Hungary dissolved in 1918. Cueball: Well, I come from a long line of people who hate updating stuff.

Horror Movies 2

Horror Movies 2

https://www.xkcd.com/2076

https://www.explainxkcd.com/wiki/index.php/2076:_Horror_Movies_2

[White Hat and Cueball are walking, with Cueball holding his arms out in front of him.] White Hat: So you don't like any horror movies? Cueball: Spooky stuff is neat but I hate jump scares and watching people get murdered. Why would you want to see that? [Zoom in on the two.] White Hat: It's like roller coasters. People like experiencing powerful feelings in a safe, controlled setting. Cueball: But why not good feelings? [In a frame-less panel Cueball stops and turns towards White Hat.] White Hat: We've always been into tragic stories. Romeo and Juliet, Titanic... Cueball: See, that's another thing I don't get! [Zoom out again as White Hat walks past Cueball who now hold his arms out to the side as he looks after White Hat.] Cueball: I loved Titanic because Rose and Jack found each other and seemed so happy! I just hated the ending. White Hat: I'll be sure to give James Cameron and Shakespeare your feedback.

This comic is the second in the Horror Movies series, and is the follow-up to 2056: Horror Movies released a month earlier. While the first Horror Movies comic was about giving voice to Randall's inability to enjoy horror movies, this comic takes Randall's previous position and exaggerates it. White Hat and Cueball (as Randall) discuss the appeal of horror movies and tragic plots. Cueball expresses his dissatisfaction with stories that focus on evoking negative feelings. As an example he mentions how he disliked the ending of Titanic where Jack sacrifices his life in order to save Rose. White Hat does not seem to share Cueball's point of view on successful storytelling and sarcastically promises to send feedback to the movie director James Cameron as well as the 16th century playwright and writer William Shakespeare , whose most famous works include tragedies like Romeo and Juliet . In the title text Cueball (as Randall?) discusses the ending of the science fiction novel The Giver where the fate of the main character Jonas [sic, see Trivia ] had been left ambiguous. The joke is a stereotype that the Newbery Medal , a children's literature award, is only given to books with tragic endings. However, the protagonist lives, as there are three more titles in the series, two of which have the main character as a side character. However, those three books are rather obscure. This was the first of two comics in a row to reference a specific movie genre, this one horror movies, the next one, 2077: Heist , heist movies. [White Hat and Cueball are walking, with Cueball holding his arms out in front of him.] White Hat: So you don't like any horror movies? Cueball: Spooky stuff is neat but I hate jump scares and watching people get murdered. Why would you want to see that? [Zoom in on the two.] White Hat: It's like roller coasters. People like experiencing powerful feelings in a safe, controlled setting. Cueball: But why not good feelings? [In a frame-less panel Cueball stops and turns towards White Hat.] White Hat: We've always been into tragic stories. Romeo and Juliet, Titanic... Cueball: See, that's another thing I don't get! [Zoom out again as White Hat walks past Cueball who now hold his arms out to the side as he looks after White Hat.] Cueball: I loved Titanic because Rose and Jack found each other and seemed so happy! I just hated the ending. White Hat: I'll be sure to give James Cameron and Shakespeare your feedback.

Heist

Heist

https://www.xkcd.com/2077

https://www.explainxkcd.com/wiki/index.php/2077:_Heist

[A man in a cap with a toolbox approaches Cueball, who is shown to be thinking with a cloud like bubble above his head with his thoughts.] Man: Do you have the key to the server room? I'm from the building and I'm here to check the fire alarm. Cueball [thinking]: Oh no oh no [Caption below the panel:] Thanks to movies, whenever anyone asks me to open any door, I immediately assume I'm a minor character in a heist.

In heist films , a heist or other crime is carried out, sometimes involving the criminal(s) posing as some type of repairman or similar. The criminal then gains access to their target through the disguise, as humans do not normally critically assess someone if their appearance fit expectations. Due to the prevalence of this trope, Cueball is concerned whenever somebody comes by to ask for access as he believes the person may be planning a crime, and his inadvertent assistance will make him a "minor character" in the wider heist story. In such movies, minor characters are sometimes held hostage or even killed in the course of the crime being committed, particularly if the heist goes wrong. The risk of being a minor character could also perhaps include the risk of being harmed. In general people would probably prefer to be the main character in a film, rather than a bystander. In this case, he is asked to open the server room - ostensibly to allow the fire alarm to be checked. However, gaining physical access to the server allows the criminal to bypass most security features that should prevent unauthorized access to the data (a scenario known as an evil maid attack ). If the hard disks are not encrypted it is trivial to copy all files or even remove and abscond with the disk drives - allowing the theft of sensitive information stored on the network. Even if the files are encrypted physical access to the server will allow the attacker to corrupt the system either by installing malware or adding malicious hardware components, which will then allow them to retrieve passwords and/or encryption keys. Being aware of these dangers Cueball immediately assumes that he (or his employers) are the target of a heist. The title text seems to be Cueball's internal monologue trying to calm himself down. He points out to himself that the repairman has both a hat (possibly with a company logo) and a toolbox full of tools, then sarcastically asks himself how a thief could possibly get their hands on such a disguise. This is the second comic in a row to reference a specific movie genre, this one heist movies the previous one, 2076: Horror Movies 2 , horror movies. [A man in a cap with a toolbox approaches Cueball, who is shown to be thinking with a cloud like bubble above his head with his thoughts.] Man: Do you have the key to the server room? I'm from the building and I'm here to check the fire alarm. Cueball [thinking]: Oh no oh no [Caption below the panel:] Thanks to movies, whenever anyone asks me to open any door, I immediately assume I'm a minor character in a heist.

Popper

Popper

https://www.xkcd.com/2078

https://www.explainxkcd.com/wiki/index.php/2078:_Popper

[Miss Lenhart is teaching a class of three students; Hairy, Ponytail, and Science Girl, sitting behind their desks.] Miss Lenhart: There's no evidence that Karl Popper wasn't born on July 28th, 1902. Miss Lenhart: No one has proven that he didn't grow up in Vienna...

In this comic, Miss Lenhart teaches to a class comprising of Hairy , Ponytail , and Science Girl about Karl Popper . Karl Popper was a philosopher of science who endorsed the idea that science is distinguished from non-science by treating its theories as falsifiable. This means that science does not treat any theory as definitive, because future research could show that it is false. A not uncommon reading of Popper assumes that instead of proving hypotheses, scientists are disproving hypotheses. This reading leads to technicalities like the ones stated in the comic: Instead of asserting that Popper was indeed born on July 28, 1902, and grew up in Vienna, a scientist can only assert that there is no evidence disproving these facts, which seems counter-intuitive because one cannot disprove the facts of Popper's birthdate and childhood residence. Note however that falsifiability is often interpreted to mean that there has to be a way to disprove a given statement if it is wrong, or to distinguish between two mutually competing hypotheses; not that a statement is accepted solely due to the lack of evidence to the contrary, e.g. a birth certificate is often used to establish a date of birth and falsifying that date of birth would then mean calling into question the birth certificate's authenticity or accuracy, but without any historical records of the date of birth one would normally not even speculate at all about the precise date of birth. As such reasoning solely on the absence of proof to the contrary would be considered unusual in most contexts. The humor comes when the comic applies this idea to the life and biographical information of Karl Popper himself. Note that in real life, such a subject would be a matter for historical proof, not scientific, and would thus fall outside the realm of study Popper was thinking of. The title text takes this reading a couple of steps further in a kind of meta-analysis. It points out that Miss Lenhart 's claim of no evidence has not been proven false, and also that we're dealing with only the knowledge of a single individual who may not be aware of evidence that might exist. Another reading of Popper points out that Popper’s philosophy discarded proofs altogether as a defining feature of science. Thus there is no such thing as definitive evidence in Popper’s notion of science: Even falsifying assertions themselves are seen as falsifiable. [Miss Lenhart is teaching a class of three students; Hairy, Ponytail, and Science Girl, sitting behind their desks.] Miss Lenhart: There's no evidence that Karl Popper wasn't born on July 28th, 1902. Miss Lenhart: No one has proven that he didn't grow up in Vienna...

Alpha Centauri

Alpha Centauri

https://www.xkcd.com/2079

https://www.explainxkcd.com/wiki/index.php/2079:_Alpha_Centauri

[Ponytail stands on a podium giving a presentation in front of a slide with an image of a Voyager-like spacecraft.] Ponytail: Our probe can reach Alpha Centauri in under 35 years. Offscreen voice: We should go somewhere else. Alpha Centauri sucks. Ponytail: Huh? It's the closest, most convenient system! Offscreen: Yeah, but I checked online and it only has three stars.

Alpha Centauri is the closest star system to our solar system, being about 4.37 light-years away. As such, there are numerous ongoing plans and projects to journey to, and explore the star system, especially since the exoplanet Proxima Centauri b was found in 2016 to possibly have liquid water oceans and a very thin atmosphere. Similar to this project , Ponytail announces such a project using a Voyager -like probe. However, an offscreen person is against the idea of sending a probe to that particular part of the galaxy, as they think that "Alpha Centauri sucks". The person says that they looked "online" and that the system "only has three stars". This is a pun playing on the stars used in online reviews and stars as celestial objects. Online rating systems, such as Yelp , often use star rating systems , with more stars indicating higher quality, up to an arbitrary maximum, such as five stars to indicate the best rating. Due to the nature of 5 star rating systems, as shown in in comic 1098: Star Ratings , anything scoring less than 4 out of 5 in a 5 star rating system is crap; and in a 10-star rating system, scoring a mere 3 stars out of a possible 10 stars would be exceedingly low quality. The Alpha Centauri star system has 3 physical stars : Alpha Centauri A, Alpha Centauri B, and Proxima Centauri. The offscreen person has misconstrued this fact of the system as some kind of review. The title text furthers the pun. Some online star rating systems also allow partial stars, such as a half-star, to allow more precision in rating (e.g. rating 2.5 stars instead of being forced to chose 3 stars or 2 stars), or display an average collective rating as partial stars (e.g. showing 2.5 stars when five people have rated 3 stars and five people have rated 2 stars). Alpha Centauri's "half star" refers to Proxima Centauri, a red dwarf , which is a type of low-mass star. According to the offscreen person, this barely qualifies it to be a star. Furthermore, Proxima Centauri is nearly 13,000 AU (0.21 light years) away from the other 2 stars in the system, so it was long unknown whether Proxima Centauri was gravitationally bound to the Alpha Centauri star system. All numbers are rounded after subsequent calculations. According to space.com the fastest spacecraft ever will be the Parker Solar Probe which will reach 430,000 mph (692,000 km/h) as it reaches its closest point orbiting the sun. This is just over half of 1% of the needed speed of the Alpha Centauri vehicle proposed in the comic. The Voyager 1 spacecraft, launched in 1977, is currently traveling at about 38,000 mph (61,000 km/h). Distance to Alpha Centauri system = 4.367ly 4.367 light years / 35 years = 0.12477ly per year 0.12477 light years/year * 5.879e+12 miles/light year = 733,484,000,000 miles/year 733,484,000,000 miles/year / 365 days/year / 24 hours/day = 83,000,000 Miles/hour / 1.60934 miles/kilometer = 134,000,000 Kilometers/hour The above math assumes a constant speed, and requires a speed of ~0.124855c. Assuming a constant acceleration from rest (non-relativistic math follows): 35*365.25*24*60*60 = 1.10e+9 seconds in 35 years 4.367 * 5.879e+12 = 2.57e+13miles, 4.13e+13 km, 4.13e+16 m. x = 1/2*a*t 2 a = 2*x*t -2 Assuming constant acceleration to the halfway point and constant deceleration to the destination, (otherwise you streak through the system, barely observing anything): t trip = 2*t halfway a = 2*2.06e+16*(5.50e+8) -2 = 0.136 m/s 2 , roughly 1/80 gravity. v halfway = a*t halfway . Top Speed: 75,000,000 m/s ~ 1/4*c. Assuming E = F*d, 0.136*1*4.13e+16 = 5.37e15 Joules will be required for each kilogram carried to Alpha Centauri in 35 years. This would require an unimaginable amount of mass for a conventional chemical rocket, and is a completely impractical power requirement for any sort of passive solar sail concept. Further, the top speed is fast enough to require a recalculation using relativistic physics to model the problem. This means that the energy budget will need to increase, as the relativistic mass of the probe will increase, requiring more force (and thus more energy) to accelerate and decelerate near its top speed than this calculation returns. Active , laser based propulsion methods require currently non-existent and purely specualtive laser and materials technologies, as well as a powerplant equivalent to 12,500 of the World's Largest Nuclear Plant to transport sub-gram masses on this timescale. This also assumes that any probes can be steered accurately enough across interstellar distances to come close enough to image with any resolution the bodies they will be passing at a non-trivial fraction of c. Short of FTL travel or near-perfect mass-energy conversion technology, transporting more than a fraction of a gram of material to Alpha Centauri in a human lifetime will be unachievable. Short of an enormous breakthrough in power generation, transporting even a fraction of a gram is impossible. Nonetheless, Breakthrough Starshot is attempting to send many gram-sized probes to Alpha Centauri within the century. Following current technological trends, they expect the efficiency of laser-based propulsion to increase by launch time, allowing launches driven by an unreasonably-large-but-achievable amount of power. The top speed needed is halved by refraining from slowing at all at the destination: the probes will aim a distance away from the target, so that it traverses by slowly enough for a camera to rotate and track it, even at near-light speeds. To account for error and space dust, the plan is to launch many tiny probes simultaneously. They may only be able to accomplish their goal if they can get enough funding to actually affect the global economy enough to make the technologies they require more efficient to produce. Launches would additionally burn incredible quantities of natural gas. [Ponytail stands on a podium giving a presentation in front of a slide with an image of a Voyager-like spacecraft.] Ponytail: Our probe can reach Alpha Centauri in under 35 years. Offscreen voice: We should go somewhere else. Alpha Centauri sucks. Ponytail: Huh? It's the closest, most convenient system! Offscreen: Yeah, but I checked online and it only has three stars.

Cohort and Age Effects

Cohort and Age Effects

https://www.xkcd.com/2080

https://www.explainxkcd.com/wiki/index.php/2080:_Cohort_and_Age_Effects

[Cueball as a news anchor is sitting at a desk with hands folded in front of him on the table.] Cueball: Tonight: Are Millennials killing the joint replacement industry? [To the left of Cueball is a presentation which includes a two by two table with a header above the table. Each of the two rows and columns are labeled, with rows entitled 'Baby Boomers' and 'Millennials', and columns entitled 'Knee' and 'Hip'] Operation rate per 100,000 Baby Boomers: Knee: 720 Hip: 390 Millennials: Knee: 1 Hip: 3 [Caption below the panel:] Stats Pet Peeve: People mixing up cohort effects and age effects.

Another of Randall's many Pet Peeves , this time it's statistics. It is the first in more than four years, since 1368: One Of The . " Millennials " are the generation of Westerners who were born between the early 1980s and the late 1990s, whereas baby boomers are the generation born during the "baby boom", a period of high birth rates from the late 1940s to early 1960s. A common headline on news websites is "Millennials are killing the X industry" where X is a product whose sales have dropped in recent years, such as jungle gyms for kids . One of the most famous is the diamond industry , where a combination of the wage gap , stigma over conflict diamonds , increased knowledge of ( in Randall's words ) "complicated gemstone market" and less desire to get married early has seen millennials buying less diamond jewelry than previous generations. Randall spoofs this idea. In the comic, Cueball , as a news anchor , presents a heading which opens his story by asking if millennials are killing the industry of surgical joint replacements , illustrating it with numbers of joint replacement procedures among millennials compared to baby boomers. The joke is that millennials are simply too young for most of them to need joint replacements (which are usually used to treat senile osteoarthritis ), so most people will see that so there really isn't a news story here. Randall is using this example to highlight that this kind of story is ridiculous. Millennials will likely need joint replacements in the future as they get older, potentially keeping sales of joint replacements at close to their current rate. A cohort effect is a cultural difference between generations (such as buying fewer diamonds), whereas an age effect is one that is simply related to getting older (such as getting arthritis). Joint replacement rates are an age effect, but the newscast is presenting them as if they were a cohort effect. (More correctly, the table rows would be labelled e.g. “people aged 50–70” and “people aged 22–37”.) The title text points out that although numbers of millennials receiving joint replacements are low, they are higher than the numbers of baby boomers who received them at the same age —i.e. in their 20s—due to advances in medical diagnosis and technology in the last 50 years, as well as (in some countries at least) better access to healthcare. This statistic can be used to create a headline which is the reverse of the one in the comic, namely "millennials are getting more joint replacements than ever". Randall notes that you could therefore use either headline to back up your argument, depending on the agenda you are trying to present. [Cueball as a news anchor is sitting at a desk with hands folded in front of him on the table.] Cueball: Tonight: Are Millennials killing the joint replacement industry? [To the left of Cueball is a presentation which includes a two by two table with a header above the table. Each of the two rows and columns are labeled, with rows entitled 'Baby Boomers' and 'Millennials', and columns entitled 'Knee' and 'Hip'] Operation rate per 100,000 Baby Boomers: Knee: 720 Hip: 390 Millennials: Knee: 1 Hip: 3 [Caption below the panel:] Stats Pet Peeve: People mixing up cohort effects and age effects.

Middle Latitudes

Middle Latitudes

https://www.xkcd.com/2081

https://www.explainxkcd.com/wiki/index.php/2081:_Middle_Latitudes

[Cueball and Megan standing and talking, Megan with her arms raised.] Cueball: It would be nice if the sun could rise and set at normal times. But it would also be cool to experience 24-hour darkness for weeks on end. Megan: Well, what if we split the difference, so all winter everything was normal but slightly more dim and bleak? Cueball: Perfect! [Caption below the frame:] Middle latitudes are the worst.

Because of the Earth's axial tilt, the apparent daily path of the Sun through the sky - in particular, how long it takes and how high in the sky it gets - is different depending on how far North or South of the Equator you are (your latitude), and also changes throughout the year as the Earth revolves around the Sun. This fact yields two very important pairs of latitudes: and The latitudes that lie within these two bands are called the middle latitudes - also sometimes referred to as the North Temperate Zone and the South Temperate Zone respectively. The Tropics of Cancer and Capricorn are the latitudes beyond which, if you go any further from the Equator, it is no longer possible for the Sun to be directly overhead at any time of the year. Similarly, the Arctic and Antarctic Circles represent the latitudes beyond which it is possible for the Sun not to rise or set at all at some times of the year. In the middle latitudes - which occur between these extremes - we instead get the rather less impressive phenomenon of daylight simply being a bit longer in summer and a bit shorter in winter. In the comic, the middle latitudes are sarcastically proffered as a compromise between two extremes described by Cueball: day lengths that don't vary that much (as occurs in the torrid zone near the Equator), and the possibility of days with no daylight at all (as occurs in the Arctic/Antarctic zones). However, it is clear that Megan's compromise merely results in seasonal weather that has no interesting or useful features at any time of the year. In particular, winter is singled out as a season that is generally just dim and bleak in the middle latitudes, with days that don't last long and are cold and dull anyway. The title text extends the idea with another spurious compromise, this time between snowy blizzards and warm sunny beaches - both of which are enjoyable in their own ways, but "splitting the difference" and combining the two would result in unpleasant icy slush. There are other comics that refer to the length of the day, and how it is different each day, for example, 2050: 6/6 Time . [Cueball and Megan standing and talking, Megan with her arms raised.] Cueball: It would be nice if the sun could rise and set at normal times. But it would also be cool to experience 24-hour darkness for weeks on end. Megan: Well, what if we split the difference, so all winter everything was normal but slightly more dim and bleak? Cueball: Perfect! [Caption below the frame:] Middle latitudes are the worst.

Mercator Projection

Mercator Projection

https://www.xkcd.com/2082

https://www.explainxkcd.com/wiki/index.php/2082:_Mercator_Projection

[Cueball is holding a hand up as he talks to White Hat.] Cueball: Did you know Canada is actually a smallish island in Lake Ontario? White Hat: What? Cueball: Yeah, it only appears to have a land border with the U.S. due to the Mercator Projection. White Hat: Wow! I had no idea. [Caption below the frame:] At this point people feel so misled by the Mercator Projection that you can use it to convince them of basically any map fact.

The Mercator projection is a map projection (a way to present the spherical Earth surface into a flat 2-D map) presented by Flemish cartographer Gerardus Mercator in 1569. It was the standard map projection for some time, because it does preserve all angles in their true shape (i.e. it is a conformal map projection ). This means that if you measure an angle on the map you get the right direction in the real world - a very useful feature if you're using the map for navigating. However, preserving the angle leads to severe distortions of the surface area, especially in the higher latitudes where countries appear much larger than they actually are. For example on the Mercator Projection, Greenland (the largest non-continent island in the world) is shown to be much larger than Australia (the smallest continent), although the latter in reality is nearly 4 times as big. Other examples of regions having distorted sizes and shapes due to the Mercator Projection can be explored in this link . Cueball uses White Hat's mistrust of the Mercator projection to convince him of ridiculous facts about Canada, namely that it is simply a small island in Lake Ontario . Map projections are generally continuous functions , meaning that they never map a disconnected space onto a connected one and therefore can never give the false impression that two areas that don't border each other do. The title text continues on these falsehoods, claiming that the Great Lakes are simply "water on the far side of Canada Island", and that it is possible to drive directly into Alaska from the Pacific Northwest region of the US (it's not, Canada is in the way). Cueball can possibly make these statements as Canada is a country in the northern regions, where the Mercator Projection would show it larger than it actually is. However, Canada is the second largest country in the world by total area (land and water), after Russia. The Mercator Projection was previously mentioned in 977: Map Projections of "what your favorite map projection says about you". People who preferred the Mercator Projection was listed as "You're not really into maps." It is also the second comic in a row that relates somehow to latitudes. Bad Map Projections is a series in xkcd, showing that it is really something on Randall's mind. It is not the first time Cueball (or Randall) tries to spread misinformation, for instance it also has White Hat as the target in 1677: Contrails , but it can also be other people that are fooled like in 1405: Meteor . [Cueball is holding a hand up as he talks to White Hat.] Cueball: Did you know Canada is actually a smallish island in Lake Ontario? White Hat: What? Cueball: Yeah, it only appears to have a land border with the U.S. due to the Mercator Projection. White Hat: Wow! I had no idea. [Caption below the frame:] At this point people feel so misled by the Mercator Projection that you can use it to convince them of basically any map fact.

Laptop Issues

Laptop Issues

https://www.xkcd.com/2083

https://www.explainxkcd.com/wiki/index.php/2083:_Laptop_Issues

[Cueball, carrying a laptop, is walking past a sign with a right-pointing arrow reading "Tech Support".] Off panel voice #1: Oh no. Off panel voice #2: What? Off panel voice #1: This guy. He has the worst tech problems. [Cueball standing at a tech support desk with an open laptop facing Hairy and Ponytail on the other side of the desk.] Cueball: My laptop's battery won't hold a charge. Hairy: We can replace it. Cueball: Tried that. Now the new ones won't either. [Close-up of Cueball gesturing with left hand] Cueball: Also, random files get corrupted on the first day of every month. Factory reset didn't help. Off panel voice: You weren't kidding. [Close-up of Cueball with right hand on chin, gesturing with left hand] Cueball: When it's plugged in, I get static shocks from my plumbing. Off panel voice: What the... Cueball: And it reboots if someone uses an arc welder nearby. [Same tableau as second panel except that the laptop is slightly closed now.] Cueball: Transitions® lenses go dark when exposed to the screen, and when I open too many tabs, it fogs nearby photographic film. Hairy: We don't usually do this, but I've gotten permission from my manager to have you and the laptop hurled into the ocean. Cueball: That's probably for the best.

Cueball goes to tech support with his laptop. Hairy and Ponytail are waiting behind the counter; one has dealt with Cueball's bizarre tech issues before, and warns the other. Sure enough, Cueball sets the computer down and offers a detailed list of the arcane problems his computer is giving him. "My laptop's battery won't hold a charge." A common problem; most laptops use lithium ion batteries due to their high power to weight ratio. Whilst the charge storage capacity of all batteries decreases over repeated charging and discharging cycles, lithium ion batteries are particularly prone to degradation over time. This is because charge is stored by lithium ions intercalated between layers of a 2D metal oxide material. When the battery is discharged the lithium ions move out of the metal oxide layers, allowing the material to contract, and it is this mechanical expansion and contraction of the material over repeated charging cycles that damages the battery, reducing storage capacity. However... "Tried [replacing the battery]. Now the new ones won't either." ...the problem persisting despite the battery's replacement fails to make any significant sense. It may be a problem with his laptop's charging port, but his comment that the "new ones" now fail to hold a charge seems to imply it is persisting despite the replacement batteries being used elsewhere after attempting to use them for his laptop and failing... Many modern batteries have firmware built in now that reports their charge level. It is possible that his laptop is installing a faulty firmware to any batteries that get connected. Alternatively, an electrical fault within the laptop may be shorting the battery, leading to high currents which damage the battery. "Also, random files get corrupted on the first of every month." Some devices may be scheduled to do a " disk cleanup " on the first of every month. Somehow, this task is corrupting files that should be kept. "Factory reset didn't help." A factory reset of a device deletes all files, undoes all customizations, and generally puts the system back to square one. Under normal circumstances, this is an effective last-resort measure for dealing with glitches, viruses, and malware, so the fact that it doesn't offer any help suggests that the device's factory settings were already corrupt when they were first made or that the problem is hardware-related, although the typical hardware issues would tend to occur at random times and not be dependent on the calendar. External factors are likely here, such as visiting somewhere highly magnetic monthly. That or the people who coded the factory reset made improper assumptions about what is unchangeable and should not be checked; most Android factory resets won't fix a botched rooting, for instance, because low-level binary executables shouldn't need resetting, right? Nobody should be able to knacker that deep (although Cueball apparently just did). "When it's plugged in, I get static shocks from my plumbing." Static discharge from a portable device while it's charging is common. Static charge on other items in the building is not. However, plumbing systems on older houses were often used to provide a ground instead of using grounding rods, which are now the accepted norm. This could imply that Cueball's house is old, and for some reason his laptop is pumping a large amount of charge directly to ground. "And it reboots if someone uses an arc welder nearby." The high power draw of an arc welder will occasionally cause less devoted power supplies to flicker. Coupled with the bad battery that cannot keep the computer running when the power dips, this might cause his laptop to reboot. This could also be just because the arc welder is causing a large amount of electromagnetic interference. "Transitions® lenses go dark when exposed to the screen," Photochromic lenses (commonly known by the brand name Transitions® lenses) in prescription glasses darken when exposed directly to UV rays; this is to avoid the wearer any hassle of needing prescription sunglasses . This seems to indicate that the screen of Cueball's laptop is emitting UV radiation. Whilst Cathode-ray tube (CRT) monitors can emit small amounts of UV light and X-rays, most laptops use either Liquid-crystal or OLED displays which do not emit significant amounts of UV-light, and would not be expected to cause photochromic lenses to darken. Most displays would also be expected to contain a filter to block any harmful UV-light from damaging the eyes of the user. Since UV-light is very damaging to the eyes, a screen that emits sufficient UV-light to darken sunglasses would be hazardous to look at. "and when I open too many tabs, it fogs nearby photographic film." Photographic film used in old analogue (not digital) cameras contains light-sensitive chemicals which change from transparent to opaque when exposed to light. The photographic film ' negatives ' are then printed onto paper, inverting the colors (i.e. areas that appear dark on the film appear bright on the print, as they do in real life). If photographic film is exposed to light, either intentionally or unintentionally (such as by accidentally opening the back of the camera whilst the film is unwound) then the film will become over-exposed, leading to a bright 'fog' that obscures the image. Fogging can also occur as a result of chemical degradation of the film or by exposure to radiation sources including X-rays. In order to cause fogging, the screen would have to be emitting X-rays that can pass through the film's container and expose the film. It is unclear why this should only occur when too many tabs are opened. Combined with the previous statement this indicates that a worrying range of light being emitted by the screen. The sheer incongruity of everything Cueball has reported, in combination with past issues, leads Hairy to report that his manager has authorized Cueball and his laptop be thrown into the ocean. Cueball accepts this without objection. This is a reference to 1912: Thermostat , where Cueball has an issue with his thermostat, and the Tech support employee asks him if he has tried walking into the sea. It seems this suggestion has evolved into forcefully throwing him into the sea, for lack of a better idea. It could also be that this is a reference back to the first of the series of comics on Cueball's many computer problems , 349: Success , where he ended up in the ocean. Alternatively, it seems very similar to the account of Jonah in the Bible, who was thrown overboard into the ocean during a violent storm after which the storm ceased. The title text contains mention of the Environmental Protection Agency (EPA), a part of the United States government responsible for preventing pollution. In real life, most of a laptop computer's components are considered toxic waste, and the EPA, as part of their mission, would not want it dumped in the ocean. More to the point, it's implied that whatever Cueball did to it renders it far more dangerous than an ordinary laptop, and the EPA really doesn't want his cursed possessions in the ocean; thus they are sending a hazmat team to collect the laptop and safely dispose of it. However, in the comic, the EPA do not seem to be bothered with Cueball himself being thrown into the ocean. [Cueball, carrying a laptop, is walking past a sign with a right-pointing arrow reading "Tech Support".] Off panel voice #1: Oh no. Off panel voice #2: What? Off panel voice #1: This guy. He has the worst tech problems. [Cueball standing at a tech support desk with an open laptop facing Hairy and Ponytail on the other side of the desk.] Cueball: My laptop's battery won't hold a charge. Hairy: We can replace it. Cueball: Tried that. Now the new ones won't either. [Close-up of Cueball gesturing with left hand] Cueball: Also, random files get corrupted on the first day of every month. Factory reset didn't help. Off panel voice: You weren't kidding. [Close-up of Cueball with right hand on chin, gesturing with left hand] Cueball: When it's plugged in, I get static shocks from my plumbing. Off panel voice: What the... Cueball: And it reboots if someone uses an arc welder nearby. [Same tableau as second panel except that the laptop is slightly closed now.] Cueball: Transitions® lenses go dark when exposed to the screen, and when I open too many tabs, it fogs nearby photographic film. Hairy: We don't usually do this, but I've gotten permission from my manager to have you and the laptop hurled into the ocean. Cueball: That's probably for the best.

FDR

FDR

https://www.xkcd.com/2084

https://www.explainxkcd.com/wiki/index.php/2084:_FDR

[Close-up of a form. Each field has a label (the first is assumed) and a handwritten entry. The name and country are each half visible. The numeral "4" has been only partially written before being scratched out.] [ NAME ] Randall Munroe DATE Dec 7, 194 12, 2018 COUNTRY United States [Caption below the frame:] FDR was so good at speeches that I spend a whole month each year writing the date wrong.

The United States Naval base at Pearl Harbor, Hawaii was attacked in 1941 , and is credited with starting the United States' involvement in World War II. The then US president, Franklin D. Roosevelt (FDR), issued a speech to the American people which begins with the line "Yesterday, December 7th, 1941, a date which will live in infamy... ". Whenever Randall writes "December" he feels compelled to complete the line, a mistake which is visible in this comic. This may be a parody of a more common type of error in which people writing dates during January (particularly early in the month) accidentally write the previous year instead of the current one because the previous year number is an established pattern while the new one is a recent change. The title text confuses the date of the northern hemisphere summer solstice (June 21st) with the date of the 365 Crete earthquake that happened on July 21st 365AD. The earthquake had a magnitude of at least 8.0 which caused widespread destruction across the Eastern Mediterranean. Then it mentions Guy Fawkes Night , the anniversary of the famous failed attempt to bomb Parliament on the night of November 5th, 1605. The latter event is immortalized in the rhyme "remember remember, the fifth of November, the gunpowder, treason, and plot", the former event less so. Randall also may be suggesting that Roosevelt implied the degree of "infamy" of an event can be measured by how long its date is remembered. Pearl Harbor resulted in 2,458 deaths and obviously extensive damage to a military base and fleet. It has been remembered 77 years, thus far. The earth quake of 365AD resulted in an estimated 230,000 killed and numerous cities severely damaged or destroyed. Randall states it was remembered for a few centuries. The Gunpowder Plot resulted in the death of a couple of conspirators and no notable damage. It has been remembered, at least in song, for "over 400 years". [Close-up of a form. Each field has a label (the first is assumed) and a handwritten entry. The name and country are each half visible. The numeral "4" has been only partially written before being scratched out.] [ NAME ] Randall Munroe DATE Dec 7, 194 12, 2018 COUNTRY United States [Caption below the frame:] FDR was so good at speeches that I spend a whole month each year writing the date wrong.

arXiv

arXiv

https://www.xkcd.com/2085

https://www.explainxkcd.com/wiki/index.php/2085:_arXiv

[Megan and Ponytail are standing together. Megan is talking to Ponytail.] Megan: Wait, all the papers in your field are posted as free PDFs on arXiv? That must be killing big science journals, since they charge such huge subscription/publication fees. [Ponytail responds with her arms wide, palms up.] Ponytail: Nah, we’ve been doing it since the 90s and nobody seems to care. [Megan contemplates, speechless.] [Megan slightly raises her arms and Ponytail puts up a hand to shush her.] Megan: That makes no sense at all!! Ponytail: Shhh, you’ll jinx it!

arXiv is a free online repository of electronic preprints of scientific papers in various fields, particularly in physics, math, and computer science. Scientists typically publish "preprint" versions of journal articles to arXiv, which are free to publish to and read. In this comic Megan remarks that academic journals must have a hard time getting by since their primary revenue is from researchers who pay to publish articles and readers who pay for subscriptions. Her remark seems to assume that arXiv must be a recent development, perhaps similar to the Sci-Hub project which began in 2011. However, Ponytail informs her that the arXiv project has been around since the 1990s (1991 to be exact). After a panel of Megan looking contemplative, she remarks that that does not make sense at all. After all, why would publishing companies be able to make money from something that is free online? Ponytail tries to stop her from freaking out, so that her outrage does not inform others about the current arrangement and thus ruin the system. She uses the term " jinx ", which in common usage means to affect negatively by speaking about, to imply that this system is one that could break down if discussed. Ponytail expressing confusion about the continued existence of scientific journals previously happened in 2025: Peer Review . The title text refers to another project that is invaluable for internet research, the Internet Archive ( link to it here ). Internet Archive is a public archive of information, including public domain books and music. Internet Archive runs the Wayback Machine , an archive of backups of web pages all over the Web at various times that can be used to see past versions of a page, even if that site has since shut down. Internet Archive accepts submissions of any type of information, including new backups of web pages and newly-made public domain content. The title text argues that these two projects are so useful, yet make so little economic sense, that, if they did not exist, we would dismiss them as ideas that would never be viable. In addition, as "arXiv" is intended to be pronounced the same as "archive", both sites have URLs with a common pronunciation. [Megan and Ponytail are standing together. Megan is talking to Ponytail.] Megan: Wait, all the papers in your field are posted as free PDFs on arXiv? That must be killing big science journals, since they charge such huge subscription/publication fees. [Ponytail responds with her arms wide, palms up.] Ponytail: Nah, we’ve been doing it since the 90s and nobody seems to care. [Megan contemplates, speechless.] [Megan slightly raises her arms and Ponytail puts up a hand to shush her.] Megan: That makes no sense at all!! Ponytail: Shhh, you’ll jinx it!

History Department

History Department

https://www.xkcd.com/2086

https://www.explainxkcd.com/wiki/index.php/2086:_History_Department

[Ponytail is standing behind a lectern holding a hand up indicating the presentation screen next to her with a list of time periods. The screen has a string ending in ring, attached to it, to pull it down.] Ponytail: 2018 was a productive year for the history department - we were able to fully analyze over four months of history. Ponytail: Unfortunately, over that same period, an entire year of new history was produced. Ponytail: I'm afraid we're falling behind. [Presentation:] Studied November 1833 April 19-22, 1979 May 21-25, 585 BCE June-August 1848 May 16, 2001

In this comic Ponytail is a representative of the history department, which might be a department of a university or other organisation. She presents the year report of 2018. In this, she explains, the department has fully analyzed over four months of history. In the meantime, due to the passage of time, another year of history has been added to their workload (implied to be the year spanning between the current meeting and the previous one). This presents a cycle in which the department would only be able to keep up if they could analyze, within a one year period, more than or exactly one year of history. A department in a business, such as the finance department, is typically required to keep up with their own workload and complete an entire year's worth of workload every year. A business that fails to manage this minimum would almost certainly fail: bills would not get collected, invoices would not get paid, employees would not get paid, etc. A history department fails to follow this model in two very important ways. First, the subject of history cannot be fully processed. New discoveries change what we know about certain time periods. Even current events cannot be fully processed, as future events will cause historians to see connections in things not previously thought to be connected. Second, the standard model for history departments focuses on specific eras or specific subjects for the purpose of explaining the events to students. History departments do not process years, but instead process the subject so that it stays relevant to the understanding of the current student body. There are, however, long running historical projects that have suffered this very problem. An example is the Histoire littéraire de la France which began publication in 1733 with a volume covering up to the year 300. By 1995 over 40 volumes had been published, but the historical account had only reached the 14th century. The volumes for the 14th century had taken 130 years to produce. Although over the 250 years of the project publication had been proceeding faster than time elapsed, the proliferation of literary content following the dawn of printing in the 15th century is likely to cause the project to slip further into reverse. The title text further expands this problem by indicating the discovery of a new era of history that had previously gone un-analyzed, which would have added more undiscovered history than it removed. The 1750s decade is possibly a reference to the adoption of the Gregorian Calendar by the British Empire . Randall previously mentioned that history is huge in 1979: History . Events in the dates listed: June – The Serbians from Vojvodina start a rebellion against the Hungarian government. June 2–June 12 – The Prague Slavic Congress brings together members of the Pan-Slavism movement. June 17 – The Austrian army bombards Prague , and crushes a working class revolt. June 21 – Wallachian Revolution of 1848 : The Proclamation of Islaz is made public, and a Romanian revolutionary government led by Ion Heliade Rădulescu and Christian Tell is created. June 22 – The French government dissolves the national workshops in Paris, giving the workers the choice of joining the army or going to workshops in the provinces. The following day, the June Days Uprising begin in response. July – The Public Health Act establishes Boards of Health across England and Wales . July 5 – The Hungarian national revolutionary parliament starts to work. July 19 – Women's rights – Seneca Falls Convention : The 2-day Women's Rights Convention opens in Seneca Falls, New York and " Bloomers " are introduced at the feminist convention. July 26 – The Matale Rebellion breaks out, against British rule in Sri Lanka . July 29 – Young Irelander Rebellion : A nationalist revolt in County Tipperary , against British rule, is put down by the Irish Constabulary . August 6 – HMS Daedalus reports a sighting of a sea serpent. August 14 – American President James K. Polk annexes the Oregon Country , and renames it the Oregon Territory as part of the United States. August 17 – Yucatán officially unites with Mexico. August 24 – The U.S. barque Ocean Monarch is burnt out off the Great Orme , North Wales , with the loss of 178, chiefly emigrants. August 28 – Mathieu Luis becomes the first black member to join the French Parliament , as a representative of Guadeloupe . [Ponytail is standing behind a lectern holding a hand up indicating the presentation screen next to her with a list of time periods. The screen has a string ending in ring, attached to it, to pull it down.] Ponytail: 2018 was a productive year for the history department - we were able to fully analyze over four months of history. Ponytail: Unfortunately, over that same period, an entire year of new history was produced. Ponytail: I'm afraid we're falling behind. [Presentation:] Studied November 1833 April 19-22, 1979 May 21-25, 585 BCE June-August 1848 May 16, 2001

Rocket Launch

Rocket Launch

https://www.xkcd.com/2087

https://www.explainxkcd.com/wiki/index.php/2087:_Rocket_Launch

[The major stages of a rocket launch are shown, with the rocket trajectory indicated by dotted lines. Each stage is annotated with a description and an arrow. A title above the image reads 'Outline of a typical rocket launch'.] [A rocket with two boosters is shown at the bottom left hand corner of the image taking off from a launch pad on the ground, surrounded by clouds of smoke.] Liftoff [The rocket ascends vertically] Max-Q: Peak aerodynamic stress [Separation of the two external booster rockets is shown, with the main rocket continuing to ascend vertically with a slight rightward tilt and the two boosters curving off to the right.] Booster separation [The main rocket stage starts to curve over to the right.] Max-CB: Highest chance of collision with care bears [Separation of the second rocket stage. Main rocket heads right, whilst second booster stage curves downward to meet trajectory of first booster stages.] Main stage separation [Main rocket continues towards the right.] GPS silenced so it will stop saying "make a U-turn" [First and second stage booster rocket trajectories meet and become a single trajectory heading upwards and right.] Reunification [Trajectory of main rocket wobbles slightly.] Pilot panics, copilot takes command after struggle [Booster stage rockets continue to head upwards and right towards the main rocket trajectory.] Pursuit phase [Main rocket and booster stage trajectories meet and cross three times.] Inter-stage dogfight [The trajectory for one of the stages ends in an explosion.] [The remaining trajectory, indicated with dashed-lines and question marks, continues towards the right and off the edge of the page.] Winner proceeds to space

This comic was posted on a week with a notably high number of rocket launches . Originally, there were to be four orbital rocket launches from the United States on December 19, 2018 (the publish date for the comic), which would have tied with the prior record for number of orbital rocket launches in one day. While these launches were ultimately delayed, breaking the event, the comic was doubtless under production by then. Only some of the steps listed are actually typical. Liftoff The traditional start of a launch, when the rocket leaves the ground. The engines will typically have been ignited a short time before, often one-by-one in a specifically engineered sequence to reduce shock stress on the rocket, but need to throttle up to produce enough thrust to overcome the rocket's weight. Some launch pad configurations physically restrain the rocket (at least to some degree) until the engines are known to produce the required thrust then the rocket is released (e.g. by pyrotechnically crushing restraining bolts such as in NASA Space Shuttle configuration, or by hydraulic actuators opening a sturdy "clamp", such as in SpaceX Falcon 9 configuration). "Liftoff" refers to the moment this happens, making the rocket lift off the ground. Max-Q : Peak aerodynamic stress. A rocket accelerates from the moment it leaves the ground. The faster a rocket goes, the bigger volume of air it pushes through per second - but the higher a rocket goes, the thinner the air. (Before liftoff, the rocket is not moving, and thus is not pushing through air. Once in orbit, there is essentially no air to push through, so the rocket is not pushing through air. Between those two times, the rocket is pushing through some amount of air, the exact amount increasing before Max Q and decreasing after Max Q.) "Max Q" is the moment where these two factors produce a maximum, and is the point where the rocket's structure must withstand the most air pushing back against it. Booster separation Rockets are designed in stages , so they do not have to carry the empty fuel tanks all the way to orbit. (Carrying any mass to orbit is expensive, so the more that can be dropped off earlier, the better.) Two or three stages are typical. "Booster separation" marks the point where the first of these stages (the " booster "), its fuel expended, is typically ejected. Max-CB: Highest chance of collision with Care Bears . This is entirely fictitious. Care Bears are fictitious characters, which have a toy line, television series, and movies. The existence of a basketball sneaker named the "Nike Air Force Max CB" may or may not be relevant. Main stage separation See "booster separation" above. This marks the point where the second stage (the "main stage") is ejected. GPS silenced so it will stop saying "Make a U-turn" Again, this is fictional. While some rockets do make use of signals from the Global Positioning System ("GPS"), no rockets are known to use the navigational devices that incorporate GPS readers and street maps, providing directions - often with optional text-to-speech - along the Earth's surface. Some such devices are notorious for getting confused in extreme situations (such as the high Mach numbers that rockets achieve); constantly uttering "make a U-turn" would be one such confusion, and any device in such a confused state might well be silenced for being more annoying than helpful. Navigation of this nature is neither necessary nor useful on a rocket, which will have its entire route from ground to orbit computed before launch, and piloting typically left entirely to computers given the precise timing required. Reunification (of boosters) Another fictional step. Discarded stages fall back into the Earth's atmosphere, either hitting the ground (or, more often, water) or burning up because of the heat-up resulting from high compression of air in front of them while re-entering thick layers of atmosphere at extreme speed. The booster and main stage would not be on a course to come anywhere near each other, and would not have enough fuel to change their course (running out of fuel being why they were discarded in the first place). Even if they did, landing for reuse (as SpaceX has attempted , often successfully) would be far more likely than a mid-air reunion. Pilot panics, copilot takes command after struggle Another fictional step. Astronauts are not the sort of people who panic easily, nor struggle with their crewmates. More importantly, in any modern rocket the "pilot" is not a human being, but a computer incapable of panic [ citation needed ] (as in the human emotion). It is possible that part of the flight computer could fail, causing redundant failsafes to take over, but the process could not correctly be described as a "struggle", and in any case this sort of failure is uncommon enough that it is not part of a "typical" rocket launch. Pursuit phase Fictional. This assumes the (nonexistent) reunified booster would have enough fuel to pursue the top stage of the rocket, and a reason to do so. See "Reunification". This might be a reference to Pursuit guidance . The comic indicates that a fight ensues with only one of the pair continuing to orbit. Inter-stage dogfight Fictional. See "Pursuit phase". A dogfight is an aerial battle between fighter aircraft, conducted at close range. This step claims that the rocket booster and the top stage of the rocket engage in a battle. Winner proceeds to space Fictional. As noted above, in a real rocket launch there is no dogfight of which there can be a "winner". A careful reading would note that the bottom stage "wins" by default; in contrast, in a real (orbital) rocket launch, the top stage typically proceeds to space. The title text refers once again to the Care Bears franchise. The Care Bears live in a castle made of clouds, called Care-a-Lot Castle , so the comic claims that NASA aims to avoid launching into their castle, but sometimes cannot avoid hitting "stray" Care Bears. That being said, the point about the strike has a basis in truth; at the speeds a rocket moves, impact with something roughly the size and weight of a human (or a Care Bear) has the potential to be catastrophic. If something should threaten to connect with the rocket, the best that the humans involved can do is hope for a glancing blow with a part of the rocket sturdy enough to endure the impact. [The major stages of a rocket launch are shown, with the rocket trajectory indicated by dotted lines. Each stage is annotated with a description and an arrow. A title above the image reads 'Outline of a typical rocket launch'.] [A rocket with two boosters is shown at the bottom left hand corner of the image taking off from a launch pad on the ground, surrounded by clouds of smoke.] Liftoff [The rocket ascends vertically] Max-Q: Peak aerodynamic stress [Separation of the two external booster rockets is shown, with the main rocket continuing to ascend vertically with a slight rightward tilt and the two boosters curving off to the right.] Booster separation [The main rocket stage starts to curve over to the right.] Max-CB: Highest chance of collision with care bears [Separation of the second rocket stage. Main rocket heads right, whilst second booster stage curves downward to meet trajectory of first booster stages.] Main stage separation [Main rocket continues towards the right.] GPS silenced so it will stop saying "make a U-turn" [First and second stage booster rocket trajectories meet and become a single trajectory heading upwards and right.] Reunification [Trajectory of main rocket wobbles slightly.] Pilot panics, copilot takes command after struggle [Booster stage rockets continue to head upwards and right towards the main rocket trajectory.] Pursuit phase [Main rocket and booster stage trajectories meet and cross three times.] Inter-stage dogfight [The trajectory for one of the stages ends in an explosion.] [The remaining trajectory, indicated with dashed-lines and question marks, continues towards the right and off the edge of the page.] Winner proceeds to space

Schwarzschild's Cat

Schwarzschild's Cat

https://www.xkcd.com/2088

https://www.explainxkcd.com/wiki/index.php/2088:_Schwarzschild%27s_Cat

[A graph is shown. The x-axis is labeled "Cat size" and the y-axis, "Cat cuteness". Parallel to and a short distance from the y axis is a dashed line the same length as the y-axis line, representing a vertical asymptote; the space between the y axis and the dashed line is labelled "Critical Limit". Graphed is a function coming down from infinity, starting close to the dashed line; it then levels off and does not reach zero on-screen. At the top end of the graph is the text "Schwarzschild's Cat" and an arrow pointing upwards outside of the graph.]

This comic is primarily a wordplay joke about the Schwarzschild radius , or the distance from a black hole corresponding to the event horizon .The Schwarzschild radius for a given body is the limit to which a given mass can be shrunk down before it becomes a black hole - the Schwarzschild radius also represents the event horizon of this newly-created black hole. The event horizon, in turn, is the limit from which nothing can leave a black hole; not even light. The joke is that, apparently, smaller cats are cuter, and there is a limit below which a sufficiently small cat (but larger than zero) will approach infinite cuteness, in a similar pattern to the way time's rate for an observer will approach infinity, the closer they get to the event horizon of a black hole. It's also an oblique reference to the Schrödinger's cat thought-experiment, since the names (Erwin) "Schrödinger" and (Karl) "Schwarzschild" are somewhat similar and both men were early 20th-century physicists who exchanged ideas with Albert Einstein. However, the actual comic doesn't bring up quantum superposition . The title text makes two allusions. First, it alludes to what happens when an object falls into a black hole. From an outside observer's point of view, such objects appear to slow down and take an infinite amount of time to cross the event horizon due to the time dilation of General relativity . The object's photons become increasingly red-shifted, fading as they lose energy to the black hole's gravity well. The scientific consensus suggests that from the falling object's point of view, it should continue to experience time and cross the Schwarzschild radius, but that event is unobservable from the outside (hence the term "event horizon"). Second, the title text is a play on the Cheshire Cat from Alice in Wonderland, which slowly fades from view until only its grin remains. Randall previously discussed the superiority of tiny mammals in 1682: Bun , and drew graphs relating to the perceived cuteness of cats in 231: Cat Proximity . [A graph is shown. The x-axis is labeled "Cat size" and the y-axis, "Cat cuteness". Parallel to and a short distance from the y axis is a dashed line the same length as the y-axis line, representing a vertical asymptote; the space between the y axis and the dashed line is labelled "Critical Limit". Graphed is a function coming down from infinity, starting close to the dashed line; it then levels off and does not reach zero on-screen. At the top end of the graph is the text "Schwarzschild's Cat" and an arrow pointing upwards outside of the graph.]

Christmas Eve Eve

Christmas Eve Eve

https://www.xkcd.com/2089

https://www.explainxkcd.com/wiki/index.php/2089:_Christmas_Eve_Eve

[Cueball with his arms out is talking with White Hat and Megan. In Cueball's long last remark the letters get smaller from line to line.] Cueball: Today is Christmas Eve. Yesterday was Christmas Eve Eve. Megan: Uh huh... Cueball: Of course, tomorrow is Christmas. And then, my favorite... Megan: Oh no. Cueball: ...Christmas Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve! Megan: I'm returning the presents I got you. 11 14 14 14 15 16 17 17 18 20 21 22 24 25 27 30 32 27 364 total! The first line also has Christmas along with the 11 eves, and do take up more space than the 14 eves below. The last line is only partially filled, with 4 eves from the line above on each side (so room for more than 35, probably 40, eves in one line with that font size.) The first three lines with 14 eves becomes clearly shorter, before more is added almost in every line after this, except two lines with 17 each.

This year's Christmas comic was posted on December 24, 2018, the Christmas Eve of 2018. The evening or day preceding a special day such as a holiday is often referred to as the eve of that day (derived from the same word from which we get evening ). Thus December 24 is Christmas Eve. Some people extend this and call December 23 "Christmas Eve Eve," as Christmas Eve is itself a noted holiday. The day before that would be "Christmas Eve Eve Eve," adding one "Eve" for each night before Christmas morning, although the increasing extension leads to each additional "Eve" being continuously less common. Cueball notes the general idea, and Megan acknowledges it. Cueball follows by naming December 24 as Christmas Eve, December 25 as Christmas, and then mentions that the following day is his favorite. Megan's "Oh no" implies that she knows what Cueball will say next. Since December 26 is the 364th day before Christmas (when the following year is not a leap year, which was correct in 2018 when the comic was released), it follows that it is "Christmas" followed by "Eve" 364 times. Megan finds listening to Cueball recite this unacceptable. As such, she announces that she will not give him gifts, taking the extra step of returning the gifts she'd already bought. As Christmas presents in America are first handed out on Christmas Day's morning (unless the giver and recipient are aware in advance they will be unable to meet in person on that day; Megan's presence on Christmas Eve indicates this is not a threat), she has not given it to him yet. The title text refers to the Boxing Day holiday celebrated the day after Christmas in the UK and many parts of the former British Empire. Although the exact origin of the name is unknown, it is believed to be in reference to the Alms Box placed in areas of worship to collect donations to the poor, which was then opened right after Christmas. Most Americans don't know this and make jokes about how it refers to the sport of boxing . In this title text we can presume Cueball was punched (or boxed ) after his litany of 364 Eve s, to which he replies, "Oh, so that's why they call it Boxing Day." As this is a pun of groan-inducing triviality, he receives another punch . [Cueball with his arms out is talking with White Hat and Megan. In Cueball's long last remark the letters get smaller from line to line.] Cueball: Today is Christmas Eve. Yesterday was Christmas Eve Eve. Megan: Uh huh... Cueball: Of course, tomorrow is Christmas. And then, my favorite... Megan: Oh no. Cueball: ...Christmas Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve Eve! Megan: I'm returning the presents I got you. 11 14 14 14 15 16 17 17 18 20 21 22 24 25 27 30 32 27 364 total! The first line also has Christmas along with the 11 eves, and do take up more space than the 14 eves below. The last line is only partially filled, with 4 eves from the line above on each side (so room for more than 35, probably 40, eves in one line with that font size.) The first three lines with 14 eves becomes clearly shorter, before more is added almost in every line after this, except two lines with 17 each.

Feathered Dinosaur Venn Diagram

Feathered Dinosaur Venn Diagram

https://www.xkcd.com/2090

https://www.explainxkcd.com/wiki/index.php/2090:_Feathered_Dinosaur_Venn_Diagram

[The comic shows a rectangular panel containing two circles, side by side and not intersecting. A caption is underneath each circle.] [Left circle caption:] People Who Don't Think Feathered Dinosaurs Sound Scary [Right circle caption:] People Who Have Tried To Fight An Ostrich

Translated plainly, this comic reads "People who don't think feathered dinosaurs sound scary have never tried to fight an ostrich." This comic is a jab at people who dismiss the idea feathered dinosaurs sound scary. Adding feathers to a reptile can trigger a cognitive dissonance; people today see feathers and think of harmless birds. However, the ostrich and a few other avian species, which are feathered dinosaurs ( 1211: Birds and Dinosaurs ) are in fact deadly. The diagram points out that anyone who has tried to fight an ostrich would be scared of a dinosaur with feathers, and anyone who thinks a feathered dinosaur doesn't sound scary has never tried to fight one. The two groups of people are exclusive because the two circles do not overlap. Ostriches are not typically considered scary or dangerous because its appearance is comical or awkward to most people; they are also herbivorous and not typically aggressive, choosing to use its great speed to outrun predators rather than fight them. In reality, however, ostriches are much larger than a human and will attack when cornered or when their family is threatened; their powerful legs can kick hard enough to kill lions and other predators, and their feet are equipped with large claws which can disembowel a human. Thus, the actual experience of fighting an ostrich would quickly convince any human that survives the experience that ostriches (and by extension other feathered dinosaurs) are, in fact, scary. The title text refers to " Volunteer Boy ", a kid in the beginning of Jurassic Park who dismisses a raptor fossil as a "six-foot turkey". Dr. Grant uses a fossil of a raptor talon to imply that a raptor would slice open his belly and eat him while he's still alive. This scares the kid into respecting the raptor. The title text theorizes that if he didn't get that pep talk, and continued to think of dinosaurs as "six-foot turkeys", then he would grow up to make some of the contested sequels in the franchise. Raptors play a central role throughout the series of movies, with some even being trained by a raptor handler like dogs. Technically , the diagram is an Euler diagram , rather than a Venn diagram . A Venn diagram shows all possible combinations of two or more sets, including those with no elements, and so all of the regions must intersect in all possible combinations. An Euler diagram only depicts the non-empty combinations, and therefore does not have this constraint. However, this is a technicality, and many people use the words interchangeably. [The comic shows a rectangular panel containing two circles, side by side and not intersecting. A caption is underneath each circle.] [Left circle caption:] People Who Don't Think Feathered Dinosaurs Sound Scary [Right circle caption:] People Who Have Tried To Fight An Ostrich

Million, Billion, Trillion

Million, Billion, Trillion

https://www.xkcd.com/2091

https://www.explainxkcd.com/wiki/index.php/2091:_Million,_Billion,_Trillion

[A graph with Y-axis labeled “Perceived size of number” and X-axis labeled “Actual size of number (log scale)”.] [The line graph shows points that are labeled with the following numbers from “1 million” to “100 trillion”:] [ Points on graph: ] 1 million [ (2, 1.5) ] 10 million [ (3, 3.5) ] 100 million [ (4, 4.8) ] 1 billion [ (5, 2.8) ] 10 billion [ (6, 4.4) ] 100 billion [ (7, 5.3) ] 1 trillion [ (8, 4.3) ] 10 trillion [ (9, 5.1) ] 100 trillion [ (10, 5.6) ] [The perceived size increases between most numbers, but decreases between 100 million and 1 billion, and between 100 billion and 1 trillion. The decreases are shown as dashed lines labeled “?”, in contrast to the solid unlabeled lines between the increases. The increases and decreases in perceived size become smaller as the numbers grow in actual size.] [Caption below the panel:] Talking about large numbers is hard

Much like comic 558 , this comic addresses the difficulty ordinary people have with large numbers. Though most if not all people intuitively understand the difference between one object and two objects, or one object and ten objects, or even one object and a hundred objects, as numbers increase most people's ability to innately conceive of the numbers being discussed decreases remarkably quickly. When numbers reach the millions and the billions, and especially the trillions, most people don't truly process the numbers at all, and instead conceive of them as some version of a drastically-oversimplified concept such as "very big." Where comparing one to ten is simple, comparing "very big" to a different "very big" can prove extremely challenging, and will certainly require non-intuitive, conscious thinking. The comic represents this challenge by providing a graph which represents Randall 's intuitive conception of the values of various very large numbers, and said conception's misalignment with reality. Though some trends reflect the real value of the numbers on the graph, i.e. 100 million larger than 10 million larger than 1 million and 1 billion larger than 1 million, the curve is far from the linear (exponential on the log-scaled axes) path it should take, with 1 billion being intuitively understood as less than 100 million, based, presumably, on the fact, easily comprehended on an intuitive level, that 100 is larger than 1 , and therefore the presence of 100 in 100 million places it at a higher value than the 1 in 1 billion would place the latter. In reality, of course, 1 billion is ten times larger than 100 million, but the comic deals not with actual reality, but with the perception of reality of these numbers before conscious thought is applied . The most interesting parts of the graph, and the parts where the disconnect between intuition and reality becomes clearest, are the dashed sections labeled with question marks, the one between 100 million and 1 billion, the other between 100 billion and 1 trillion. Here two competing intuitive understandings compete for dominance. On the one hand, the intuitive understanding described above, with 100 trumping 1, would see the curve taking a sharp downturn. On the other hand, the path from 100 million to 1 billion is paved with such numbers as 500 million, 700 million, and 900 million, all of which would theoretically be seen intuitively as larger than 100 million, thanks to the fact that 9 is greater than 7, and 7 greater than 5, and so on, bending the curve up rather than down. These two conflicting intuitions leave Randall with no single intuitive path for the two dashed sections, leading to their dashed and questioned state. The comic's caption and title highlight another problem surrounding the intuitive grasping of large numbers: the flaws in the English words used for them. For instance, nothing about the word "million" suggests smallness relative to the word "billion" on an intuitive scale. This unintuitive language contributes greatly to the "100 trumps 1" intuitive fallacy described above. The title text references a highly relevant disconnect between the long and short scales of large numbers . For all English speakers, and for most languages, 1 million constitutes 1,000 thousands, or, less ambiguously, 10^6. However, this is the last of the consensus numbers, and the definition of what should be the "next step" varies depending on how each country's language evolved. In other words, 1 billion objects in a country using the short-scale would be 1,000 million objects in a country using the long-scale; at the "next step", 1 trillion in the short-scale would be named 1 billion in the long-scale, despite the fact that the number of objects has remained the same. This difference between languages using the short-scale and the long-scale often causes confusion when translating articles with large numbers in them, as translators sometimes fail to change between short-scale and long-scale schemes, wrongly translating large numbers to incorrect values. The fact that such a staggering difference of terminology was able to exist and be almost completely unknown to many supports Randall's point about the failure of human intuition in the discussion of extremely large numbers. [A graph with Y-axis labeled “Perceived size of number” and X-axis labeled “Actual size of number (log scale)”.] [The line graph shows points that are labeled with the following numbers from “1 million” to “100 trillion”:] [ Points on graph: ] 1 million [ (2, 1.5) ] 10 million [ (3, 3.5) ] 100 million [ (4, 4.8) ] 1 billion [ (5, 2.8) ] 10 billion [ (6, 4.4) ] 100 billion [ (7, 5.3) ] 1 trillion [ (8, 4.3) ] 10 trillion [ (9, 5.1) ] 100 trillion [ (10, 5.6) ] [The perceived size increases between most numbers, but decreases between 100 million and 1 billion, and between 100 billion and 1 trillion. The decreases are shown as dashed lines labeled “?”, in contrast to the solid unlabeled lines between the increases. The increases and decreases in perceived size become smaller as the numbers grow in actual size.] [Caption below the panel:] Talking about large numbers is hard

Consensus New Year

Consensus New Year

https://www.xkcd.com/2092

https://www.explainxkcd.com/wiki/index.php/2092:_Consensus_New_Year

[A graph labeled “Percentage of the world's population living in 2019” with Y-axis markers at 0%, 50%, and 100%, and X-axis markers at 10:00 AM EST Dec 31st, 1:30 PM EST, 7:00 PM EST, Midnight EST, 3:00 AM EST Jan 1st, and 7:00 AM EST.] [The line graph shows the percentage increasing from 0 to 100% in several steps, with 50% reached at 1:30 PM EST.] [Caption below the panel:] Consensus New Year: as of 1:30PM Eastern Time (6:30PM UTC) a majority of the world's population will be living in 2019. Randall has mislabeled the leftmost point of the graph: the Earth's earliest time zone ( UTC+14:00 ) should have the midnight at 5:00 AM EST rather than 10:00 AM EST. The number of one-hour increments on the x-axis does not match Randall's label.

In this New Year comic , Randall is proposing a compromise for when to celebrate, or recognize, New Year's Day . These celebrations traditionally take place at the stroke of midnight between Dec. 31st and Jan. 1st, at the local time of the event's location. With "Consensus New Year", these celebrations would happen at the same time, world over, and would be at exactly 1:30 pm EST (6:30 pm UTC ). At this time, about half the world's population would be in 2018 local time and the other half would be in 2019. This is due to the various time zones throughout the world, and the graph is based on the proportion of the population in these zones. This is based on the assumption that the entire world uses the same calendar system. Randall's graph shows the year starting on the same day for the entire world. While the Gregorian calendar is used as the civil calendar in most countries of the world, the Eastern Orthodox churches uses the Julian calendar, on which the year will begin 13 days later, and the year (as of December 2018-January 2019) is 1440 on the Muslim calendar and 5779 on the Hebrew calendar. Other countries have the same New Year as the Gregorian calendar but count years differently; for example, 2019 is the year 108 in Taiwan and 2562 in Thailand. The Wiktionary entry for " consensus " includes multiple definitions, including these two meanings: In an attributive grammar structure, a noun is placed before another noun to assign an attribute to it. When "consensus" is used this way, it's a statistical term which means the average projected value of the modified noun. Randall properly uses this first definition for both the title of the comic and the graph itself, where the graph represents the average projected value of the percentage of the world population reaching the new year at any given time. Randall may be purposefully misusing the second definition of the word "consensus" to reflect the common misuse of the term consensus for the practice of majority vote . In scenarios involving group decision-making, consensus means that all or almost all members of the group will accept the decision. Depending on how it is done, this generally results in a slower decision-making process due to discussion, but decisions that many more people are happy with. Consensus can scale to large groups of people using approaches such as the spokescouncil model to speed dialogue. By this definition, Consensus New Year happens at one of the last four time zones as the last to "agree" enter 2019, so (nearly full consensus definition) 4:00 am, 5:00 am, 6:00 am, or (full consensus definition) 7:00 am EST on January 1, 2019. Consensus lies in contrast to majority vote, where a decision passes when over 50% of the people desire it. Majority vote is used in most current large democracies and is what most people are familiar with. It is quick to describe and implement, but can result in polarized political parties and a stark lack of minority rights, unless enough people develop concern for the issues that they are tempered with constitutions and logrolling . The leftmost horizontal axis label (10am EST Dec 31st) was an error. The point marked as 0% should be 5am EST (see table below). Additionally, some of the lines are shown with a slope, which is inaccurate. Since sun time is not used anywhere, a correct graph line would only consist of horizontal and vertical lines. [A graph labeled “Percentage of the world's population living in 2019” with Y-axis markers at 0%, 50%, and 100%, and X-axis markers at 10:00 AM EST Dec 31st, 1:30 PM EST, 7:00 PM EST, Midnight EST, 3:00 AM EST Jan 1st, and 7:00 AM EST.] [The line graph shows the percentage increasing from 0 to 100% in several steps, with 50% reached at 1:30 PM EST.] [Caption below the panel:] Consensus New Year: as of 1:30PM Eastern Time (6:30PM UTC) a majority of the world's population will be living in 2019. Randall has mislabeled the leftmost point of the graph: the Earth's earliest time zone ( UTC+14:00 ) should have the midnight at 5:00 AM EST rather than 10:00 AM EST. The number of one-hour increments on the x-axis does not match Randall's label.

Reminders

Reminders

https://www.xkcd.com/2093

https://www.explainxkcd.com/wiki/index.php/2093:_Reminders

[Cueball at his desk using a laptop.] Laptop: You got this email six days ago. Do you want to follow up? Cueball: Oh, right, I should do that. [Cueball types on laptop.] *type type* Laptop: Did you forget the attachment? Cueball: Oops, yes. Laptop: Today is the recipient's birthday. Did you want to mention that? Cueball: Wait, it is? [Caption below the panel:] These reminders make me uncomfortable, not because computers are getting too smart, but because it reminds me how often I fall short of even baseline levels of conscientiousness.

In this comic, Cueball is using an email client program on a laptop, which is a popular tool for communicating by email with others. In recent years, many email clients have started implementing helpful warnings and reminders to catch common human mistakes and ease the process of communication. One such feature, demonstrated in this comic, is that many clients will now warn you if you've mentioned an attachment in your email but haven't actually attached anything, a common error people make when emailing. This has gotten to the point where email clients are increasingly stepping in to help with social obligations too; for example, reminding you if you've left an email unanswered for too long, or that someone is celebrating a birthday today and should be congratulated. With the increasing availability of social data and advances in machine learning, these features have the potential to become very sophisticated, to the point that they can effortlessly make social inferences and connections that might have slipped a human user's mind. Such features are meant to be helpful aids, but have led people to be worried about privacy issues, or about how "smart" technology is becoming. However, in this comic, Cueball (likely representing Randall himself) has come to the uncomfortable realization that technology is now easily surpassing his own ability to maintain social relationships with other people, by being more aware of his friends' social lives than he is. He is disturbed by how unwittingly unconscientious he has become. The title text suggests that the problem of keeping up a baseline level of interest in other people's lives eventually solves itself; implying, somewhat darkly, that if you don't put in even the bare minimum effort to keep up, you'll end up with fewer friends as some get annoyed by your lack of interest in their lives. [Cueball at his desk using a laptop.] Laptop: You got this email six days ago. Do you want to follow up? Cueball: Oh, right, I should do that. [Cueball types on laptop.] *type type* Laptop: Did you forget the attachment? Cueball: Oops, yes. Laptop: Today is the recipient's birthday. Did you want to mention that? Cueball: Wait, it is? [Caption below the panel:] These reminders make me uncomfortable, not because computers are getting too smart, but because it reminds me how often I fall short of even baseline levels of conscientiousness.

Short Selling

Short Selling

https://www.xkcd.com/2094

https://www.explainxkcd.com/wiki/index.php/2094:_Short_Selling

[Cueball and Ponytail are walking together, talking.] Cueball: I don't understand shorting stocks. Ponytail: It's like when you promise your firstborn to a witch for five magic beans. [Ponytail close up] Cueball (off-panel): Is that a common– Ponytail: She's a sucker, right? You know your awful kid will be worth one or two beans at best . [Ponytail and Cueball stopped, facing each other] Ponytail: But then it turns out you love your kid, a love worth 200 beans! You can't afford that loss! Ponytail: There's only one way out: Ponytail: You gotta fight the witch. [Ponytail and Cueball stopped, facing each other] Ponytail: So you send your kid up the beanstalk to battle the giant, who represents interest rates. Cueball: This analogy is getting less helpful by the minute. Ponytail: If only you'd somehow shorted my wisdom before you asked.

Shorting stocks (short selling stocks) is a stock market practice. If we think of normal investing where we buy into a stock as betting on the stock rising in value then shortselling is a corresponding betting on a stock to fall in value. This inverse procedure is accomplished by getting the stock on a loan or "front" basis to begin with, then selling the stock that isn't actually owned, so that when the stock loses value you're able to pay back a lower amount and keep the difference. We could say someone takes a risk because they believe that a certain stock's price is going to drop. The risk-taker borrows stock from someone, and then sells the stock that they've just borrowed, keeping the money from the sale. They then owe that stock to the lender. But the risk-taker believes that they will be able to buy the same stock back on the stockmarket later on at a lower price, and then give it to the lender to replace what they borrowed. If everything goes according to plan and the stock drops in price, the risk-taker will walk away with a profit. Of course, if things don't go according to plan and the stock rises in price instead, the risk-taker winds up losing money, because they have to buy back the stock for more than they sold it. Cueball asks Ponytail to explain shorting stocks. Ponytail starts out with a fairy tale story that falls apart almost before she even starts. The process of short selling a stock functions similarly to the initial parts of the story. The major steps in normal shorting are described here alongside the analogous (sort of) parts of the story: An investor decides that stock S is likely to decrease in value, and wants to make money from this difference. Stock S is currently selling for $5, but the investor believes it will drop in value to $1 or $2 in the near future. The person in the story is going to have a child, and believes that the child will be worth one or two magic beans. They have been offered a price of five beans for the child, and they see this as a benefit. The investor finds a person willing to allow them to borrow stock S now. This is usually done through a broker. The investor then sells the stock they borrowed, adding $5 to their account. They plan on waiting until stock S is selling for $1, then buying it again. They will have made $4 in profit, and can return the stock they borrowed. The parent in the story sells the rights to their child for five beans because their child is worth one or two beans to them, so they will end up making a profit of three or four beans. Stock S does not decrease in price, but increases dramatically to $200. The investor has promised to return the stock within a specific timeframe, and they must do this or they will be in violation of various laws and contracts. They can wait in the hopes that the value will drop again, but they will eventually have to buy the stock for the new price of $200. They will lose $195 on this transaction. The child is born, and the parent involved decides that they love the child. They would put a valuation of this child at two hundred magic beans, and would prefer not to turn the child over to the witch. They have no choice, however, as they have formerly agreed to do this. This part of the story somewhat matches the process of short selling a stock, except that there is a convenient market for buying and selling stocks at a common price, while a network of witches buying children or a method of valuing them does not exist. [ citation needed ] Ponytail's version does not make exact analogies to the process of short selling. The first major difference occurs when the parent sells a child they haven't had yet to a witch. Like short selling, the parent is selling something they don't own. But unlike short selling, the parent is selling something that doesn't exist yet. The somewhat broken analogy breaks further when Ponytail says the parent now is going to fight the witch instead of paying the witch with the child. There is no legal option to "fight" the other person if a shorted stock or call-writing strategy fails. You simply lose money. Our now definitely broken analogy breaks down even further (if possible) by sending the kid up the beanstalk to fight the giant - a giant that Ponytail says represents high interest rates. Interest rates have nothing to do with shorting stocks. (Technically they can, but the short seller would have / should have calculated that when determining if their investment strategy would work.) In addition, it is not possible for the investor, on their own, to fight interest rates that are harming their strategy, as those rates are set by lenders and are based on the credit worthiness of the borrower, the stated use case for the funds, and the nation's government's monetary policy. Cueball comments that the analogy is rapidly losing its value to him. Ponytail fires back with the comment that he should have shorted her advice before asking for it, thus making a profit. The decreased helpfulness of her wisdom is analogous to the decreased value of a shorted stock price. She once again proves that she lacks the knowledge of how short selling functions, or at least the knowledge to explain it, as her advice does not have a price to anyone, was presumably given to Cueball for free, and cannot be traded. Her story appears to be based on plot elements of multiple fairy tales. It begins by mixing up the story of Rapunzel with Jack and the Beanstalk . In one version of Rapunzel a Father breaks into a witch's garden to steal the Rapunzel plant for his pregnant wife. The Witch catches him and agrees to let him go and not punish him in exchange for the child. In one version of the " Jack and the Beanstalk " fairy tale story, Jack sells a cow for magic beans. His mother, thinking the beans are fake, is angry with Jack. Jack plants the beans and a magic beanstalk grows up into the clouds. Jack climbs the beanstalk and explores the land above the clouds. He finds the home of a cruel giant and proceeds to steal from the giant. The giant discovers the theft and chases Jack back down the beanstalk. Jack reaches the bottom of the beanstalk first and cuts the beanstalk down. The giant falls to his death, and Jack uses his stolen wealth to take care of himself and his mother. The combination of the two stories is similar to the story from the musical " Into the Woods ," in which a Father sneaks into the Witch's garden to steal vegetables, then trades his soon to be born child for the vegetables, but also steals beans in the process. The title text is actually the most useful part of this comic when it comes to investment advice. The witch (the broker) is offering the father (short seller) 20 magic beans now if the father/short seller buys all of the analogies (stocks) later. However, multiple witches/stock brokers trick multiple people into this strategy. Since every father/seller now needs the same analogies/stocks, and multiple witches need the exact same complete set of analogies, a bidding war erupts and it's impossible to please all the witches. The "winner" pays a much higher price than expected (limiting how much of a win it really is). And the losers wind up either dead or enslaved (bankrupt). In the stock market the corresponding phenomenon is known as a short squeeze , hence Cueball's comment. However, if the witches implement this strategy by discussing among themselves to orchestrate the phenomenon, it would be in violation of various trading regulations, and brokers rarely have a reason to hope for their clients to go bankrupt. [Cueball and Ponytail are walking together, talking.] Cueball: I don't understand shorting stocks. Ponytail: It's like when you promise your firstborn to a witch for five magic beans. [Ponytail close up] Cueball (off-panel): Is that a common– Ponytail: She's a sucker, right? You know your awful kid will be worth one or two beans at best . [Ponytail and Cueball stopped, facing each other] Ponytail: But then it turns out you love your kid, a love worth 200 beans! You can't afford that loss! Ponytail: There's only one way out: Ponytail: You gotta fight the witch. [Ponytail and Cueball stopped, facing each other] Ponytail: So you send your kid up the beanstalk to battle the giant, who represents interest rates. Cueball: This analogy is getting less helpful by the minute. Ponytail: If only you'd somehow shorted my wisdom before you asked.

Marsiforming

Marsiforming

https://www.xkcd.com/2095

https://www.explainxkcd.com/wiki/index.php/2095:_Marsiforming

[Cueball is on a stage giving a presentation, with a diagram behind him. The diagram shows Earth and Mars side-by-side, along with some writing below the two.] Cueball: Earth and Mars may look different now, but with some orbiting mirrors and atmospheric adjustments, we could change that. [Caption below the panel:] I'm having trouble selling people on my proposal to terraform Earth to resemble Mars.

Terraforming is the (so far only suggested) process of changing a planet, usually to make it more habitable for humans or other Earth life. A very common example is Mars , which is known to harbour water ice and believed to have previously been warm enough to have liquid water. Normally, plans for terraforming try to adjust temperatures to be compatible with liquid water, and an atmosphere containing significant amounts of oxygen but little carbon dioxide. The word Terra is the Latin name for Earth , so terraforming would be "Earth Forming". In this comic Cueball is suggesting doing the opposite: change Earth to be more like Mars, i.e. extremely dry, cold, and with a very thin atmosphere, approximately 1/160 of Earth's surface pressure. In addition, Mars has no magnetic core, so it is possible that Cueball wants to remove the magnetic field from Earth. The comic title combines Mars with Forming (with a linking "i") to create the new word Marsiforming. He is having trouble getting the enthusiastic response to his proposal that he expects. The title text provides examples of how this could improve things: preserving Martian life (a proposed reason to terraform Mars would be to provide a second planet to preserve Earth life at the cost of destroying any potential [undiscovered] Martian organisms, so by marsiforming Earth, we would provide a second planet to preserve Martian life, if there is any life on Mars), needing fewer interplanetary launches (no need to leave this planet's atmosphere in order to visit itself, and Martians who might otherwise need to return to their home planet could instead settle on Earth), and making it easier to field-test Mars rovers (field-test means to test in the environment of actual use, which would readily be available on Earth). While the second and third items would indeed be advantages, and the first would be as well if Mars has developed life, they are severely outweighed by the fact that most life on Earth, including humans, would die. Unstated in the comic are the extreme costs such a proposal would incur, which would surely be grounds for rejection. Between the thin atmosphere, harsh solar radiation, and other changes, Earth would become uninhabitable for most life currently on Earth, most notably humans. Almost all humans value the continued existence of the human race far more than Martian exploration [ citation needed ] (if nothing else, it is for the benefit of humans that Mars is being explored, so exterminating the human race would render the benefits moot). There are known extremophile species that would survive underground on Mars. If similar life is hiding on Mars, marsiforming the Earth would benefit their possible eventual interplanetary efforts. There is an existing project to begin experimental terraforming on Mars by nurturing some of our extremophile species on it. [Cueball is on a stage giving a presentation, with a diagram behind him. The diagram shows Earth and Mars side-by-side, along with some writing below the two.] Cueball: Earth and Mars may look different now, but with some orbiting mirrors and atmospheric adjustments, we could change that. [Caption below the panel:] I'm having trouble selling people on my proposal to terraform Earth to resemble Mars.

Mattresses

Mattresses

https://www.xkcd.com/2096

https://www.explainxkcd.com/wiki/index.php/2096:_Mattresses

[Cueball and Ponytail are talking to each other] Cueball: ...It's firmer than my old mattress, which I thought I wouldn't like, but it's actually really nice. Ponytail: Cool, maybe I should get one. Cueball: Now let's take some listener questions! Ponytail: What? [Caption below the panel:] I can't talk about mattresses, underwear, or the Post Office anymore without feeling the urge to segue back into a podcast. The image was originally posted as an indexed image with only a 3-color map (white, black, and grey), leading to graphical artifacts in place of a smooth blur between black and white. Most of Randall's comic images are indexed images with over 200 different grayscale colors. The original image can be seen here .

Cueball is talking to Ponytail about his mattress, in what appears to be just a casual conversation. Cueball suddenly offers to take any questions from listeners, as though the conversation were part of a podcast; this confuses Ponytail. The subtitle explains that Randall has heard so many advertisements for certain products on podcasts that he can't discuss them without feeling as though he's in a podcast himself. Podcasts are typically audio-only programs available online, which frequently generate income through advertisements. Ads are often read by the podcast host. Hosts will often include segues or personal anecdotes to further reduce the "topical whiplash" caused by abruptly switching subjects from that of the podcast to an unrelated brand plug, and back. In 2018, many podcasts (or at least many podcasts that Randall listens to) contained ads by Casper or Helix Sleep (both mattress brands), MeUndies or Tommy John (both underwear brands), and Stamps.com (an internet-based mailing/shipping service). The title text refers to "The War To Sell You A Mattress Is An Internet Nightmare" , about the pressures companies put on reviewers, and the legal battle between a mattress review site that makes money through affiliate sales, and a mattress company, which was unhappy with a review. Since saying anything unfavorable about mattresses might open one to legal action, the title text author opted to avoid them entirely. However, that could be seen as an endorsement of sleeping on the floor, thus requiring a disclaimer. It also references the way that podcast hosts will often note when they intentionally or unintentionally endorse a product sponsor in an attempt to remain transparent about their financial supporters. [Cueball and Ponytail are talking to each other] Cueball: ...It's firmer than my old mattress, which I thought I wouldn't like, but it's actually really nice. Ponytail: Cool, maybe I should get one. Cueball: Now let's take some listener questions! Ponytail: What? [Caption below the panel:] I can't talk about mattresses, underwear, or the Post Office anymore without feeling the urge to segue back into a podcast. The image was originally posted as an indexed image with only a 3-color map (white, black, and grey), leading to graphical artifacts in place of a smooth blur between black and white. Most of Randall's comic images are indexed images with over 200 different grayscale colors. The original image can be seen here .

Thor Tools

Thor Tools

https://www.xkcd.com/2097

https://www.explainxkcd.com/wiki/index.php/2097:_Thor_Tools

[A wide image is shown in a single frame.] Hand tools Thor could have ended up with [Below is a small centered horizontal line with arrows at both ends, labeled "Best" to the left and "Worst" on the right.] [The rest of the image shows an other horizontal line in the middle, also with arrows at both ends, covering the full width. Items are marked by a dot with a text above or below, and sometimes a figure wearing a winged helmet, above the line, uses a tool mentioned below:] Hammer Axe Claw hammer Circular saw [Above, the winged helmet guy uses a circular saw:] Bzzzz zzzz Shovel Jackhammer Socket wrench [Above, the winged helmet guy spins the socket of a socket wrench with a tiny sound.] Bolt cutters Hacksaw Nail gun Staple gun [Above, the winged helmet guy fires staples into the ground in front of him:] Kachunk kachunk Coping saw Screwdriver (flat) Ball-peen hammer Screwdriver (Phillips) Awl Digital Caliper Dremel [Above, the winged helmet guy shows a running Dremel to the left:] Bzzzzz Plane

In Norse mythology, Thor is the name of a god of thunder and lightning. His signature weapon is a magic hammer called Mjölnir . In popular culture Thor might be best known for his role in Marvel comics and films , which his appearance here seems to be referencing. In the Marvel Cinematic Universe movie, Avengers: Infinity War, Thor also wields an axe named Stormbreaker. Although this hammer was historically a weapon, this comic interprets it as it would more commonly be interpeted today -- as a tool. The comic is listing various hand tools in order of utility and viability as Thor's weapon, besides his actual, enchanted hammer. Hammers are heavy, blunt, and can do large amounts of damage to an opponent, whereas a hand plane is sharp, but only in one place, and will only inflict surface wounds. Some of these tools require power, which would generally require Thor to stay near an outlet or keep a battery charging, such as the circular saw, or Dremel. However, being the god of lightning may allow him to circumvent this, by producing electricity for the direct current (D.C.) tools, although he would need an inverter to convert the lightning (D.C.) to alternating current (A.C.) for the tools requiring it. Thor would also need compressed air for the nail gun or jackhammer, only allowing Thor so many shots before reloading the air tank at an outlet, or via a concentrated wind storm. The nail gun and staple gun would also require nails or staples respectively to function as a weapon. Although Mjölnir is believed to return to Thor if thrown, it's not clear how a similar system could work with nails and staples. The usefulness of the nail gun as a weapon might depend on whether it was an older one that can be bump-fired or a newer one that requires a separate trigger pull for each nail. In the title text, Randall writes that the order of the axis label should be reversed, making the plane the best tool and Mjölnir the worst. Considering that the title of the comic is "Thor Tools" ("tools", instead of "weapons"), the argument seems to be that a hammer is less useful than the rest, by seeing them as tools and not as weapons. A few other interpretations of this could be: The title may be a reference to Gary Larson's The Far Side comic, Cow Tools . The comic depicted a cow next to a set of crude tools, and was famous for no one understanding it. All shown tools are explained below: Hammer A hammer is a tool consisting of a weighted "head" fixed to a long handle that is swung to deliver an impact to a small area of an object . Thor was a hammer-wielding god and produced the lighting by using this tool. A war hammer was an actual blunt weapon used for combat in medieval times, and is the original Thor's attribute. There exists a variety of craftsman's hammers designed for specific purposes which can be used as weapons of opportunity to various degrees, depending on the tool's size, weight and material. Axe An axe or just ax is another old human tool used to split and cut wood, but it also was used as a dangerous weapon in the medieval times. The battle-axes of old were of considerably different design than the woodworking ones, being lighter and having thinner and wider blades. A woodworking axe, though not designed for combat, could be a formidable weapon of opportunity. Notably, this tool is placed slightly below the hammer, possibly indicating Randall's thoughts on Thor's axe, 'Stormbreaker' which features in the Marvel films. (Note: In Norse mythology Thor is depicted exclusively with a hammer rather than an axe). Claw hammer A claw hammer is a hammer tool primarily used for driving nails into other objects, but also for pulling nails from them. This item seems a bit redundant in the presence of a general hammer on the axis, but could be seen as more scary because it has a pointed, curved and split back head (used for pulling nails). In fact, the usefulness of its back head for combat is debatable at least. On the other hand, it is smaller and lighter than some other craftman's hammers, and less scary than a true war hammer, so its place on the axis may be justified. Circular saw A circular saw is using a, mostly electric powered, fast-revolving toothed disc to cut materials. A stationary version is called a table saw but the figure of Thor drawn above presents him using a lighter hand-held version making a buzzing sound. Since the power of the saw is far beyond the human power it is quite a dangerous tool and could be fatal to the user himself. However, it would be rather unwieldy in combat, as it is quite heavy and bulky. Also, electric circular saw would be limited by its cord length, however cordless (battery-operated) saws exist today. This item could be a mock reference to a common trope in horror movies or computer games, when a chainsaw (not a circular saw) is used a weapon. Shovel A shovel is also a historic tool. It can be used to dig into the ground, move snow or dirt, harvest, and much more. Because it has a relatively thin, sharp metal blade at the end of a pole, it can be used as a weapon of opportunity. Indeed, a small (sometimes foldable), sturdy spade was and still is a standard issue item for an infantryman in some countries, intended mainly for entrenching work, but also usable as a weapon – and the soldiers are trained to use it as such, sometimes to a high skill, specifically among special forces. It is rumored that Russian Spetznaz operators are specifically trained to use their spades as throwing weapons. It is therefore more useful in combat than a circular saw – but may be seen as less scary. Jackhammer A jackhammer is a power tool used to drill and crush hard but brittle materials like stone, concrete etc. It has heavy body with a protruding shaft that makes hard and rapid back-and-forth (and optionally also rotary) movements that drive an implement (a drill, a chisel etc.) into the worked material. Like the circular saw jackhammer is a tool that is powered far beyond single human capabilities. Most jackhammers are very heavy and can be reasonably used only in a facing-down position to work on floors, pavements and other near-horizontal surfaces, nullifying combat application. However, since Thor is purportedly very strong, he may be able to hold it horizontally for some combat... Socket wrench A handle attached to a socket wrench is mostly used to tighten bolts or nuts. But since it is quite heavy and resembles a hammer it could also be used in a similar fashion. It may be a self-reference to comic 538 . Bolt cutters Bolt cutters are cutters with very long handles, typically 2 or 3 feet long, and comparatively tiny jaws. The length of the handles provides the user enough mechanical advantage to sheer through things like bolts, chain links, and lock shackles. Although this tool can cut some fairly tough objects, its usefulness in combat is limited – as far as the cutting action goes at least. On the other hand they are quite heavy and can be used as a blunt weapon. Hacksaw A hacksaw is a type of hand saw with very small teeth. Hacksaws are well suited to cutting materials like metal and plastic, where the larger teeth of a wood saw would tend to bind or damage the material around the cut. Hacksaw blades are fairly unlikely to seriously injure people, though a hacksaw may be useful against metal baddies like Ultron. Nail gun A nail gun is a tool for driving nails or other fasteners into various materials ranging from soft wood to hard concrete by a single powerful "shot" to the nail being driven. There are models powered by compressed air, electricity (several types of mechanisms) or explosive charges similar to firearm ammunition (most often compatible with .22 Short blank cartridges). They are normally used by slightly pushing the "nozzle" against an object, disengaging a safety nose contact mechanism, and pulling the trigger. These are quite dangerous tools and can be potentially modified – by removing safety mechanisms – to act similarly to a handgun, shooting nails as high-speed projectiles. Its place in the middle of the axis seems not right compared to the work hazard level of other tools placed left of it. If safety mechanisms are left intact, a nail gun would need to be used in close combat by pressing it against an opponent which would make it difficult to apply, but if applied successfully it would inflict grievous wounds. Staple gun A staple gun is a tool used to drive staples (C-shaped pieces of hard wire) into relatively soft materials such as wood, plastics and light masonry in order to fix something to them. There exist spring-loaded hand-operated staple guns as well as power ones utilizing either electricity or compressed air. The power discharged during staple action is a lot less than that of a nail gun and would inflict minor skin wounds at most. If one manages to eject a staple into the air (not against an object) it won't travel very far. A figure of Thor is drawn above the axis showing him using a staple gun this way, with staples falling short onto the ground. The gun held by Thor makes kachunk sounds characteristic for a spring-loaded version of the tool. Coping saw A coping saw is a hand saw with a thin replaceable blade and is used to cut curves and shapes in wood or other relatively soft materials. While it could produce a surface wound and draw blood, a person would generally not stand still long enough to be seriously hurt by being sawed at by a coping saw, plus they could bend or break the blade relatively easily. Screwdriver (flat) A (flat) screwdriver is a metal rod with a handle, flattened and ground at the other end to form a fairly sharp but short edge perpendicular to the rod. It is normally used to drive screws into a material, by putting the edge into a groove on the screw's head and turning it while pressing firmly. It is not very dangerous normally, but many people have cut their fingers while driving screws in, or sometimes whilst using it incorrectly to unscrew a bolt . It could potentially be used as a stabbing weapon similarly to a dagger, but much less effectively, or alternatively the heavy handle may be used as a bludgeon, though the smooth rod would be difficult to grip. Some nations seem to regard it so much dangerous as to ban its possession in public along knives. Ball-peen hammer Like a regular hammer, a ball-peen hammer has a flat head designed to hammer things like nail. However instead of the "claw" a regular carpenter's hammer has to pull out nails, it has a second head that is shaped like a ball and which is used to bang surfaces such as sheet metal directly. A ball-peen hammer is probably the smallest of traditional hammers, and usually used for more delicate work. Thor's Hammer has two flat surfaces for pounding (no claw), so a ball peen might be like a smaller Thor's Hammer and could be pretty deadly in his hands. The ball part would probably not be any more or less effective than the flat part, except it might bounce or deflect off some surfaces where a flat one might not. Screwdriver (Phillips) Similar to a flat screwdriver, but with a cross-shaped tip, designed to drive screws with matching cross-shaped heads. While a Phillips screwdriver could potentially be used as an improvised weapon to stab or strike like a flat screwdriver, the blunter, cross shape is less likely to inflict cutting injury, likely leading to its lower position on the list. Awl An awl is a hand tool, basically a rather short, thin, sharp (sometimes curved) spike with a handle. It is used for punching holes through soft material (leather, fabrics) or to mark points or lines on wood or metal to assist further work such as cutting or drilling. In a pinch, it could be used as a stabbing weapon like a dagger, but a screwdriver is more sturdy for such purpose. Digital Caliper Digital calipers are an instrument for precisely measuring the dimensions of small objects. Typically, digital calipers can measure inner diameters, outer diameters, and depth. The reason they are considered more formidable than Dremels and planes is likely how surprisingly sharp the calipers are. They need to be sharp to make accurate measurements, but it is not uncommon for people to cut themselves while using a digital caliper. Dremel Dremel is a brand name (often used in a generic sense) of small rotary power tools that can be used in precise work involving small objects such as engraving, milling, drilling, grinding, cutting, polishing etc. It consists of a relatively small and lightweight body housing a high-speed electric motor driving a shaft equipped with a chuck . Various implements can be fixed to the chuck – drills, milling cutters of various shapes, small cutting disks, grinding stones, brushes, soft polishing disks etc. Typically the tool is used handheld against an object held in a vice. It can also be mounted in a stand with a flexible shaft attached, at the other end of which an implement is fixed in a chuck, allowing for still more precise work. A Dremel would be rather useless in combat, effecting in superficial wounds only. It could be seen as a baby circular saw, therefore much less scary and placed much more to the right of the scale. However, it is still a heavy object with a firm grip, and could plausibly be wielded as a bludgeon, making it slightly more effective than a plane. Plane A hand plane is a tool for shaping wood using muscle power to force the cutting blade over the wood surface. It is designed to scrape layers of wood off the surface. While a plane does have a sharp edge and can cause painful injuries if misused, its awkward shape and the small size of the cutting edge would make it impractical to wield and nearly useless as a combat weapon, even for bludgeoning. A hand plane could plausibly be used as a particularly brutal torture device on a restrained victim, but as Thor is typically depicted as an honorable and heroic character it is unlikely that he would use one in this manner. Could also mean an actual plane that is meant to fly. Most likely to be used as a thrown projectile or, since Thor can fly using Mjölnir, he can use the plane to fly as well. [A wide image is shown in a single frame.] Hand tools Thor could have ended up with [Below is a small centered horizontal line with arrows at both ends, labeled "Best" to the left and "Worst" on the right.] [The rest of the image shows an other horizontal line in the middle, also with arrows at both ends, covering the full width. Items are marked by a dot with a text above or below, and sometimes a figure wearing a winged helmet, above the line, uses a tool mentioned below:] Hammer Axe Claw hammer Circular saw [Above, the winged helmet guy uses a circular saw:] Bzzzz zzzz Shovel Jackhammer Socket wrench [Above, the winged helmet guy spins the socket of a socket wrench with a tiny sound.] Bolt cutters Hacksaw Nail gun Staple gun [Above, the winged helmet guy fires staples into the ground in front of him:] Kachunk kachunk Coping saw Screwdriver (flat) Ball-peen hammer Screwdriver (Phillips) Awl Digital Caliper Dremel [Above, the winged helmet guy shows a running Dremel to the left:] Bzzzzz Plane

Magnetic Pole

Magnetic Pole

https://www.xkcd.com/2098

https://www.explainxkcd.com/wiki/index.php/2098:_Magnetic_Pole

[White Hat and Cueball are talking to each other. White Hat has a cellphone in his hand, while Cueball is raising his hands in the air in mock exasperation.] White Hat: I just read that the Earth's North magnetic pole is drifting rapidly. Cueball: Oh no! I must update our declination tables post haste, lest our merchant schooners run aground on the shoals! [Caption below the panel:] I like when the Earth's magnetic field does weird stuff, because it's a huge, cool, urgent-seeming science thing, but there's nothing I personally need to do about it.

Over the last couple of months, Earth's magnetic fields have been shifting rapidly . Although the magnetic fields do move regularly, the current shift has been unexpected and unprecedented. As many location systems are reliant on the magnetic fields to function, the accuracy of such tools is being shifted beyond the maximum acceptable error. Locational and navigational systems use the magnetic field, combined with a model of field behavior, to do fancy math and pop out data. Because of the rapid shifts, a new model was scheduled to be created; however, the model has been considerably delayed by the US government shutdown , As shifts occur, the error of geopositional data will increase until a new model is released. The effect is especially pronounced as you move toward the poles. Cueball is saying that because of the currently published magnetic declination data being slightly incorrect, his schooners (old merchant sailing ships) may go off-course and crash on shoals . This is to illustrate how magnetic pole shift doesn't actually affect many people's daily lives. Modern ships' navigation systems do not rely on magnetic pole location – in contrast to old vessels which mostly used a compass . Since the movement is only about two-fifths of a degree, it wouldn't cause much disruption for Cueball or require him to adjust anything about his lifestyle, but since the speed of the change has been steadily increasing over the past few years, it may mean we are heading for a geomagnetic reversal in the next few decades, something very exciting indeed. During a magnetic reversal, the poles wouldn't just switch places; several different poles would form and interact chaotically, and it's likely that one of them would end up close enough to where Randall lives to cause auroras to become more common at some point during the transition. In the title text, Randall mentions that there are reasons people could be concerned, but says that they would be more than made up for by newly being able to experience mid-latitude auroras. Since auroras occur between 10° and 20° from the magnetic poles, the migration of the poles to middle latitudes would cause the auroras to occur there as well; since more people live at middle latitudes than in the Arctic and Antarctic Circles, and since auroras are considered aesthetically attractive, the psychological benefits of the drifting poles might more than make up for the technical difficulties it causes. [White Hat and Cueball are talking to each other. White Hat has a cellphone in his hand, while Cueball is raising his hands in the air in mock exasperation.] White Hat: I just read that the Earth's North magnetic pole is drifting rapidly. Cueball: Oh no! I must update our declination tables post haste, lest our merchant schooners run aground on the shoals! [Caption below the panel:] I like when the Earth's magnetic field does weird stuff, because it's a huge, cool, urgent-seeming science thing, but there's nothing I personally need to do about it.

Missal of Silos

Missal of Silos

https://www.xkcd.com/2099

https://www.explainxkcd.com/wiki/index.php/2099:_Missal_of_Silos

[A passage from the Wikipedia page for Missal of Silos is shown, with underlined heading and with links in the text in blue font. The last line is partly cut off by the comics panel, but can be read.] Missal of Silos From Wikipedia, the free encyclopedia The Missal of Silos is the oldest known paper document created in the Christian West; it is 11th century in date. [1] The missal is held in the library of the Monastery of Santo Domingo de Silos near Burgos, Spain . It is one of a number of liturgical manuscripts... [Caption below the panel:] Spain would like to remind everyone not to use fuzzy string matching in their nuclear strike target lists.

This comic plays on the similarity in name between missile silos, places where long range weapons are deployed, and the missal of Silos, an old document residing in Spain . In Christianity , a missal is a priest 's book of instructions , texts and music for the proper celebration of Mass . The Missal of Silos is an 11th-century missal from the Abbey of Santo Domingo de Silos in northern Spain ; it is famous for being the oldest known paper document in Europe, written at a time when the usual writing material was parchment . Missile silos are often thought to be the first targeting priority in event of a nuclear strike, in hopes of preventing retaliation. If one was searching for potential nuclear missile targets, the Missal of Silos could conceivably be returned as a result of a fuzzy search for "missile silos", and be made a target. Fuzzy, or approximate, string matching is a technique used for searching text for sequences of characters similar to a given sequence. Normal string matching would only find results that matched the search exactly (searching for " missile " would find only occurrences of " missile "). Fuzzy string matching instead finds results that are "close enough" by some metric (searching for " missile " would find " missile " but also close variants like " missal " or " missel "). Fuzzy string matching is often used in search engines, as typos, misspellings, and inexact searches are common. Cheyenne Mountain is a mountain in Colorado , which houses an underground military compound (aptly named the Cheyenne Mountain Complex ) designed to withstand a nuclear strike and host to the North American Aerospace Defense Command . Cheyenne, Wyoming , on the other hand, is the capital of Wyoming . The residents of Cheyenne, Wyoming would prefer their town not to be the target of a nuclear attack because of confusion with Cheyenne Mountain. [ citation needed ] However, Cheyenne, Wyoming is likely a listed target because of the nearby 90th Operations Group at Francis E. Warren Air Force Base operating Minuteman III ICBMs from missile silos. There have been several comics with nuclear weapons as a part of the plot. See for instance 1655: Doomsday Clock , where several other comics are mentioned in the explanation. [A passage from the Wikipedia page for Missal of Silos is shown, with underlined heading and with links in the text in blue font. The last line is partly cut off by the comics panel, but can be read.] Missal of Silos From Wikipedia, the free encyclopedia The Missal of Silos is the oldest known paper document created in the Christian West; it is 11th century in date. [1] The missal is held in the library of the Monastery of Santo Domingo de Silos near Burgos, Spain . It is one of a number of liturgical manuscripts... [Caption below the panel:] Spain would like to remind everyone not to use fuzzy string matching in their nuclear strike target lists.

Models of the Atom

Models of the Atom

https://www.xkcd.com/2100

https://www.explainxkcd.com/wiki/index.php/2100:_Models_of_the_Atom

[Heading:] Models of the Atom over time [What follows is a progression of depictions of atoms.] [A ball.] 1810 Small hard ball model [A 'pudding' inside of which there are electrons.] 1904 Plum pudding model [A ball, with four birds perched on it and two of them singing.] 1907 Tiny bird model [A ball with electrons orbiting chaotically, in all directions, around it.] 1911 Rutherford model [A ball with electrons circling around it.] 1913 Bohr model [A nunchuck swinging, with the left stick filled with protons and the right stick filled with electrons.] 1928 Nunchuck model [A nucleus with protons and neutrons, with electrons circling around it like the Bohr model.] 1932 Chadwick model [A pie chart. 38% is allocated to neutrons, 31% to protons, and 31% to electrons.] 2008 538 model [A nucleus with clover-like orbitals around it and surrounded by two outer partly dashed circles.] Today Quantum model [A ball surrounded with numbers.] Future "Small hard ball surrounded by math" model

This comic humorously describes the changing view of what an atom is. This has happened so much it seems that we never really knew what we are looking at, and there have been many competing theories aside from the mainstream ones we are taught in school. He lists major depictions in the history of our understanding of an atom, and adds a few humorous ones in to poke fun at how diverse, contentious, and in retrospect often foolhardy, this history has been. Small hard ball model The first model shown, in 1810, is said to be a "small hard ball model." Around this time, John Dalton published his textbook A New System of Chemical Philosophy which linked existing ideas of atomic theory and chemical reactivity to produce a combined law of multiple proportions which proposed that each chemical element is comprised of a single unique type of atom, and introduced the concept of molecular weight . Dalton's theories form the basis of what is known today as stoichiometry , which underpins chemical reactivity. As atoms were considered at this time to be the smallest possible division of matter the scientific community thought of them as "hard round balls" of different sizes; thus the name described here. The "small hard ball" model is still commonly used when teaching and discussing chemical molecules which do not require the level of detail provided by more advanced models, with atoms represented as small, hard, round balls connected by sticks representing chemical bonds. Plum pudding model In the late 19th and early 20th centuries, the study of these "atom" things faced a crisis: where would the newly discovered " electrons " go? In 1904, physicist J. J. Thomson , who discovered electrons, had an idea: maybe the electrons were small point charges moving around in a big mass of positive charge. This was the " plum pudding model ", the second model on the comic, called this because people imagined the positively charged mass as a " plum pudding ". (The title text references Thomson (although misspelled as "J.J. Thompson") as well, along with the humorous observation that plum puddings themselves are made of atoms.) The problem with this approach is that same charges generally repel, resulting in the more mobile or unbalanced charges forming a surface shell around the others, attempting to escape, rather than being content to being randomly distributed among them. Tiny bird model There were many competing ideas in the formative years of what-are-atoms-made-of-ology; Randall makes up a 1907 "tiny bird model," which he suggests might have fit well in the relative chaos of the period. In this model, four birds surround the small hard ball at equal distances to one another. Two of them are singing and the other two are not and all birds are opposite to their identical bird. The non-singing birds balance the singing birds like electrons and protons. This model might be mocking the strange and sometimes illogical models that were presented for the shape of an atom. Rutherford model The tentative winner in the battle was the model of Thomson's student Ernest Rutherford , who discovered from electrostatic scattering experiments that the positive charge seemed to be concentrated in the center of the atom, and proposed his Rutherford model , or "planetary model", in 1911, where electrons orbit a very concentrated positive charge. This model has often been compared to the orbit of the planets around the sun, with the electrostatic attraction of the electrons and protons shaping the orbits, rather than gravity. This is the fourth model in the comic. Bohr model The Rutherford model could not explain the discrete spectral lines in absorption and emission spectra. It also did not explain why electrons did not spiral in to the nucleus. Niels Bohr patched the model up by proposing that electrons could only exist in distinct "energy levels" at discrete distances from the nucleus. The 1913 " Bohr model ", the fifth model shown here, was part of beginning quantum mechanics. Physics behaves differently at the small scale of atoms than the large scales we are more familiar with. Nunchuck model Randall facetiously suggests a " nunchuck model", the sixth model shown, of a packet of protons swinging a packet of electrons around. One can imagine a handle filled with electrons bonded by the strong nuclear force to a chain made of neutrons, bonded again by the strong nuclear force to a handle made of protons. The heavier protonic handle acts loosely as an orbital center as the electron-filled opposite handle swings wildly around it, attempting to resolve its electrostatic attraction within the restraints of its chain. Chadwick model The next refinement was in the structure of the nucleus. Note that at this time, nobody thought of splitting up the nucleus into protons and neutrons . But pretty soon people noticed that protons and neutrons existed; James Chadwick , who discovered the neutron, figured that the atom had a nucleus of neutrons and protons, along with a bunch of electrons orbiting around it in a Bohrish manner. This is what the layman today often thinks of as an atom, and is the seventh model shown here. 538 model The eighth model shown is a made up "538 model," in 2008. FiveThirtyEight is a statistical analysis website that gained fame in 2008 for predicting every race but 2 correctly in the US presidential election and predicting every state and Obama's win in the 2012 election. Unlike most other media and polling institutes it saw a rather high probability of 29% for Trump to win the 2016 election by summing up the uncertainties in all the battle states. It has since been known for making mathematical models for everything; the model jokingly suggests that 538 has modeled and presumably made predictions about the atom. The pie chart shows the statistical composition of neutrons, protons and electrons, 38%, 31%, and 31% respectively. This could either be the average of a massive body with several isotopes or represent gallium-69, the most abundant isotope of gallium , with 31 protons, 31 electrons and 38 neutrons. FiveThirtyEight has previously been mentioned in several xkcd comics, including in 477: Typewriter , 500: Election , 635: Locke and Demosthenes , 1130: Poll Watching , 1779: 2017 , and 2002: LeBron James and Stephen Curry . It's appropriate to list the 538 model as a precursor to the quantum model, as it is a step towards considering the likelihood of different quantities of subatomic particles to be in different volumes of space, rather than considering them as strictly kinematic particles. The comic moves this development into 2008 in support of this joke, when it was actually made much earlier. Quantum model But is the Chadwick model what scientists endorse today? No! The theory of electromagnetism says that accelerated charges, like the electrons circling, would lose energy emitted as electromagnetic waves and would quickly orbit into the nucleus. Bohr only postulated that this would not happen, but his model could not explain why. Another problem [ citation needed ] is that atoms, even the hydrogen atom are not flat - which they would be, if a single electron orbited in a circular or elliptical trajectory (the circular motion of charge results in a magnetic moment; Otto Stern and Walter Gerlach showed that independent from the direction of the measurement the angular momentum - for certain elements - always has the maximum positive or negative value, i.e. not only the radius, but also the angular momentum is quantized - and never zero. You cannot 'look at' the atom from above and 'see' the orbital circle. It always 'seems', as if you 'looked' from the side and would measure the full magnetic dipole. Stern and Gerlach actually saw the spin of an electron of the silver atom instead of the angular momentum, which is according to quantum mechanics 0). Today (i.e. actually since 1926, 29 years after the discovery of the electron) physicists subscribe to a quantum model, which is the ninth model shown here. Instead of electrons with definite location and momentum (~speed), the parts of the atom are described by probability fields of possible locations and momentums. The changes in momentum probability normally cancel each other out, so there is no electromagnetic radiation. This is very abstract, and in the last model, the model is postulated to get so abstract that it is just a "small hard ball surrounded by math" model, the last model shown. This then is remarkably similar to the model we started out from, the "small hard ball model" (without the math). “Small hard ball surrounded by math” model The picture for the "small ball surrounded by math" depicts a circle with several numbers around it. While the numbers seem to symbolize the "surrounding math" in a general sense, some of them suggest constants used in actual mathematical equations or other numbers related to the quantum model. The shapes and densities of the atomic orbitals are calculated with the Schrödinger equation , which is complex and difficult to solve. For this reason atoms are generally precisely considered in only very simple simulations, and the details of interactions of many atoms at large scales that form our daily lives are incredibly hard to precisely understand and predict on an atomic level. It comes down to "these roundish things we call atoms are moving around in these approximate ways obeying this complex equation with too many numbers involved in most situations to accurately model, so let's use a different, empirically derived formula that describes the behavior of the system in general." This model is probably a reference to the mathematical universe hypothesis and, as a striking case of prescience , may be seen as a prediction of April 2020’s Wolfram Physics Project . [Heading:] Models of the Atom over time [What follows is a progression of depictions of atoms.] [A ball.] 1810 Small hard ball model [A 'pudding' inside of which there are electrons.] 1904 Plum pudding model [A ball, with four birds perched on it and two of them singing.] 1907 Tiny bird model [A ball with electrons orbiting chaotically, in all directions, around it.] 1911 Rutherford model [A ball with electrons circling around it.] 1913 Bohr model [A nunchuck swinging, with the left stick filled with protons and the right stick filled with electrons.] 1928 Nunchuck model [A nucleus with protons and neutrons, with electrons circling around it like the Bohr model.] 1932 Chadwick model [A pie chart. 38% is allocated to neutrons, 31% to protons, and 31% to electrons.] 2008 538 model [A nucleus with clover-like orbitals around it and surrounded by two outer partly dashed circles.] Today Quantum model [A ball surrounded with numbers.] Future "Small hard ball surrounded by math" model