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Conjunction

Conjunction

https://www.xkcd.com/2401

https://www.explainxkcd.com/wiki/index.php/2401:_Conjunction

[Caption above the first panel:] What people imagine astronomers observing a conjunction are like [Cueball and Ponytail are both looking through telescopes at the conjunction of Jupiter and Saturn.] Cueball: 6.15 arcminutes! Ponytail: Stupendous! This confirms Einstein! [Caption above the second panel:] What they're actually like [The same picture with different spoken sentences.] Cueball: Wow! Look how close they are! Ponytail: It's so cool!! Cueball: Now kiiiisssss!! Ponytail: Dooo iiit!

Cueball and Ponytail are observing the 2020 Jupiter-Saturn conjunction . This comic is similar to other comparisons between expectation and reality, such as 2176: How Hacking Works , 683: Science Montage , 2341: Scientist Tech Help , and 538: Security . The expectation is that the scientists will remain professional and serious throughout the event, testing Einstein's theory of General Relativity and using technical terms such as arcminute , a unit of measurement often used in astronomy. In reality, however, they are actually treating the event quite whimsically and are having fun with it, even jokingly commenting about the event. Other astronomical phenomena, such as solar eclipses, actually have been used to test Einstein's theories, but in this case the interest is purely aesthetic. The title text references the misconception that the planets physically get very close at conjunction, rather than merely appearing to do so. The wording suggests a quick and uneventful merger, possibly alluding to the way drops of water merge when the surface tension between them is broken. If Jupiter and Saturn really did come into contact and "blooped together", most of the mass would stay collected as an extremely hot [ citation needed ] and turbulent blob that would eventually settle down as a new planet (which Randall suggests might be called "Jaturn" ), but more than a bit would be spewed outwards. The possible outcomes vary enormously, depending on factors such as how direct the impact was, and its alignment relative to the planets' spins. However, while such a collision would be preceded by a conjunction, a conjunction does not necessarily indicate an imminent collision, as Jupiter and Saturn, although on the same sightline from Earth, are still separated by 734 million km (456 million mi) at the time of the conjunction - almost five times the distance from Earth to the Sun. [Caption above the first panel:] What people imagine astronomers observing a conjunction are like [Cueball and Ponytail are both looking through telescopes at the conjunction of Jupiter and Saturn.] Cueball: 6.15 arcminutes! Ponytail: Stupendous! This confirms Einstein! [Caption above the second panel:] What they're actually like [The same picture with different spoken sentences.] Cueball: Wow! Look how close they are! Ponytail: It's so cool!! Cueball: Now kiiiisssss!! Ponytail: Dooo iiit!

Into My Veins

Into My Veins

https://www.xkcd.com/2402

https://www.explainxkcd.com/wiki/index.php/2402:_Into_My_Veins

[Close up of Cueball.] Cueball: Yesssss Cueball: Inject this directly into my veins [Beat panel. Ponytail looks down at a clipboard while Cueball is looking at her.] [Zoom out to reveal that Cueball is standing by a stool, with Ponytail in front of him with a clipboard and syringe and Hairy behind him with a box of bandages and a first-aid kit.] Ponytail: Ok, but the vaccine is intramuscular... Hairy: Why do people keep saying that? Cueball: Sorry, sorry. Cueball: Just excited.

This comic is another in a series of comics related to the COVID-19 pandemic . It also references a common meme . Two of the next four comics also contain references to the vaccine, 2404: First Thing and 2406: Viral Vector Immunity , and the first of these, like this one, additionally references a common Internet trend. The COVID-19 Pandemic has been one of the most consequential and broadly unpleasant events in living memory. [ citation needed ] As of the publication of this strip, it is estimated to have caused over 1.5 million deaths worldwide, with over 300,000 deaths in the United States, and many more serious cases, often with lasting impacts. Even for those who have been spared infection, measures to slow the spread of the virus have been highly impactful, and have been ongoing for nearly a year. As a consequence of all of this, many people (including, presumably, Randall ) are excited for the vaccine, which will hopefully end the pandemic. This comic shows Cueball clearly thrilled to receive the vaccine. "Inject this directly into my veins" is a meme based on a line (from The Simpsons ): in the episode " A Star Is Burns ", an alcoholic character wins a lifetime supply of beer, and replies "just hook it to my veins". The meme is typically applied to things that are not injected at all (such as a form of media or entertainment) to express exaggerated enthusiasm. When Cueball applies the meme to the COVID-19 vaccine, it causes some confusion, because the vaccine is delivered by injection, but not directly into a vein . The medical staff delivering the vaccine have apparently heard this or similar lines frequently, and appear to take it literally, repeatedly explaining that it's not actually possible. The title text references another such meme, "Shut up and take my money," which derives from the 2010 " Attack of the Killer App " episode of Futurama . This meme, like the first, expresses extreme and immediate desire for something, with the implication that the speaker is not only willing but eager to pay whatever it costs, and is too excited to wait for a sales pitch or for any warnings or disclaimers. The COVID-19 vaccine is being provided free of charge to Cueball, so taking his money is entirely unnecessary (and possibly illegal). Once again, this is a source of potential confusion because, under the American healthcare system, many people likely will have to pay at least part of the cost of vaccination. The workers administering it could easily confuse the meme for a genuine request. This was the last comic before this years Christmas comic . It was about the Covid-19 vaccine. The last comic before the 2021 Christmas comic, 2558: Rapid Test Results , was about Covid-19 tests. [Close up of Cueball.] Cueball: Yesssss Cueball: Inject this directly into my veins [Beat panel. Ponytail looks down at a clipboard while Cueball is looking at her.] [Zoom out to reveal that Cueball is standing by a stool, with Ponytail in front of him with a clipboard and syringe and Hairy behind him with a box of bandages and a first-aid kit.] Ponytail: Ok, but the vaccine is intramuscular... Hairy: Why do people keep saying that? Cueball: Sorry, sorry. Cueball: Just excited.

Wrapping Paper

Wrapping Paper

https://www.xkcd.com/2403

https://www.explainxkcd.com/wiki/index.php/2403:_Wrapping_Paper

[Cueball is standing at the left of a decorated Christmas tree, with present boxes underneath it. The presents are wrapped with the undecorated side of the wrapping paper facing out. Megan is kneeling at the right side, unwrapping a gift, revealing stripes on the inside.] Megan: Cool! I got the entire universe and every object within it except for a pair of headphones! [Caption below the panel]: Presents get a lot more impressive if you turn the wrapping paper inside out

This comic was published on Christmas Day, 2020, a day where people who celebrate Christmas traditionally open presents. In this comic, Megan is unwrapping a present while Cueball looks on (perhaps it's the present he gave her). The premise is that the definition of a present is not what's inside the box, but what's inside the region of space that the blank side of the wrapping paper faces. So if you wrap the box with the printed side towards the box, everything in the universe outside the box is the gift. Apparently, the box contains a pair of headphones, which would be a nice present, but not nearly as impressive as almost everything in the universe. [ citation needed ] And since the rest of the universe contains millions of headphones, many of which are probably nicer than the ones in this box, she still gets headphones as well. The title text extends this to regifting , which is the practice of using a received present (usually unwanted and hopefully unused) as a present for someone else. This practice is often considered to be impolite because it's assumed to simultaneously show a lack of appreciation of a gift you've received (because you want to get rid of it), and an unwillingness to spend much time, effort, or money on a gift for someone else. But if you wrap an ordinary present inside out, all the gifts you've ever received in the past are part of the entire universe except for that present, so you're actually doing an enormous amount of regifting including stuff belonging to other people , which is as rude as regifting can get. Douglas Adams 's novel So Long, and Thanks for All the Fish , the fourth in the The Hitchhiker's Guide to the Galaxy series, contains a similar joke. A man living in an inside-out room in a desert treats the rest of Earth as an insane asylum, with himself living outside of it as the only sane man. This may also refer to a math joke about how to create the smallest fence around a group of animals. Rather than finding the obvious fence, a mathematician would build a small, circular fence around themselves and declare the region on the other side of the fence "inside", thus enclosing all the animals! The mention of headphones might be a reference to the AirPods Max , which were released by Apple on December 9, just 16 days before this comic, and stirred much debate for their USD$549 price tag. [Cueball is standing at the left of a decorated Christmas tree, with present boxes underneath it. The presents are wrapped with the undecorated side of the wrapping paper facing out. Megan is kneeling at the right side, unwrapping a gift, revealing stripes on the inside.] Megan: Cool! I got the entire universe and every object within it except for a pair of headphones! [Caption below the panel]: Presents get a lot more impressive if you turn the wrapping paper inside out

First Thing

First Thing

https://www.xkcd.com/2404

https://www.explainxkcd.com/wiki/index.php/2404:_First_Thing

[Ponytail and Cueball are walking toward the right side of a single panel. Ponytail is gesturing with one arm.] Ponytail: The first thing I'm going to do after I get the vaccine? Ponytail: Definitely make a bunch of spike proteins and engulf them with dendritic cells. Ponytail: Then I'll probably display the antigens to my T-cells...

This comic is another in a series of comics related to the COVID-19 pandemic , specifically regarding the COVID-19 vaccine . This comic, somewhat like 2402: Into My Veins , references both the COVID-19 vaccine and a common Internet trend. Two comics later in 2406: Viral Vector Immunity , the vaccine is again referenced. The COVID-19 pandemic has been one of the most consequential and broadly unpleasant events in living memory [ citation needed ] . As of the publication of this strip, it is estimated to have caused over 1.5 million deaths worldwide and over 300,000 deaths in the United States. Many more cases that have not resulted in fatality often need serious medical support and/or have lasting implications. Even for those who have been spared infection, measures to slow the spread of the virus have been highly impactful and have been ongoing for nearly a year. In consequence of all of this, many people are excited for the vaccine (which will hopefully end the pandemic). Many people online have been sharing plans for what they'll do after getting the vaccine, like "see my friends" or "travel the world." In this comic, Ponytail takes the phrase literally, listing not what she will voluntarily choose to do but what low-level involuntary systems in her body will do immediately after getting the vaccine: The next step is mentioned in the title text: The last point, which are the only things that Ponytail will choose to do is important, for a number of reasons. The vaccines currently available offer a great deal of protection to an individual patient, but that protection takes several days to even begin in a significant way. Full immunity will likely require several weeks and an additional dose. In addition, while highly effective, the current crop of vaccines are not 100% effective. And even those who develop immunity can become contaminated with the virus on their person and then transmit it to others. For all of these reasons, there is a very real fear of people who receive vaccinations immediately abandoning all other precautions and continuing to spread the virus. Genuinely ending the pandemic will require precautions to remain in place until enough of the population is vaccinated that a combination of high levels of population immunity and other distancing precautions lower the infection rate to a controllable level. Abandoning safety precautions before this occurs could extend the pandemic and cost lives. Accordingly, Ponytail's intent is to be responsible and maintain all appropriate precautions until such time as it's safe to change them. [Ponytail and Cueball are walking toward the right side of a single panel. Ponytail is gesturing with one arm.] Ponytail: The first thing I'm going to do after I get the vaccine? Ponytail: Definitely make a bunch of spike proteins and engulf them with dendritic cells. Ponytail: Then I'll probably display the antigens to my T-cells...

Flash Gatsby

Flash Gatsby

https://www.xkcd.com/2405

https://www.explainxkcd.com/wiki/index.php/2405:_Flash_Gatsby

[Cueball is sitting at a desk using his laptop.] Off-panel voice: 3... 2... 1... Happy New Year! Cueball: Okay, it’s up! Cueball: Annnnnd ... support was pulled, it’s down again. [Caption below the panel:] There's only a very short window of time in which I can post my unauthorized Flash® adaptation of The Great Gatsby .

This comic unfolds over the last few seconds of 2020 and the first few seconds of 2021. Cueball is attempting to do something requiring the overlap of two eras that only abut: creating an "unauthorized" adaptation of The Great Gatsby , using the Adobe Flash plugin platform. The Great Gatsby is a classic novel written by F. Scott Fitzgerald in 1925. Copyright law in the United States of America, where The Great Gatsby was first published, was retroactively extended several times in the 1990s and early 2000s, causing the copyright on The Great Gatsby to extend until the end of 2020 . In 2021, it finally entered the public domain so that it became legal to make a copy without violating copyright law. Adobe Flash , formerly known as Shockwave Flash, is a web plugin that was commonly used by many websites in the late 1990s and 2000s. It allowed website creators to add animations, sound, and complex logic to build games, videos, and other interactive experiences. Presumably, the Flash version of the novel is some kind of interactive reader, animated cartoon, or perhaps even a game. Over the years, Adobe Flash was repeatedly exploited by hackers, incurring heavy costs on Adobe as they tried to update Flash against these attacks after rushing features out before stabilizing them. Newer technologies are now able to provide comparable features with more compatibility, more community involvement, and less risk, so support for Flash is being phased out by most web browsers. Adobe officially ended support for Flash after December 31, 2020. In line with Adobe's decision, Chrome is blocking Flash in January . This will make entire internet culture histories spanning many years of making and engaging Flash experiences unusable for most people. Therefore, Cueball's Flash version of The Great Gatsby will become legal at the very moment that everyone should stop using it. In this comic, Cueball suggests that the withdrawal of Flash support occurs after the copyright expiration rather than simultaneously with it. This is most likely because the applicable copyright law in the United States states that the creative work becomes public domain at the end of the year 2020 and Flash gets disabled at the beginning of the year 2021. So it is conceivable (but not practical) that there is one second when the novel is public domain and Flash is still enabled. By late 2020, Flash Player was already blocked by most browsers, but could still be whitelisted on individual sites. Using old versions of browsers, or workarounds to run blocked extensions, Cueball's Great Gatsby may still be readable after the official Flash End of Life date of January 1, 2021. Even with these workarounds, Flash Player itself will block Flash content from playing on January 12, 2021, making that the final death date for official modern versions of Flash. After January 12, Flash content may still be accessible through older builds of Flash Player, and through various archival and emulation projects, such as the Internet Archive , Ruffle , BlueMaxima's Flashpoint , and SuperNova . The title wording has a number of possible meanings to it. It's the 'Gatsby' book via the medium of the electronic Flash format. Because of the briefest of availability (at best, a single moment), it appears and disappears again 'in a flash'. Being 'flash' is a very apt description of the millionaire Gatsby character himself ('Flash the cash' is being ostentatious). And, if the endeavor is not actually as legitimate as hoped, the word has also referred to felonious behaviors and forged copies. The title text references using excuses for not having read a book considered a classic. Before the end of 2020, a possible excuse for not trying to read it was it may not have been available in the format a person wanted it (such as via a flash program in this case) and it might have been illegal (copyright violation) to get it in that format. After 2020, the new excuse to not read it could be a technical one (flash doesn't work/nothing capable of running flash). Both excuses are quite flimsy; it's apparent the person really just doesn't care to read The Great Gatsby. [Cueball is sitting at a desk using his laptop.] Off-panel voice: 3... 2... 1... Happy New Year! Cueball: Okay, it’s up! Cueball: Annnnnd ... support was pulled, it’s down again. [Caption below the panel:] There's only a very short window of time in which I can post my unauthorized Flash® adaptation of The Great Gatsby .

Viral Vector Immunity

Viral Vector Immunity

https://www.xkcd.com/2406

https://www.explainxkcd.com/wiki/index.php/2406:_Viral_Vector_Immunity

[A large wooden horse statue on wheels stands before a city wall, upon which are standing several warriors who are shouting and brandishing spears.] Warrior 1: Look! It's a statue of that horrible animal that trampled Steve! Warrior 2: Burn it! Warrior 3: Smash it! Warrior 4: Push it into the gorge! [Caption below the panel:] How vaccine failure due to viral vector immunity works

This comic is another in a series of comics related to the COVID-19 pandemic . This comic is the third of five releases, following 2402: Into My Veins and 2404: First Thing , which reference the new COVID-19 vaccine . It was released on New Years day, without being a New Year comic . This had not happened since 2010. The comic attempts to explain a virus vector vaccine and one way it can fail, using the story of the Trojan Horse as an analogy. Note that neither the Pfizer/BioNTech nor Moderna vaccines are virus vector vaccines, using lipid nanoparticles for delivery rather than viruses. A vaccine is a way to familiarize a host's immune system with a pathogen without actually causing the host to fall ill. There are many types of vaccines that have been developed, all of which are ways to present a significant segment of a pathogen's molecular structure to the host body, so that the immune system recognizes the pathogen and mounts an immune response faster when a real infection happens. A viral vector is a tool used by molecular biologists to deliver genetic materials into cells. A viral vector vaccine, also known as a live vector vaccine, uses a modified virus, different from the pathogen being immunized against, as a carrier to deliver a molecular payload into the host body. This modified virus is called the vector because it is the method of delivery of a piece of the pathogen's genetic code. If the recipient has a strong immune response to the vector itself (i.e., the proteins making up the surface of the vector virus), the immunization may be less effective because the vector virus, and hence its payload of viral genetic material, will be destroyed before they can enter the host's cells. It is to some degree a dice roll, with regard to whether some recipients will already be immune to a vector. For example, a modified (to be harmless) cold virus can be used to deliver genetic material (RNA or DNA) of another virus into the patient's cells. The cells are induced to manufacture protein found in the pathogenic protein, which the patient's immune system detects and reacts to. That way the immune system recognizes the pathogenic virus without actually being infected with it, which decreases the time needed to react to a real infection. Any patients whose immune systems recognize the modified cold virus (the vector), and destroy it rapidly, won't get the full intended benefit of creating a strong immune response to the second virus (the payload inside). The comic represents this idea with the Trojan horse being the vector, carrying a payload of Greek soldiers into the cell, as represented by the City of Troy. In the original Trojan Horse story, Greek soldiers hid inside a statue of a horse which the Trojans were told was a gift to Athena; the Trojans brought it within their walls (which the Greek army had failed to penetrate in an extended siege), allowing the soldiers in the horse to undermine the city's defenses and let in the rest of their army to take the city. Note: In a viral vector vaccine, the payload inside the vector works to the benefit of the person receiving the vaccine - opposite to the soldiers inside the Trojan horse, who had only malice in mind for the city receiving the "gift" horse. In the comic the warriors, rather than finding the wooden horse a benign object, recognize the shape of the delivery vehicle (the Trojan horse) as being similar to an animal that trampled one of their own earlier and therefore refuse it entry. An amusing point here is that they are not as such surprised at the arrival of a wooden vehicle at their doorstep, rather that its shape resembling an animal they have found threatening before, which is similar to how simple in its judgements the immune system can be. (In addition, although the warriors suggest pushing the wooden horse into a gorge, there are no gorges very close to Troy, which is situated close to the sea on the Plain of Troy .) The title text is a further riff on this theme, playing on an advertising campaign for freeze dried coffee. In the advertisements a narrator would claim to have secretly replaced fresh brewed coffee with that made from freeze dried to see if subjects could tell the difference, the contents of the coffee cup being the payload and the narrator the virus vector. The test subject's use of a sword relates the situation back to the Trojan scenario of the panel. [A large wooden horse statue on wheels stands before a city wall, upon which are standing several warriors who are shouting and brandishing spears.] Warrior 1: Look! It's a statue of that horrible animal that trampled Steve! Warrior 2: Burn it! Warrior 3: Smash it! Warrior 4: Push it into the gorge! [Caption below the panel:] How vaccine failure due to viral vector immunity works

Depth and Breadth

Depth and Breadth

https://www.xkcd.com/2407

https://www.explainxkcd.com/wiki/index.php/2407:_Depth_and_Breadth

[Five panels, each containing identical copies of a rooted tree graph, grayed out in the background. The tree has a height of 3 and 15 nodes.] [In all five panels, a black twisty arrow in the foreground indicates the order in which nodes are traversed. The arrow does not complete the entire traversal but cuts off at some point. Backtracking is indicated with a dotted line.] [In the descriptions below, node 1 is the root, nodes 2 and 3 are its child nodes, nodes 4 and 5 are 2's child nodes, nodes 6 and 7 are 3's child nodes, nodes 8 and 9 are 4's child nodes, and so on up to node 15.] [Backtracking is omitted from the descriptions below, as they increased confusion when read.] Depth-first search [The arrow visits nodes 1, 2, 4, 8, 9, 5, 10, 11.] Breadth-first search [The arrow visits nodes 1, 2, 3, 4, 5, 7 [ sic ] , 6, 8.] Brepth-first search [The arrow visits nodes 1, 2, 4, 5, 8, 9, 3, 6, 10, 11.] Deadth-first search [The arrow visits nodes 1, 2, 4, 4, 2, 4, 3, 6, 12, 13, 12.] Bread-first search [The arrow starts at node 1, then immediately leaves the tree off to the right to point to a small loaf labeled "Bread".]

Tree structures are one of the most common data structures used in computer science. The common ways of enumerating items arranged in a tree is either depth-first , or breadth-first , which are depicted accurately in the comic. Randall humorously combines the words, to produce "brepth-first", "deadth-first", "bread-first", and "death-first" search algorithms. Depth-first search explores down a full branch of the tree before working back to a higher level. This type of tree structure was already discussed as inefficient for human needs in 761: DFS . The "opposite" of this is breadth-first search, which explores each level of the tree at a time. In the "brepth-first" algorithm, a depth-first and a breadth-first search are hybridized where the left-most node is visited more frequently than the right node, but the right node is still visited. This might be good for exploring data that is loosely but not strictly weighted to the left, or where data in deeper nodes needs some time to be loaded before it can be used. As implied by 761: DFS , this might be the best algorithm for a human to employ, where one can explore several topics briefly before deciding which one to explore more deeply, rather than blindly following the first rabbit hole to an absurd conclusion. Informed search algorithms like A* search , Beam search , and other Best-first search algorithms show this type of behavior by expanding the most promising node in the current set (under some appropriate metrics). The nature of the "deadth-first" algorithm is unclear and inefficient, since it searches the same nodes multiple times before moving to an entirely different region of the tree. It might be useful in a context where examining nodes has some probability of returning a noisy or incorrect result, such as searching for small objects that may be overlooked. The bread-first search is taken literally. Bread is searched for first. Since the computer user now has already met their want to find bread, the computer has no reason to explore the tree at all. [ citation needed ] The title text introduces a "death-first" search, in which the user explores what it is like to be dead, before considering anything else. Specifically, the title text refers to hell, which calls to mind the adventures of Dante Alighieri in his Inferno , and is a less likely place for keys to be left than one's coat pockets [ citation needed ] . In 2021 (the year this comic was published) there are commemorations for the 700th anniversary of Dante's Death. These are expected to take place among the living only, and not in Hell. [ citation needed ] A much more pleasant death-first algorithm might be to skip hell and purgatory and search heaven first, perhaps multiple times (which in itself would be a use of the deadth-first approach). [Five panels, each containing identical copies of a rooted tree graph, grayed out in the background. The tree has a height of 3 and 15 nodes.] [In all five panels, a black twisty arrow in the foreground indicates the order in which nodes are traversed. The arrow does not complete the entire traversal but cuts off at some point. Backtracking is indicated with a dotted line.] [In the descriptions below, node 1 is the root, nodes 2 and 3 are its child nodes, nodes 4 and 5 are 2's child nodes, nodes 6 and 7 are 3's child nodes, nodes 8 and 9 are 4's child nodes, and so on up to node 15.] [Backtracking is omitted from the descriptions below, as they increased confusion when read.] Depth-first search [The arrow visits nodes 1, 2, 4, 8, 9, 5, 10, 11.] Breadth-first search [The arrow visits nodes 1, 2, 3, 4, 5, 7 [ sic ] , 6, 8.] Brepth-first search [The arrow visits nodes 1, 2, 4, 5, 8, 9, 3, 6, 10, 11.] Deadth-first search [The arrow visits nodes 1, 2, 4, 4, 2, 4, 3, 6, 12, 13, 12.] Bread-first search [The arrow starts at node 1, then immediately leaves the tree off to the right to point to a small loaf labeled "Bread".]

Egg Strategies

Egg Strategies

https://www.xkcd.com/2408

https://www.explainxkcd.com/wiki/index.php/2408:_Egg_Strategies

[3x3 grid of egg cartons, each containing between 5-8 eggs in an arrangement matching a description of lawful/neutral/chaotic paired with good/neutral/evil. Each egg carton is depicted from a top-down view, with the lid open and the eggs and their places visible.] Top Left - Lawful Good [6 eggs centered 3 in the top row, shifted to the right 3 in the bottom row, shifted to the left] Top Center - Neutral Good [7 eggs 4 in the left side 3 in the right side, with one in the top row and two in the bottom row] Top Right - Chaotic Good [6 eggs spread randomly while preserving reflective symmetry between eggs and non-eggs] Middle Left - Lawful Neutral [5 eggs all on the bottom row, starting on the left side] Middle Center - True Neutral [7 eggs all to the left side 4 in the top row 3 in the bottom row] Middle Right - Chaotic Neutral [6 eggs staggered in every other space so that each egg is diagonal from the two nearest no two eggs are directly next to each other side-to-side or up-and-down 3 in the top row, starting in the left-most position 3 in the bottom row; starting position second from the left side] Bottom Left - Lawful Evil [8 eggs 6 in the egg carton, centered but offset one place to the left; 3 eggs each on the top and bottom 2 eggs are on top of the 6 that are placed in the carton] Bottom Center - Neutral Evil [8 eggs 3 on the bottom edge of the lid 2 in the top center positions in the egg carton 3 centered on the edge and on top of/between the eggs on the lid and the eggs in the proper positions] Bottom Right - Chaotic Evil [broken eggs in the center of the carton and spilling/splattering over the rest of the carton and onto the lid 6 or 7 yellow-orange yolks are visible the spilled egg whites are colored light yellow-greenish several pieces of eggshells, varying in size from approximately one-half to very small chips are mixed in with the yolks and whites]

Steepen the Curve

Steepen the Curve

https://www.xkcd.com/2409

https://www.explainxkcd.com/wiki/index.php/2409:_Steepen_the_Curve

[Line graph shown with a rising curve drawn in black. There is an underlined label above and another label below the graph. The Y-axis line is ending in an arrowhead and also has a label. All this is in black. But the last number in the upper label as well as one word in each of the other two labels, have been scribbled out in red and then another number or word has been written behind or beneath in red.] [Caption above the graph:] 202 0 1 [Y-Axis:] COVID Deaths Vaccinations [Caption below the graph:] Flatten Steepen The Curve

This comic is another in a series of comics related to the COVID-19 pandemic . In early 2020, the COVID-19 pandemic rapidly became the main public concern. The virus spread at an exponential rate before initial lockdowns started to reduce the trajectory for a time. The graphic drawn in black depicts exponential growth in the measure of deaths — though it is not clear (without proper units or values on either axis) if this is because it is a cumulative count of deaths or the rate of deaths per day. Such graphs were common in the spring of 2020, enough that Randall has previously parodied them in 2294: Coronavirus Charts . These graphs often showed future projections that compared continued exponential growth vs. curves that did not grow as fast, or even flattened out. Governments around the world realized that if the trend was to continue healthcare services would become overwhelmed, thus all kinds of political, civic and personal efforts were put towards doing things that would cause the 'curve' to flatten and not rise as rapidly as it would do unchecked. "Flatten the curve" thus became the rallying cry for all measures taken to reduce the spread of the virus. In 2021, the pandemic is ongoing (with second or even third 'waves' of resurgence affecting some populations that had temporarily flattened the curve) but now we have a handful of vaccines available. In 2278: Scientific Briefing , White Hat remarked that many scientific briefings use similar or identical charts, but in this briefing, a chart from the beginning of the pandemic is reprinted verbatim and then crudely updated with red ink. The red overlay intends to update the 'original' graphic to portray the number of vaccines provided (again, it could easily be either cumulative or rate-wise). With the change to what is represented, the line remains the same but the hoped-for outcome is changed accordingly. Making the curve steeper represents getting more people vaccinated faster. In both cases, there would be an upper limit on the cumulative value, but the ceiling must be well beyond the upper limits (x and y axes) of this graph. If this is a rate-graph, it would show a peak and subsequent decline at the same point in time where a cumulative graph would show an inflection in its gradient, but neither are visible here. Additionally, the analogy between the number of deaths and the number of vaccinated people could be considered as questionable, as the number of deaths in the initial stages of a pandemic is expected to follow an exponential law, whereas the same cannot be said for the number of vaccinated people. The title text gives a summary of the overall goal. Flatten the curve (of infections/deaths), Steepen the curve (of vaccinations/immunizations), Hang out. We've done the first, we're starting the second... and the third is where we can (hopefully) all hang out together again, in person, without masks or social distancing. But we have to finish the first two steps successfully to get to the third one. [Line graph shown with a rising curve drawn in black. There is an underlined label above and another label below the graph. The Y-axis line is ending in an arrowhead and also has a label. All this is in black. But the last number in the upper label as well as one word in each of the other two labels, have been scribbled out in red and then another number or word has been written behind or beneath in red.] [Caption above the graph:] 202 0 1 [Y-Axis:] COVID Deaths Vaccinations [Caption below the graph:] Flatten Steepen The Curve

Apple Growers

Apple Growers

https://www.xkcd.com/2410

https://www.explainxkcd.com/wiki/index.php/2410:_Apple_Growers

[Beret Guy and Cueball stand on either side of Megan with her hair unkempt. They stand behind a lectern with an image of an apple on the front of it. Unreadable text is written on both side of the apple in two rows.] Megan: *Ahem* Megan: The state apple-growers' association has decided to formally call on President Donald Trump to resign. [A wider shot shows Beret Guy, Megan, and Cueball on a podium behind the lectern. The visible audience consist of a Cueball-like guy, Hairy, and Ponytail, who is holding a microphone to her mouth as she addresses those on the podium.] Ponytail: Weren't you meeting to update the standards for new apple varieties? Megan: Yes, but we talked it over and this is what we decided. Megan: We feel strongly that this is important. [There is a narrow shot with a zoom in on Megan.] Ponytail (off-panel): Did you discuss anything on your actual agenda? Megan: Thanks for the question! Megan: We did not. [Beret Guy, Cueball and Megan is again seen from the front behind the lectern, Megan's hair even more unkempt.] Ponytail (off-panel): Do you have any apple-related announcements at all? Megan: Uh, apples are great. Best fruit. Everyone should buy 1,000 of them. Megan: We're a little distracted right now, okay??

On January 6, 2021, a group of supporters of President Donald Trump stormed the United States Capitol while Congress was in session to certify the results of the 2020 election , in which President Trump lost a bid for re-election. The attack resulted in an evacuation of Congress, a disruption of the operations of the legislature, and the deaths of several people. While Trump was not directly involved with the riot, he has been accused of contributing to it by consistently refusing to accept the election results, claiming that his opponent's victory was fraudulent, and using inflammatory rhetoric when speaking to his supporters. As a result, officials from both major political parties have called upon Trump to resign, and other avenues to remove him from office have been proposed. At the time of publication, Trump's second impeachment had been mooted but it, and all other events that followed, had not yet happened. Normal American life, already strained under the COVID-19 pandemic , was dealt another blow by the conflict. Normally planned events continue to be held, but the shadow of current events impacts everything. This comic depicts one such event, a news conference hosted by the State Apple Growers (of an unspecified state). This group apparently had a scheduled meeting to discuss apple variety standards, but their meeting was instead dominated by discussions of events in government, resulting in them issuing a formal statement calling upon President Trump to resign. This statement obviously has nothing to do with apples, [ citation needed ] and when pressed, the spokesperson makes generic statements in favor of apples, but points out that they're too distracted by more urgent matters to focus on their normal jobs. This strip appears to be based on a number of private companies and other organizations without specific political missions, which nonetheless felt the need to respond to the event. Famously, both Twitter and Facebook banned the president from their platforms in the aftermath. The events of the strip are reminiscent of Signature Bank and the National Association of Manufacturers calling on Trump to resign. Many national brands released statements of condemnation and announced plans to cut political contributions for legislators who voted against certification of the election results. The joke appears to be that even small and local organizations feel compelled to weigh in on an issue of this significance, even though their influence in the matter is likely minimal. Cosmic Crisp , mentioned in title text, is a variety of apples developed in the Washington State University that has been on sale since 2019, amid a large marketing campaign. The implication of the title text is that the people involved are in fact, very interested in and concerned with details of apple cultivation and marketing, and hope to return to a state in which they they can focus on those. But the more immediate draw of events makes it difficult to focus on what they usually like to talk about. Beret Guy is shown to be a member of the State Apple Growers' Association; in 2209: Fresh Pears , he sells "fresh pears" (so fresh, he doesn't even plant seeds until a customer pays for one) and expresses an interest in growing apples, and evidently has either figured out robotic grafting or chosen another approach (or maybe, given his usual eccentricity, he is only a member of the Association as an aspiring apple grower). This is one of very few comics with Beret Guy where he is not really doing anything, although this is also a weird turn of events that the Apple Growers discuss Trump. However, usually Beret Guy is not interested in real-life problems. [Beret Guy and Cueball stand on either side of Megan with her hair unkempt. They stand behind a lectern with an image of an apple on the front of it. Unreadable text is written on both side of the apple in two rows.] Megan: *Ahem* Megan: The state apple-growers' association has decided to formally call on President Donald Trump to resign. [A wider shot shows Beret Guy, Megan, and Cueball on a podium behind the lectern. The visible audience consist of a Cueball-like guy, Hairy, and Ponytail, who is holding a microphone to her mouth as she addresses those on the podium.] Ponytail: Weren't you meeting to update the standards for new apple varieties? Megan: Yes, but we talked it over and this is what we decided. Megan: We feel strongly that this is important. [There is a narrow shot with a zoom in on Megan.] Ponytail (off-panel): Did you discuss anything on your actual agenda? Megan: Thanks for the question! Megan: We did not. [Beret Guy, Cueball and Megan is again seen from the front behind the lectern, Megan's hair even more unkempt.] Ponytail (off-panel): Do you have any apple-related announcements at all? Megan: Uh, apples are great. Best fruit. Everyone should buy 1,000 of them. Megan: We're a little distracted right now, okay??

1/10,000th Scale World

1/10,000th Scale World

https://www.xkcd.com/2411

https://www.explainxkcd.com/wiki/index.php/2411:_1/10,000th_Scale_World

[At the top of the image, inside the panel, a large title is floating in the air.] RULES For visitors to my 1/10,000th scale world 1 meter = 10 km 1 ft = 10,000 ft ~ 2 miles [Each of the following rules is written near a character or point of interest on the map.] [Two small dots with thin lines coming out of them horizontally are in the air near Cueball, who is brushing them off.] Watch out for airliners cruising near shoulder level [Small mountains are seen near the left edge of the screen, by Cueball's feet.] Trip hazard: Appalachian Mountains [A young Hairy is climbing on mountains reaching approximately Cueball's waist.] Do not stand or climb on Mt. Everest [Under the water, a small bump in the ground expells bubbles.] Caution: Hydro-thermal vents underfoot [Science Girl stands shoulder-deep in the ocean, peering down into the trench below.] Children must be supervised while in the ocean, especially near trenches [Megan's hand is extended, and lightning from the cloud is jumping to her hand.] Danger: positive lightning! Do not touch cloud tops [Ponytail sits near some mountains, with a dotted line in the air stretching across her forehead.] Avoid hypoxia by regularly sitting to bring your lungs below the death zone [A blob-shaped thing with wiggly grey texture lines drawn all over is underground.] Do not dig near Yellowstone [A second Cueball is jumping in the air, a hand reached back, in position to smack a weather balloon.] Please do not smack weather balloons [Some very tiny vertical lines extend from the ground.] Be careful not to step on cities with especially pointy towers, like Toronto, Seattle, and Dubai Megan, who is touching the top of a cloud, appears to be standing on top of the ocean, but as other characters are visibly either in front of hills and mountains or standing upon their slopes, it is likely that she is stood upon the ground (at an imperceptible height above 'local' sea-level) on or just beyond a shoreline located in the almost mythical third dimension.

This comic is the first in the Scale World series. Large objects (cars, airplanes, etc.) are often reproduced as scale models , which are proportionally smaller physical models of the original objects. The scale of such a model is typically expressed as the ratio of the size of the model (the first number) to the size of the original object (the second number). For example, a 1/10,000th scale model means that 1 meter in the model represents 10,000 meters in the original object. The same applies to maps and globes . What Randall has here, though, is neither a map nor a model but a seemingly complete copy of Earth , at a 1:10,000 scale. Various features and warnings are labeled. Miniature parks , also known as model villages, are tourist attractions around the world of a scale between 1:9 and 1:72. For example, the finale of the movie Hot Fuzz features a battle amongst a miniature of the streets and buildings seen so far in the film. Normally a miniature park would feature a representation of one geographical location rather than a geologically/technologically accurate depiction of our current planet. Whether or not Randall is aware of it, the reputed largest outdoor relief map in the world is set out at a horizontal scale of 1:10,000. Real-world phenomena are reproduced at scale, for humorous effect. A real 1/10,000th scale "Earth" would have a diameter of less than a mile, and a surface area of around 2 square miles, the approximate dimensions of a medium-sized asteroid. On such an object, constrained by known physics, there would be no air, standing water, weather, or large magma bodies, and any sort of rough-housing would irrecoverably catapult the visitor into space. Normally in a miniature model, most warnings try to prevent the visitors from accidentally doing something cataclysmic to the model. Likewise, the "ocean play area rules" in the title text tell visitors not to create any megatsunamis , which could conceivably be induced by a cannonball dive. But as digging seems to be discouraged mainly where it causes volcanoes to break out, the visitors seem to be given far greater freedom than usual. Visitors are also instructed not to try to pry the model of the wreck of the Titanic off the ocean floor. In our world, the wreck is at a depth of 12,500 feet, which would be 1 foot and 3 inches in Randall's model world. The Titanic was over 882 feet long, but the ship split in half as she sank, and now lies in two pieces about a third of a mile apart. Randall's model would have two pieces about a half-inch in size separated by about two inches. If the models are rusted and sunk in mud just like the real wreck is, trying to pry them loose would certainly damage them, but all of Randall's other rules seem to be about preventing harm to guests, not preventing damage to the model, so maybe he just doesn't want guests bending over and exerting themselves in the water where they could slip, submerge their faces, and be at risk of drowning. Scale models, and the problems with them, were the subject of 878: Model Rail . In general, illustrating relative scale is a recurring subject on xkcd. This comic is also somewhat reminiscent of 941: Depth Perception . [At the top of the image, inside the panel, a large title is floating in the air.] RULES For visitors to my 1/10,000th scale world 1 meter = 10 km 1 ft = 10,000 ft ~ 2 miles [Each of the following rules is written near a character or point of interest on the map.] [Two small dots with thin lines coming out of them horizontally are in the air near Cueball, who is brushing them off.] Watch out for airliners cruising near shoulder level [Small mountains are seen near the left edge of the screen, by Cueball's feet.] Trip hazard: Appalachian Mountains [A young Hairy is climbing on mountains reaching approximately Cueball's waist.] Do not stand or climb on Mt. Everest [Under the water, a small bump in the ground expells bubbles.] Caution: Hydro-thermal vents underfoot [Science Girl stands shoulder-deep in the ocean, peering down into the trench below.] Children must be supervised while in the ocean, especially near trenches [Megan's hand is extended, and lightning from the cloud is jumping to her hand.] Danger: positive lightning! Do not touch cloud tops [Ponytail sits near some mountains, with a dotted line in the air stretching across her forehead.] Avoid hypoxia by regularly sitting to bring your lungs below the death zone [A blob-shaped thing with wiggly grey texture lines drawn all over is underground.] Do not dig near Yellowstone [A second Cueball is jumping in the air, a hand reached back, in position to smack a weather balloon.] Please do not smack weather balloons [Some very tiny vertical lines extend from the ground.] Be careful not to step on cities with especially pointy towers, like Toronto, Seattle, and Dubai Megan, who is touching the top of a cloud, appears to be standing on top of the ocean, but as other characters are visibly either in front of hills and mountains or standing upon their slopes, it is likely that she is stood upon the ground (at an imperceptible height above 'local' sea-level) on or just beyond a shoreline located in the almost mythical third dimension.

1/100,000th Scale World

1/100,000th Scale World

https://www.xkcd.com/2412

https://www.explainxkcd.com/wiki/index.php/2412:_1/100,000th_Scale_World

[At the top of the image, inside the panel, a large title is floating in the air.] RULES For visitors to my 1/100,000th scale world 1 meter = 100 km, 1 ft=100,000ft≈20 miles [Each of the following rules is written near a character or point of interest on the map.] [Dark-colored aurorae are floating in the air.] Our aurora are probably non-toxic but please stop trying to taste them [Ponytail is kneeling and breaking off part of an ice cap. In her other hand, she holds a wine glass.] No breaking off pieces of the ice caps to put in your drink [At around ankle height, a mountain is shown.] Do not step on Mount Everest [A relatively small ocean is shown on the right of Mount Everest.] Caution! [A pictogram of a person slipping.] Ocean floor slippery when wet [A cell coverage icon with one cell bar.] Warning: Limited cell network coverage above the ionosphere. Crouch down to get more bars [Megan is facing the aurorae. Thin horizontal lines are at her knees.] Wear sunscreen; the ozone layer only protects you below the knees. [Cueball is standing with three meteors whizzing both at and away from him.] Beware of chest-level meteors [A dotted line is at the Cueball from the last rule's chest.] -100°C mesopause vest recommended [A wine glass is resting on the ground near a shallow depression.] If Lake Tahoe or the Dead Sea dries up, refill them with this 5oz wine glass [​Another Cueball is standing, holding both hands up to his face.] Safety glasses required for protection from reentering spacecraft Cueball: OW! (off-panel voice): What? Cueball: I got a Soyuz in my eye [A tornado-shaped lightning sprite is hovering over a cloud.] Do not anger the sprites [A dotted line weaves belowground.] Please stop digging through the Moho. Staff are tired of cleaning up large igneous provinces. [An arrow pointing above the panel top.] ISS (14 feet up) Returns every 90 minutes Hit it with a Nerf dart, win a prize!

This comic is the second in the Scale World series. Randall has another seemingly complete scale model of Earth , this time at a smaller scale of 1:100,000 – that is, 1 meter in this scale world represents 100,000 meters in the real world. (This is one tenth the size of his previous scale world .) Again, real-world features and phenomena are depicted at scale and labeled with warnings. Details on the various remarks are in the table below. The title text states that the floor should be slightly curved. In fact, given that the model in the comic is about 10 meters long, it represents about 1000 km of Earth, which spans about 9 degrees of a great circle. Therefore, if the model wasn't larger than the part shown in the panel, its edges would have a very noticeable slope of 4.5 degrees. What's more, the note that they haven't invented artificial gravity reveals that the scale worlds are nothing more than a mundane model, rather than some supernatural phenomenon that allows giants to roam about the surface of the Earth. [At the top of the image, inside the panel, a large title is floating in the air.] RULES For visitors to my 1/100,000th scale world 1 meter = 100 km, 1 ft=100,000ft≈20 miles [Each of the following rules is written near a character or point of interest on the map.] [Dark-colored aurorae are floating in the air.] Our aurora are probably non-toxic but please stop trying to taste them [Ponytail is kneeling and breaking off part of an ice cap. In her other hand, she holds a wine glass.] No breaking off pieces of the ice caps to put in your drink [At around ankle height, a mountain is shown.] Do not step on Mount Everest [A relatively small ocean is shown on the right of Mount Everest.] Caution! [A pictogram of a person slipping.] Ocean floor slippery when wet [A cell coverage icon with one cell bar.] Warning: Limited cell network coverage above the ionosphere. Crouch down to get more bars [Megan is facing the aurorae. Thin horizontal lines are at her knees.] Wear sunscreen; the ozone layer only protects you below the knees. [Cueball is standing with three meteors whizzing both at and away from him.] Beware of chest-level meteors [A dotted line is at the Cueball from the last rule's chest.] -100°C mesopause vest recommended [A wine glass is resting on the ground near a shallow depression.] If Lake Tahoe or the Dead Sea dries up, refill them with this 5oz wine glass [​Another Cueball is standing, holding both hands up to his face.] Safety glasses required for protection from reentering spacecraft Cueball: OW! (off-panel voice): What? Cueball: I got a Soyuz in my eye [A tornado-shaped lightning sprite is hovering over a cloud.] Do not anger the sprites [A dotted line weaves belowground.] Please stop digging through the Moho. Staff are tired of cleaning up large igneous provinces. [An arrow pointing above the panel top.] ISS (14 feet up) Returns every 90 minutes Hit it with a Nerf dart, win a prize!

Pulsar Analogy

Pulsar Analogy

https://www.xkcd.com/2413

https://www.explainxkcd.com/wiki/index.php/2413:_Pulsar_Analogy

[Cueball and Ponytail are standing next to each other.] Cueball: Why do pulsars spin so fast? Ponytail: Hmm, let me think of an analogy... [A tape measure is retracting above Ponytail's head. To the right of her head, a tape measure is spinning rapidly.] Retracting tape measure: zzzzzzzzzzzzzzz Spinning tape measure: SNAP Ponytail: You know how when you retract a tape measure and let go, it leaves it spinning? Ponytail: It's like that. Cueball (off-panel): Oh, I see. [A tape measure with a laser instead of a measuring tape is spinning slowly.] Cueball (off-panel): And if the tape measure is the kind with a laser level, that's the beam of radiation? Ponytail (off-panel): Exactly! [Cueball and Ponytail are walking next to each other in silhouette.] Ponytail: And when the tape whips around and smacks your hand, that's the neutron degeneracy shockwave. Cueball: Sounds painful! Ponytail: Top cause of astronomer hand injuries.

Pulsars are a kind of old, shrunken, fast-spinning star. They are usually neutron stars . They no longer shine in all directions, but instead produce beams of radiation out of their magnetic poles, which blip by us in rapid pulses as they spin. Ponytail, an astronomer in this comic, explains a pulsar's fast rotation with an analogy about a tape measure retracting. The analogies that Ponytail picks are incredibly poor ones. Since the analogy does result in something that spins, the reader might think that, while they don't immediately see how it helps in understanding pulsars, they're willing to reserve judgment to see what is then done with the analogy; Cueball's response may suggest this sort of wait-and-see attitude. However, the analogy is likely to be useless or misleading, as the tape measure starts to rotate because the retracting tape is not moving only in a radial (in/out) direction. As a star collapses into a pulsar, its natural rotation rate is greatly amplified by its shrinking moment of inertia. Further elaborations of the analogy, rather than clarifying matters, are successively more surreal. More misleading than the tape-measure is the idea of a laser measure being "exactly" like the emissions of a pulsar, which, although both pulse, are produced in entirely different ways and are at best simply helping the mind hold the concept. When a tape measure retracts, the part of the tape outside the tape measure is not going directly towards the tape measure's center but rather towards a hole in the side. This means the tape possesses some angular momentum relative to the tape measure. In addition, when the tape measure retracts, the part of the tape inside the tape measure rotates around a spool (which pulls the part of the tape outside the tape measure inside), so it also has angular momentum relative to the tape measure. When the tape is completely retracted, the tape can no longer rotate relative to the tape measure. Because of the conservation of rotational momentum, the tape measure will start spinning at this point. While pulsars also rotate quickly due to the conservation of angular momentum, the exact mechanism is completely different. Pulsars are formed when stars collapse due to no longer performing enough fusion to produce enough heat and energy to cancel out gravity. This causes the star to contract, which causes its mass, on average, to be closer to its axis of rotation, which causes the rotational inertia (also called the moment of inertia) to decrease. If the star's angular velocity stayed constant, this would cause the angular momentum to decrease, so the star's angular velocity must increase in order to offset the decrease in rotational inertia, i.e. the star (which is now a pulsar) spins faster. This is demonstrated here . This method requires an initial rotation, which comes from the star. (The star's rotation comes from the dynamics of the gas cloud which forms the solar system in the first place.) Some tape measures have a built-in laser line level and others have a built-in laser rangefinder . Pulsars emit electromagnetic radiation out of their magnetic poles, which is similar to a laser, but unlike the laser of a tape measure, the pulsar beam is emitted through the axis of the magnetic field. The pulsing nature of a pulsar comes from when the axis of rotation is not precisely aligned with the axis of the magnetic field, and the location of the viewer as the beam sweeps by. In the tape measure analogy the beam is at a right angle to the axis of rotation, so as long as the viewing angle isn't parallel with the rotation axis, the viewer would see the laser increase and decrease periodically as it the rotating tape measure points towards or away from the viewer. While pulsars do demonstrate incredible starquakes and rotational glitches , neutron degeneracy is part of the mechanisms in which they are originally formed. During the formation of a neutron star, usually in the form of an initial inward implosion, the neutron degeneracy (basically the impossibility of neutron of occupying the same space because of fundamental constraints in physics that are studied by quantum mechanics) stops the implosion and redirects the shockwave outwards, thus producing a Supernova explosion. The analogy is with a tape measurer that hits a hand (the constraint) during its rapid rotation due to its retracting tape (the implosion) thus redirecting part of the energy towards the hand (s the supernova energy is redirected outside). However, astronomers do not usually let go of laser tape measures frequently, so they are probably not the top cause of any type of hand injuries, as Ponytail said. The title text mentions the right-hand rule in three-dimensional space. In a typical 3D coordinate system the Y-axis will point counterclockwise to the X-axis when looking down from the positive Z-axis. In academia, students are often taught to remember a number of mathematical conventions by using their actual physical right and left hands to align the axes. When the axes are in a different order, the left hand can be used instead of the right, but there are a number of common operations in engineering and physics that use the cross product in systems where the first axis might point in absolutely any direction relative to the viewer. Using the hand rules, the thumb is aimed along the first axis, the forefinger along the second, and the middle finger along the third — all at ninety degrees. So, when the first axis points off to the right, the right wrist is torqued to its full extension to make the thumb point that way while the other two fingers don't. During exams, students can be seen performing this feat. People who learn cross products early in their life may develop other approaches for remembering these things, that don't stretch the hands as much, but then adopt the common approach once taught it. [Cueball and Ponytail are standing next to each other.] Cueball: Why do pulsars spin so fast? Ponytail: Hmm, let me think of an analogy... [A tape measure is retracting above Ponytail's head. To the right of her head, a tape measure is spinning rapidly.] Retracting tape measure: zzzzzzzzzzzzzzz Spinning tape measure: SNAP Ponytail: You know how when you retract a tape measure and let go, it leaves it spinning? Ponytail: It's like that. Cueball (off-panel): Oh, I see. [A tape measure with a laser instead of a measuring tape is spinning slowly.] Cueball (off-panel): And if the tape measure is the kind with a laser level, that's the beam of radiation? Ponytail (off-panel): Exactly! [Cueball and Ponytail are walking next to each other in silhouette.] Ponytail: And when the tape whips around and smacks your hand, that's the neutron degeneracy shockwave. Cueball: Sounds painful! Ponytail: Top cause of astronomer hand injuries.

Solar System Compression Artifacts

Solar System Compression Artifacts

https://www.xkcd.com/2414

https://www.explainxkcd.com/wiki/index.php/2414:_Solar_System_Compression_Artifacts

[Irregular bands of gray are shown, shading from a white circular segment on the lower left side of the panel to completely black on the right. The bands have pixelated edges. A small white space probe is shown just outside the last dark gray band, in the completely black area. A dotted line starting from inside the dark gray area and ending at the space probe indicates that it is moving to the right, out of the gray area. Close to the white area, there are many bands packed closely together and with hard to define edges. But there are five gray areas clearly separated from the white, with a tendency to be elongated in the space probe's direction.] [Caption below the panel]: Milestone: Voyager has passed through the streaming video compression artifacts that mark the edge of the solar system

Voyager 1 is a space probe launched by the United States in 1977. Originally designed to study the outer planets of the Solar System , it is now several decades into an extended mission beyond Neptune (see #Trivia ). The Voyager probe has made history for passing many milestones of our solar system. When images are compressed by a lossy compression format (e.g. JPEG ), visual artifacts are created. Randall here is suggesting that the probe has passed the artifacts as if the artifacts were an actual feature of the solar system rather than a consequence of our technology. The banding lines he has drawn are commonly seen in old images with low bit depth. The 'solar system' in the snapshot appears to be a 4-bit greyscale-plane at a more pixelated level than the image given. It contains 16 'banded' levels from the brightest (closest zones, within this image, to the Sun) to darkest (the furthest illustrated expanses, including interstellar space), with irregular or non-trivial transitional edges but no obvious or dominant dithering/speckling or 'noise'. The Voyager image (and track) is overlaid in a white 'line drawing' format. Each apparent pixel in this low-res rendering is approximately 1 AU², where 1 AU ( astronomical unit ) is the distance from the Sun to the earth. The Sun is off the left side of the image by about 30 pixels, meaning that of all the planets in the solar system, only Neptune would have an orbit that is within the image at all (at the left edge). The heliosphere is 120 AU from the sun, in the direction that Voyager 1 is travelling: Voyager crossed that milestone in August 2012. At time of publication Voyager was just over 150 AU from the Sun, as shown in the image. Continuing on its course at 38,000 mph, or 3.6 AU/year, Voyager will reach the outer edge of the Oort cloud , the edge of our solar system, in about 300 years. The title text refers to 'our spacetime codec ', suggesting a representation of reality itself as a series of ones and zeros. If empty space is the darkest possible thing that can be represented--which may be the case when only 16 levels are available (see above)--then it is possible that dark matter is so dark that it cannot be represented: it would require a negative number, which is not available. This is the dynamic range issue mentioned. Artefacts are evident in 1683: Digital Data , and mentioned in the title text of 331: Photoshops . [Irregular bands of gray are shown, shading from a white circular segment on the lower left side of the panel to completely black on the right. The bands have pixelated edges. A small white space probe is shown just outside the last dark gray band, in the completely black area. A dotted line starting from inside the dark gray area and ending at the space probe indicates that it is moving to the right, out of the gray area. Close to the white area, there are many bands packed closely together and with hard to define edges. But there are five gray areas clearly separated from the white, with a tendency to be elongated in the space probe's direction.] [Caption below the panel]: Milestone: Voyager has passed through the streaming video compression artifacts that mark the edge of the solar system

Allow Captcha

Allow Captcha

https://www.xkcd.com/2415

https://www.explainxkcd.com/wiki/index.php/2415:_Allow_Captcha

[Header at the top of the image with white text inside a light blue rectangle]: To prove you're human, please click every box containing a verb that starts with "A" [Below the header, a series of panels in a 4x4 grid. Each panel has a word in capitals. Most of the words appear to be in buttons, and several have illegible text above or below. Some are tilted or off-center] Alike Elope Aloe Ale Avow Danny Allele Allot Askew [Two buttons, both saying]: Deny [The next two panels are joined together, with two buttons next to each other. One says "Deny" and the other "Allow". The text above reads]: [illegible].com wants to install a helper tool [With the word "Allow" printed clearly above and illegible text below]: Alto Allow Deal Delay

Captcha is designed to prevent spambots from being able to post on websites by posing challenges that humans can easily solve but that spambots and other automated programs cannot solve. The original version (used in 632: Suspicion ) asked users to identify text that was rotated, warped, or otherwise modified in order to make it more difficult for automated programs to solve. Once automated programs got good at that, new captchas were put out that exploited the fact that computers tend to be bad at image recognition, e.g. asking the user to select only images that contain cats from a grid of images of cats, dogs, and other objects (used in 1897: Self Driving ). This captcha appears to combine the two methods—with the additional hurdle that in order to pass the captcha, users must be able to not only read but also understand (i.e. know the definitions of words). However, if the goal is to allow humans but not computers to pass (although, as the next paragraph will describe, it is not the goal), this is not a good method of differentiating between the two. Any computer program that can accurately read text (and there are now many programs that can do so) would know which words start with 'A' and would be able to look up the definitions (including parts of speech) online, so this would not be effective as a captcha. Humans on the other hand, would often get confused between "ale" and "ail" or between "allot" and "a lot". The English language has no distinction between nouns and verbs by spelling, only grammatical usage, and many words in English are both nouns and verbs, depending on context and placement. In reality, however, the window is merely disguised as a captcha in order to trick human visitors into allowing the website to install "a helper tool", which may be malware, on their computer. The top of the window uses a similar shade of blue to the current version of reCAPTCHA (currently the most common brand of captcha), the prompt includes the phrase "to prove you're human", and the grid is similar to the grid used by reCAPTCHA. However, positioned to appear to humans as two reCAPTCHA boxes is a window asking viewers whether they want to allow or deny the website's request to install the supposed "helper tool". The idea is that because "allow" is a verb beginning with the letter A, human visitors would click on what they think is the box with the word allow in it but actually allow the website to install potential malware on their computer. The window attempts to disguise this by formatting many of the words in boxes as buttons and including other text in smaller font on other boxes. In addition, the captcha may be intentionally difficult so that users will be too distracted by wondering whether ale is a verb to process the meaning of the request. It should be noted that simply tricking humans would not necessarily be enough to install malware on their computer. First of all, while a person can select any part of a grid box in order to select that box, only clicking on the actual button that says allow will allow malware unto the computer. If a person clicks on another part of the supposed box, nothing will happen, so the person will likely take a closer look in order to see why the window is not being selected and then possibly realize that this is a trick as a result. Further, the website would likely not be able to specify where the permission window appears, so would not be able to fit it into the fake reCAPTCHA. In addition, the user's computer may have an anti-virus software that will prevent the computer from executing malicious code downloaded by the website. Or in order for the user to install software, a second window may pop up requiring the user to type in an administrator password, which will likely startle the user. Shady websites often use similar tactics to trick you into allowing notifications, including saying " Please allow notifications to confirm you are not a robot ". This comic combines that with a traditional reCAPTCHA to try and trick savvier users too. The title text is a another trick reCAPTCHA which is trying to make you give out your social security number by clicking the pairs of numbers that appear in your Social Security number. A social security number is a form of identification used in the United States, originally used for the Social Security Administration. Over time, this number has become a type of national identification number, so stealing these numbers would allow a scammer to commit identity fraud. Of course, it would use a different grid, as the grid pictured in the comic has words, not pairs of digits. If you can find all of the pairs then they would be able to guess your real number and thus this would be a weird kind of phishing attempt. If the grid is 4×4 (and some reCAPTCHA grids are only 3×3), then it can only show 16 of the possible 100 pairs of two digits, so any people who are successfully tricked likely would not reveal their entire Social Security numbers because some digit pairs in their Social Security numbers would not appear. However, it should be noted that this trick likely will not be as successful as the captcha-based trick because the phrase "Social Security number" will likely raise alarm bells concerning identity theft, and people who are not citizens or permanent or temporary residents of the United States will not have Social Security numbers, so they will not be able to be tricked into revealing personal information this way even if they are especially gullible. It should also be noted that the phrase "to prove you're human", while also attempting to disguise the trick, has a somewhat different implication. In the first example, the idea of the supposed captcha is that it asks the user to complete a task that human brains but not computer programs can perform accurately easily, such as image recognition. In the example in the title text, the idea of the fake captcha appears to be that humans are issued Social Security numbers (at least if they live or have lived in the United States), but computers are not. As the website does not already know the users' Social Security numbers, it would not actually be able to tell whether the user's response was correct. There is nothing to prevent programming an automated spambot program to randomly select zero to four of the boxes. Likewise, users could lie and not reveal their actual Social Security numbers, although those who realize that the supposed captcha is an attempt at identity theft will likely not complete it at all and could report it to law enforcement instead. [Header at the top of the image with white text inside a light blue rectangle]: To prove you're human, please click every box containing a verb that starts with "A" [Below the header, a series of panels in a 4x4 grid. Each panel has a word in capitals. Most of the words appear to be in buttons, and several have illegible text above or below. Some are tilted or off-center] Alike Elope Aloe Ale Avow Danny Allele Allot Askew [Two buttons, both saying]: Deny [The next two panels are joined together, with two buttons next to each other. One says "Deny" and the other "Allow". The text above reads]: [illegible].com wants to install a helper tool [With the word "Allow" printed clearly above and illegible text below]: Alto Allow Deal Delay

Trash Compactor Party

Trash Compactor Party

https://www.xkcd.com/2416

https://www.explainxkcd.com/wiki/index.php/2416:_Trash_Compactor_Party

[An ongoing party of five people is placed between two walls on wheels. There are two machines on either side of the walls, moving the walls on the left and right ever-closer in. The machines have pistons that push the walls together. Their rods are not long enough for the walls to meet in the middle, only to push the people close together. Near the left wall, Megan is sitting on a chair pushing on the approaching wall with hands and feet. Next to her is (and adult) Science Girl looking toward the other wall with her hands held up to her neck. Then follows White Hat, also with his arms raised towards his neck, he is looking at Megan's wall. Next to him is a small table with a glass and a plate with something on it, probably snacks. On the other side of the table stands Ponytail with a wine glass in her hand. She is looking to the right at Cueball, who is standing on the other side of a chair standing between them. Seems like he just got up after having been sitting there looking at the advancing wall. Now he is standing pressed up against it pushing on it with both hands.] [Caption below the panel:] I'm planning a trash-compactor-themed party for when this is all over so we can get used to standing near each other again.

This comic is another in a series of comics related to the COVID-19 pandemic . Randall is planning a party for when the pandemic is under control and it will again be acceptable to meet with people in close proximity and without a face mask or other kinds of protection. But he has realized that after more than a year, where social distancing has been a thing, it will be difficult to get people to voluntarily move closer than 1-2 m from each other. Thus to break the ice, and the social distancing, his party will have a theme - it will be a Trash Compactor Party. So he plans to install two moving walls on either side of the party room, which will slowly move together pressing people closer together. It is supposed to be a theme party, so the walls are not supposed to crush people in the end, but force them to get much closer than one meter apart. In the comic Randall shows how people might react to this after more than a year without being close to anyone not from their own family/corona bubble. Cueball and Megan are trying to push each of the walls of the trash compactor back in order to prevent it from pushing them closer to the three other people. Two of the other attendees, Science Girl and White Hat appear to be anxiously shying away from the inexorably increasing proximity of both of their neighboring guests, as they hold their arms nervously and protectively around their chests and necks. Thus reflecting the common current trend for many normal people to maintain increased personal space when meeting or passing other people out and about, compared with the pre-COVID era. Randall's claim is that this will not just go away because the restrictions are completely lifted if the pandemic comes under control. Ponytail is the one that seems least concerned; she even stands with a wine glass in her hands. She is looking at Cueball, maybe amused at the other people's reactions to a now safe situation. The title text references a high-profile instance of the trope from the original Star Wars film (later retitled Star Wars: Episode IV — A New Hope ). Han Solo utters this quip shortly after he and several other main characters bail out of a firefight and land in a trash compactor. The walls then start closing in and, as in the comic, the characters are not enthused about being pushed ever closer together, and seek to push back on the walls before being crushed. Here, the quote also expresses a sense of (a new) hope: since a common symptom of COVID-19 is a loss of smell, the fact that the characters are all able to smell their surroundings suggests that the pandemic is gone. [An ongoing party of five people is placed between two walls on wheels. There are two machines on either side of the walls, moving the walls on the left and right ever-closer in. The machines have pistons that push the walls together. Their rods are not long enough for the walls to meet in the middle, only to push the people close together. Near the left wall, Megan is sitting on a chair pushing on the approaching wall with hands and feet. Next to her is (and adult) Science Girl looking toward the other wall with her hands held up to her neck. Then follows White Hat, also with his arms raised towards his neck, he is looking at Megan's wall. Next to him is a small table with a glass and a plate with something on it, probably snacks. On the other side of the table stands Ponytail with a wine glass in her hand. She is looking to the right at Cueball, who is standing on the other side of a chair standing between them. Seems like he just got up after having been sitting there looking at the advancing wall. Now he is standing pressed up against it pushing on it with both hands.] [Caption below the panel:] I'm planning a trash-compactor-themed party for when this is all over so we can get used to standing near each other again.

1/1,000th Scale World

1/1,000th Scale World

https://www.xkcd.com/2417

https://www.explainxkcd.com/wiki/index.php/2417:_1/1,000th_Scale_World

[At the top of the image, inside the panel, a large title is floating in the air.] RULES For visitors to my 1/1,000th scale world 1 meter = 1 km 1 ft = 1,000 ft [Each of the following rules is written near a character or point of interest on the map.] [Keep hot objects off the ice sheet over the south pole neutrino observatory] [Do not bother the meteor crater ducks] [No connecting the dead sea to the ocean] [Be patient: Niagara falls will take a few minutes to fill your water glass] [Trip hazard: the Gateway arch] [Do not let ants into the Sudbury neutrino observatory] [Megan balances on the Golden Gate bridge,her legs wobbling.] [Only one person on the Golden Gate tightrope at a time] [Watch for small planes] [Drone altitude limit] [Do not remove statue of liberty LEGO minifig] [Do not remove safety caps] [Caution: sharp] [Do not mix up the USS enterprises:] [Two zeppelins float in the sky.] [No open flames in zeppelin area] [A fish at a size relevant to the characters in the strip faces towards two small two small horizontal lines, presumably whales.] [Please stop releasing goldfish in the ocean. They keep eating all the blue whales.] [An arrow points to a small line in the sky resembling an airplane.] [Warning! Choking hazard! Keep small children away from ascending/ descending airliners]

This comic is the third in the Scale World series. Yet again, Randall has a seemingly complete scale model of Earth , this time at a larger scale of 1:1000 – that is, 1 meter in this scale world represents 1000 meters in the real world. (This is ten times the size of Randall's original scale world .) Again, real-world features and phenomena (such as several underground neutrino detectors ) are depicted at scale and labeled with warnings. Several of the warnings point out humorous consequences of the scale, such as non-scaled goldfish eating scaled-down blue whales. Other than the usual homo sapiens, the introduction of non-scaled animals into the scaled world (with consistently humorous consequences) is an addition to the earlier comics of the series. [At the top of the image, inside the panel, a large title is floating in the air.] RULES For visitors to my 1/1,000th scale world 1 meter = 1 km 1 ft = 1,000 ft [Each of the following rules is written near a character or point of interest on the map.] [Keep hot objects off the ice sheet over the south pole neutrino observatory] [Do not bother the meteor crater ducks] [No connecting the dead sea to the ocean] [Be patient: Niagara falls will take a few minutes to fill your water glass] [Trip hazard: the Gateway arch] [Do not let ants into the Sudbury neutrino observatory] [Megan balances on the Golden Gate bridge,her legs wobbling.] [Only one person on the Golden Gate tightrope at a time] [Watch for small planes] [Drone altitude limit] [Do not remove statue of liberty LEGO minifig] [Do not remove safety caps] [Caution: sharp] [Do not mix up the USS enterprises:] [Two zeppelins float in the sky.] [No open flames in zeppelin area] [A fish at a size relevant to the characters in the strip faces towards two small two small horizontal lines, presumably whales.] [Please stop releasing goldfish in the ocean. They keep eating all the blue whales.] [An arrow points to a small line in the sky resembling an airplane.] [Warning! Choking hazard! Keep small children away from ascending/ descending airliners]

Metacarcinization

Metacarcinization

https://www.xkcd.com/2418

https://www.explainxkcd.com/wiki/index.php/2418:_Metacarcinization

[White Hat and Cueball are walking together. White Hat has his smartphone out in his hand. White Hat: Have you seen this video of a crow sledding on a roof? Cueball: Yeah! It's always cool to see animals using tools. Cueball: Like how sea otters use rocks to open crab shells. Cueball: Hey, did you know the "crab" body plan has evolved multiple times? [Caption below the panel:] Regardless of the starting topic, any conversation with me eventually converges to carcinization.

The comic strip opens with a conversation between White Hat and Cueball as they are walking together. White Hat asks Cueball if he has seen a video of a crow sledding on a roof — presumably this one , or one of its later viral reposts. ( Animals sledding seems to be a thing lately). In this case, the crow is a Hooded Crow . Cueball remarks that it's a cool example of tool use by animals , a sign of intelligence (which corvids [Corvidae; the crow family], including crows, ravens, and jackdaws , are famous for). He then points out that sea otters use tools too, namely using stones to crack open crab shells. This in turn leads him to bring up the fact that the 'crab' body plan has evolved multiple times, a phenomenon known as carcinization , previously discussed in 2314: Carcinization . In that strip, Cueball turned into a crab shortly after hearing about carcinization, so perhaps White Hat will likewise be transformed momentarily. The conversation serves as an example of a wiki walk , where a conversation naturally diverts from the original topic into a seemingly unrelated topic through a series of logical associations. Although a sledding crow has little to do with carcinization in and of itself, the conversation has managed to bridge the two topics through intermediary steps (crow using a sled, animals using tools in general, otters using stones to open crabs, crab evolutionary process). The title and caption is a joke that, much like natural life-forms have evolved into crab-like forms multiple independent times, so too do all of Cueball's (or Randall's) conversations wiki-walk into a discussion of that evolutionary process. In the title text, Randall jokes that marine biologists have a similar tendency to bring up whalefall (or "whale fall") ecosystems, which arise whenever a whale's carcass falls onto the deep ocean floor and are thought to provide "stepping stones" for species migration across the generally barren seafloor. Such occurrences are relatively rare, perhaps occurring once every few miles on whale migration routes, but they happen anyway, much like conversations about them. Another example of scientists tending to bring up facts from their field of study can be found at 1610: Fire Ants , and Randall often brings up the fact that birds evolved from dinosaurs. [White Hat and Cueball are walking together. White Hat has his smartphone out in his hand. White Hat: Have you seen this video of a crow sledding on a roof? Cueball: Yeah! It's always cool to see animals using tools. Cueball: Like how sea otters use rocks to open crab shells. Cueball: Hey, did you know the "crab" body plan has evolved multiple times? [Caption below the panel:] Regardless of the starting topic, any conversation with me eventually converges to carcinization.

Hug Count

Hug Count

https://www.xkcd.com/2419

https://www.explainxkcd.com/wiki/index.php/2419:_Hug_Count

[A bar graph is shown with 25 black bars and one gray at the far right. Most of the bars have a height around the center of the graph, but the one in the middle is clearly higher than all others, and the two before and after are lower than average. There are also a couple of high bars in pairs on either side of the central spike. The far-right, however, are two very low bars, with the last in gray less than half the height of the previous, which was already only a third of the next lowest bar. There are numbers on both axes. The X-axis has the year for every fifth year below the relevant bar, and the number of hugs is given in intervals of 10 on the Y-axis. The Y-axis has ticks for every number, but those with labels are longer. The chart has a title written above:] Estimated Number of Distinct People Hugged per Year [Y-axis:] 30 20 10 0 [X-axis:] 2000  2005  2010  2015  2020

This comic is another in a series of comics related to the COVID-19 pandemic . The comic displays a bar chart showing the number of Individuals Randall has hugged per year, spanning from 1996 to 2021, and goes up to 35 individuals hugged in 2007. The apparent spike in the estimate for 2007 may have been chance or may have been a known social event that Randall remembers, such as a family reunion or anticipated parting from a social group (such as a school or job from which he left), where he hugged many people he otherwise would not have hugged. While it varies a decent amount for the first 24 years, it drops sharply in 2020 and goes even lower in 2021. However, it should be noted that 2021 (at the time of the comic) had just begun, which is why the final bar is grey. It seems he is down to only two people hugged in 2021, one of which is most likely his wife. In 2020 he managed 5 different hugs, but the extra three may have been before the onset of COVID-19 precautions in the US. This is because in 2020 when the pandemic happened, everyone had to social distance and avoid contact with strangers. This was a widely used method of slowing the spread of COVID-19. People are asked to not closely associate with those outside a very limited 'bubble' or even isolate themselves in their own household. As such, people have had less physical contact with each other since the beginning of this pandemic, including hugs. No explanation is given for the variations year-to-year preceding 2020, and much of it may be random walks . However, one can see a major spike in hug levels in 2010 and 2011; Randall's wife was diagnosed with cancer in late 2010 (see Category:Cancer ). Loved ones of those with cancer tend to receive much compassion from others, and compassion tends to beget hugs. The title text states that, while Randall isn't very big on hugs, he too desires hugs. It plays on the common phrase "I'm not too big of an (x) person", which is used to indicate that someone isn't extremely fond of said activity. One could then infer the person is not fond of the activity at all, though in this case, he indicates his desire for hugs is non-zero, as presumably demonstrated by the frequency being now less than even he would prefer. [A bar graph is shown with 25 black bars and one gray at the far right. Most of the bars have a height around the center of the graph, but the one in the middle is clearly higher than all others, and the two before and after are lower than average. There are also a couple of high bars in pairs on either side of the central spike. The far-right, however, are two very low bars, with the last in gray less than half the height of the previous, which was already only a third of the next lowest bar. There are numbers on both axes. The X-axis has the year for every fifth year below the relevant bar, and the number of hugs is given in intervals of 10 on the Y-axis. The Y-axis has ticks for every number, but those with labels are longer. The chart has a title written above:] Estimated Number of Distinct People Hugged per Year [Y-axis:] 30 20 10 0 [X-axis:] 2000  2005  2010  2015  2020

Appliances

Appliances

https://www.xkcd.com/2420

https://www.explainxkcd.com/wiki/index.php/2420:_Appliances

[The comic is laid out like a grid, with usages for common household appliances the left-hand side (Make toast / Wash dishes / Cook a frozen dinner / Wash clothes / Cook eggs / Dry clothes) and appliances for these activities across the top (Toaster / Dishwasher / Microwave / Washing machine / Stove/oven / Dryer). The grid illustrates the "match-ups", with a green square denoting a "correct" match-up, a yellow square denoting something that may work somewhat, and a red square denoting something that most certainly won't work.] [From the top left corner, going from left to right, top to bottom, with each first item being on its own line in the grid, the images in the squares are as follows:]

This comic shows a confusion matrix of the applicability of various household appliances to different tasks. Green indicates an excellent performance, yellow not ideal, but usable, and red dismal or destroyed. The diagonal is green as it shows the tasks done by the machines they are supposed to be performed by. See table below. The comic is similar to 1890: What to Bring , but that comic does not use yellow or another intermediate color. Salmon can be easily cooked in a dishwasher , so it's marked "cooked", and thus "cook a frozen dinner" is only yellow on the dishwasher entry. The stove/oven has three green as it can also cook a microwave frozen dinner, although slower, and can toast bread, again slower than the toaster. It is by far the machine that has the fewest red entries, only one, as it cannot wash clothes. It can also not clean dishes, but it might sterilize them, thus that entry is yellow. It may actually dry the clothes, but is liable to burn them and is therefore yellow. The microwave oven can also cook eggs, thus it has two green, the only other than the stove/oven with more than one green. The toaster and the washing machines are the only ones without any yellow, and with only one green, for making toast/washing clothes - they are thus the appliances with the fewest other potential uses (zero). The washing machine will at least not destroy the clothes if you try to dry them, but it has the opposite effect, thus still red. The toaster will not destroy the dishes, but will potentially just make the dirt burn harder. The title text mentions that it would be theoretically possible to cook eggs in a dryer, but it is not a common use for a dryer. [ citation needed ] The joke is that it is not called scrambled eggs but tumbled eggs. It also mentions that the dryer has to become hotter than usual for a dryer (maybe dangerously hot for the clothes for it to work). And then the eggs should be cracked and put in an oven bag, that really needs to be tight and well zipped. [The comic is laid out like a grid, with usages for common household appliances the left-hand side (Make toast / Wash dishes / Cook a frozen dinner / Wash clothes / Cook eggs / Dry clothes) and appliances for these activities across the top (Toaster / Dishwasher / Microwave / Washing machine / Stove/oven / Dryer). The grid illustrates the "match-ups", with a green square denoting a "correct" match-up, a yellow square denoting something that may work somewhat, and a red square denoting something that most certainly won't work.] [From the top left corner, going from left to right, top to bottom, with each first item being on its own line in the grid, the images in the squares are as follows:]

Tower of Babel

Tower of Babel

https://www.xkcd.com/2421

https://www.explainxkcd.com/wiki/index.php/2421:_Tower_of_Babel

[The Tower of Babel is shown. It has a broad two sectioned base and above that extends straight up out of the top of the frame, with 10 identical segments. This is seen from afar, so the three people standing at the base of the tower is very small. But Cueball and Megan can be easily identified. They are standing on either side of a woman with big curly hair (which is first clear in the next panel). The text spoken is written over the tower in white sections that hides the tower. But the tower can be seen above, between and below these two text segments:] Cueball: The Tower of Babel is complete! Megan: Let's go meet God! [Cueball, the curly haired woman and Megan are now standing at the top of the Tower of Babel. The top is made of bricks, but the part of the last segment before the top looks like those shown in the first panel. God is represented by an off-panel voice coming from a star burst at the top of the panel. The three people look up in that direction.] Cueball: Hi God! God (off-panel): Wow, nice tower! God (off-panel): You did a great job! I'm so proud! Megan: Thanks! [Same settings but Megan has turned towards the curly haired woman holding an arm out towards her. The woman has taken one hand to her chin.] God (off-panel): I'm going to give you a reward. God (off-panel): What do you like about the world? Curly haired woman: Hmm. Words are really cool. Megan: No, wait- [Same settings, in a broader panel. The curly haired woman lifts her hands up curled into fists. Her yell comes from a starburst over her head, to indicate the difference to normal speech. Megan has taken her arm down.] God (off-panel): Great! I'm going to give you lots of languages to study, each with its own phonology, word ordering, morphosyntactic alignment... Curly haired woman: YESSSSSS! Megan: We should not have brought a linguist. In 2381: The True Name of the Bear , sentences spoken by the curly haired-woman, the suspected Gretchen McCulloch do not have periods at their ends, a fact which she mentioned on Twitter. However, in this comic, she uses periods, so her previous periodlessness might be a coincidence and not a trait of her character on xkcd.

The story of the Tower of Babel is the Biblical explanation for the existence of different languages in the world. In the story, humans endeavor to build a tower reaching heaven. Their arrogance angers God and prompts him to sabotage the project. He does this by "confounding their speech" (commonly interpreted as giving everyone their own language), inhibiting their ability to work together. In this retelling, however, the events are the same, but the motives changed. God is pleased with the tower, and promises to create a diversity of languages, not as a punishment, but as a reward for the member of the party who finds words interesting. Megan seems to recognize the potential issues this would cause, but the word-loving woman is enthusiastic. This plays on Randall 's various geeky interests, recognizing that complexities of the world, which frustrate many people, are a source of great joy and interest to others. A world with only one language would make travel and global communication much easier, but for those with an interest in linguistics, it would be deeply limiting, as there would be only one language to study. The party that ascends to the top of the tower consists of Cueball , Megan and a curly-haired woman, who may be the linguist Gretchen McCulloch as she was depicted in 2381: The True Name of the Bear . Phonology is the study of the sounds used in a language or dialect, or of the systems that languages use to organize sounds. For example, English has the words "light" and "right", indicating a distinction between /l/ and /r/, but other languages, such as Japanese, do not, resulting in the (in)famous stereotype. On the other hand, English does not make a distinction between /u/ and /y/, while French does, having words such as "le but" (the goal) and "le bout" (the tip). Word order is the study of order of the parts of a language, e.g. the subject, object, verb, and other modifiers. English uses the subject–verb–object order ("She loves him"), but other languages use subject-object-verb ("She him loves") and other permutations of these orders. Morphosyntactic alignment is the relationship between the "roles" in a sentence, and how they relate to transitivity. The vast majority of world languages, including English, use nominative-accusative alignment. In nominative-accusative languages, the subjects of transitive verbs (verbs with objects) and the subjects of intransitive verbs (verbs without objects) are treated the same, and differently from the objects of transitive verbs. For example, "She sees him" and "She runs" use the same word "she". However, other forms exist like ergative-absolutive alignment, where the subject of an intransitive verb matches the object of a transitive verb ("She sees him" and "Her runs"), transitive alignment, where the subject and object of a transitive verb are the same and different from the subject of an intransitive verb ("Her sees him" and "She runs"), or split-S and split ergativity, where it follows nominative-accusative or ergative-absolutive based on context. For example, if it depends on animacy, you could have "She (the person) runs", but "Them (the trees) fall". The title text expands the joke by suggesting that the miscommunication caused by the Tower of Babel is not due to language barriers, but instead because linguists have created intentionally meaningless sentences to illustrate points about grammar, and identifies two famous examples of such. " Colorless green ideas sleep furiously ", coined by linguist Noam Chomsky in 1957, is an example of a sentence that is structurally correct but contains paradoxes and meaningless comparisons: Something cannot be both colorless AND green (see Invisible Pink Unicorn ), ideas do not sleep, and sleeping generally is not done furiously. [ citation needed ] That said, the sentence "colorless green ideas sleep furiously" is so well known in linguistics that a competition to make the sentence meaningful was held in 1985 and attracted a number of entrants . "More people have been to Russia than I have" is an example of comparative illusion . This sentence seems to make sense at first, but upon deeper analysis does not. Many people misinterpret its meaning as "I do not own/have in my household as many people as those who have been to Russia." [The Tower of Babel is shown. It has a broad two sectioned base and above that extends straight up out of the top of the frame, with 10 identical segments. This is seen from afar, so the three people standing at the base of the tower is very small. But Cueball and Megan can be easily identified. They are standing on either side of a woman with big curly hair (which is first clear in the next panel). The text spoken is written over the tower in white sections that hides the tower. But the tower can be seen above, between and below these two text segments:] Cueball: The Tower of Babel is complete! Megan: Let's go meet God! [Cueball, the curly haired woman and Megan are now standing at the top of the Tower of Babel. The top is made of bricks, but the part of the last segment before the top looks like those shown in the first panel. God is represented by an off-panel voice coming from a star burst at the top of the panel. The three people look up in that direction.] Cueball: Hi God! God (off-panel): Wow, nice tower! God (off-panel): You did a great job! I'm so proud! Megan: Thanks! [Same settings but Megan has turned towards the curly haired woman holding an arm out towards her. The woman has taken one hand to her chin.] God (off-panel): I'm going to give you a reward. God (off-panel): What do you like about the world? Curly haired woman: Hmm. Words are really cool. Megan: No, wait- [Same settings, in a broader panel. The curly haired woman lifts her hands up curled into fists. Her yell comes from a starburst over her head, to indicate the difference to normal speech. Megan has taken her arm down.] God (off-panel): Great! I'm going to give you lots of languages to study, each with its own phonology, word ordering, morphosyntactic alignment... Curly haired woman: YESSSSSS! Megan: We should not have brought a linguist. In 2381: The True Name of the Bear , sentences spoken by the curly haired-woman, the suspected Gretchen McCulloch do not have periods at their ends, a fact which she mentioned on Twitter. However, in this comic, she uses periods, so her previous periodlessness might be a coincidence and not a trait of her character on xkcd.

Vaccine Ordering

Vaccine Ordering

https://www.xkcd.com/2422

https://www.explainxkcd.com/wiki/index.php/2422:_Vaccine_Ordering

[Megan and Cueball are talking. Megan is looking down and reading a news story on her phone.] Megan: The CDC says it's okay to mix and match the mRNA vaccines for doses 1 and 2, but only in "exceptional situations". Cueball: I wonder which order works better, if either. [A slimmer panel. Megan has her finger raised and her phone to her side] Megan: Well you know what they say. Megan: Moderna before Pfizer, you'll be none the wiser. [A regular panel, Megan and Cueball still standing next to each other.] Megan: Pfizer before Moderna then you'll... rule ancient Smyrna. Cueball: Weird side effect. Megan: A lot of hard-to-rhyme drugs have those.

This comic is another in a series of comics related to the COVID-19 pandemic , specifically regarding the COVID-19 vaccine . Two COVID-19 vaccines have been approved in the United States (one from Moderna , the other from a joint venture between Pfizer and BioNTech ). Each of these vaccines require 2 doses, taken 3-4 weeks apart. Megan is reading an article on her phone to Cueball. A report from the CDC says that it's possible to get effective immunity against COVID-19 when mixing mRNA vaccine doses from Pfizer and Moderna, but that this practice should not be the norm. The report in question can be viewed here ; it stresses that mixing the vaccines is acceptable only in exceptional circumstances, such as "when the first-dose vaccine product cannot be determined." Cueball wonders whether the order in which you receive the vaccines matters. Megan then attempts to create mnemonic devices to help them remember which mix-and-match strategy is best for the mRNA vaccines (e.g., "Beer before wine and you'll feel fine; wine before beer and you'll feel queer"). She "concludes" that receiving the Pfizer vaccine after the Moderna one will be just as effective as having two doses of either, but that having the Moderna vaccine after Pfizer's will lead to the patient becoming the ruler of an ancient city. Megan might mean that the patient will be literally transported back in time, as she and Cueball (and Black Hat ) were in 2321: Low-Background Metal . The apparent truthiness of these mnemonics might be attributed to the rhyme-as-reason effect , a cognitive bias that is often misleading - very much so in this case. Megan succeeds by rhyming "Pfizer" and "wiser," but struggles with finding a rhyme for "Moderna," settling for Smyrna , an ancient city located in what is now Izmir , Turkey. A side effect of a drug is an effect incidental to the intended purpose of the drug. Side effects can be positive or negative, though in vaccine trials the greater concern is usually about negative side effects. Becoming ruler of an ancient city that is now only a historical ruin would certainly be an unexpected side effect. [ citation needed ] The title text continues the theme of difficult rhymes, using the full names of both the Moderna vaccine drug ( mRNA-1273 , rhymed with banshee ) and the Pfizer one ( tozinameran , rhymed with catamaran ). [Megan and Cueball are talking. Megan is looking down and reading a news story on her phone.] Megan: The CDC says it's okay to mix and match the mRNA vaccines for doses 1 and 2, but only in "exceptional situations". Cueball: I wonder which order works better, if either. [A slimmer panel. Megan has her finger raised and her phone to her side] Megan: Well you know what they say. Megan: Moderna before Pfizer, you'll be none the wiser. [A regular panel, Megan and Cueball still standing next to each other.] Megan: Pfizer before Moderna then you'll... rule ancient Smyrna. Cueball: Weird side effect. Megan: A lot of hard-to-rhyme drugs have those.

Project Orion

Project Orion

https://www.xkcd.com/2423

https://www.explainxkcd.com/wiki/index.php/2423:_Project_Orion

[Cueball is raising his arm, holding the hand tilted down with palm up towards White Hat. Above them is the words Cueball says (without a speech line showing this). The first three lines are in normal font, but then successive lines fade to lighter and lighter gray and finally in the fourth line, just above their heads, the text is almost white. The overall effect is that Cueball's words gradually become background noise to White Hat.] Cueball: Our garden grew really well last year, so we think we might put a second raised bed along the garage, if we can find a... [Only White Hat is shown, without text, as he stares away from where Cueball must be off the edge of the panel.] [Only White Hat again, who now seems to look straight out of the panel.] [Back to the original setting. Cueball has lifted both hands up in front of him. He once again has the attention of White Hat. The text above begins with a line half hidden under the top of the panel, almost white font, and then the text fades back to black font over the next three lines, with the next, and last, line in his first paragraph all in black. And then a small gap and connecting line between this and the last two lines of text in his second paragraph. This time there is also with a speech line down to Cueball. The text from "..." to the first comma is difficult to read as only bottom half is shown, and in very faded font.] Cueball: ...thanks to X ray ablation, the pusher plate would absorb the nuclear blast, recoil, and then return to position for the next bomb. Cueball: Such a wild idea! Probably good that it was abandoned. [Caption below the panel:] If you temporarily tune out while a physicist is talking, when you tune back in they'll be talking about Project Orion.

White Hat and Cueball are having a conversation. In the first panel, Cueball is telling White Hat about his gardening experiences. White Hat tunes out for the middle two panels, and when he starts paying attention again, Cueball is discussing Project Orion . Project Orion was an ambitious idea, funded briefly by the US government in the 1960s, to launch enormous spaceships into orbit by detonating a series of nuclear bombs below them. The force from the explosions would be absorbed by a pusher plate on the bottom of the rocket, which is the detail Cueball is sharing when White Hat tunes back in. In Ad Astra , Roy McBride uses a similar mechanism to get from Neptune back to Earth. It was considered feasible for construction, but abandoned because of the 1963 Partial Test Ban Treaty as well as out of concerns for both cost and the idea of spaceships literally armed with atomic bombs. People probably daydream about this project because it seems like it could provide for rapid and massive entry into space, but it was halted due to the intense danger. We may have sufficient technology to somehow make this safe with extensive additional engineering, but the risk is still so large it has not been pursued. The fact that physicists' conversations tend to converge towards Project Orion is similar to how Randall's conversations tend to converge towards carcinization in 2418: Metacarcinization . Cueball turned into a crab (i.e., he carcinized) when Megan first told him about carcinization in 2314: Carcinization ; hopefully physicists don't do something analogous when discussing Project Orion. The title text transitions to another cool nuclear rocket technology, dusty plasma fission fragment rockets , which also uses nuclear energy, and would fit well in the 2326: Five Word Jargon collection. Project Orion has been mentioned before, in 786: Exoplanets , where Beret Guy sums it up as "nuke-riding city ships", and on what if? . [Cueball is raising his arm, holding the hand tilted down with palm up towards White Hat. Above them is the words Cueball says (without a speech line showing this). The first three lines are in normal font, but then successive lines fade to lighter and lighter gray and finally in the fourth line, just above their heads, the text is almost white. The overall effect is that Cueball's words gradually become background noise to White Hat.] Cueball: Our garden grew really well last year, so we think we might put a second raised bed along the garage, if we can find a... [Only White Hat is shown, without text, as he stares away from where Cueball must be off the edge of the panel.] [Only White Hat again, who now seems to look straight out of the panel.] [Back to the original setting. Cueball has lifted both hands up in front of him. He once again has the attention of White Hat. The text above begins with a line half hidden under the top of the panel, almost white font, and then the text fades back to black font over the next three lines, with the next, and last, line in his first paragraph all in black. And then a small gap and connecting line between this and the last two lines of text in his second paragraph. This time there is also with a speech line down to Cueball. The text from "..." to the first comma is difficult to read as only bottom half is shown, and in very faded font.] Cueball: ...thanks to X ray ablation, the pusher plate would absorb the nuclear blast, recoil, and then return to position for the next bomb. Cueball: Such a wild idea! Probably good that it was abandoned. [Caption below the panel:] If you temporarily tune out while a physicist is talking, when you tune back in they'll be talking about Project Orion.

Normal Conversation

Normal Conversation

https://www.xkcd.com/2424

https://www.explainxkcd.com/wiki/index.php/2424:_Normal_Conversation

[Randall, drawn as Cueball wearing a white face masks, is talking to Cueball wearing a face mask with striped pattern.] Randall: So how's...everything. Randall: I mean, I know everything is, um...but are you, uh... Randall: Sorry, I feel like the pandemic has destroyed my ability to have a conversation like a normal human. Cueball: Haha, I know, right? [Caption below the panel:] I'm at least glad I have this excuse now.

This comic is another in a series of comics related to the COVID-19 pandemic . Randall / Cueball has shown in many comics the difficulty of making small talk, or having a "normal" conversation, when you spent your developing years developing work skills ( comics of this are here ), a trait of nerds such as engineers that is frequently used as material in comics . With the COVID-19 pandemic, he feels that others may have difficulty having normal conversations as well, and so this seems to be a "silver lining" for the pandemic. He can now use this excuse instead of having to admit that he has difficulty in social situations (and always has, even before the pandemic). Randall also uses a false but plausible excuse to cover unusual nerd behavior in 1900: Jet Lag . He also uses another excuse which can get him out of life in general in 880: Headache . In the title text, he shows his dislike, which existed prior to the pandemic, of going to crowded bars. In the future, even after the pandemic passes, Cueball will still have the excuse that the pandemic made him feel uncomfortable in crowded bars due to possible virus spread and that the feeling has persisted past the pandemic. Cueball remarked on his good fortune in 2276: Self-Isolate , as it turns out he has been "practicing social distancing" all his life, but that it has now finally become common practice. [Randall, drawn as Cueball wearing a white face masks, is talking to Cueball wearing a face mask with striped pattern.] Randall: So how's...everything. Randall: I mean, I know everything is, um...but are you, uh... Randall: Sorry, I feel like the pandemic has destroyed my ability to have a conversation like a normal human. Cueball: Haha, I know, right? [Caption below the panel:] I'm at least glad I have this excuse now.

mRNA Vaccine

mRNA Vaccine

https://www.xkcd.com/2425

https://www.explainxkcd.com/wiki/index.php/2425:_mRNA_Vaccine

[Cueball seated in a doctor's office getting a dose of a COVID-19 vaccine. Both he and the doctor are wearing masks; the doctor is also wearing a scrub cap.] Doctor: The vaccine contains mRNA instructions for making the virus spike protein. Cueball: Weird, so the vaccine is just blueprints? Doctor: Yup! Your body reads the mRNA, makes the proteins, and then has an immune reaction to them. Cueball: Why would my body attack something it made itself? Doctor: Well... [Princess Leia and General Dodonna in frame.] Leia: Here are the Death Star plans. Dodonna: Thank you, Princess. [Dodonna, Ponytail, and White Hat in frame.] Dodonna: These blueprints are from Princess Leia. Ponytail: Ugh, she's always giving us projects. [Ponytail and Cueball in frame.] Ponytail: Here, take these blueprints to your construction crew. Cueball: Affirmative. What is it? Ponytail: No idea. Something the Princess wants. Cueball: Copy that. Panel heading: Soon... [A view from outside of the Death Star.] Voice from Death Star: Hi, Commander? Construction crew B here. [A view from inside the Death Star, with a planet visible through two adjacent windows. Cueball is standing at some kind of control/communications panel.] Cueball: We finished building the Princess's big metal orb thing. [A view from outside the Death Star again, with the curve of the planet in the foreground.] Voice from Death Star: Do you know if she wants us to park it somewhere, or— Voices from the planet: AAAAAA!!! [A view from the planet's surface with the Death Star in the sky. 3 Cueballs, a Megan-like character, and Ponytail are on the planet's surface.] Voice from Death Star: ...Is everything ok? Cueball 1: AAAAAAA! Cueball 2: Imperial battle station!!! Ponytail & Cueball 3: AAAAAAAAAA Offscreen voice: Red Alert Red Alert [Another view from the planet's surface. There is some type of military encampment surrounded by an open field, with trees and mountains in the background. People are running around on the field, which also contains several currently grounded craft and several flying craft streaming toward the Death Star.] Death Star voice: Hello? Generic field voices: Get the fighters in the air! Red Alert Blow it up! Blow it up! AAAAA Generic tree voices: AAAAAaa Generic spacecraft voices: Kill it kill it kill it kill it kill it kill it [A zoomed-in view of the outside of the Death Star, which is accumulating light damage. Numerous spacecraft are shooting at it; various explosions occur on the Death Star's surface and in space nearby.] Death Star voice: Hello? Generic spacecraft voices: Shoot it! Shoot it! Shoot it! That armor's too strong! We're not getting through! Keep firing! [A view from inside the Death Star again with Cueball at the control panel and the planet in the background windows; various projectiles and explosions can be seen through the window.] Cueball: Can everybody please just chill? We don't even have the laser thing wired up. We— BOOM Hey!! I said , we... [Ponytail enters from the left, and points to her left. Princess Leia points at her.] Ponytail: We can't get through! We're running out of proton torpedoes! Leia: Send every crew to build more torpedoes! Ponytail: There aren't enough ships to— Leia: Build more ships!! [Ponytail is standing still and Princess Leia is walking to the right with her fists raised.] Ponytail: That thing is just sitting there. Are you sure we— Leia: Keep building ships! Build ships forever! Destroy the orb! [A view of the Death Star in space and the curvature of the planet off to the side. An enormous torrent of (barely visible) ships is seen streaming from the planet's surface to the Death Star. The damage to the Death Star is slightly worse.] Generic ship voices: aaaaAAAAAAAAaaaaa Death Star voice: What is wrong with you people? [Back in the real world, Cueball is standing with arms hunched and a cartoon helix above his head. Megan stands next to him.] Cueball: Definitely feeling a little sore. Megan: Yeah, they said you might have some side effects. Megan: You lie down—I'll get you some hot tea and a blanket. [An outside view of the damaged Death Star with ships swarming it.] Generic voices: Die die die die! Die! [An inside view; Cueball appears injured, and the control panel is damaged with a fire on the ground nearby.] Cueball: I hate you all so much. [The outside of the Death Star again.] Ship 1: What's that?! Ship 2: Looks like a thermal exhaust port. Ship 3: I'm going in! [The outside of the Death Star.] pew pew pew pew pew pew [Beat panel.] [The Death Star explodes.] [A disheveled Dodonna, Princess Leia, and Ponytail in frame.] [The same frame.] Leia: Good work. [In the real world, Cueball sits on top of a bed with a blanket draped over his lap. Megan stands next to the bed.] Cueball: I'm feeling better today. Megan: That's great! Panel heading: A few months later... [Cueball and White Hat walking past each other. Cueball is wearing a face mask; White Hat isn't but coughs into his elbow.] White Hat: Cough cough [The real Death Star drifts toward the planet.] Death Star voice: We have reached the rebel system, Lord Vader. [View from inside the real Death Star.] Vader: Now they shall witness the firepower of this fully armed and oper— [Leia, Ponytail, and Cueball in frame.] Leia: Thermal exhaust port!! Ponytail: Aaa Cueball: Aaa [An equally large torrent of ships stream from the planet to the real Death Star.] Death Star voice: What. Various ships: aA AAAAAAA aaa aAAAAAAA aaa AAAAAA aaa aAAAAA [The Death Star explodes, leaving debris trailing away.] [In the real world, White Hat and Cueball continue to walk past each other.] Cueball: ♫ ♫

This comic is another in a series of comics related to the COVID-19 pandemic , specifically regarding the COVID-19 vaccine . This one is another analogy to how mRNA vaccines work, by creating inactive fragments of the virus to prime the immune system to be prepared to stave off the real thing. This is done in response to Cueball's question to the person vaccinating him, "Why would my body attack something it made itself?", using elements of the film Star Wars: Episode IV as an analogy. The analogy starts in the second panel, where the Rebel Alliance has retrieved the Death Star plans, conveyed by Princess Leia to General Jan Dodonna (in Star Wars , via R2-D2 and some adventures, but shown as a simple handoff here). The Death Star is a space station the size of a small moon that has the power to destroy planets. In the film, the plans are analyzed to find a weakness in the enemy Death Star and destroy it; however, in this panel, the "Death Star plans" are passed down a line of people until they are interpreted as a construction assignment and are used to build a Death Star. In the analogy, the mRNA in the vaccine corresponds to the plans for the Death Star, the spike proteins (inactive COVID-19 virus fragments) correspond to the benign Death Star itself, and the cellular processes that build spike proteins correspond to the builders of the benign Death Star. Just as merely having the plans on hand led to the Death Star being built, the mere presence of the mRNA in the cellular environment leads to it being translated, producing the viral protein. Amusingly, as the plans are handed off to the construction crew leader, he replies "Copy that," which both acknowledges the handoff in conversation and presages his actions. After Leia's Death Star has been built, it is positioned near a planet/moon. This Death Star is benign : it only looks dangerous and isn't about to actually hurt anyone; the Death Star crew are Rebels, after all, and state that they don't have the laser wired up. The Rebels mobilize to destroy this benign Death Star because it looks like an enemy battle station, evidently not listening to the construction crew's transmissions. Analogously, immune cells cannot think [ citation needed ] or directly communicate, basing their determination of friend from foe entirely on external chemical signatures. However, the Death Star operators are confused, because they believe Leia (a member of the Rebels) had ordered its construction. The Rebels initially attack the surface of the benign Death Star, without much effect; Leia orders the factories to continue developing torpedoes and ships as they run out, presumably putting an extra workload on the factory workers and tiring them out, or at least diverting resources away from other projects. In the analogy, the Rebels correspond to the immune system's B cells and T cells , which mobilize to attack the spike proteins (the benign Death Star) made as a result of the vaccine, but are often ineffective at first. The body keeps producing these immune cells, trying many variants (many ways of attacking the benign Death Star) in an attempt to find one that works well against the spike proteins. This results in Cueball experiencing side effects from the vaccine, including soreness and tiredness, and he lies down and rests. After much effort on the Rebels' part, they find a weakness in the benign Death Star, a "thermal exhaust port" vulnerable to "proton torpedoes" that can destroy the Death Star. Firing a proton torpedo down the exhaust port destroys a Death Star very rapidly, compared to the initial, ineffective frontal assault on the surface. After this benign Death Star is destroyed, Princess Leia allows the fleet to stand down. Up to this point, the entire thing seems like a comedy of errors, with huge expenditures being made for no apparent reason, due to a simple lack of communication. But during this process, the Rebel Alliance has both built a huge fleet and figured out how to target the Death Star's weakness and destroy it. Later on, when a real, dangerous Death Star approaches the planet (with the apparent intent of destroying it), the Rebels immediately deploy their fleet, target the weakness, and destroy it almost immediately, much to the shock of the Imperial troops, who had believed they were on an invulnerable ship and are surprised by the Rebels' immediate response and overwhelmed by it. The analogy is that the immune system (the Rebel Alliance) figures out a way to attach to the spike proteins (attack the benign Death Star) made by the mRNA vaccine; the immune system's antibodies (Rebel planners) now "know" how to recognize and destroy things that have these spike proteins — including SARS-CoV-2 virus particles (real, dangerous Death Stars). Hence, when the vaccinated Cueball approaches White Hat, who is maskless, coughing, and presumably sick with COVID-19, Cueball's immune system is able to destroy dangerous SARS-CoV-2 virus particles because it knows about the virus's spike proteins. This is represented by Cueball not experiencing any suffering from COVID-19, and he goes on his way whistling merrily, perhaps to the tune of The Throne Room/End Title (from the ceremony celebrating the destruction of the Death Star). It's notable that Cueball continues to wear a mask after being vaccinated. This is in accordance with CDC guidelines, which recommend continuing to wear a mask, practicing social distancing, etc. after getting the vaccine; doctors at CDC "don’t yet know whether getting a COVID-19 vaccine will prevent you from spreading the virus that causes COVID-19 to other people, even if you don’t get sick yourself." [1] None of the vaccines available as of when the comic was posted are 100% effective at preventing infection, with the best ones about 94% effective at preventing symptomatic cases, but all vaccines that are approved or submitted for approval are completely (100.00%) effective at preventing death from COVID-19. The title text references the fact that the two COVID-19 vaccines authorized for use in the United States as of the date of publication (the Pfizer-BioNTech one and the Moderna one ) require two doses of vaccine to be fully effective, as do many others in use worldwide (AstraZeneca, Gameleya Institute, Sinovac, etc.). The second dose strengthens the body's immune response to the spike proteins and causes it to "remember", via antibodies, how to attack those proteins for a long time — hopefully years or even decades. Likewise, the Rebels in the movies destroy two Death Stars, the second one in Return of the Jedi . Incidentally, that second Death Star was destroyed while it was apparently incomplete, much like the Death Star here was destroyed before it could destroy Cueball; however, in the film, the Emperor had deliberately left it with an incomplete outer structure to lure the Rebellion into attacking it, only for the Rebels to find that its superlaser was fully operational. Vaccination was also explained, xkcd-style, in 2406: Viral Vector Immunity . References to the Star Wars franchise are a recurring theme on xkcd. [Cueball seated in a doctor's office getting a dose of a COVID-19 vaccine. Both he and the doctor are wearing masks; the doctor is also wearing a scrub cap.] Doctor: The vaccine contains mRNA instructions for making the virus spike protein. Cueball: Weird, so the vaccine is just blueprints? Doctor: Yup! Your body reads the mRNA, makes the proteins, and then has an immune reaction to them. Cueball: Why would my body attack something it made itself? Doctor: Well... [Princess Leia and General Dodonna in frame.] Leia: Here are the Death Star plans. Dodonna: Thank you, Princess. [Dodonna, Ponytail, and White Hat in frame.] Dodonna: These blueprints are from Princess Leia. Ponytail: Ugh, she's always giving us projects. [Ponytail and Cueball in frame.] Ponytail: Here, take these blueprints to your construction crew. Cueball: Affirmative. What is it? Ponytail: No idea. Something the Princess wants. Cueball: Copy that. Panel heading: Soon... [A view from outside of the Death Star.] Voice from Death Star: Hi, Commander? Construction crew B here. [A view from inside the Death Star, with a planet visible through two adjacent windows. Cueball is standing at some kind of control/communications panel.] Cueball: We finished building the Princess's big metal orb thing. [A view from outside the Death Star again, with the curve of the planet in the foreground.] Voice from Death Star: Do you know if she wants us to park it somewhere, or— Voices from the planet: AAAAAA!!! [A view from the planet's surface with the Death Star in the sky. 3 Cueballs, a Megan-like character, and Ponytail are on the planet's surface.] Voice from Death Star: ...Is everything ok? Cueball 1: AAAAAAA! Cueball 2: Imperial battle station!!! Ponytail & Cueball 3: AAAAAAAAAA Offscreen voice: Red Alert Red Alert [Another view from the planet's surface. There is some type of military encampment surrounded by an open field, with trees and mountains in the background. People are running around on the field, which also contains several currently grounded craft and several flying craft streaming toward the Death Star.] Death Star voice: Hello? Generic field voices: Get the fighters in the air! Red Alert Blow it up! Blow it up! AAAAA Generic tree voices: AAAAAaa Generic spacecraft voices: Kill it kill it kill it kill it kill it kill it [A zoomed-in view of the outside of the Death Star, which is accumulating light damage. Numerous spacecraft are shooting at it; various explosions occur on the Death Star's surface and in space nearby.] Death Star voice: Hello? Generic spacecraft voices: Shoot it! Shoot it! Shoot it! That armor's too strong! We're not getting through! Keep firing! [A view from inside the Death Star again with Cueball at the control panel and the planet in the background windows; various projectiles and explosions can be seen through the window.] Cueball: Can everybody please just chill? We don't even have the laser thing wired up. We— BOOM Hey!! I said , we... [Ponytail enters from the left, and points to her left. Princess Leia points at her.] Ponytail: We can't get through! We're running out of proton torpedoes! Leia: Send every crew to build more torpedoes! Ponytail: There aren't enough ships to— Leia: Build more ships!! [Ponytail is standing still and Princess Leia is walking to the right with her fists raised.] Ponytail: That thing is just sitting there. Are you sure we— Leia: Keep building ships! Build ships forever! Destroy the orb! [A view of the Death Star in space and the curvature of the planet off to the side. An enormous torrent of (barely visible) ships is seen streaming from the planet's surface to the Death Star. The damage to the Death Star is slightly worse.] Generic ship voices: aaaaAAAAAAAAaaaaa Death Star voice: What is wrong with you people? [Back in the real world, Cueball is standing with arms hunched and a cartoon helix above his head. Megan stands next to him.] Cueball: Definitely feeling a little sore. Megan: Yeah, they said you might have some side effects. Megan: You lie down—I'll get you some hot tea and a blanket. [An outside view of the damaged Death Star with ships swarming it.] Generic voices: Die die die die! Die! [An inside view; Cueball appears injured, and the control panel is damaged with a fire on the ground nearby.] Cueball: I hate you all so much. [The outside of the Death Star again.] Ship 1: What's that?! Ship 2: Looks like a thermal exhaust port. Ship 3: I'm going in! [The outside of the Death Star.] pew pew pew pew pew pew [Beat panel.] [The Death Star explodes.] [A disheveled Dodonna, Princess Leia, and Ponytail in frame.] [The same frame.] Leia: Good work. [In the real world, Cueball sits on top of a bed with a blanket draped over his lap. Megan stands next to the bed.] Cueball: I'm feeling better today. Megan: That's great! Panel heading: A few months later... [Cueball and White Hat walking past each other. Cueball is wearing a face mask; White Hat isn't but coughs into his elbow.] White Hat: Cough cough [The real Death Star drifts toward the planet.] Death Star voice: We have reached the rebel system, Lord Vader. [View from inside the real Death Star.] Vader: Now they shall witness the firepower of this fully armed and oper— [Leia, Ponytail, and Cueball in frame.] Leia: Thermal exhaust port!! Ponytail: Aaa Cueball: Aaa [An equally large torrent of ships stream from the planet to the real Death Star.] Death Star voice: What. Various ships: aA AAAAAAA aaa aAAAAAAA aaa AAAAAA aaa aAAAAA [The Death Star explodes, leaving debris trailing away.] [In the real world, White Hat and Cueball continue to walk past each other.] Cueball: ♫ ♫

Animal Songs

Animal Songs

https://www.xkcd.com/2426

https://www.explainxkcd.com/wiki/index.php/2426:_Animal_Songs

[A man with a bit of hair, later shown to represent Dr. Fauci, is putting on a white lab coat as he walks past his fish tank. The tank, on a small table, has one small fish in it, looking at him. Inside the tank there is also a seaweed-like plant and a small castle and an even smaller pyramid. Seven music notes, 4 double and 3 single notes, are scattered about Fauci's speech which is written with lower case letters (normal capitalization) as opposed to normal xkcd text with all small caps.] Dr. Fauci: ♫ Putting on my doctor coat ♫ [Dr. Fauci is buttoning the coat. He is now standing to the right of the fish tank. The fish has turned towards him and has moved to the end of the tank near him. He still sings with the same letter type and six music notes, 3 double and 3 single notes, are scattered around the text.] Dr. Fauci: ♫ It's the coat I wear ♫ [Dr. Fauci is back to the left of the fish tank, looking at himself in a mirror, and touching his face. There is a small shelf with three items on the wall beneath the mirror. The fish has swam back to its original position turned towards him. He is still singing, with one double and one triple note on either side of his lyrics. An off-panel voice addresses him from the right, and he replies. These exchanges are written in normal xkcd small caps style.] Dr. Fauci: ♫ so they know how good a doctor I am ♫ Off-panel voice: Dr. Fauci? The press conference is in five. Dr. Fauci: Be right there! [Caption below the panel:] It's nice to think about how serious and important people probably also absentmindedly sing made-up songs to pets.

This comic is another in a series of comics related to the COVID-19 pandemic . Jokes about professionals not being so professional in private have been presented before, for example in 2401: Conjunction and 1463: Altitude . Dr. Anthony Fauci is the Director of the National Institute of Allergy and Infectious Diseases who was largely responsible for informing the public in the United States on how to avoid spreading SARS-CoV-2 in the beginning of the COVID-19 pandemic . He was recently awarded a one million dollar prize for his recent work. This may be the press conference he is going to. The comic shows him singing a silly made-up song to his pet fish as he goes about his daily routine - a counterintuitively childlike (albeit delightful and relatable) habit for an authority figure who normally presents himself to the public in a professional and prosaic "grown-up" manner. Incidentally, this characterization of Dr. Fauci doesn't seem to be far from the truth: Fauci's daughter Jenny is quoted in the Washington Post as saying of her father: "He's a goofball[...] He works hard and he does his thing, but he comes home and he's singing opera in the kitchen and dancing around." In 231: Cat Proximity , it's presented as 'normal' for people to make inane statements and use baby talk near cats , but here, Dr. Fauci is singing to his fish. The title text explains that, as he is the director of the National Institute of Allergy and Infectious Diseases, he is forbidden from owning a pet cat, because petting the cat would be "giving aid and comfort" to an allergen, which is (a reference to) one definition of treason under the United States Constitution . The “allergen” refers to the hypothetical cat—some people are allergic to cats . [A man with a bit of hair, later shown to represent Dr. Fauci, is putting on a white lab coat as he walks past his fish tank. The tank, on a small table, has one small fish in it, looking at him. Inside the tank there is also a seaweed-like plant and a small castle and an even smaller pyramid. Seven music notes, 4 double and 3 single notes, are scattered about Fauci's speech which is written with lower case letters (normal capitalization) as opposed to normal xkcd text with all small caps.] Dr. Fauci: ♫ Putting on my doctor coat ♫ [Dr. Fauci is buttoning the coat. He is now standing to the right of the fish tank. The fish has turned towards him and has moved to the end of the tank near him. He still sings with the same letter type and six music notes, 3 double and 3 single notes, are scattered around the text.] Dr. Fauci: ♫ It's the coat I wear ♫ [Dr. Fauci is back to the left of the fish tank, looking at himself in a mirror, and touching his face. There is a small shelf with three items on the wall beneath the mirror. The fish has swam back to its original position turned towards him. He is still singing, with one double and one triple note on either side of his lyrics. An off-panel voice addresses him from the right, and he replies. These exchanges are written in normal xkcd small caps style.] Dr. Fauci: ♫ so they know how good a doctor I am ♫ Off-panel voice: Dr. Fauci? The press conference is in five. Dr. Fauci: Be right there! [Caption below the panel:] It's nice to think about how serious and important people probably also absentmindedly sing made-up songs to pets.

Perseverance Microphones

Perseverance Microphones

https://www.xkcd.com/2427

https://www.explainxkcd.com/wiki/index.php/2427:_Perseverance_Microphones

[Megan is sitting in an office chair at a desk, typing on her laptop. The laptop is connected to an audio mixer box on the floor. The box has several buttons and indicators etc. Cueball is standing on the other side of the box, holding an electric guitar ready to play. The guitar is plugged into the box. From the box there is also a wire going to a small pedal on the floor. Cueball has one foot on top of this pedal.] Megan: Perseverance's microphones are active! Downlinking audio! Cueball: I'm ready with the looper pedal. [Caption below the panel:] The first Mars sample return

This comic is a play on dual meanings of the word "sample". The day before this comic was published, NASA successfully landed a new rover, Perseverance , on Mars; part of its mission is to drill and scoop Martian rock and dust from the surface, store it in tubes, and leave them on the surface for collection by a future mission which will return them to Earth. If successful, this would be the "first Mars sample return" in history. “ Samples ” can also refer to short snippets of recorded sound used in music. Perseverance is the first Mars mission to land on Mars with microphones too, so it would be possible to use audio samples from those microphones musically, e.g. using a looper pedal , which lets a musician play short samples of music and then repeats them back live as if it were another musician. Using a loop pedal would make sense if the sample includes a tune that repeats throughout the song—or that could repeat throughout the song. This is similar to 411: Techno . The joke is that these audio samples, as opposed to rock samples, would be "the first Mars sample return." Additionally, the comic might be a reference to Samples from Mars , a company that sells sampled audio from older instruments for digital music production. The title text anthropomorphises the rover, suggesting that the drop to the surface was so frightening for it that it was screaming as it descends. The period between entry into the Martian atmosphere and touchdown on its surface has been dubbed the "Seven Minutes Of Terror", mainly for the terror felt by the mission controllers on Earth, rather than the lander, as they are unable to make any useful corrections to a craft that is hundreds of millions of miles/kilometres away. The round-trip communication delay significantly exceeds the whole of the passage through the thin atmosphere, so they have to rely on whatever pre-arranged autonomy they engineered and programmed into their craft beforehand, and hope they anticipated all eventualities . You can view the landing here . The landing was the topic of the next comic 2428: Mars Landing Video . [Megan is sitting in an office chair at a desk, typing on her laptop. The laptop is connected to an audio mixer box on the floor. The box has several buttons and indicators etc. Cueball is standing on the other side of the box, holding an electric guitar ready to play. The guitar is plugged into the box. From the box there is also a wire going to a small pedal on the floor. Cueball has one foot on top of this pedal.] Megan: Perseverance's microphones are active! Downlinking audio! Cueball: I'm ready with the looper pedal. [Caption below the panel:] The first Mars sample return

Mars Landing Video

Mars Landing Video

https://www.xkcd.com/2428

https://www.explainxkcd.com/wiki/index.php/2428:_Mars_Landing_Video

[Hairbun is standing, arms spread out, on a podium in front of a lectern. There is a "Crash" on the top right of the panel with several lines around to indicate the position, and an off panel voice coming from there. As indicated in the caption below the voice is from Randall.] Hairbun: We're excited to share the first ever full-speed video of a Mars landing. Sound: Crash Randall (off-panel): Doesn't that mean it's also the worst ever full-speed video of a mars landing? Randall (off-panel):Do you expect that record to stand forever, or is NASA working on a worse one? [Caption below the comic]: NASA tried to ban me from their press briefings, but ironically their security was totally unprepared to deal with a skycrane.

Three days before this comic was published, NASA successfully landed a new rover, Perseverance , on Mars. This was also the subject of the previous comic 2427: Perseverance Microphones . This comic was published shortly before a NASA press briefing that showed, as mentioned in the comic, the first ever full-speed video of a Mars landing. This comic is set at that press briefing and was published shortly before NASA, either unaware of Randall's threat or recognizing that it was not serious, went ahead and hold the briefing in real life. "Full-speed" here means that the video was captured at a frame rate high enough that it looks continuous when played back, as opposed to low-frame-rate imagery that looks jerky when played back. The comic plays on the fact that if there is only one of something in a set, that one thing is the most/least in that set by lack of comparison. As there is only one full speed video of a Mars landing, that makes the video the best one as well as the worst one. Randall , who has often been banned from conferences , has apparently also been banned from NASA's press briefings. So he decided to crash the conference (literally, see below) solely to ask the question, "Is this then not also the worst video ever", flouting his ban and embarrassing NASA (a prior case of the latter is possibly why the former is currently active). He follows up with the question of whether NASA is planning to make a worse Mars landing video, which is silly because people generally don't intend to make something worse. [ citation needed ] However, because this video is the worst full-speed video of a Martian landing by virtue of being the only full-speed video of a Martian landing, it is likely that if enough full-speed videos of Martian landings are made in the future, this video will not be the worst forever. Although this is merely a consequence of the fact that it is the only full-speed video of a Martian landing so far, the fact that it is technically true, as well as the way that Randall phrases it, makes it look embarrassing for NASA. The tendency of Randall (the character, not the real-life person) to make rude, embarrassing, and otherwise unwelcome comments is probably why he has been banned from NASA's press briefings, as well as all those conferences. Judging by the sound effects, Randall has chosen to literally crash his way through the roof, using a "skycrane" — a general term for aerial vehicles that can lower or raise objects similarly to standard cranes. Specifically, one of these was used to land the Perseverance rover three days before. On Earth one might use the Sikorsky S-64 Skycrane helicopter, while NASA used a custom-built skycrane delivery system for the Perseverance rover. Randall deems using a skycrane to crash a conference about a skycrane ironic, especially since NASA's security was totally unprepared to stop him from using this method - a method NASA developed - to crash the press-briefing. The title text refers to the 11-minute communications delay (one-way; 23-minute delay round-trip) between Mars and Earth, due to the speed of light and the distance between the planets at the time of the rover's landing. The Perseverance mission control must wait this long before they can even begin to respond to anything that happens to the rover, which Randall here twists into an 11-minute period in which he can ask whatever questions he likes before NASA can respond. This would only make sense if the conference he was crashing was on Mars and they were waiting for his questions here on Earth, or vice versa and plays on the ambiguity of the expression "Mars briefing", which can mean both a briefing about Mars and a briefing taking place on Mars. [Hairbun is standing, arms spread out, on a podium in front of a lectern. There is a "Crash" on the top right of the panel with several lines around to indicate the position, and an off panel voice coming from there. As indicated in the caption below the voice is from Randall.] Hairbun: We're excited to share the first ever full-speed video of a Mars landing. Sound: Crash Randall (off-panel): Doesn't that mean it's also the worst ever full-speed video of a mars landing? Randall (off-panel):Do you expect that record to stand forever, or is NASA working on a worse one? [Caption below the comic]: NASA tried to ban me from their press briefings, but ironically their security was totally unprepared to deal with a skycrane.

Exposure Models

Exposure Models

https://www.xkcd.com/2429

https://www.explainxkcd.com/wiki/index.php/2429:_Exposure_Models

[Cueball is sitting in an office chair at a desk typing on his laptop as Megan walks in.] Cueball: I built another COVID exposure model to help me limit my risk. [Megan stands behind Cueball, who has turned in his chair to face her. He is leaning his arm on the back of the chair.] Megan: Any new insights? Cueball: Yeah: "If you spend all day debugging models, you don't have close contact with a lot of people." [Cueball turns away from Megan to type on his laptop again. The back of his chair has disappeared.] Megan: Well, I guess it worked. Cueball: According to my meta-model, the end of the pandemic is only four more models away. Megan: So close!

This is another comic in a series related to the COVID-19 pandemic . Cueball (or Randall ) created another COVID exposure model to help lower his risk of catching COVID-19 in the pandemic. Megan inquires about the model's result, to which Cueball admits that he's been sitting at his computer continuously debugging models, and draws the conclusion that debugging COVID-19 models lessens close contact with other people. This is similar to the premise of 1445: Efficiency and 1708: Dehydration , except with the situation reversed — where before, researching a situation made the situation worse, here Cueball's time "wasted" has actually benefited him. By "model," Randall likely means a manually crafted model, since he describes debugging it, but he may also mean the form of automatically generated software that is used in modern machine learning. Cueball is too busy making models to figure out how to actually lower his risk other than sitting around repeating the work of others and improving his model-building skill. He has also created a meta-model, reporting the number of models Cueball has to create to wait the pandemic out. The fact that Megan refers to having to wait for the time that it would take Cueball to create four more models as "so close" implies that Cueball goes through models quickly, which makes sense because he spends all of his time working on new ones. In the title text Randall mentions that he is dangerously close to making a spreadsheet about how many spreadsheets about coronavirus he has made cumulative over time. This would be a recursive graph, a recurring theme on xkcd. [Cueball is sitting in an office chair at a desk typing on his laptop as Megan walks in.] Cueball: I built another COVID exposure model to help me limit my risk. [Megan stands behind Cueball, who has turned in his chair to face her. He is leaning his arm on the back of the chair.] Megan: Any new insights? Cueball: Yeah: "If you spend all day debugging models, you don't have close contact with a lot of people." [Cueball turns away from Megan to type on his laptop again. The back of his chair has disappeared.] Megan: Well, I guess it worked. Cueball: According to my meta-model, the end of the pandemic is only four more models away. Megan: So close!

Post-Pandemic Hat

Post-Pandemic Hat

https://www.xkcd.com/2430

https://www.explainxkcd.com/wiki/index.php/2430:_Post-Pandemic_Hat

[A ballcap with an image of a webcam lens and a message reading "Excuse me, my eyes are actually down here" above a downward-facing arrow] [Caption below the panel]: Hat for post-pandemic socializing

This is another comic in a series related to the COVID-19 pandemic . During the COVID-19 pandemic, there was a significant shift from in-person to computer-mediated interactions for both recreational and professional activities. For many, the computer setup used for these interactions is a laptop with a webcam above the screen. As people have become accustomed to looking directly into the camera, i.e. above where the other people's faces are, to simulate eye contact for meetings, Randall implies that there will be issues returning to pre-COVID life. In response, he has designed a baseball cap with an image that resembles a laptop webcam that sits above the wearer's eyes and a message that humorously acknowledges that the reader is likely reverting to virtual meeting habits for in-person interactions and that reminds people that for in-person interactions, one must look the other person's face, not above it like there's a webcam there. The cap in this strip likely references a tradition of novelty tee-shirts, intended to be worn by women, feature "my eyes are up here!" or similar words written across the chest, and an arrow pointing upwards. These shirts are designed to both tease and parody the tendency of heterosexual men to look at a woman's breasts, usually automatically and without conscious thought. The cap, as a result, compares the conditioned response of looking at a webcam with the instinctive response of looking at a woman's chest, both of which would result in failure to make eye contact during a conversation. Actual shirt-based text (as in the Title Text) would represent where a video-conferencer is not staring at the screen-top camera to 'fake' eye contact on the other screen(s) but truly aimed at the image of the eyes. The view of such an 'honest' stare could look like a 'chest gaze'. 1889: xkcd Phone 6 'solved' all these problems by putting a camera in the middle of the screen. [A ballcap with an image of a webcam lens and a message reading "Excuse me, my eyes are actually down here" above a downward-facing arrow] [Caption below the panel]: Hat for post-pandemic socializing

Leap Year 2021

Leap Year 2021

https://www.xkcd.com/2431

https://www.explainxkcd.com/wiki/index.php/2431:_Leap_Year_2021

[Cueball checking his phone in a narrow panel.] Cueball: Can't believe it's already March. Black Hat (off-screen): Nah, it's February 29th. [Cueball has put his phone away and is standing next to Black Hat.] Cueball: It's not a leap year. Black Hat: I decided to make it one. Every year deserves to leap. Cueball: Can you do that? Black Hat: Can anyone stop me? [Zoom in on Cueball.] Cueball: I guess if you just encourage people to call March 1st "February 29th", they can go along with it if they want. Just a one-day renaming. Black Hat (off-screen): No, tomorrow will be March 1st. [Cueball standing to Black Hat, who is walking off screen to the right, with his finger raised.] Cueball: So you're causing calendar drift for future generations. Black Hat: If they didn't want to experience consequences, they shouldn't have decided to live in the future.

Cueball , checking his phone, comments on how fast time goes, saying it is already March. (This comic was posted on March 1, 2021.) Black Hat overhears him and says that it's actually February 29. February 29 exists in the Gregorian calendar and its predecessor, the Julian calendar , as a correction mechanism for the fact that one tropical year on Earth is not exactly 365 days long. It's closer to 365.2422, and to prevent the dates from precessing relative to the seasons, an extra day is added once every fourth year, also called a leap year. This is still not enough to completely match Earth's orbital period, and for that reason the Gregorian calendar changed the leap year rules to be as follows: Every year that is exactly divisible by four is a leap year, except for years that are exactly divisible by 100, but these centurial years are leap years if they are exactly divisible by 400. This makes the average year 365.2425 days long, which approximates the 365.2422 days in the tropical year. Black Hat wants every year to have a February 29, for no clear reason. Cueball acknowledges that he could accomplish this, if he could convince enough people to go along with it. Calendar systems are all invented, and whatever date systems are commonly acknowledged become the "correct" date. Cueball initially considers the change minor, assuming that they would simply change March 1st to February 29th on non-leap years, which would merely rename a single day and skip "March 1st" by going directly from February 29th to March 2nd. Black Hat clarifies that he actually wants to add another day, and the day AFTER that will be March 1. This could still be a minor change, if March were changed to a 30 day month on non-leap years, but Black Hat apparently wants the changes to propagate throughout the year. This would result in a 366-day year, causing the months to drift out of alignment with the seasons over the course of years, needlessly complicating time-keeping. Black Hat is unconcerned with the effect this will have on the "people of the future", and, as in the past , people around him are much more concerned about the time problems he's creating than he is. This once happened in ancient Egypt, where the priests had leap years every three years instead of every four years, so ancient Egypt had to have no leap years for several decades afterwards in order to fix the calendar. In the last frame, Black Hat states that if the those people cared about the problems he's causing, "they shouldn't have decided to live in the future." Of course, it is at present impossible to choose the time period in which you live, [ citation needed ] yet Black Hat intends on penalizing them for it. Any number of positions could be proposed as a motive for his actions (for example, he may envy them for having the technology or benefits of the future, and wants to counteract that), but it is most likely that he is simply honing his sociopathic tendencies on a defenseless target. In the title text, Cueball responds that this change would also cause issues for him, who is "living in the present", and he should not be forced to "move into the future". Alternatively, viewing the quote as a continuation of Black Hat's text at the end of the comic, he could mean that the effect of his new calendar is placed mostly on future people, and since he literally lives in the present and doesn't intend on travelling to the future, he can do what he wants without many repercussions. In this second interpretation, the phrase "move now" can be taken to have a double meaning: not only does Black Hat not intend to move presently, he also does not intend to move where the present currently is (i.e., move the "now" into the future). [Cueball checking his phone in a narrow panel.] Cueball: Can't believe it's already March. Black Hat (off-screen): Nah, it's February 29th. [Cueball has put his phone away and is standing next to Black Hat.] Cueball: It's not a leap year. Black Hat: I decided to make it one. Every year deserves to leap. Cueball: Can you do that? Black Hat: Can anyone stop me? [Zoom in on Cueball.] Cueball: I guess if you just encourage people to call March 1st "February 29th", they can go along with it if they want. Just a one-day renaming. Black Hat (off-screen): No, tomorrow will be March 1st. [Cueball standing to Black Hat, who is walking off screen to the right, with his finger raised.] Cueball: So you're causing calendar drift for future generations. Black Hat: If they didn't want to experience consequences, they shouldn't have decided to live in the future.

Manage Your Preferences

Manage Your Preferences

https://www.xkcd.com/2432

https://www.explainxkcd.com/wiki/index.php/2432:_Manage_Your_Preferences

[Cueball is sitting in an office chair at a desk in front of his laptop computer. A black zigzag line points to the screen, and above this is shown what is displayed on Cueball's screen. This is shown as a black rectangle, with a white box, with black frame, overlaid over the top of the black section, extending half way above it. The text in this white box is in gray font. Inside the black rectangle are two gray rectangles, with white borders and black text. A small rectangle at the top has "Manage your Preferences" inside it, and a large rectangle below has 6 lines of text.] Agree to whatever Transport me to an immersive Myst-like game where I click confusingly-labeled toggle switches, only some of which work, perhaps never to find my way back to the page I wanted. The title-text originally said "Atrius" instead of "Atrus". A few hours after the comic's release, this was changed.

This comic illustrates the complex dialogues often employed by webpage or software designers to hide settings from the user. Many pages provide controls to set privacy-related preferences but make those settings opaque in an attempt to dissuade users from using them. The idea is that a user will become impatient by the confusing options and select the defaults, which provide the site or software with more access or information. This situation is compared to Myst , a 1990s puzzle video game. Companies which collect or process personal information are required by privacy legislation to give their users the option to withhold personal information, although regulations vary depending on the region-specific laws. The operators of such services usually want to collect as much personal data as they can in order to target advertisements or sell their information to someone else, and wish to incentivize their users not to activate those features. One tactic that is frequently used to accomplish this goal is to provide the user an option which enables all the data collection, but to make the process of disabling the collection time-consuming or difficult. This type of action is generally illegal under the same privacy legislation, but regulation of it has been lax so many companies still try it. "Atrus" in the title text is the main non-player character in the Myst series. In the first game these people were imprisoned within books. Pages needed to be collected to complete the books, and it was incredibly hard to find a single page, involving extensive laborious navigation and exploration, and the finding and solving of hidden puzzles. In the Myst mythos, the books open portals to other worlds, a little like web hyperlinks. Some sites' privacy settings are similarly labyrinthine. For example, some sites will run scripts from a variety of providers but will only allow users to disable them one site at a time without an explanation of what each one does. The black background possibly shows how many sites are providing tools to switch between light and dark backgrounds now. For a long time white backgrounds were the usual default style, and only people who understood esoteric browser configurations could redisplay many things with a black background - possibly to help with perceived eyestrain or power usage in certain displays. More recently, it is a fashionable setting for content providers to compose as a selectable option. It is out-of-place for Randall to show a black background, as many of his comics take place in technical computer systems that often have a black background anyway, as most computer terminals still do. Some browsers and websites do have actual games embedded within their various configuration interfaces. Chrome , for example, has the famous dinosaur game . [Cueball is sitting in an office chair at a desk in front of his laptop computer. A black zigzag line points to the screen, and above this is shown what is displayed on Cueball's screen. This is shown as a black rectangle, with a white box, with black frame, overlaid over the top of the black section, extending half way above it. The text in this white box is in gray font. Inside the black rectangle are two gray rectangles, with white borders and black text. A small rectangle at the top has "Manage your Preferences" inside it, and a large rectangle below has 6 lines of text.] Agree to whatever Transport me to an immersive Myst-like game where I click confusingly-labeled toggle switches, only some of which work, perhaps never to find my way back to the page I wanted. The title-text originally said "Atrius" instead of "Atrus". A few hours after the comic's release, this was changed.

Mars Rovers

Mars Rovers

https://www.xkcd.com/2433

https://www.explainxkcd.com/wiki/index.php/2433:_Mars_Rovers

[A scatter plot is shown with two labeled axis, each with 5 ticks and ending in an arrow. Two types of Mars rovers are drawn in the top left part, at the top tick and the next highest tick. Each rover type has a label with two names. A third smaller drone is drawn in the lower right part close to the third tick on the Y-axis, with a single name label. It has two arrows pointing up and down to question marks, and two small lines of either side of the rotor blades, indicate movement. Far to the right, about twice the length of the drawn X-axis from the origin of the chart, and at the height of the lowest tick on the Y-axis, is a third type of rover, also with a single name label. The entire chart also has a label:] Mars Rovers Y-Axis: Capabilities X-Axis: Cuteness Curiosity & Perseverance Spirit & Opportunity Ingenuity Sojourner

In this comic, Randall has made a scatter plot displaying 6 different Mars rovers on a cuteness versus capabilities chart. Only three rover pictures are shown in the main plot, as two of the four rovers are near identical to other rovers sent to Mars, and the last rover is displayed off the cuteness chart. He finds the Curiosity and Perseverance rovers to be very capable / useful, but not very cute. Spirit and Opportunity are cuter than the first two, but less capable. The recently launched Perseverance rover contains a drone helicopter, Ingenuity , which Randall finds pretty cute, but is unsure how exactly to grade for capability. The error bars make Ingenuity look like it's bobbing up and down, as helicopters sometimes do. It's debatable if a flying drone can be considered a Mars Rover, since a rover is usually something that drives over a surface, but the anticipated flight plan for Ingenuity is to cover some distance (by air) and then land on the ground again. Finally, on the very right far off the cuteness chart is the Sojourner rover, launched in 1997. He considers this rover extremely cute, but ultimately not that capable. To indicate the extreme cuteness of Sojourner (previously mentioned in 1585: Similarities ), he has drawn it far outside the axis of the plot to indicate it falls off the chart. In the title text, Randall is disappointed that there aren't many people who have modified their Roomba vacuums to look like (or act like?) the Sojourner rover. Roombas are a recurring theme on xkcd. Search results at the time of posting are mainly reports mentioning the iRobot company, makers of the Roomba line, since one of its founders worked on the Sojourner rover. The end of the title text, "be the change," is a truncated form of the expression "be the change you want to see in the world"; basically, if there's something you want to see happen, be the one who makes it happen. This implies that Randall will be modifying his Roomba to look/act like Sojourner . [A scatter plot is shown with two labeled axis, each with 5 ticks and ending in an arrow. Two types of Mars rovers are drawn in the top left part, at the top tick and the next highest tick. Each rover type has a label with two names. A third smaller drone is drawn in the lower right part close to the third tick on the Y-axis, with a single name label. It has two arrows pointing up and down to question marks, and two small lines of either side of the rotor blades, indicate movement. Far to the right, about twice the length of the drawn X-axis from the origin of the chart, and at the height of the lowest tick on the Y-axis, is a third type of rover, also with a single name label. The entire chart also has a label:] Mars Rovers Y-Axis: Capabilities X-Axis: Cuteness Curiosity & Perseverance Spirit & Opportunity Ingenuity Sojourner

Vaccine Guidance

Vaccine Guidance

https://www.xkcd.com/2434

https://www.explainxkcd.com/wiki/index.php/2434:_Vaccine_Guidance

[Megan's face is seen at the bottom of the panel with the CDC-logo slightly above her and to the left; it is a black rectangle with the letters in white, and with a white jiggly line to the left of the first C.] Megan: Our new guidance: Fully vaccinated people can gather privately with no masks or distancing, and can visit with unvaccinated low-risk people in one household. Megan: Any questions? Logo: CDC [Blondie, Hairy and Megan are seen at the bottom of the panel in three separate rectangular panels with Blondie and Hairy's panels at the left above one another. Those panels are almost square and also smaller than Megan's, more rectangular panel to the right of theirs. This panel is centered at the middle of those two panels to the left, and the logo is still visible. It is also shown that Megan is standing behind a lectern. Blondie, above Hairy, is the one asking questions to Megan.] Blondie: If my neighbors and I are all vaccinated, can I visit them unmasked and drink milk straight from the jug in their fridge? Megan: I...You can visit, yes. Blondie: And the jug thing? Megan: ...Next question? Logo: CDC [In a frame-less panel there are two panels at the bottom, with Science Girl in the largest to the left and Megan in the smaller to the right, with the logo still visible, but unreadable still the lectern is shown.] Science Girl: I'm fully vaccinated. Can I ride my bike in my sister-in-law's house? Megan: In her house? Science Girl: Like, down the stairs. Megan: I guess? You should at least wear a helmet. Science Girl: Even if she's not high-risk? Megan: Any other questions? [White Hat is in a rectangular box at the bottom of the panel. Megan is replying from off-panel to the right from a star burst at the edge of the panel. At the bottom there is a message in a black rectangle with white text.] White Hat: I'm two weeks past my second dose. White Hat: Can I get a horse? Megan: Thank you all for coming. White Hat: What if I wear a mask? White Hat: What if the horse does? Message: Meeting ended by host.

This is another comic in a series related to the COVID-19 pandemic . On the day this comic was published, the Centers for Disease Control and Prevention (CDC) released new guidelines relating to COVID-19, lifting many of the existing restrictions for people who have been fully vaccinated for two weeks. Megan , speaking as a CDC spokesperson, is introducing these new guidelines in a video press conference. However, the other participants in the press conference quickly start asking about actions that have little or nothing to do with the vaccine, some of which would be dangerous whether COVID-19 was a risk or not, similarly to 2238: Flu Shot . It's possible that they do not remember life before the pandemic very well, as in 2391: Life Before the Pandemic . Blondie asks whether it would be okay to visit neighbors and drink milk directly from the carton. In most Western cultures, drinking directly from a container that could be shared with others (such as a milk carton) is considered unsafe, due to the risk of diseases being transmitted, and generally gross, as saliva and other biological material is passed that way. While these risks are arguably worse during the pandemic, it was unacceptable before the pandemic and will presumably be so afterward. Science Girl asks whether it would be okay to ride a bike down the stairs of a family member's house, which has a severe risk of injury. White Hat follows up asking whether he can get a horse, and whether it would help for him and/or the horse to wear masks. This has basically no relation to anything else that was said. In response, Megan gives up trying to answer the increasingly irrelevant questions and ends the call. In the title text, Randall mentions that when he is fully vaccinated, he will be able to write messages in ALL CAPS . This is generally used to indicate shouting, an activity which could spread COVID-19 and cause infection if done in person. [Megan's face is seen at the bottom of the panel with the CDC-logo slightly above her and to the left; it is a black rectangle with the letters in white, and with a white jiggly line to the left of the first C.] Megan: Our new guidance: Fully vaccinated people can gather privately with no masks or distancing, and can visit with unvaccinated low-risk people in one household. Megan: Any questions? Logo: CDC [Blondie, Hairy and Megan are seen at the bottom of the panel in three separate rectangular panels with Blondie and Hairy's panels at the left above one another. Those panels are almost square and also smaller than Megan's, more rectangular panel to the right of theirs. This panel is centered at the middle of those two panels to the left, and the logo is still visible. It is also shown that Megan is standing behind a lectern. Blondie, above Hairy, is the one asking questions to Megan.] Blondie: If my neighbors and I are all vaccinated, can I visit them unmasked and drink milk straight from the jug in their fridge? Megan: I...You can visit, yes. Blondie: And the jug thing? Megan: ...Next question? Logo: CDC [In a frame-less panel there are two panels at the bottom, with Science Girl in the largest to the left and Megan in the smaller to the right, with the logo still visible, but unreadable still the lectern is shown.] Science Girl: I'm fully vaccinated. Can I ride my bike in my sister-in-law's house? Megan: In her house? Science Girl: Like, down the stairs. Megan: I guess? You should at least wear a helmet. Science Girl: Even if she's not high-risk? Megan: Any other questions? [White Hat is in a rectangular box at the bottom of the panel. Megan is replying from off-panel to the right from a star burst at the edge of the panel. At the bottom there is a message in a black rectangle with white text.] White Hat: I'm two weeks past my second dose. White Hat: Can I get a horse? Megan: Thank you all for coming. White Hat: What if I wear a mask? White Hat: What if the horse does? Message: Meeting ended by host.

Geothmetic Meandian

Geothmetic Meandian

https://www.xkcd.com/2435

https://www.explainxkcd.com/wiki/index.php/2435:_Geothmetic_Meandian

F(x1,x2,...xn)=({x1+x2+...+xn/n [bracket: arithmetic mean]},{nx,x2...xn, [bracket: geometric mean]} {x n+1/2 [bracket: median]}) Gmdn(x1,x2,...xn)={F(F(F(...F(x1,x2,...xn)...)))[bracket: geothmetic meandian]} Gmdn(1,1,2,3,5) [equals about sign] 2.089 Caption: Stats tip: If you aren't sure whether to use the mean, median, or geometric mean, just calculate all three, then repeat until it converges Geothm means "counting earths" (From Ancient Greek γεω- (geō-), combining form of γῆ (gê, “earth”) and ἀριθμός arithmos, 'counting'). Geothmetic means "art of Geothming" based on the etymology of Arithmetic (from Ancient Greek ἀριθμητική (τέχνη) (arithmētikḗ (tékhnē), “(art of) counting”). This is an exciting new terminology that is eminently suitable for modern cosmology & high energy physics - particularly when doing math on the multiverse. However, it is unlikely this etymology is related to the term "geothmetic meandian" as coined by Randall, as it can be more simply explained as a portmanteau of the three averages in its construction: geo metric mean, ari thmetic mean , and me dian . The following Python code (inefficiently) implements the above algorithm: Here is a slightly more efficient version of the Python code: And here is an implementation of the Gmdn function in R:

There are a number of different ways to identify the " average " value of a series of values, the most common unweighted methods being the median (take the central value from the ordered list of values if there are an odd number - or the value half-way between the two that straddle the divide between two halves if there are an even number) and the arithmetic mean (add all the numbers up, divide by the number of numbers). The geometric mean is less well-known but works similarly to the arithmetic mean. The geometric mean of n positive numbers is the n th root of the product of those numbers. If all of the numbers in a sequence are identical, then its arithmetic mean, geometric mean and median will be identical, since they would all be equal to the common value of the terms of the sequence. However, if the sequence is not constant, then the arithmetic mean will be greater than the geometric mean , and the median may be different than either of those means. The geometric mean, arithmetic mean and harmonic mean (not shown) are collectively known as the Pythagorean means , as specific modes of a greater and more generalized mean formula that extends arbitrarily to various other possible nuances of mean-value rationisations (cubic, etc.). Outliers and internal biases within the original sample can make boiling down a set of values into a single 'average' sometimes overly biased by flaws in the data, with your choice of which method to use perhaps resulting in a value that is misleading, exaggerating or suppressing the significance of any blips. In this depiction, the three named methods of averaging are embedded within a single function that produces a sequence of three values - one output for each of the methods. Being a series of values, Randall suggests that this is ideally suited to being itself subjected to the comparative 'averaging' method. Not just once, but as many times as it takes to narrow down to a sequence of three values that are very close to one another. It can be shown that the xkcd value of 2.089 for GMDN(1,1,2,3,5) is validated: The function GMDN in the comic is properly defined in the second row since F acts on a vector to produce another three vector, however GMDN in the last line is shown to produce a single real number rather than a vector and is thus missing a final operation of returning a single component. Each row in this table shows the set Fn(..) composed of the average, geomean and median computed on the previous row, with the sequence {1,1,2,3,5} as the initial F0. While GMDN is not differentiable, due to the median, this can be interpreted as somewhat similar to a heat equation which approaches equilibrium through averaging. Interestingly, the maximum value alternates between the average and the median (highlighted in bold in the table), while the minimum value alternates between the geomean and the median. This holds for many inputs thus providing the basis for a possible proof-by-induction of convergence on the range (see discussions). The comment in the title text about suggests that this will save you the trouble of committing to the 'wrong' analysis as it gradually shaves down any 'outlier average' that is unduly affected by anomalies in the original inputs. It is a method without any danger of divergence of values, since all three averaging methods stay within the interval covering the input values (and two of them will stay strictly within that interval). The title text may also be a sly reference to an actual mathematical theorem, namely that if one performs this procedure only using the arithmetic mean and the harmonic mean, the result will converge to the geometric mean. Randall suggests that the (non-Pythagorean) median, which does not have such good mathematical properties with relation to convergence, is, in fact, the secret sauce in his definition. The question of being unsure of which mean to use is especially relevant for the arithmetic and harmonic means in following example. Cueball and Megan decide to complete the exchange between themselves in order to save the Bid-ask spread of the Exchange rate which is the cost the bank imposes on Cueball and Megan for its service as a Market maker . In one direction (€/$), Cueball is using the arithmetic mean but Megan is using the harmonic mean while in the other direction ($/€), Megan is using the arithmetic mean but Cueball is using the harmonic mean. This creates two new exchange rates which are closer than the orginal rates, but the new rates are still different for each other. Megan and Cueball can then iterate this process and the rates will converge to the geometric mean of the original rates, namely: There does exist an arithmetic-geometric mean , which is defined identically to this except with the arithmetic and geometric means, and sees some use in calculus. In some ways it's also philosophically similar to the truncated mean (extremities of the value range, e.g. the highest and lowest 10%s, are ignored as not acceptable and not counted) or Winsorized mean (instead of ignored, the values are readjusted to be the chosen floor/ceiling values that they lie beyond, to still effectively be counted as "edge" conditions), only with a strange dilution-and-compromise method rather than one where quantities can be culled or neutered just for being unexpectedly different from most of the other data. The input sequence of numbers (1, 1, 2, 3, 5) chosen by Randall is also the opening of the Fibonacci sequence . This may have been selected because the Fibonacci sequence also has a convergent property: the ratio of two adjacent numbers in the sequence approaches the golden ratio as the length of the sequence approaches infinity. Here is a table of averages classified by the various methods referenced: F(x1,x2,...xn)=({x1+x2+...+xn/n [bracket: arithmetic mean]},{nx,x2...xn, [bracket: geometric mean]} {x n+1/2 [bracket: median]}) Gmdn(x1,x2,...xn)={F(F(F(...F(x1,x2,...xn)...)))[bracket: geothmetic meandian]} Gmdn(1,1,2,3,5) [equals about sign] 2.089 Caption: Stats tip: If you aren't sure whether to use the mean, median, or geometric mean, just calculate all three, then repeat until it converges Geothm means "counting earths" (From Ancient Greek γεω- (geō-), combining form of γῆ (gê, “earth”) and ἀριθμός arithmos, 'counting'). Geothmetic means "art of Geothming" based on the etymology of Arithmetic (from Ancient Greek ἀριθμητική (τέχνη) (arithmētikḗ (tékhnē), “(art of) counting”). This is an exciting new terminology that is eminently suitable for modern cosmology & high energy physics - particularly when doing math on the multiverse. However, it is unlikely this etymology is related to the term "geothmetic meandian" as coined by Randall, as it can be more simply explained as a portmanteau of the three averages in its construction: geo metric mean, ari thmetic mean , and me dian . The following Python code (inefficiently) implements the above algorithm: Here is a slightly more efficient version of the Python code: And here is an implementation of the Gmdn function in R:

Circles

Circles

https://www.xkcd.com/2436

https://www.explainxkcd.com/wiki/index.php/2436:_Circles

[Five small circles, looped together in the style of the Olympics logo is drawn in the center. On the left, a larger circle surrounds two of the prior ones, incidentally overlapping a third circle. A larger circle surrounds four of the small circles, thus also the previous mentioned circle, cutting over the last of the five circles. Finally a very large circle fully contains all the other circles. The three larger circles have labels, with the small ones label above, and with a small clarifying line from the label towards the top of this circle. The middle sized circle has the label standing on a break in the circle at it's bottom, and the largest circle has the label just beneath it. From smallest to largest of the circles the labels are:] Mastercard Audi Olympics

The comic depicts five overlapping circles, themselves encircled by circles of various sizes which enclose two, four, or all five of the smaller overlapping circles, as in an Euler diagram . Several well-known logos consist of overlapping circles, and the larger circles reference these logos. These are: Mastercard , which consists of two side-by-side overlapping circles (technically, disks, since they're filled in); Audi , which is four side-by-side overlapping circles, and the Olympic rings , which are five topologically linked rings in a "W" shaped pattern. To indicate that the Mastercard logo comprises two overlapping circles, the diagram draws a larger circle around the first two circles, inscribed with a label. Other than its size and the label, this new circle is identical to the five smaller circles. Similarly, to indicate that the Audi logo comprises four overlapping circles, the diagram again provides a larger circle, this time encompassing the first four smaller circles, inscribed with a label. The "Audi" circle completely encloses the "Mastercard" circle, indicating that the four circles of the "Audi" logo include the two circles of the "Mastercard" logo. Finally, an even larger circle, enclosing all of the other circles, indicates that the Olympic Rings use all five original circles. The comic was released only about four months before the postponed 2020 Summer Olympics was scheduled to start on 23 July 2021. It was postponed because of the COVID-19 pandemic , which has spawned a series of comics on xkcd. The title text is a textual representation of the Mastercard name as a Venn diagram containing the letters in the words "master" and "card" — A and R are shared by both, while MSTE and CD are unique to their respective elements. [Five small circles, looped together in the style of the Olympics logo is drawn in the center. On the left, a larger circle surrounds two of the prior ones, incidentally overlapping a third circle. A larger circle surrounds four of the small circles, thus also the previous mentioned circle, cutting over the last of the five circles. Finally a very large circle fully contains all the other circles. The three larger circles have labels, with the small ones label above, and with a small clarifying line from the label towards the top of this circle. The middle sized circle has the label standing on a break in the circle at it's bottom, and the largest circle has the label just beneath it. From smallest to largest of the circles the labels are:] Mastercard Audi Olympics

Post-Vaccine Party

Post-Vaccine Party

https://www.xkcd.com/2437

https://www.explainxkcd.com/wiki/index.php/2437:_Post-Vaccine_Party

[The comic consists of four underlined headings, two by two grid, with three or four lines of text beneath each. Almost all of the original lines of text have been fully or partially crossed out (marked with <del> below), and five new items have been added (marked with <ins> below), plus some brackets and one arrow. Even one of the added items has been modified.] Drinks Soda Wine Beer Cocktails Small cups of ice water Food Pizza Nachos Various snacks Three M&Ms and a saltine per person Entertainment Music (ambient) Karaoke Big screen TV showing sports Bob Ross Activities Board games 52-card pickup [The "52" is then stricken out and replaced with "3"] Video Games Ping ( Pong ) [A red arrow points from "Video Games" to "(Pong)"] Good conversation [Caption below the panel:] We're planning our first post-vaccine party, but we want to start slow.

This is another comic in a series related to the COVID-19 pandemic . As more and more people are getting vaccinated against COVID-19, and as the CDC has released guidelines suggesting vaccinated people can start gathering in larger groups, there is increasing excitement about the possibility to resume get-togethers, and have a party. However, being very cautious, Randall is cutting down the scope for his first "post-pandemic" party from that of a normal party. Not all of the scope reductions make sense. [ citation needed ] The title text mentions that in the end, despite Randall's efforts, even the incredibly mild disruption of an M&M's falling into a cup of water caused the party-goers to panic and flee, much as Cueball and Ponytail did in a similar situation . [The comic consists of four underlined headings, two by two grid, with three or four lines of text beneath each. Almost all of the original lines of text have been fully or partially crossed out (marked with <del> below), and five new items have been added (marked with <ins> below), plus some brackets and one arrow. Even one of the added items has been modified.] Drinks Soda Wine Beer Cocktails Small cups of ice water Food Pizza Nachos Various snacks Three M&Ms and a saltine per person Entertainment Music (ambient) Karaoke Big screen TV showing sports Bob Ross Activities Board games 52-card pickup [The "52" is then stricken out and replaced with "3"] Video Games Ping ( Pong ) [A red arrow points from "Video Games" to "(Pong)"] Good conversation [Caption below the panel:] We're planning our first post-vaccine party, but we want to start slow.

Siri

Siri

https://www.xkcd.com/2438

https://www.explainxkcd.com/wiki/index.php/2438:_Siri

[Science Girl is holding her phone up in one hand looking at the screen. A starburst from the phone indicates the voice coming from the phone] Phone: Your timer is set. Science Girl: Thanks [The picture broadens and shows that Science Girl, with the phone now held down, is standing in front of a desk, where Cueball, facing her, is sitting in an office chair using a laptop.] Science Girl: Is Siri alive? Cueball: No. [Back to only showing Science Girl, her phone and arm still held down at her side.] Science Girl: Oh, ok. [Same setting but Science Girl has raised her arm with the phone, looking at it again.] Science Girl: How did she die?

Science Girl thanks Siri on her smartphone for setting an alarm. In the next panel, she asks Cueball , "Is Siri alive?", since AI assistants can seem to be almost human on a very superficial level. Cueball answers "No," since Siri is entirely software, and we don't generally attribute life to computer programs (the closest might be computer viruses , since they replicate). Science Girl then asks "How did she die?" She may have already been treating Siri as alive because she could talk to 'her,' and treats this lack-of-life as a new state of being. So rather than interpreting the answer in a philosophical sense of whether Siri is something that ever can be alive, which might normally have been presupposed, she treats it as meaning that Siri had (just) expired. This may require a credulous certainty of 'facts' taken literally - it is not clear what could then be understood if Siri were 'proven' to be alive and talking again, afterwards. Or perhaps she thinks that the software Siri is a software embodiment of an actual person (or possibly ghost of actual person), and Cueball was talking about the original person. We don't currently have the technology to upload a person's personality into a computer , [ citation needed ] but it's a popular science fiction trope and many scientists think we will eventually be able to do this . Another explanation could be that she associates everything into two categories, 'alive' and 'dead', without considering any intermediate or altogether separate categories, such as 'was never alive' or 'was programmed by people who are/were alive, but is not itself alive'. This false dichotomy causes Science Girl to misinterpret Cueball's answer of Siri not being alive as "Siri is dead." Finally, she could have actually been asking about Susan Bennett , the voice actress that recorded the base sounds for the synthesizer, perhaps thinking she recorded the full line rather than just base sounds for the software to synthesize. Assuming Science Girl meant the default voice, Bennett is very much alive, and Science Girl simply asked her question wrongly. The title text explains that, contrary to the above explanations, Siri actually died in a battle with Alexa , another personal assistant, hinging on their abilities to set multiple timers. Siri can set multiple timers, but this feature must be enabled via shortcuts. Alexa's ability to do so is much simpler and more user friendly. Of the many actions that these programs are able to perform, this is probably one of the more trivial, so it's not very comprehensible, at least to those not themselves living as digital assistants, that it would be the chosen method for a duel to the death. One possible explanation is that Alexa itself led the battle to that arena, where she knew she could win thanks to her superiority. [Science Girl is holding her phone up in one hand looking at the screen. A starburst from the phone indicates the voice coming from the phone] Phone: Your timer is set. Science Girl: Thanks [The picture broadens and shows that Science Girl, with the phone now held down, is standing in front of a desk, where Cueball, facing her, is sitting in an office chair using a laptop.] Science Girl: Is Siri alive? Cueball: No. [Back to only showing Science Girl, her phone and arm still held down at her side.] Science Girl: Oh, ok. [Same setting but Science Girl has raised her arm with the phone, looking at it again.] Science Girl: How did she die?

Solar System Cartogram

Solar System Cartogram

https://www.xkcd.com/2439

https://www.explainxkcd.com/wiki/index.php/2439:_Solar_System_Cartogram

[Above a chart are two paragraphs with explanation:] Most solar system diagrams are misleading. This chart offers a more accurate view by showing the planets sized by population. [Below the explanation is a list of the eight planets in the solar system. They are shown in order with labels. All but Earth show up only as dots. Earth is large and clearly drawn, with a view approximately centered on Indonesia. The spacing between the dots is equal, and the same distance as from those closest dots to Earth to Earths surface. Earth's label floats below it, while the other planets' labels connect to their respective dots with lines, with text either above or below the line of planets:] Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune

In this comic, Randall has made a cartogram showing the planets in the solar system . Cartograms are a type of map in which geographic area is displayed proportionately to some secondary characteristic - in this case, population. From the title text it is clear that the population in question is human (persons) (but even if all life forms where counted it it wouldn't matter, since the only confirmed life in the Solar System is on Earth). Thus the other planets have a population of 0 and are shown as nothing more than dots. This comic is a joke about cartograms, which are used, for instance, to show electoral representation. A standard American electoral map is very misleading. Though the split between the two major parties, Democrats and Republicans, is about 50-50, most of the area of the U.S. map is shown in the color associated with the Republican Party, red. That's because many Democrats live in densely packed districts occupying little land area, while many Republicans live in rural districts with large land area but few people. This has led to the rise of electoral cartograms in which district areas are shown in proportion to population, correcting the misimpression that most of America is conservative. Solar system diagrams are likely also to be misleading. Illustrators are overwhelmingly forced to use a far more scaled-down spacing between planets, compared to their scaled sizes, even if they can (or care to) maintain consistency in the relative distances and/or radii on linear scales. (The huge factors of difference involved instead may lend themselves to being physically modeled to better give some sense of the spacing and sizing differences.) Here, Randall has intentionally applied the wrong solution to the problem. Interestingly, the side of the Earth shown includes China and India, two countries that alone account for over a quarter of all humans on Earth. The title text states that even though Randall counts every active Mars rover as a person (for sentimental reasons), they are almost nothing compared to Earth's roughly 7,900,000,000 persons. Mars therefore is still nothing more than a dot compared to the Earth. There are a total of five rovers at the time of the comic's publication; in chronological order, they are Sojourner, Spirit and Opportunity, Curiosity, and Perseverance. Only the latter two were functional at the time of the comic's publication, giving Mars a rover population of two. A third rover, China's Tianwen-1 , landed on Mars on 2021 May 14, making for an all-time high of three active rovers. Mars rovers are a recurring theme on xkcd and only a few weeks earlier, a comic named 2433: Mars Rovers was released. This is the fourth comic this year to reference Mars Rovers. [Above a chart are two paragraphs with explanation:] Most solar system diagrams are misleading. This chart offers a more accurate view by showing the planets sized by population. [Below the explanation is a list of the eight planets in the solar system. They are shown in order with labels. All but Earth show up only as dots. Earth is large and clearly drawn, with a view approximately centered on Indonesia. The spacing between the dots is equal, and the same distance as from those closest dots to Earth to Earths surface. Earth's label floats below it, while the other planets' labels connect to their respective dots with lines, with text either above or below the line of planets:] Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune

Epistemic Uncertainty

Epistemic Uncertainty

https://www.xkcd.com/2440

https://www.explainxkcd.com/wiki/index.php/2440:_Epistemic_Uncertainty

[Two panels are shown with labels above them.] Regular Uncertainty Epistemic Uncertainty [In both panels Megan stands in front of a data presentation on a slide behind her. She is pointing at the slide with a stick.] [In the left panel titled 'Regular Uncertainty'. Megan standing in front of a presentation of a graph showing, from top to bottom, the number 74%, a horizontal line with a small black diamond near the middle representing an average with error bars, and a line of dots representing data in a horizontal scatter plot.] Megan: Our study found the drug was 74% effective, with a confidence interval from 63% to 81%. 74% [In the right panel titled 'Epistemic Uncertainty'. Megan stands in front of a presentation of data with a silhouette of a man with a hat labelled with a white question mark. Above this are three guesses of the "real" result and its relation to the study result.] Megan: Our study found the drug to be 74% effective. Megan: However, there is a 1 in 4 chance that our study was modified by George the Data Tamperer, whose whims are unpredictable. 73 -> 74?? 47 -> 74?? 0 -> 74?? ?

This comic is a comparison of two different research studies. One of these studies shows "regular uncertainty". One of these studies shows "epistemic uncertainty." In both panels, the core data is the same. The drug in question is 74% effective. However, the uncertainty qualities are different. The first is straightforward. The confidence interval (the error bars on the chart) is from 63 to 81%. The second panel includes the additional wrinkle of "George the Data Tamperer, whose whims are unpredictable." In statistics, a confidence interval is an estimate which provides a range of values. These values are based on the statistical probability that the data collected represents a certain result. The confidence interval is a reflection on the uncertainty imposed by the limits of study sample sizes. No study will ever have an infinite data set. [ citation needed ] As a result, it is possible for different studies to give slightly different results. Averaging the results of multiple studies can give a result that is probably more accurate. The result given may still be skewed. A small skew is more probable than a large one, though. For example, if a drug was 80% effective it would be possible for several small studies to show a spread of different results with an average of 74% effectiveness. If the drug was 99% effective it would still be possible to randomly end up with the same data. However, this would be highly unlikely. This gives us a spread of "likely" predictions. Predictions outside a certain interval are considered too unlikely to be realistic. George the Tamperer and Evangeline the Adulterator (from the title text) are analogous to the characters from Alice and Bob cryptography thought experiments. In the most basic examples, Alice and Bob are communicating. A third party, Eve the Eavesdropper, is spying on them. Both George and Evangeline have the ability to alter the study's results. George and Evangeline add uncertainty to the final data product. Specifically, they add epistemic uncertainty. Epistemology – unlike epidemiology – is the branch of philosophy related to knowledge. Thus epistemic uncertainty is the ultimate impossibility to be sure that what we know is accurate. We are not unsure what is accurate beause of failures in measurement. We are unsure what is accurate because of the intrinsic limits of knowledge. It seems that the "epistemic uncertainty" data has a 25% chance of data tampering by George. In the previous study, the data is known but its reflection of the general case is uncertain to an extent. In contrast, in this study even the knowledge of whether any single data point is correct is uncertain. Thus, their data has a 25% chance of being incorrect. There is no possible statement about how incorrect it may be. The title text mentions an individual called "Evangeline the Adulterator." She adulterates their drug doses. If this happened, the researchers would not even be sure the patients received the dosages (or exacting medicines/placebos) as prescribed. The study methodology itself would be in doubt. [Two panels are shown with labels above them.] Regular Uncertainty Epistemic Uncertainty [In both panels Megan stands in front of a data presentation on a slide behind her. She is pointing at the slide with a stick.] [In the left panel titled 'Regular Uncertainty'. Megan standing in front of a presentation of a graph showing, from top to bottom, the number 74%, a horizontal line with a small black diamond near the middle representing an average with error bars, and a line of dots representing data in a horizontal scatter plot.] Megan: Our study found the drug was 74% effective, with a confidence interval from 63% to 81%. 74% [In the right panel titled 'Epistemic Uncertainty'. Megan stands in front of a presentation of data with a silhouette of a man with a hat labelled with a white question mark. Above this are three guesses of the "real" result and its relation to the study result.] Megan: Our study found the drug to be 74% effective. Megan: However, there is a 1 in 4 chance that our study was modified by George the Data Tamperer, whose whims are unpredictable. 73 -> 74?? 47 -> 74?? 0 -> 74?? ?

IMDb Vaccines

IMDb Vaccines

https://www.xkcd.com/2441

https://www.explainxkcd.com/wiki/index.php/2441:_IMDb_Vaccines

[Cueball is sitting in an office chair at a desk typing on a laptop. There is a large thought bubble of his thoughts above his head, and his typing on the laptop makes sounds.] Cueball's thoughts: For the throne room scene, I think it's all three until the Emperor dies, then Vader only. It can't be Luke only, since he's visiting Vader, who is clearly at elevated respiratory risk. Plus, he removes Vader's mask! Keyboard: Type type. [Caption below the panel]: My Hobby: Editing IMDb to note the minimum set of people who need to be vaccinated in each scene for it to pass muster under current CDC guidance.

This comic is another in a series of comics related to the COVID-19 pandemic . This is another entry in the My Hobby series. Cueball is evaluating movies on IMDb (the Internet Movie Database ), based on how many people would need to be vaccinated for COVID-19 , in order for them to follow the CDC's most recent guidelines. The guidelines tell how fully vaccinated people should act ( at time of posting ). The evaluation assumes that the COVID-19 pandemic spread to the universes where the movies take place by the time at which they take place. This is part of a continuing pattern of comics . In these comics Randall applies COVID-19 safety standards to pre- or post-COVID situations. At the moment, Cueball is viewing the final confrontation between Luke Skywalker, Darth Vader (formerly Anakin Skywalker), and Emperor Sheev Palpatine. This confrontation takes place on the second Death Star in Return of the Jedi . Darth Vader wears a breathing apparatus in a mask that fully covers his face. Vader wears this because he sustained massive respiratory damage several movies earlier. During the confrontation, the Emperor is killed. Then Luke removes Vader's mask to see his face. (It is revealed in a previous film that Vader is Luke's father.) COVID-19 would be impossible for the Star Wars movies. It would be impossible because the Star Wars movies take place "a long time ago in a galaxy far, far away". This time was well before COVID-19 existed. [ citation needed ] Cueball notes that if only Luke had been vaccinated, he would still be a possible risk to Vader. The various vaccines seem to do well to protect recipients from the harsher outcomes of the virus. The vaccines may not completely prevent them from mild infection and potentially then passing it onwards. Luke is young and healthy. Luke is probably less susceptible, if Luke were to be exposed to the virus at any point. Vader's health issues mean that Vader would be in much greater danger from such a respiratory disease without Vader's own personal inoculation. The Emperor is elderly, but probably not at as great of a risk as Vader is. However, the Emperor, too is susceptible if the Emperor were infected. Cueball judges that Darth Vader's mask and breathing apparatus would protect Vader from the virus, a topic that was previously considered in 2367: Masks . The protection is at least to a limited extent. This is not an unreasonable assumption. Vader's suit has allowed Vader to survive the vacuum of space for short periods of time . Cueball concludes that all the characters in this fight need to be vaccinated in order to prevent the spread of the virus. This will be true until the Emperor dies. After the Emperor dies, only Vader needs to be vaccinated. The title text refers to two separate CDC recommendations. If you are visiting with people from a single household when vaccinated, all at low risk of serious complications from COVID-19, you do not have to take precautions. The precaution that you do not have to take include physical distancing or masks. If you are visiting with people from multiple households, then it is recommended that you take precautions against the spread of the disease regardless. Cueball is unsure whether or not Darth Vader and the Emperor live in close enough proximity to count as a single household. Whether Vader and the Emperor live in a single household would change how Cueball decides who should and should not be vaccinated. It is unknown, based on the Original Trilogy of Star Wars movies alone, how much time Vader and the Emperor spend in proximity. The "weird black egg thing" refers to Darth Vader's meditation chamber . The meditation chamber first seen in The Empire Strikes Back , which allows Vader to spend some time outside of his suit. [Cueball is sitting in an office chair at a desk typing on a laptop. There is a large thought bubble of his thoughts above his head, and his typing on the laptop makes sounds.] Cueball's thoughts: For the throne room scene, I think it's all three until the Emperor dies, then Vader only. It can't be Luke only, since he's visiting Vader, who is clearly at elevated respiratory risk. Plus, he removes Vader's mask! Keyboard: Type type. [Caption below the panel]: My Hobby: Editing IMDb to note the minimum set of people who need to be vaccinated in each scene for it to pass muster under current CDC guidance.

Mask Opinions

Mask Opinions

https://www.xkcd.com/2442

https://www.explainxkcd.com/wiki/index.php/2442:_Mask_Opinions

[Cueball and White Hat are standing and talking. Both are wearing masks.] Cueball: I am so excited not to have so many opinions about different kinds of masks at the forefront of my brain at all times. White Hat: Seriously. [The panel is zoomed in on Cueball's upper body. His hands are raised.] Cueball: "Do you know any tricks for getting a good seal around the bridge of your nose?" Cueball: I do, and I want to stop knowing them. [Cueball is walking away from White Hat with his hands raised above his head.] White Hat: You could always try talking about something else. Cueball: Honestly not sure I can! White Hat: Well. White Hat: Soon.

This comic is another in a series of comics related to the COVID-19 pandemic . Cueball and White Hat are having a conversation about face masks, which have become everyday essentials during the COVID-19 pandemic. Cueball has become exasperated with the weight of mask-related knowledge on his mind at all times, citing examples of instances of conversation in which he irritably divulges his knowledge of face masks. White Hat tries to placate him with the idea that this won't go on forever. He suggests thinking and talking about other things, but given Cueball's obsessive tendencies in the past, this is unlikely to occur. The final words of the comic, "Well. Soon." may be a pun on the phrase "Get Well Soon", commonly said as an expression of sympathy for someone who is sick or injured. In this case, White Hat hopes that Cueball will be able to stop talking about masks soon, which in turn means that he hopes for an end to the coronavirus pandemic. (It is not stated whether he hopes for an end to the coronavirus pandemic simply so that he can stop hearing Cueball talk about masks or because of the lives that would be lost if the pandemic continued.) In the title text, Randall implicitly endorses White Hat's hope, while suggesting that the new norm of wearing a mask when you feel sick will still be useful after the pandemic ends. Given that masks lower the transmission rates of many viral infections, including the common cold, this could be a wise strategy for avoiding illnesses in the future. Such a practice has been present for some time before the pandemic in other countries, Japan among them, where the habit of masks is the result of the last big pandemic (Spanish Flu, 1919/1920), but in North America the practice began (and may end) with COVID-19. Eliminating the common cold through masks, in this case via hazmat suits, has been examined in the What If? chapter 'Common Cold'. [Cueball and White Hat are standing and talking. Both are wearing masks.] Cueball: I am so excited not to have so many opinions about different kinds of masks at the forefront of my brain at all times. White Hat: Seriously. [The panel is zoomed in on Cueball's upper body. His hands are raised.] Cueball: "Do you know any tricks for getting a good seal around the bridge of your nose?" Cueball: I do, and I want to stop knowing them. [Cueball is walking away from White Hat with his hands raised above his head.] White Hat: You could always try talking about something else. Cueball: Honestly not sure I can! White Hat: Well. White Hat: Soon.

Immune Response

Immune Response

https://www.xkcd.com/2443

https://www.explainxkcd.com/wiki/index.php/2443:_Immune_Response

[Megan is walking toward Cueball, who is holding his arm.] Megan: How you feeling? Cueball: Not bad. Tired. A little sore. [Zoom in on Cueball. He looks down at his arms, which are held out.] Cueball: I feel bad for my immune system. It doesn't know this isn't a real virus. It must be freaking out. Cueball: Hey buddy, don't worry! We're going to be fine. This is just practice! [Zoom out. Megan gestures at Cueball, as he holds his arm.] Megan: No, don't tell it that . You want it to panic and build defenses that will be able to handle the real thing. Cueball: I guess. Cueball: Okay, let me try that again. Cueball: *ahem* [Cueball dramatically clutches at his chest.] Cueball: Woe! My arm is stricken by a dreadful plague! Cueball: I feel death draw near! My only hope is those heroic immune cells! Megan: Perfect. Cueball: Psst - you're doing great! I'm so proud of you.

This is another comic in a series related to the COVID-19 pandemic . As with a number of previous strips , Randall has a tendency to anthropomorphize both pathogens and the immune system, envisioning the process of infection and immune response as an epic battle . In this case, he treats his immune system as he would a child trying to accomplish something difficult, and worries about its emotional reaction. The COVID-19 vaccines (like all viral inoculations) work by introducing viral proteins into the body, causing the immune system to react as if the actual virus were present, creating the antibodies to fight it. As a result, if the actual virus is introduced, the immune system will have the capacity to quickly eliminate it. In this comic, Cueball has just received the COVID-19 vaccine and anthropomorphizes this process. He worries that his immune system is "freaking out", as the vaccine causes the body to 'think' it's under attack and respond as it would to a deadly threat. Cueball accordingly tries to reassure his immune system that the threat isn't real. However, Megan reminds him that the "panic" is the entire point, as that's what causes the body to build defenses, which will allow it to handle the real virus. Cueball then switches tactics, melodramatically announcing that the virus is about to kill him, and encouraging his "heroic immune cells" to save the day. The joke is that the basic elements of their response is accurate: the vaccine is essentially a ruse intended to "trick" the immune system into developing antibodies. However, the immune system obviously lacks a separate consciousness, and can neither hear nor understand their comments, [ citation needed ] making both reassurance and encouragement entirely moot. In the title text, Cueball continues to treat his immune system like a conscious entity. Specifically, all of his communications sound like a parent, or other adult, trying to encourage a child who was trying to win a game: giving it a pep talk about how he doesn't care if it wins or loses as long as it has fun. This is a common refrain when parents or other adults try to reassure children in contexts where victory isn't especially important, and where enjoyment is the real goal. Cueball then remembers that this particular event is much more consequential. If his immune system were to 'lose' to the vaccine, that would presumably mean it was incapable of responding properly to the viral threat, meaning he'd be in serious risk of death if he contracted the actual virus. As a result, he corrects himself and states that winning, in this case, is "very important". [Megan is walking toward Cueball, who is holding his arm.] Megan: How you feeling? Cueball: Not bad. Tired. A little sore. [Zoom in on Cueball. He looks down at his arms, which are held out.] Cueball: I feel bad for my immune system. It doesn't know this isn't a real virus. It must be freaking out. Cueball: Hey buddy, don't worry! We're going to be fine. This is just practice! [Zoom out. Megan gestures at Cueball, as he holds his arm.] Megan: No, don't tell it that . You want it to panic and build defenses that will be able to handle the real thing. Cueball: I guess. Cueball: Okay, let me try that again. Cueball: *ahem* [Cueball dramatically clutches at his chest.] Cueball: Woe! My arm is stricken by a dreadful plague! Cueball: I feel death draw near! My only hope is those heroic immune cells! Megan: Perfect. Cueball: Psst - you're doing great! I'm so proud of you.

Ingenuity

Ingenuity

https://www.xkcd.com/2444

https://www.explainxkcd.com/wiki/index.php/2444:_Ingenuity

[Ingenuity/Perseverance is on the surface of Mars.] Perseverance: Ingenuity helicopter has been lowered. Perseverance: Preparing to release it onto the surface. [A cut to mission control on Earth. Cueball trips and clicks on a key on his workstation, while Ponytail stands nearby.] Cueball: Oops Control panel: Click Trip [Back on Mars, Ingenuity's rotor blades start spinning.] Ingenuity: Bzzzzzz [Perseverance is being lifted into the air atop Ingenuity.] Perseverance: Wheeee! Ingenuity: Bzzzzzz

Ingenuity is a drone-like helicopter deployed to the surface of Mars. It rode on the underside of the Perseverance rover and at the time of publication its protective housing had been released from the rover and it was being prepared for a flight in early April. The helicopter is supposed to take off after the rover fully releases it and clears its takeoff trajectory. The comic projects what might happen if the mission controllers activated the helicopter early. In this case, the process is approaching the point of detaching the part-deployed Ingenuity. Ponytail and Cueball are present in mission control when Cueball trips and hits a button that clearly triggers the Ingenuity drone to take off. Perserverance, still firmly above/attached is seen to easily ride atop it. The rover exclaims "Wheee!", presumably from excitement or happiness. In the title text, some character discovers powered flight is easier on Mars, which contradicts our current understanding that powered flight is very difficult on Mars . Mars may have less gravity, but Mars's atmosphere is 1% the density of Earth's. It's so thin that you couldn't move a feather with a fan. This is why the character mumbles his explanation of the science, because they know any explanation doesn't actually make sense. The total mass of the two vehicles is about 556 times that of the helicopter alone, meaning the unexpected lift effect 'described' would have to be several hundred times more effective than that anticipated, depending upon the factor of overdesign already built in to avoid an expensive marginal failure. It also seems to be trivially easy to balance the extremely top-heavy loading upon the small solar-panel that tops out the counter-rotating coaxial blades, which adds yet more questions of both the dynamic and structural performance, never mind questions about the available power to accomplish this and the later possibilities to recharge. It is not the first time that we have seen a Mars vehicle vastly exceed expectations in these pages. It is also not the first time a character has caused an incident by tripping and hitting a control panel . [Ingenuity/Perseverance is on the surface of Mars.] Perseverance: Ingenuity helicopter has been lowered. Perseverance: Preparing to release it onto the surface. [A cut to mission control on Earth. Cueball trips and clicks on a key on his workstation, while Ponytail stands nearby.] Cueball: Oops Control panel: Click Trip [Back on Mars, Ingenuity's rotor blades start spinning.] Ingenuity: Bzzzzzz [Perseverance is being lifted into the air atop Ingenuity.] Perseverance: Wheeee! Ingenuity: Bzzzzzz

Checkbox

Checkbox

https://www.xkcd.com/2445

https://www.explainxkcd.com/wiki/index.php/2445:_Checkbox

[A small box is in the middle of a large white frame. The box can have a check-mark, but it is alternating between being checked or unchecked. At the bottom right there is a muted speaker (which can be unmuted). If the user press the checkbox gray dots or lines will appear below depending on the length of the press. These will move from right to left and then disappear.]

This was the 11th April fools' comic released by Randall . The previous fools comic was 2288: Collector's Edition , which was delayed two days and released on Friday April 3, 2020. The next became 2601: Instructions released on Friday April 1, 2022 (a regular release day). The comic looks similar to a loading screen. The actual comic (this “loading screen”) consists of an animated gif of a checkbox (hence the name). The frame is replaced with an interactive panel. In the center is a check box, which clears itself immediately when checked. In the bottom right is a mute button, which begins muted. By unmuting, and changing it to a loudspeaker, sounds are played when the check box is checked. This was the first comic with audio on xkcd. But the very similar Fool's comic from the next year, 2601: Instructions , used audio as the main part of the joke. This comic and also has a mute button (but here the sound was on when the mute button is shown, seems like an error). This comic is also very similar to this one, as it only has one thing in the center, but not a check box, but a radio button . Under the checkbox is a scrolling visual representation of the timing and duration of clicks in the check box, which also produce matching beeping sounds when unmuted. The representation consists of a dot for a short press, or a bar for a longer press. All long presses are represented by a bar of a pre-determined length; in other words, a longer press does not result in a longer bar. By varying between brief and long presses, and brief and long intervals between presses, it is possible to enter characters in Morse Code. The check box then begins operating by itself, producing sounds which can be decoded as Morse Code. These responses are also printed in the browser's JavaScript console in both plain text and a textual representation of Morse code. If left without any initial input for 30 seconds it would send the message CQ (meaning "Seek You"). The title text hints at the use of Morse Code in the comic; interpreting the "check" as a Morse Code dot and the "chhecck" (a long check) as a Morse Code dash gives ...---..., which is the Morse Code for "SOS", the international distress signal. Incidentally, inputting the SOS signal gives "YOU TOO?". For the majority of inputs, the check box responds with a random selection from the following list: Some keywords, however, have special responses . This comic has a unique header text , see the details here . The header is: "This comic was put together by Max Goodhart, Patrick, Amber, Benjamin Staffin, Kevin Cotrone, and Michael Leuchtenburg." Read Max's blog post on development of the comic. [. represents a short signal, - represents a long signal, and / represents pauses between words. Sojourner is a Mars rover which has been referenced by Randall in the past and is the entity operating the morse code device.] See also QRS and QRQ. An explanation of Q codes can be found here . Steps to complete (directions can be abbreviated as their first letter): After successfully repairing and rebooting Sojourner, a comic is opened which depicts it seeking out and finding its friends, Spirit, Opportunity, Curiosity, Perseverance, and Ingenuity. Curiosity and Perseverance are locked in a swordfight, and either Spirit or Opportunity is carried off by Ingenuity while the other speeds off a small mound of dirt. Ingenuity carrying a rover is a reference to the previous comic. The page's JavaScript creates a global object morse with encode and decode methods. From the developer console, it is possible to write morse.encode("A PHRASE") , which will print the Morse code corresponding to the text provided, or morse.decode("... --- ...") which will translate the Morse code to text. BeepComic.hurryUp() to get the reply immediately in the console. BeepComic.send(...) to send directly to SOJOURNER. [A small box is in the middle of a large white frame. The box can have a check-mark, but it is alternating between being checked or unchecked. At the bottom right there is a muted speaker (which can be unmuted). If the user press the checkbox gray dots or lines will appear below depending on the length of the press. These will move from right to left and then disappear.]

Spike Proteins

Spike Proteins

https://www.xkcd.com/2446

https://www.explainxkcd.com/wiki/index.php/2446:_Spike_Proteins

[Cueball is sitting in an office chair at a desk with an open laptop in front of him. Megan stands behind him looking over his shoulder. Beret Guy is in front of the desk, walking away and looking back at the two while holding a hand to his shoulder, where he got the vaccine shot.] Beret Guy: Got the vaccine! Megan: Congrats! Beret Guy: Time to go make spike proteins. [Cueball continues to work on his laptop while Megan is looking on.] [In a frameless, narrow panel, Beret Guy walks back carrying a large object in his arms that looks like a spike protein. But it is about half as long as he is tall, fluffy and dripping wet, flexing slightly along its length, with the Y-shaped head pointed forwards, away from Beret Guy] Beret Guy: OK! Beret Guy: Here's my first try. [Beret Guy drops the spike protein onto Cueball's desk with the Y-shaped end on the desk up against the back of Cueball's laptop. The movement is shown with several lines and a sound follows when it hits the desk. The head of it takes up the entire desk area not covered by the laptop, while the tail overhangs the desk. Cueball is grabbing the lid and base of his laptop with both hands, pulling it partially closed and away from the spike protein, and Megan reflexively leans away.] Spike Protein: Plop [Beret Guy turns to leave, with an outstretched finger pointing skyward. The overhanging part of the spike protein has sagged, and it is dripping some wet material over both the floor and desk. Cueball is sitting with his hands on the partially closed laptop, Megan stands normally again.] Beret Guy: More! Cueball: Ewww. Megan: Why is it so wet??

This is another comic in the COVID-19 series related to the COVID-19 pandemic . This is also another comic about the current vaccine against COVID-19 . A vaccine is designed to provoke an immune response from the body of the recipient, which "trains" the immune system to attack actual viruses (or bacteria). For COVID-19, the spike protein , necessary for the virus to bind a receptor on human cells and invade them, is the key protein for an immune response. Almost all vaccines approved for human use pre-COVID actually contain either inactivated pathogen (e.g., flu vaccine), live but safe pathogen variants (e.g., measles), or some protein from the pathogen that the immune system can respond to (e.g., pertussis). The four COVID-19 vaccines approved in the United States or the European Union as of the date of this comic, however, are all a relatively new type of vaccine that instead cause human cells to temporarily produce spike proteins, which the immune system then "learns" to attack. The Oxford-AstraZeneca and Johnson & Johnson ’s Janssen vaccine use a technique first approved for the July 2020 Ebola vaccine, in which a genetically modified adenovirus is used to deliver DNA to the nuclei of the vaccine recipients' cells, which convert the DNA to Messenger RNA (mRNA). The recipients' cells then use the mRNA as instructions to produce spike proteins. The Pfizer BioNTech and Moderna vaccines are of an even newer type: m RNA vaccines , which directly inject the mRNA into the body for the cells to use, and never have to enter the cell nuclei. Beret Guy , in his usual fashion , misunderstands how reality works, then reality alters to fit his view of it. After receiving the vaccine, as he informs Cueball and Megan , he claims he will now go away to make spike proteins. For him, this literally means that he (not his cells) will build them, by unexplained means. When he returns he is carrying his constructed protein, which is roughly 8 orders of magnitude larger than the normal version, and also appears to be dripping. He then drops it on the desk, where a laptop is being used. Cueball part-closes his screen to try to prevent the mass from landing on it - though he's only partially successful. When a normal living body is coerced into making a spike protein, they are microscopic particles that distribute internally around the body to provoke an immune response. Beret Guy's macroscopic version provokes an understandable response of both disgust and confusion from both Cueball and Megan, who choose to ask why it is so wet. Proteins are highly hydrated molecules where water — through the moderation of its presence and absence in specific locations — plays a central role in shaping the structure and function of the protein (although it is not clear how Beret Guy knows that the spike protein should be hydrated since this is his first try). Though, of the many questions that might have been asked, it is not an entirely unreasonable snap reaction. Beret Guy remains typically oblivious to the fuss he causes. His enthusiastic intention, apparently, is to leave his first proud creation there as he departs to construct further examples. They will likely be no less unwelcome. Anything damp and squidgy (as this creation seems to be) would not be welcome around a laptop, for a number of reasons, and Beret Guy seems to have made a particularly messy contact with the part of the case where most such devices are likely to have clusters of heat vents or unruggedised ports/connections that may not react well to the ingress of liquids. The title text is a pun on Acer, ACER2, and ACE2. Acer is a brand of computers including laptops. The ACE2 receptor , is an entry point on a cell to which the SARS-COV-2 virus attaches during the process of entering the cell. ACER2 is a real enzyme in humans which, although unrelated to ACE2 or SARS-COV-2, may also help bind the pun together. [Cueball is sitting in an office chair at a desk with an open laptop in front of him. Megan stands behind him looking over his shoulder. Beret Guy is in front of the desk, walking away and looking back at the two while holding a hand to his shoulder, where he got the vaccine shot.] Beret Guy: Got the vaccine! Megan: Congrats! Beret Guy: Time to go make spike proteins. [Cueball continues to work on his laptop while Megan is looking on.] [In a frameless, narrow panel, Beret Guy walks back carrying a large object in his arms that looks like a spike protein. But it is about half as long as he is tall, fluffy and dripping wet, flexing slightly along its length, with the Y-shaped head pointed forwards, away from Beret Guy] Beret Guy: OK! Beret Guy: Here's my first try. [Beret Guy drops the spike protein onto Cueball's desk with the Y-shaped end on the desk up against the back of Cueball's laptop. The movement is shown with several lines and a sound follows when it hits the desk. The head of it takes up the entire desk area not covered by the laptop, while the tail overhangs the desk. Cueball is grabbing the lid and base of his laptop with both hands, pulling it partially closed and away from the spike protein, and Megan reflexively leans away.] Spike Protein: Plop [Beret Guy turns to leave, with an outstretched finger pointing skyward. The overhanging part of the spike protein has sagged, and it is dripping some wet material over both the floor and desk. Cueball is sitting with his hands on the partially closed laptop, Megan stands normally again.] Beret Guy: More! Cueball: Ewww. Megan: Why is it so wet??

Hammer Incident

Hammer Incident

https://www.xkcd.com/2447

https://www.explainxkcd.com/wiki/index.php/2447:_Hammer_Incident

[Cueball, holding a palm up in front of him, stands before a long desk, behind which is a seated panel of four people, consisting of Ponytail, Hairy, a Cueball-like guy and Hairbun. Hairy is the only one to have one arm on the desk, all other arms are held down with hands below the desk.] Cueball: Yes, I know you're mad that I dropped that hammer. Cueball: But think about me— Cueball: Seven years of bad luck! [Caption below the panel]: Man, NASA is really on my case about the James Webb Space Telescope.

The James Webb Space Telescope (JWST) is a space telescope created to be the successor of the Hubble Space Telescope under construction at time of publishing and launched December 25, 2021, though in 2014: JWST Delays , xkcd predicted its launch would actually occur during late 2026. It's implied that Cueball dropped a hammer on the mirror of the JWST and broke it. In superstition, breaking a mirror causes seven years of bad luck. The cost estimate for the JWST is currently US$10 billion, and Cueball is at a NASA official hearing for breaking this very expensive piece of equipment, no doubt costing NASA (and thus the nation) hundreds of millions of dollars more for repair work. However, Cueball is more concerned about personally experiencing seven years of bad luck. In actuality the mirror panel is not made of glass, so it's likely that a dropped hammer would dent and distort the panel rather than shattering it. Presumably Cueball's hammer drop would damage or destroy only one mirror panel out of the JWST's eighteen panels. (If he had destroyed the entire telescope, he would have been facing 7×18=126 years of bad luck, and the damage costs would be much higher. Then again, this depends on the altitude that the destruction happened. ) Even breaking a single panel would likely be very expensive because it would require extremely accurate machinery and extensive calibration tests to make and install a replacement panel, especially because the back of JWST's mirrors are made of beryllium. Beryllium is expensive to purchase, since it is relatively scarce, and is very hard and abrasive, so making things out of it is difficult (and expensive due to the specialized machinery required and the precautions necessary to prevent inhalation). Breaking a beryllium mirror would lead to dust formation; single exposures to beryllium dust can cause acute beryllium poisoning and massively increase the risk of lung cancer, which is very bad luck on behalf of Cueball. In addition to the property damage, Cueball is probably liable for injuring his coworkers, which is probably the main reason why the NASA workers are so angry at him because human lives are more valuable than mere money. [ citation needed ] The title text refers to the Cold Stone Creamery , a chain that mixes ice cream with various other ingredients, such as fruit or candy, in front of the customer before serving it. The usual surface for mixing is a piece of granite which is kept cold (about -10°C). It's implied that Cueball had tried mixing his ice cream and flavorings in the style of Cold Stone Creamery on the JWST mirror, which is also kept cold -- in fact much colder, as it's cooled to as low as 7 K (-266°C, or -447°F). If Cueball had mixed ice cream this way on the JWST, he would likely have scratched and/or stained the surfaces on the telescope and perhaps have gotten gunk into the instrumentation, and possibly, due to the localized temperature differential from ice cream hundreds of degrees warmer than the material, promoted damaging distortions or fractures -- hardly the 'good idea' mentioned in the title text. (It also would not have worked: at sufficiently low temperatures, ice cream hardens and cannot be mixed.) The bad luck from breaking a mirror is also referenced in 1136: Broken Mirror . [Cueball, holding a palm up in front of him, stands before a long desk, behind which is a seated panel of four people, consisting of Ponytail, Hairy, a Cueball-like guy and Hairbun. Hairy is the only one to have one arm on the desk, all other arms are held down with hands below the desk.] Cueball: Yes, I know you're mad that I dropped that hammer. Cueball: But think about me— Cueball: Seven years of bad luck! [Caption below the panel]: Man, NASA is really on my case about the James Webb Space Telescope.

Eradication

Eradication

https://www.xkcd.com/2448

https://www.explainxkcd.com/wiki/index.php/2448:_Eradication

[Megan holding a hand up, palm held out, is walking with Cueball.] Megan: Even if the threat eventually fades, thanks to vaccines and stuff, [They walk on, both with their arms down.] Megan: And it becomes just another circulating common cold virus, [Megan holds her hand up in a fist, while Cueball hold his hand to his chin as they walk on.] Megan: I think we should pursue global eradication of SARS-CoV-2 out of spite . Cueball: Revenge-based public health policy. I like it.

This is another comic in the COVID-19 series related to the COVID-19 pandemic . Megan and Cueball are discussing the possibility of SARS-CoV-2 eventually becoming "another circulating common cold virus". This is considered to be a serious possibility , as a combination and vaccines and acquired immunity cause most people to have some degree of immunity as they age. This is particularly likely because SARS-CoV-2 poses little risk to small children, and if most people are infected with it in childhood, they'll likely be immune as adults. Multiple other coronaviruses are common in the human population, and fall under the category of "the common cold", causing only minor and temporary symptoms, with little serious risk for most people. If SARS-CoV-2 does transition to being a minor disease, there will be little reason to continue focused eradication efforts, because the ongoing harm will be too little to justify such efforts. It's extremely difficult to wipe out a virus altogether, as it requires every human population to be either isolated from the disease, or vaccinated until herd immunity is achieved. There are only two viruses which have been totally eliminated in the wild: Smallpox and rinderpest , and rinderpest infects only cattle and other ruminants, not humans. The elimination of smallpox was one of the greatest public health accomplishments of the 20th century, and resulted from an aggressive and ambitious global vaccination effort. Smallpox is now considered to be extinct in the wild, with only a small number of samples still preserved in government labs. Where diseases continue to be dangerous, ongoing global efforts are made to eliminate them entirely (polio, measles and rubella are currently targets of such programs). If a disease ultimately becomes more or less harmless, its elimination is less of a priority. The joke of this strip is that, in the aftermath of the COVID-19 pandemic, Megan feels so much rage and ill-will toward the disease that vaccination efforts are no longer only a matter of protecting health, but an expression of hostility toward the virus. Her argument is that, even if global elimination efforts are no longer justified by the danger of the virus, they should be pursued "out of spite". Like many other strips in this series, the characters tend to anthropomorphize the virus, treating it as an intelligent and sentient enemy, rather than mere force of nature. Given that mindset, the idea that the virus could cause so many deaths and so much disruption, and then continue to exist without consequence, would upset many people. Cueball agrees with her perspective, approvingly referring to it as "revenge". Cueball has also previously shown a merciless attitude towards endemic infections , even those that aren't particularly deadly, and so the idea of eliminating one entirely would probably appeal to him on its own merits. The title text refers to the aforementioned extinction (in the wild) of smallpox. This is the type of line one might see in fiction , delivered to someone who is about to be killed, taunting them about the death of one of their friends or associates. The line treats the virus like a villain in an action movie, and revelling in the fact that we're finally going to kill it. [Megan holding a hand up, palm held out, is walking with Cueball.] Megan: Even if the threat eventually fades, thanks to vaccines and stuff, [They walk on, both with their arms down.] Megan: And it becomes just another circulating common cold virus, [Megan holds her hand up in a fist, while Cueball hold his hand to his chin as they walk on.] Megan: I think we should pursue global eradication of SARS-CoV-2 out of spite . Cueball: Revenge-based public health policy. I like it.

ISS Vaccine

ISS Vaccine

https://www.xkcd.com/2449

https://www.explainxkcd.com/wiki/index.php/2449:_ISS_Vaccine

[Megan and Cueball are standing talking to each other.] Megan: I just realized— Megan: The astronauts on the ISS probably can't get the vaccine until they land. Cueball: Sure they can. Cueball: NASA's good at orbital injections.

This comic is another in a series of comics related to the COVID-19 pandemic , specifically regarding the COVID-19 vaccine . Megan has just realized that the astronauts on the ISS (the International Space Station ) probably can't get a vaccine against COVID-19 before they land. That is, it will not get shipped up to them. This can be a concern because their immune system is impacted by extended stays in space. So when they come down again they may need to stay in quarantine longer, as the vaccine is not fully effective the first few weeks after administration. There could of course also be concern about getting COVID-19 while in space, but this is very unlikely due to the quarantine measures and other security measures taken by NASA and their Russian counterpart, Roscosmos . See this article with more details on these facts: What NASA is doing to keep COVID-19 off the space station . Cueball 's reply, "NASA's good at orbital injections", is a pun on "orbital injection", also called orbital insertion , which is the adjustment of a spacecraft’s momentum that puts it into a stable orbit around a planet, moon, or other celestial body. Space agencies like NASA do this routinely on spaceflight missions. Getting an injection of a COVID-19 vaccine while in orbit aboard the ISS could also be called orbital injection, hence the pun. The title text refers to the fact that, because the ISS orbits the Earth every 90 minutes, the people aboard it experience a day in that time, seeing a sunrise and sunset and crossing the International Date Line on the ground. One interpretation of this might be that 90 minutes on the ISS are equivalent to a day on the ground, making the people on board due for the second dose of the Pfizer vaccine (normally 21 days) or the Moderna vaccine (normally 28 days) after 31.5 or 42 hours, respectively, which Randall rounds to 30 or 40 hours. In reality, rather than tracking the local time of the territories it passes above, the ISS follows Coordinated Universal Time . [Megan and Cueball are standing talking to each other.] Megan: I just realized— Megan: The astronauts on the ISS probably can't get the vaccine until they land. Cueball: Sure they can. Cueball: NASA's good at orbital injections.

Post Vaccine Social Scheduling

Post Vaccine Social Scheduling

https://www.xkcd.com/2450

https://www.explainxkcd.com/wiki/index.php/2450:_Post_Vaccine_Social_Scheduling

[From top to bottom, eleven people are standing on the left side of the image: Danish, Cueball #1, Hairbun, Black Hat, Ponytail, Science Girl, White Hat, Hairy, Blondie, Cueball #2, and Megan, with even-numbered characters standing slightly further to the left. Each character’s first and second doses of the vaccine are labeled ① and ②, respectively. The time before each character’s first dose is drawn with a grey solid line; the time between their first dose and after they are fully vaccinated (two weeks after their second dose) is drawn with a grey dashed line; the time after they are fully vaccinated is drawn with a black solid line. Black Hat, Science Girl, Blondie, Cueball #2, and Megan have all received their first doses before the comic’s time frame. Social activities are drawn with an ellipse around the top and bottom members, and each participating character is identified with a large filled-in circle on their timeline. The ellipses are labeled :] DINNER GAMES MOVIE BIRTHDAY DINNER CABIN [The events that happen, in chronological order (from left to right), are: [Caption below the panel:] Post-Vaccine Social Scheduling

This comic is another in a series of comics related to the COVID-19 pandemic , specifically regarding the COVID-19 vaccine . The comic shows a timeline of a multitude of (presumably) friends and acquaintances getting two doses of the SARS-CoV-2 vaccine. Due to the recommended delay between shots, as well as the few weeks needed to build antibodies after the second shot, planning get-togethers becomes complicated by who is free to meet, or not yet. The diagram is some form of Scheduling Diagram, maybe akin to a Gantt chart , which helps to coordinate the status of several individual 'processes' (personal vaccination schedules) and demonstrate where dependent activities (meet-ups) are mutually possible. Eventually, everyone can start getting together, but during the time where some people have only received one, neither, or only got the second recently, the scheduling is complicated. The complication is increased by the fact that people who have received one or two doses of vaccine, but haven't gone through the whole waiting period, can be expected to have some protection, but possibly not full protection (as represented by the dashed line). In that case, there's the added question of how important it is that the person is at an event, and how much risk the people involved are willing to tolerate. This may be the reason for the "movie" set, in which all participants will have received both doses, but one will not have completed the final waiting period. The title text references NP-hardness, a theme that has come up in past comics. NP-hardness describes a particular level of computational difficulty. Scheduling problems are normally NP-hard. But when extra challenges such as having to deal with whether or not people are vaccinated they become even more difficult. In this case though, Critical Path dependencies seem trivial enough. Events (vertical lozenges across the dot-marked timelines of those included) are as trivial to validate as possible for those selected to attend. Fixed events in time can be scanned to show all those allowed to participate at that moment. Movable events can be rescheduled until (enough of) those hoped to be included are 'valid'. Complications may arise for those whose presence relies upon the status of others potentially attending, or the need to maintain time between two events (in either order) with part-shared attendees as a precautionary 'cool-down' isolation. It is not obvious that either of these issues factor in, any more than basic scheduling conflicts would. The third person is scheduled for a movie before being fully vaccinated may be a direct reference to 2441: IMDb Vaccines , discussing the number of people that needs to be vaccinated to record a particular scene. Other than each line's identifying portrait (which are not of the Throne Room characters) no explicit age/vulnerability information is given to justify this, presumably the chart's users are aware of the specifics. The third person in the table is included in a movie viewing (for which masks could be worn) shortly after their second immunization, but not included in the dinner group until the full benefit of the vaccine takes hold. CDC guidelines permit vaccinated individuals to visit inside a home or private setting without a mask with one household of unvaccinated people who are not at risk for severe illness. Therefore the movie gathering conforms to CDC recommendations provided that the single unvaccinated person is not at increased risk of severe illness and the movie is in a home or private setting. The third person in the table appears to have received the second shot twice. This is possibly a reference to 2422: Vaccine Ordering . Another interpretation is that she lied about her first dose being her second dose to be invited to the movie. [From top to bottom, eleven people are standing on the left side of the image: Danish, Cueball #1, Hairbun, Black Hat, Ponytail, Science Girl, White Hat, Hairy, Blondie, Cueball #2, and Megan, with even-numbered characters standing slightly further to the left. Each character’s first and second doses of the vaccine are labeled ① and ②, respectively. The time before each character’s first dose is drawn with a grey solid line; the time between their first dose and after they are fully vaccinated (two weeks after their second dose) is drawn with a grey dashed line; the time after they are fully vaccinated is drawn with a black solid line. Black Hat, Science Girl, Blondie, Cueball #2, and Megan have all received their first doses before the comic’s time frame. Social activities are drawn with an ellipse around the top and bottom members, and each participating character is identified with a large filled-in circle on their timeline. The ellipses are labeled :] DINNER GAMES MOVIE BIRTHDAY DINNER CABIN [The events that happen, in chronological order (from left to right), are: [Caption below the panel:] Post-Vaccine Social Scheduling

AI Methodology

AI Methodology

https://www.xkcd.com/2451

https://www.explainxkcd.com/wiki/index.php/2451:_AI_Methodology

[Cueball is standing on a podium in front of a projection on a screen and points with a stick to a bar chart histogram with a bell curve to the left and a single bar to the far right marked with an arrow.] Cueball: Despite our great research results, some have questioned our AI-based methodology. Cueball: But we trained a classifier on a collection of good and bad methodology sections, and it says ours is fine.

The joke in this comic is that the people are using artificial intelligence (AI) without understanding how to, and that by doing this the research concerned is at best unreliable and possibly deliberately compromised. The researchers acknowledge that their approach is risky and requires extra verification, but repeatedly use equally or more unreliable AI-based solutions to these problems. Therefore, their problems are likely as bad as they ever were and any other team using one of their verification tools is likely to experience similar unreliability. For an introduction to machine learning, you can visit https://fast.ai/ . The first comment, that "some have questioned our AI-based methodology", refers to difficulty verifying the correctness of AI-based processing. A model (a program which solves a problem with AI-based statistical analysis) may appear reliable when it is instead insufficiently tested. Models are liable to experience issues due to lingering influences from its training data or a bad algorithm reducing the quality of the investigation. It is therefore necessary for research using such models to demonstrate that those models have been tested well enough that their results are likely to be useful. Frequently, additional tests are performed after training to confirm that the model can handle data collected in a different way to the data used to train it. Cueball seeks to reassure his audience by quantifying the quality of his methodology. He does this by creating yet another AI to rank methodologies. This approach is unlikely to instill confidence for a variety of reasons: While there are many red flags in the original AI and quality AI, it is theoretically possible that they operate as Cueball claims. The title text's comments about spacing and diacritics prove that this is not the case and that the quality AI, at least, is completely broken. AI models are given input in various complex ways and determine based on statistical analysis which details are important. Such models can easily find details in the training data which correlate with correct answers but make the resulting model useless. For example, a research team once created a model which was given medical information to determine how likely a patient was to have cancer. The model was trained on existing patient records and the team planned to use it on new patients. However, the original model did not use the medical information but instead simply checked the name of the hospital--a patient at a hospital with "cancer center" in the name was likely to have cancer. The model had identified a data point which correlated with the desired answer, but this correlation was not useful for the intended purpose. The model concerned was discarded and a new one created without the hospital name. In this case, the methodology sections are text written by humans, which can contain various artifacts of the writing process. These can include details like how the user chose to insert spaces, word usage, spelling, or diacritic marks which are optional in English (e.g. naive versus naïve). It appears that the training information identifies certain patterns which correlate with "good" methodologies. This indicates a few more problems for this research team: [Cueball is standing on a podium in front of a projection on a screen and points with a stick to a bar chart histogram with a bell curve to the left and a single bar to the far right marked with an arrow.] Cueball: Despite our great research results, some have questioned our AI-based methodology. Cueball: But we trained a classifier on a collection of good and bad methodology sections, and it says ours is fine.

Aviation Firsts

Aviation Firsts

https://www.xkcd.com/2452

https://www.explainxkcd.com/wiki/index.php/2452:_Aviation_Firsts

[A chart is shown with nine items. To the right of each item there are two check boxes. Above the top row of check boxes are two underlined labels for the two columns. The first four rows have both boxes checked, and the last five have only the first box checked. The last two items are so long that they take up three and four rows of text. The first seven items are written on one line each.]

This comic reflects the Ingenuity probe's first flight on Mars . Now that Ingenuity has completed its first flight, Mars can be counted among planets with controlled powered flight. The preceding milestones in this list were completed by the first space probes to reach and then land on Mars. Flight, landing and controlled landing were variously achieved by some or all of the prior landers, depending upon your definition of flight, but certainly by the Skycrane element used in landing both Curiosity and Perseverance rovers. These may not have qualified as controlled powered flight as they only used their power to control the landing, before flying off again under power without any more precise control than that needed to intentionally crash elsewhere. The remaining milestones have only been completed on Earth, if at all, and also grow more bizarre and more specific further down the comic and extending into the title text. [A chart is shown with nine items. To the right of each item there are two check boxes. Above the top row of check boxes are two underlined labels for the two columns. The first four rows have both boxes checked, and the last five have only the first box checked. The last two items are so long that they take up three and four rows of text. The first seven items are written on one line each.]

Excel Lambda

Excel Lambda

https://www.xkcd.com/2453

https://www.explainxkcd.com/wiki/index.php/2453:_Excel_Lambda

[In a narrow panel, Ponytail is walking in from the left, looking down at her phone] Ponytail: Oh cool, Excel is adding a lambda function, so you can recursively define functions. [Ponytail, holding her phone to her side stands behind Cueball, who is sitting in an office chair with a hand on a laptop standing on his desk. He has turned around to face her, leaning with the other arm on the back of the chair.] Cueball: Seems unnecessary. Cueball: When I need to do arbitrary computation, I just add a giant block of columns to the side of my sheet and have a Turing machine traverse down it. [In a frame-less panel Ponytail is standing in he same position behind Cueball, who has resumed working on his laptop with both hands on the keyboard.] Ponytail: I think you're doing computing wrong. Cueball: The Church-Turing thesis says that all ways of computing are equally wrong. [Ponytail is still behind Cueball, who has a finger raised in the air, and the other hand is on the desk. Cueball's head has a visible sketch layer which has not been erased.] Ponytail: I think if Turing saw your spreadsheets, he'd change his mind. Cueball: He can ask me to stop making them, but not prove whether I will!

Cueball is computing and Ponytail criticizes him in a way that is reminiscent of the Code Quality series , although not as harsh. Cueball has lots of strange computer problems , and this will most likely result in another one. The comic begins with Ponytail finding out that Microsoft Excel is adding a lambda function to their function library. This was announced by Microsoft for Beta users in December of 2020. A lambda function is a fundamental mathematical structure that can be used to define all possible computations, in what is known as lambda calculus . They are commonly found in programming languages such as Lisp , Python , and many others. A lambda function is also called an anonymous function because in most languages it can be passed to other functions (including another lambda function) without needing to be given any formal name. Finding that Excel is adding a lambda function pleases Ponytail. Cueball claims that the lambda function is unnecessary, as when he needs arbitrary computation he just adds a block of columns to the side of his sheet and has a Turing machine process it. This would technically work as lambda calculus is formally equivalent to Turing machines. People have created Turing machines in Excel , although not for practical purposes. Ponytail finds his solution absurd and is convinced Cueball is "doing computing wrong". But he claims that all computing is equally wrong, citing the Church-Turing thesis , a hypothesis which says that a function can be computed by executing a series of instructions if and only if that function is computable by a Turing machine. A classical Turing machine uses an infinitely long strip of tape as its memory; for Cueball, the large Excel column acts as the "tape". All ways of computing are "equally wrong" since, according to this thesis, they can all be translated to or from a Turing machine. Ponytail and Cueball appear to have different ideas of 'computing'. Ponytail, like most programmers, probably includes efficiency and readability as important characteristics of 'doing computing right'. Cueball appears interested only in computability , a more theoretical point of view than Ponytail's. Ponytail then says that Turing would change his mind if he saw Cueball's spreadsheet, presumably because of the extreme complexity of Cueball's code in the spreadsheet. Cueball's final statement is that Turing could ask him to stop, but would not be able to prove if he actually will stop. Cueball's final statement is a reference to the halting problem mentioned in the title text. It is the problem of determining whether a given Turing machine will halt. The problem has been shown to be undecidable, i.e., it is impossible to build an algorithm that computes whether any arbitrary Turing machine will halt or not. Because of the way Cueball has behaved, he has been specifically mentioned in Turing's later formulations of the halting problem. Cueball finds this very rude. This is of course a joke, since Turing has been dead since 1954, presumably long before Cueball was born. But it would be crazy indeed if a scientist became so mad at a person that they would mention this person by name in their formulation of a serious problem. Over-complicated spreadsheets were also mentioned in 2180: Spreadsheets . [In a narrow panel, Ponytail is walking in from the left, looking down at her phone] Ponytail: Oh cool, Excel is adding a lambda function, so you can recursively define functions. [Ponytail, holding her phone to her side stands behind Cueball, who is sitting in an office chair with a hand on a laptop standing on his desk. He has turned around to face her, leaning with the other arm on the back of the chair.] Cueball: Seems unnecessary. Cueball: When I need to do arbitrary computation, I just add a giant block of columns to the side of my sheet and have a Turing machine traverse down it. [In a frame-less panel Ponytail is standing in he same position behind Cueball, who has resumed working on his laptop with both hands on the keyboard.] Ponytail: I think you're doing computing wrong. Cueball: The Church-Turing thesis says that all ways of computing are equally wrong. [Ponytail is still behind Cueball, who has a finger raised in the air, and the other hand is on the desk. Cueball's head has a visible sketch layer which has not been erased.] Ponytail: I think if Turing saw your spreadsheets, he'd change his mind. Cueball: He can ask me to stop making them, but not prove whether I will!

Fully Vaccinated

Fully Vaccinated

https://www.xkcd.com/2454

https://www.explainxkcd.com/wiki/index.php/2454:_Fully_Vaccinated

[Megan is standing in front of a three-step stair leading up to an open door. She has one hand in the air while talking to someone inside the house, who replies. The ground outside has small tufts of grass.] Megan: Hi, I'm here to visit! Voice, from inside the house: Do I know you? Megan: No, it's cool, I'm two weeks past my second dose. [Caption below the panel:] Remember, once you're fully vaccinated, the CDC says you're free to visit other people's houses.

This comic is another in a series of comics related to the COVID-19 pandemic , specifically regarding the COVID-19 vaccine . The Centers for Disease Control and Prevention (CDC) has stated that once people are fully vaccinated, they are able to visit other people's houses (and not risk spreading/catching coronavirus). The implication, of course, is that you can visit people that you would also have visited before the outbreak. The humor in this comic comes from Megan who is just going to visit a random stranger's house. She explains this is okay because she is fully vaccinated, telling the person in the house that she is two weeks past her second dose. This was part of the topic of the last vaccine comic 2450: Post Vaccine Social Scheduling . Restrictions to socializing, brought in as various governments reacted to the emergent COVID-19 pandemic, often disallowed or discouraged visiting family, friends, etc, beyond a mutually isolating 'support bubble', which meant that many house visits that might have occurred beforehand were no longer advisable. With the development and distribution of vaccines, and the eventual receiving of a second dose as applicable, the rules have been modified to allow those vaccinated to once again resume some degree of their prior outgoing behavior where the risks have been mitigated. In this instance, though, Megan has taken the advice even further. Rather than opening back up to a situation closer to the 'old normal', she has taken it as an official sanction to exceed the old social limits and pester complete strangers. Alternately, this is what she always used to do, and only stopped 'for the duration', this unlucky householder being (one of) the first to be subjected to this 'guerilla visiting' now that there seems to be no reason not to continue. In the title text, the owner of the house explains to Megan that just because she has been vaccinated she just can't enter into someone's house without being invited — a commonly understood form of property law. But due to the vaccine type Megan thinks the owner has mixed this up with a commonly understood element of vampire lore, that vampires must be invited into a home before they can pass through the doorway. In vampire lore, vampires are often able to transform into bats, and these two are thematically associated with each other. Since the coronavirus is likely a bat virome that has entered into humans, Megan misunderstands the owner's objection to her entry, believing that the homeowner thinks that she has become a vampire. (The virus, and thus elements of the vaccine, having ultimately originated in bats and therefore 'possibly' actual vampire stock.) Megan thus begins to explain that the vaccine works on a bat virus and has nothing to do with bats. And since she is thus not a vampire she has no problems entering a doorway uninvited, and further explains that she is also not repelled by garlic or other classic weakness of vampires. Vampire lore states that they are repelled by garlic , crosses, holy water, sunlight, and wooden stakes through the heart (the last being a problem for humans in general, vampiric or otherwise). The owner is attempting to explain that Megan does not have the legal or moral right to enter simply because she is vaccinated, but this seems to not register with Megan . Doing ridiculous things that were never allowed, even normally, after being vaccinated or low-risk, was also the theme of 2434: Vaccine Guidance . 2391: Life Before the Pandemic also dealt with a similar theme, with Cueball and Megan reminiscing about activities they missed doing but which had not been allowed or possible before the pandemic. [Megan is standing in front of a three-step stair leading up to an open door. She has one hand in the air while talking to someone inside the house, who replies. The ground outside has small tufts of grass.] Megan: Hi, I'm here to visit! Voice, from inside the house: Do I know you? Megan: No, it's cool, I'm two weeks past my second dose. [Caption below the panel:] Remember, once you're fully vaccinated, the CDC says you're free to visit other people's houses.

Virus Consulting

Virus Consulting

https://www.xkcd.com/2455

https://www.explainxkcd.com/wiki/index.php/2455:_Virus_Consulting

[Ponytail stands in front a chart, with a labeled graph with an upward-curving line at the top, and several box-and-whisker plots below, with unreadable text and labels. She is holding a pointer towards the plot while addressing a panel in front of her to the left. The panel is seated behind a desk and is composed of Hairbun, Cueball and Megan. Cueball has one arm on the desk.] Ponytail: Now, I know you're worried about the variants, but this graph should be encouraging. Ponytail: Your rollout is going well. The vaccines are good. They work. Label on graph: Vaccinations [Same setting in a narrower panel without the chart. Ponytail has the pointer to her side. Cueball has his arms under the desk as the other two.] Hairbun: You're just telling us what we want to hear. Ponytail: If you think that, you should see the reports from my colleagues who work for COVID. [Close-up of Ponytail in a very narrow panel.] Off-screen voice: They work for who?? Ponytail: Our firm has lots of clients. [Black Hat stands in front of an identical chart as in panel one, and points to it with a pointer in the same way as Ponytail did. Only he is looking to the right at his clients. He is speaking to a panel of three large coronaviruses, two of which floats above the desk, the middle one is partly below the desk. Across the top frame of the panel there is a box with a caption:] Meanwhile... Black Hat: Now, I know you're excited about the variants, but this graph should be terrifying. Black Hat: We're in real trouble here. Label on graph: Vaccinations

This comic is another in a series of comics related to the COVID-19 pandemic , specifically regarding the COVID-19 vaccine . This comic imagines a scenario where Ponytail works for a consulting firm , which offers advice about viruses, specifically COVID-19. Ponytail tells a panel of people (the government?), consisting of Hairbun , Cueball and Megan , that though they are worried about COVID-19 variants , the fact that the number of people vaccinated is increasing considerably is a good sign. Hairbun then accuses Ponytail's firm of simply "telling them what they want to hear", accusing her firm of giving them false hope to make them keep retaining her firm. The punchline comes in the final panel where it turns out that Ponytail's colleague, Black Hat , is consulting a different set of clients, which are the viruses themselves. He presents the exact same graph to the viruses and gives them the opposite message: though COVID-19 variants seem to be exciting to them, vaccination numbers are terrible news to their propagation and survival. This repeats the idea of 2287: Pathogen Resistance where the pandemic is seen from the virus' perspective. As in that previous comic, it is the virus that is in a lot of trouble, which is another way of saying that humanity stands a good chance of surviving this situation. (That humanity will survive is also good for the virus, which needs living humans so that it can spread.) This is not the first time that Black Hat has given advice to natural disasters that can kill humans, see 1754: Tornado Safety Tips . The fact that another member of Ponytail's firm is telling clients that they should be worried is what Ponytail refers to when claiming that her firm does not simply tell clients what they want to hear. Secondarily, the comic is making fun of the perception that consulting firms will offer their services to whoever can pay, even if they are harmful to society, a perception with some basis in fact . Around the time of the comic, several SARS-CoV-2 variants , commonly called "COVID variants", had been in the news. The SARS-CoV-2 virus had already been seen to have mutated into many different strains, some of which spread more easily among humans. It was still unknown whether the different variants have a greater individual fatality rate. The contemporary SARS-CoV-2 vaccines from Pfizer-BioNTech and Moderna as well as the Regeneron therapeutic monoclonal antibodies all effectively protect against at least the New York ( Lineage B.1.526 ), South African ( Lineage B.1.351 ), and U.K. ( Lineage B.1.1.7 ) variants according to two recent study preprints released April 22, 2021. Further research and peer review was ongoing. Since the original date of this comic, the common practice changed from describing variants by geographic origins. Variants Of Concern and Variants Of Interest might indeed have arisen spontaneously in the place where their changes had first been detected in (or most directly traced back to), but there was no good reason to perpetuate a stigma upon any particular region. Instead, greek letter-names were applied to the major variations. (For the above noted versions "New York" became Iota, that South African version was identified as Beta, and U.K. (or "Kent") had been assigned as Alpha.) Not all lettered VOCs/VOIs became major players on the global stage, but by by November 2021, the ' alphabet ' had reached Omicron (the fifteenth letter but the thirteenth actually used, having just skipped the letters "nu" and "xi" to avoid undesirable sound-alike associations) and, while there is still much to study, this seems to have the capability of greater transmissability and retransmissability (even in the vaccinated) but, initially at least, also lower illness/hospitality/mortality rate. All these factors have reinforced the potential for the Omicron variety to spread more easily in the human population, as more of an endemic than a pandemic, and thus also to dominate the field against its fellow viral variations. (The "BA.2" sub-varient of Omicron has been seen to be again more dangerous and resistant to preventative/theraputic treatment than the prior Omicron but, as of April 2022, calls by some to give it a Virus Of Concern letter (probably "Pi") have not yet been acted upon.) Possibly, with hindsight, this actually suggests that Black Hat's caution (and perhaps subsequent advice) has been taken on board by the respective clients. On the other hand, it could be equally true that humanity is just becoming more blasé, or just overly weary of repeating lockdowns/masks/etc, and is no longer fulfilling the original good practice. But all this is in the future, for the comic, and even this explanation doesn't yet know how how it will turn out. Back in the original comic's time, the title text notes that the firm's "virus division" (the group advising the viruses themselves) has started to get worried that their jobs are becoming obsolete, due to vaccine efficacy. Thus, they are demanding to be paid "up front", before consulting/advising services have been rendered to their clients. Dependent upon the expectations of each party, payment can be asked for "up front", deferred for invoicing once services have been rendered, or a combination of the two. The weaker party to a contract may need to submit their transaction, or a guarantor, before the other spends too much effort in fulfilling their side of the contract. [Ponytail stands in front a chart, with a labeled graph with an upward-curving line at the top, and several box-and-whisker plots below, with unreadable text and labels. She is holding a pointer towards the plot while addressing a panel in front of her to the left. The panel is seated behind a desk and is composed of Hairbun, Cueball and Megan. Cueball has one arm on the desk.] Ponytail: Now, I know you're worried about the variants, but this graph should be encouraging. Ponytail: Your rollout is going well. The vaccines are good. They work. Label on graph: Vaccinations [Same setting in a narrower panel without the chart. Ponytail has the pointer to her side. Cueball has his arms under the desk as the other two.] Hairbun: You're just telling us what we want to hear. Ponytail: If you think that, you should see the reports from my colleagues who work for COVID. [Close-up of Ponytail in a very narrow panel.] Off-screen voice: They work for who?? Ponytail: Our firm has lots of clients. [Black Hat stands in front of an identical chart as in panel one, and points to it with a pointer in the same way as Ponytail did. Only he is looking to the right at his clients. He is speaking to a panel of three large coronaviruses, two of which floats above the desk, the middle one is partly below the desk. Across the top frame of the panel there is a box with a caption:] Meanwhile... Black Hat: Now, I know you're excited about the variants, but this graph should be terrifying. Black Hat: We're in real trouble here. Label on graph: Vaccinations

Types of Scientific Paper

Types of Scientific Paper

https://www.xkcd.com/2456

https://www.explainxkcd.com/wiki/index.php/2456:_Types_of_Scientific_Paper

[Heading:] Types of Scientific Paper [An array of 4 rows with 3 scientific papers each, is shown. We see the first page of each paper, but only its title is legible. Headings are shown as black lines, paragraphs of text are shown as several squiggly lines and figures are shown as empty white rectangles. Titles are as follows:] We put a camera somewhere new Hey, I found a trove of old records! They don't turn out to be particularly useful, but still, cool! My colleague is wrong and I can finally prove it The immune system is at it again We figured out how to make this exotic material, so email us if you need some What are fish even doing down there This task I had to do anyway turned out to be hard enough for its own paper Hey, at least we showed that this method can produce results! That's not nothing, right? Check out this weird thing one of us saw while out for a walk We are 500 scientists and here's what we've been up to for the last 10 years Some thoughts on how everyone else is bad at research We scanned some undergraduates The comic inspired many derivatives, changing the paper titles to be more relevant to specific fields. The hashtag #TypesOfScientificPapers on Twitter includes many of these. There is a generator . There is a moodboard compiling hundreds of them . Some examples include:

In this comic, Randall describes categories of scientific papers with somewhat humorous generalized titles. [Heading:] Types of Scientific Paper [An array of 4 rows with 3 scientific papers each, is shown. We see the first page of each paper, but only its title is legible. Headings are shown as black lines, paragraphs of text are shown as several squiggly lines and figures are shown as empty white rectangles. Titles are as follows:] We put a camera somewhere new Hey, I found a trove of old records! They don't turn out to be particularly useful, but still, cool! My colleague is wrong and I can finally prove it The immune system is at it again We figured out how to make this exotic material, so email us if you need some What are fish even doing down there This task I had to do anyway turned out to be hard enough for its own paper Hey, at least we showed that this method can produce results! That's not nothing, right? Check out this weird thing one of us saw while out for a walk We are 500 scientists and here's what we've been up to for the last 10 years Some thoughts on how everyone else is bad at research We scanned some undergraduates The comic inspired many derivatives, changing the paper titles to be more relevant to specific fields. The hashtag #TypesOfScientificPapers on Twitter includes many of these. There is a generator . There is a moodboard compiling hundreds of them . Some examples include:

After the Pandemic

After the Pandemic

https://www.xkcd.com/2457

https://www.explainxkcd.com/wiki/index.php/2457:_After_the_Pandemic

This comic is another in a series of comics related to the COVID-19 pandemic . There is no hidden humor in this comic, it simply states an opinion. Randall is saying that he is looking forward to not having to wear a mask everywhere after the pandemic is over. Mask mandates were a common way various organizations reduced the spread of Covid-19. Now that the vaccines exist, people are assuming that these mask mandates will soon end, and in many jurisdictions they have already. However, Randall hopes that people will continue to wear a mask when they are sick, as is common in many East Asian countries. This lets other people know the person may be sick, or trying to avoid becoming sick, so they can give the person extra distance. Wearing a mask reduces the spread of infectious droplets when one exhales or coughs, and reduces exposure to droplets from others. Both features help reduce the spread of communicable diseases. Also, Randall thinks other people coughing on him is gross, as do most people. Masking when ill would help reduce influenza, tuberculosis and colds. The flu is a deadly disease that usually kills tens of thousands of people each year. People with less common diseases, like tuberculosis, may be more likely to wear a mask if mask wearing becomes more common, so they don't feel as conspicuous. For less severe illnesses and less vulnerable populations xkcd's wish may not be such a good idea, as every cold - albeit unpleasant - constantly trains the immune system and keeps it alert. [1] The title text continues this line of reasoning by saying Randall wants to worry less about COVID-19, but hopes people would worry more about colds. Colds are generally mild and might cause someone to spend a few days home sick from work or school. However, colds cost tens of billions of dollars annually in the US. Costs include the value of lost productivity at work or school, time spent caring for the sick, cost of doctor visits and medications. Inappropriate treatment of colds with antibiotics is common, and contributes to the rise of antibiotic resistant bacteria , and clostridium difficile infections . [2] . Randall has made a specific corona comic targeted at colds before: 2306: Common Cold . And in 2015 he probably had a severe cold (or more than one) as he published these two comics 1612: Colds and 1618: Cold Medicine in December 2015.

Bubble Wrap

Bubble Wrap

https://www.xkcd.com/2458

https://www.explainxkcd.com/wiki/index.php/2458:_Bubble_Wrap

[Cueball is holding a large piece of bubble wrap in both hands, clearly pressing one of the bubbles with his fingers so it pops, indicated with several small lines going away from that spot, and a sound.] Cueball: Hmm... Cueball: WD-40, diesel fumes... Cueball: And is that sea air? I guess they're near the ocean. Bubble wrap: Pop [Caption below the panel:] If your sense of smell is good enough, popping bubble wrap gives you a tour of a bubble wrap factory.

Bubble wrap is packing material made by melting two sheets of plastic together with little pockets of air (the "bubbles") spread throughout the surface. It is wrapped around fragile items for moving or shipping because the air pockets act as a cushion if the item(s) within are struck or shaken. Many people enjoy popping bubble wrap as a mindless hobby, perhaps due to the tactility and other sensations of each bubble makes as it bursts. The premise behind this comic is that the air inside each bubble comes from the factory where it was made, and thus as each bubble is popped that air — along with anything in it — is released. If one had a very sensitive sense of smell, one could detect unique odors present in the factory at the time not present where you are popping the bubble wrap. The comic has Cueball smelling WD-40 (a penetrating oil likely to be found where machines are running), diesel fumes (likely found where trucks drop off supplies or pick up product) and what he thinks is sea air, causing him to muse that the factory is by the ocean. In reality, the air inside most factories is much like the air anywhere else. [ citation needed ] This is particularly true for modern factories which are much cleaner than the popular conception of a dirty, smelly factory from early in the days of industrialization. One would be unlikely to distinctly smell WD-40 or diesel fumes standing in such a factory unless it was right after or right near they were used. It would be even less likely to them smell them when the minuscule amounts of air in the bubbles was then diluted in the larger amount of air surrounding you when they are popped. Furthermore, although the comic suggests popping the bubbles gives one a "tour" of the factory, in fact all of the air added to the bubbles would only come from air near the machine where the wrap is made. It would be even less likely to pick up smells from other parts of the factory such as diesel fumes from the loading docks, since air is not added to bubble wrap there. Although this scenario is unlikely given human olfactory ability, scientists with very sensitive equipment have done essentially this with ice cores. As ice is laid down in places such as the Greenland or Antarctic ice sheets, it traps small bubbles from the atmosphere at the time within it. As long as the ice remains frozen, those bubbles remain trapped and do not interact with the current atmosphere, preserving a record of the chemical composition of the air in the past. There have been many scientific expeditions to drill ice cores and then melt pieces of them in a laboratory where special equipment can analyze the ancient air as it is released to study the quantity of oxygen and CO2 within in. The deeper the core is drilled, the farther in the past the sample. The title text references David Attenborough , who is famous for having narrated many influential documentaries for the BBC about life on earth. He is renowned for having brought science into the homes of tens of millions. The title text humorously suggests that Cueball thinks his "narration" about what he smells in the bubble wrap is as important and distinguished as Attenborough's award winning work. [Cueball is holding a large piece of bubble wrap in both hands, clearly pressing one of the bubbles with his fingers so it pops, indicated with several small lines going away from that spot, and a sound.] Cueball: Hmm... Cueball: WD-40, diesel fumes... Cueball: And is that sea air? I guess they're near the ocean. Bubble wrap: Pop [Caption below the panel:] If your sense of smell is good enough, popping bubble wrap gives you a tour of a bubble wrap factory.

March 2020

March 2020

https://www.xkcd.com/2459

https://www.explainxkcd.com/wiki/index.php/2459:_March_2020

[In a 3 column by 5 row grid of panels, 15 monthly wall calendars are shown. All calendars have a large header with month and year given on two lines. Below this is a black border with 7 white lines, for each day of the week, and below that 5 rows with 7 columns, making all calendars the same, with 35 spaces. Nothing is shown in these grids. Next to each of these calendars Cueball is shown. In the first 12 panels, Cueball is standing next to the calendar, in only slightly different poses. The text on the calendars only change in the top row, then it stays the same for the next nine panels:] Calendar: January 2020 Calendar: February 2020 Calendar: March 2020 Calendar: March 2020 Calendar: March 2020 Calendar: March 2020 Calendar: March 2020 Calendar: March 2020 Calendar: March 2020 Calendar: March 2020 Calendar: March 2020 Calendar: March 2020 [In the bottom row's first panel the calendar is, as always, to the left, but now Cueball is wearing a mask and sitting on a chair leaning a bit to the left while he is being vaccinated by a masked Ponytail to his right. She is inserting the needle into his left arm. To the right is a tall but small table with the vial from which she has drawn the vaccine standing next to the lid of the vial.] Calendar: March 2020 [The bottom row's second panel is similar to the previous with Cueball wearing a mask and sitting on a chair leaning a bit to the left while he is being vaccinated - although this time by a masked Hairy, standing to his right. Hairy is also inserting the needle into his left arm. To the right is a different small table, with only one leg. On it is a vial from which Hairy has drawn the vaccine. Also some other black things are lying on the table, maybe other syringes for administrating the vaccine.] Calendar: March 2020 [In the final panel Cueball again stands next to the calendar, but finally the text has changed.] Calendar: May 2021

This comic is another in a series of comics related to the COVID-19 pandemic , specifically regarding the COVID-19 vaccine . This comic shows 15 calendars and Cueball next to them. The first three months on the calendar are January, February and March 2020. It would be expected that the months would increase in order, but the calendar month stays at March 2020 until the final panel of the comic, where it switches to May 2021, the month this comic was released, indicating that Cueball is "stuck" in March 2020 for more than a year. The COVID-19 pandemic reached the United States in March 2020 and Cueball (probably representing Randall ) may feel that he has been unable to move on with life, or that time was at a standstill until he was fully vaccinated. It is plausible that Randall was past the two weeks after his final vaccination when this comic came out. He has made several comics centered around that of being fully vaccinated in the weeks up to this comic. Specifically 2450: Post Vaccine Social Scheduling and 2454: Fully Vaccinated in April. In the penultimate 2 panels, Cueball is shown getting his two doses of the vaccine, with Ponytail and Hairy administering the vaccine. Also these two panels are in March 2020, but in reality they are most likely in March 2021 and April 2021, as there are typically 3-6 weeks between first and second dose depending on the type of vaccine. In the final panel, the calendar has switched to the current month, May 2021, showing that Cueball can now resume life after getting vaccinated, and most likely having passed the two weeks after final shot mark. The title text references 630: Time Travel , another time-related comic. While it’s technically true that the vaccines were brought from the year 2020, it was through the ordinary “one day per day” form of time travel illustrated in this earlier comic. Interestingly, there are only 15 panels, so if the 'normal' months increased in sync, it would "only" be March 2021, not May 2021. This may refer to the strange distortion of time during the COVID-19 pandemic . Clearly 17 panels would have made more sense when counting months, but the point here is that time has been at a standstill the last 14 months from March 2020 to April 2021; how many panels represents those 14 month (14, 12 or 10) is not important. Using 15 panels, makes the first 3 and the last 3 stand out from the 9 in the middle, which makes sense from the flow of the comic. [In a 3 column by 5 row grid of panels, 15 monthly wall calendars are shown. All calendars have a large header with month and year given on two lines. Below this is a black border with 7 white lines, for each day of the week, and below that 5 rows with 7 columns, making all calendars the same, with 35 spaces. Nothing is shown in these grids. Next to each of these calendars Cueball is shown. In the first 12 panels, Cueball is standing next to the calendar, in only slightly different poses. The text on the calendars only change in the top row, then it stays the same for the next nine panels:] Calendar: January 2020 Calendar: February 2020 Calendar: March 2020 Calendar: March 2020 Calendar: March 2020 Calendar: March 2020 Calendar: March 2020 Calendar: March 2020 Calendar: March 2020 Calendar: March 2020 Calendar: March 2020 Calendar: March 2020 [In the bottom row's first panel the calendar is, as always, to the left, but now Cueball is wearing a mask and sitting on a chair leaning a bit to the left while he is being vaccinated by a masked Ponytail to his right. She is inserting the needle into his left arm. To the right is a tall but small table with the vial from which she has drawn the vaccine standing next to the lid of the vial.] Calendar: March 2020 [The bottom row's second panel is similar to the previous with Cueball wearing a mask and sitting on a chair leaning a bit to the left while he is being vaccinated - although this time by a masked Hairy, standing to his right. Hairy is also inserting the needle into his left arm. To the right is a different small table, with only one leg. On it is a vial from which Hairy has drawn the vaccine. Also some other black things are lying on the table, maybe other syringes for administrating the vaccine.] Calendar: March 2020 [In the final panel Cueball again stands next to the calendar, but finally the text has changed.] Calendar: May 2021

Vaccinated

Vaccinated

https://www.xkcd.com/2460

https://www.explainxkcd.com/wiki/index.php/2460:_Vaccinated

[Cueball is holding his phone up, looking at the bright screen (indicated with lines emanating from the screen). Megan stands next to him looking down at his phone.] Cueball: It's official: We're fully vaccinated. Megan: It doesn't feel real. [Cueball has put his phone away, and they are looking at each other.] Cueball: I can't wait to hang out with friends again. Megan: Seriously. [In a frame-less panel they are just standing next to each other, but looking away from each other.] [They look back at each other and continue the conversation.] Cueball: So, uh...how do we... Megan: I was hoping you knew. Cueball: I'm realizing now, I was hazy on this before the pandemic.

This comic is another in a series of comics related to the COVID-19 pandemic , specifically regarding the COVID-19 vaccine . Hooray, Cueball and Megan are finally fully vaccinated! This means that they are now able to socialize within society, as they are unafraid of being infected by COVID or spreading COVID to others. However, the punchline lies in the fact that Cueball and Megan have never been good with social interactions , and are still unsure of how to do this. The title text continues with this theme, as Cueball (or Megan?) is good at building mathematical models to know when it is safe to attend parties (and other large gatherings), but the issue remains that they are not commonly invited to these events, or are socially awkward when attending them. [Cueball is holding his phone up, looking at the bright screen (indicated with lines emanating from the screen). Megan stands next to him looking down at his phone.] Cueball: It's official: We're fully vaccinated. Megan: It doesn't feel real. [Cueball has put his phone away, and they are looking at each other.] Cueball: I can't wait to hang out with friends again. Megan: Seriously. [In a frame-less panel they are just standing next to each other, but looking away from each other.] [They look back at each other and continue the conversation.] Cueball: So, uh...how do we... Megan: I was hoping you knew. Cueball: I'm realizing now, I was hazy on this before the pandemic.

90's Kid Space Program

90's Kid Space Program

https://www.xkcd.com/2461

https://www.explainxkcd.com/wiki/index.php/2461:_90%27s_Kid_Space_Program

[A command and service module representing the tip of a spacecraft, is attached by four long trusses to four equidistant points on the edge of a giant light green pepper (a green "hill" with a round raised edge around it). The popper is in its inverted configuration, ready to pop. There is a caption beneath the panel:] The 90's Kid Space Program prepares for their first orbital launch

The "launch system" is just one of the rubber popper toys popular in the 1990s. These toys are little rubber hemispheres, about 1" (25 mm) in diameter and 1/8" (3 mm) thick. When turned inside-out and placed on a hard surface, they will, after a short wait, snap back to their original shape, popping up into the air. The joke is that kids who grew up with these toys will think they're a great idea to propel a space ship to orbit, when in fact the toys launch at mere tens of kilometers per hour, far short of the thousands needed to reach orbital speed [ citation needed ] . But now kids playing with these are those that make rockets, hence the title 90's Kid Space Program (KSP). Even if the popper-based propulsion system could generate enough acceleration to reach orbit, the abrupt impulse would likely cause serious harm to any astronauts. The title text implies that many working now at NASA were 90s kids. Both categories would include Randall , as he was born in 1984 and previously worked at NASA. The title is a reference to the Kerbal Space Program (KSP) which has been a recurring theme on xkcd, and it has previously been hinted at that NASA's employees uses this program in 1244: Six Words and 2204: Ksp 2 . And also that you learn more about orbital Mechanics by using KSP than from being hired by NASA in 1356: Orbital Mechanics . [A command and service module representing the tip of a spacecraft, is attached by four long trusses to four equidistant points on the edge of a giant light green pepper (a green "hill" with a round raised edge around it). The popper is in its inverted configuration, ready to pop. There is a caption beneath the panel:] The 90's Kid Space Program prepares for their first orbital launch

NASA Award

NASA Award

https://www.xkcd.com/2462

https://www.explainxkcd.com/wiki/index.php/2462:_NASA_Award

[Cueball, Ponytail, Hairy, and Megan stand on a two tiered platform. Ponytail and Hairy are are on the top step, with Cueball and Megan standing on the lower step looking up at the other two. Ponytail holds a necklace with a rock attached to the end up in both hands offering it to Hairy.] Ponytail: We're honored to present you with this Nobel Prize! Hairy: That's just a rock. Ponytail: Yeah, but from a certain angle... [Caption beneath the panel]: NASA has a new award for people on the internet who claim to find life in their Mars photos.

In this comic Hairy is awarded a " Nobel Prize " by NASA , represented by Ponytail handing him the award, as well as Cueball and Megan . He receives this award because he has found "life on Mars" by looking at NASA's images from their Mars missions. Hairy looks at his prize, and remarks that it is just a rock on a ribbon. To this Ponytail replies that from a certain angle... implying that if he looks hard enough the rock might look like a Nobel Prize. Just like Hairy, by looking at the pictures in the right way, found something that looked like life on Mars. This comic jabs at poorly-supported claims of discovering alien life, particularly when instances of pareidolia are used as "evidence" of such life. Pareidolia is the tendency for perception to spuriously impose a meaningful interpretation on a nebulous visual stimulus, for example a rock that is interpreted as a face. A famous example is the Face on Mars , a 2km long hill that can be said to resemble the face of a human when viewed on low resolution images, at a specific angle and lighting conditions. At the time some people claimed this was proof of an ancient Martian civilization. Later higher resolution images showed that the face was an optical illusion. Rocks make for poor prizes as they make for poor evidence [ citation needed ] , and looking from different angles is of no use for either. If you're actively looking for patterns in large amounts of data (especially if it's any pattern, largely undefined until it is 'found') then you are likely to dismiss all the data that does not support your preconceived ideas and seize upon the small randomnesses that you have managed to trawl though and classify as 'interesting'. This is an example of Confirmation Bias . It's possible that the featured NASA personnel specifically sifted rocks looking for one that looked like an award. The title text explains how you find life on Mars. Just access other people's images that have been taken on Mars, and look for plants and animals. This is lampooning the simplistic notion that life on Mars would be detected by looking at photos at all. In reality, all extraterrestrial life (in this solar system at least) is almost certainly microscopic. The notion of detecting it by studying photos of the Martian surface is just as absurd as the idea of looking at the photos and expecting to see dogs and trees and other familiar macroscopic lifeforms. Building a camera and landing it on Mars is what NASA does with their Mars rovers and other Mars missions. The camera is a small part of the entire mission, though an important part. But this is why the title text talks about landing the camera on Mars. The space probes are the cameras. [Cueball, Ponytail, Hairy, and Megan stand on a two tiered platform. Ponytail and Hairy are are on the top step, with Cueball and Megan standing on the lower step looking up at the other two. Ponytail holds a necklace with a rock attached to the end up in both hands offering it to Hairy.] Ponytail: We're honored to present you with this Nobel Prize! Hairy: That's just a rock. Ponytail: Yeah, but from a certain angle... [Caption beneath the panel]: NASA has a new award for people on the internet who claim to find life in their Mars photos.

Astrophotography

Astrophotography

https://www.xkcd.com/2463

https://www.explainxkcd.com/wiki/index.php/2463:_Astrophotography

[Cueball and Megan stand on a hill with the dark yellow sun setting behind them. Outside the Sun's disc everything is black. All that can be seen is silhouettes against the sun. Cueball is at the top-left of the hill, holding a bow in his left arm, which has been recently shot, as indicated with lines along the string. The the arrow is to right, where it has speared a ball. Megan is at the bottom-right of the hill, juggling four other balls, one near her hand, two above her and one higher up than the path of the arrow. There are two planes going in opposite directions with banners on them with words readable against the Sun. Above the planes is the shadow of the International Space Station. Finally Sun is partially eclipsed by the moon in the upper right corner.] [Banner 1]: Nice [Banner 2]: Shot [Caption beneath the panel]: Our astrophotography community's one-upsmanship[sic] is getting out of hand.

Astrophotography is the practice of taking pictures of astronomical objects. Sometimes it is specified as a hobby, as opposed to the work of professional astronomers. Astrophotographers like to take pretty pictures of all sorts of objects in the sky, but photographing the Sun is a popular subgenre within the field, especially if something is transiting in front of it. Typical things include planes, the International Space Station (ISS), and the Moon ( Solar eclipses ). During the Total Solar Eclipse 2017 visible across US it was possible to see the ISS pass in front of the Sun during a partial part of the Eclipse (from a site that was later in the total Eclipse zone.) This was photographed and filmed by Destin from Smarter Every Day and can be seen in his video Space Station Transiting 2017 ECLIPSE . (Go to the time of the flyby of the ISS in the video here ). Two years later he did another episode South American Eclipse - Argentina . In this video there was only the moon eclipsing the sun, at first, but then towards the end the sun begins to set behind the distant mountains creating a shadow scenario between Moon and mountain shadows as displayed in this comic. This comic thus combines those two videos, which Randall must have seen, and then adds several more layers caused by the Astrophotography community's One-Upmanship. The practice of "one-upmanship" refers to the practice of achieving something superior to what another has achieved, or "getting one up on" them. The term originated in the 1950s or earlier. The caption claims that the photo shown in the comic is the result of a continuous string of one-upmanship among astrophotographers in a community, each striving to one-up the other. In this comic there seems to be an abundance of things: Taking the picture required precisely scheduling and arranging the relative positions of several of the various subjects (and photographer) to coincide with the predictable but rare conjunctions of the rest of the scene, as well as special equipment: The title text describes a similarly outlandish photo attempting to one-up Cueball and Megan, done simultaneously on the next hill over, thus a place where the same ISS transit can be seen: [Cueball and Megan stand on a hill with the dark yellow sun setting behind them. Outside the Sun's disc everything is black. All that can be seen is silhouettes against the sun. Cueball is at the top-left of the hill, holding a bow in his left arm, which has been recently shot, as indicated with lines along the string. The the arrow is to right, where it has speared a ball. Megan is at the bottom-right of the hill, juggling four other balls, one near her hand, two above her and one higher up than the path of the arrow. There are two planes going in opposite directions with banners on them with words readable against the Sun. Above the planes is the shadow of the International Space Station. Finally Sun is partially eclipsed by the moon in the upper right corner.] [Banner 1]: Nice [Banner 2]: Shot [Caption beneath the panel]: Our astrophotography community's one-upsmanship[sic] is getting out of hand.

Muller's Ratchet

Muller's Ratchet

https://www.xkcd.com/2464

https://www.explainxkcd.com/wiki/index.php/2464:_Muller%27s_Ratchet

[A caption sits above a slightly greyed-out photo of Hairbun holding out a cat to Cueball, who has his hand over his face and is leaning away. Below are arrows leading to much smaller variations of the photo, all altered in some way.] [From left to right: Image with the sides cropped and black text bordered by white in the bottom center; image with black text in white box with black border above cat, on Hairbun, and on Cueball; image identical to the original but with softer edges; image cropped around all sides to exclude all negative space around frame, with white text bordered by black near the top and bottom center; image cropped to cut out half of Hairbun and Cueball's legs and featuring the cat holding a sword out at Cueball; image same as the original except with black text bordered by white on top of the cat, Hairbun, and Cueball; and image blurred out and at low resolution with black text in white oval on top of Hairbun and Cueball.] Caption above: When a photo goes around on social media, people create lots of new versions of it. [A larger depiction of an image altered to cut out some of Hairbun and Cueball's legs and the cat holding a sword to the left of a caption, with a faint, shadowed wordmark saying "Made with SwordApp ] Caption: Sometimes, one of the edited versions becomes more popular and supplants the original. But often, the new version isn't made from the best copy of the image. It may be pixelated, cropped, or watermarked. [The same image appears with a more transparent box around it showing the cropped-out areas and an arrow pointing into it saying "lost". To the left is a caption.] Caption: As long as those flaws are minor enough that they don't cancel out the big change, the new version can still win out. Each good change brings with it random background damage. The degradation only goes one way. Once an image is cropped, its descendents will be, too. This steady loss of information is called Muller's Ratchet . [The original photo and the edited replacement are side-by-side, with the original on the right and the replacement on the left. The area above the cat where the sword is shown in the replacement is circled with a dotted line in both images. In the original, the area inside is greyed out, and in the replacement, the entire image is greyed out except for that area.] [Arrows point from the emphasized parts of both images to a new photo below that combines the original image with the sword from the replacement. The dotted line is still present. A caption sits to the left.] Caption: But there's a solution. The old versions are still around, so if you have an image editor that lets you splice together parts of two images, you can make a new version with the best parts of both. This process is called recombination... ] [All previous panels are grouped in one large panel, with a caption below the entire frame] Caption: People use evolutionary metaphors to explain the spread of internet content, but at this point we have so much more experience with the internet that I feel like it often makes more sense the other way around.

In this comic, Randall reviews a passage explaining the internet with terms associated with evolution, comparing the constant resharing and changing of popular photos to evolutionary processes, namely Muller's ratchet and recombination . An image of Hairbun showing a cat to Cueball , who is apparently shocked, is used as an example of the subject phenomenon. This image is altered in various ways: Recombination is the combination of genetic material from chromosomes, shuffling genes during meiosis. In this case, it is being compared to shuffling and recombining aspects of an edited digital image. Sometimes, genetic mutation can create better genes - like the sword being given to the cat in the image. Other changes remove or degrade from the genetic history, without apparent detriment, just because the circumstances do not currently confer any significant advantage to it. If the 'lost' ability is perhaps useful in dealing with an infrequent environmental stress then the loss of its utility might be felt a generation or two later. With recombination, useful novel changes can be shuffled into the population without necessarily bringing in a less useful mutation, creating descendents with both the obvious advantages (a sword) and the previously more established resilience (the fuller frame). The degradation of digital images has previously been explored in 1683: Digital Data . The title text has a double meaning, referring both to the ways these particular images on the Internet illustrate these evolutionary processes (which are driven by the mechanisms of biological reproduction, including sexual reproduction) and to the amount of erotic imagery illustrating the mechanics of sexual activity one might find on the Internet . [A caption sits above a slightly greyed-out photo of Hairbun holding out a cat to Cueball, who has his hand over his face and is leaning away. Below are arrows leading to much smaller variations of the photo, all altered in some way.] [From left to right: Image with the sides cropped and black text bordered by white in the bottom center; image with black text in white box with black border above cat, on Hairbun, and on Cueball; image identical to the original but with softer edges; image cropped around all sides to exclude all negative space around frame, with white text bordered by black near the top and bottom center; image cropped to cut out half of Hairbun and Cueball's legs and featuring the cat holding a sword out at Cueball; image same as the original except with black text bordered by white on top of the cat, Hairbun, and Cueball; and image blurred out and at low resolution with black text in white oval on top of Hairbun and Cueball.] Caption above: When a photo goes around on social media, people create lots of new versions of it. [A larger depiction of an image altered to cut out some of Hairbun and Cueball's legs and the cat holding a sword to the left of a caption, with a faint, shadowed wordmark saying "Made with SwordApp ] Caption: Sometimes, one of the edited versions becomes more popular and supplants the original. But often, the new version isn't made from the best copy of the image. It may be pixelated, cropped, or watermarked. [The same image appears with a more transparent box around it showing the cropped-out areas and an arrow pointing into it saying "lost". To the left is a caption.] Caption: As long as those flaws are minor enough that they don't cancel out the big change, the new version can still win out. Each good change brings with it random background damage. The degradation only goes one way. Once an image is cropped, its descendents will be, too. This steady loss of information is called Muller's Ratchet . [The original photo and the edited replacement are side-by-side, with the original on the right and the replacement on the left. The area above the cat where the sword is shown in the replacement is circled with a dotted line in both images. In the original, the area inside is greyed out, and in the replacement, the entire image is greyed out except for that area.] [Arrows point from the emphasized parts of both images to a new photo below that combines the original image with the sword from the replacement. The dotted line is still present. A caption sits to the left.] Caption: But there's a solution. The old versions are still around, so if you have an image editor that lets you splice together parts of two images, you can make a new version with the best parts of both. This process is called recombination... ] [All previous panels are grouped in one large panel, with a caption below the entire frame] Caption: People use evolutionary metaphors to explain the spread of internet content, but at this point we have so much more experience with the internet that I feel like it often makes more sense the other way around.

Dimensional Chess

Dimensional Chess

https://www.xkcd.com/2465

https://www.explainxkcd.com/wiki/index.php/2465:_Dimensional_Chess

[A chessboard is depicted in the middle of a stack of boards. All pieces visible on the middle board are in their starting positions, except the white knight from a2 at d1 and the black pawn from g2 at e2. There are three boards each above and below the original, missing columns a and h. On columns c & f on each board, there are clear cubes with a small pedestal on each square. Columns d & e are similar, except with multiple cubes on each square. No chess pieces are visible, except for a white piece -- not clearly visible, but implicitly the white king's knight -- on the second board above the middle on b2 and a black pawn on the top board on f3. Below the chessboards is a caption] [Caption below the panel]: The problem with N- dimensional chess is that N is a constant across the board. In my new variant, every row has one more dimension than the one behind it.

Being good at chess is often regarded as a sign of high intelligence. A skilled player must be able to consider possibilities several moves in advance, which can be represented as an exponentially growing tree of possibilities. The branching factor of chess, the approximate number of legal moves available at any given time, is about thirty-five, although most players (human and computer) will use heuristics to prune the trees to regard only likely or promising moves. Expanding the playing field by generalizing to three-dimensional chess (or beyond) will increase the branching factor even further, and so someone who is able to competently play three-dimensional chess could be regarded as even more intelligent than someone who can only play two-dimensional chess. Making chess into an N -dimensional game thus makes it arbitrarily more difficult, even before Randall's addition of non-uniform dimensionality of the board. Regarding Randall's rule that "every row has one more dimension than the one behind it," it is easiest to see how this is applied with the first two rows on each end. The first row on each end is a like a row on a traditional two-dimensional chess board (albeit played with three-dimensional pieces): you can go from left to right, or forward into the next row. The second row then becomes a two-dimensional row of a three-dimensional space: you can go left to right, forward to back, and now top to bottom. Note that there are seven spaces (represented by "shelves") from top to bottom, as opposed to the typical eight rows from left to right/front to back. This is likely to make sure there is symmetry between how many additional spaces are on top versus on the bottom (three, in this case). Moving another row would presumably add movement in some other direction to make it more complicated/interesting. This escalates until somehow the middle two rows require moving pieces in five dimensions (the middle two rows are four-dimensional rows + moving to other rows as fifth dimension), despite humans only being able to experience three spatial dimensions. [ citation needed ] This could potentially be accomplished via playing on a computer. There are eight squares on the first row, 56 on the second row and presumably 504 on the third and 1512 on the fourth, thus making the total number of squares 4160 rather than the 64 of a traditional chess board. The drawing shows apparently five squares (or boxes) stacked on the third row and if this is also formed symmetrically, there are four hidden out of sight. The middle rows are already quite convoluted but it seems as if Randall drew three boxes along this dimension. Due to this dimensionality increase, there is plenty of free space in the middle board, drastically changing the game dynamics such that shadowing plays very little role and that movement is very unrestricted. The title text refers to the practice of writing down what happens throughout the game, so that it is possible to review how the game progressed later. Recording moves in this fashion is required in most tournament situations. There are several common forms of Chess notation used for this purpose, and as well as indicating the moves, players may add annotations indicating their opinions about whether a particular move was good, bad, or peculiar. According to the title text, every annotation is followed by "?!"—which indicates a questionable move, of dubious value but not obviously a blunder either. The joke is that the variable-dimensional game is so complicated that any move will answer this description. There appears to be the normal chess pieces (so no Fairy chess pieces ), but the game has already started (there are white and black pawns in one of the middle squares, and both white and black knights have moved. Note that "in dimensional chess" may be a pun on " N -dimensional chess." [A chessboard is depicted in the middle of a stack of boards. All pieces visible on the middle board are in their starting positions, except the white knight from a2 at d1 and the black pawn from g2 at e2. There are three boards each above and below the original, missing columns a and h. On columns c & f on each board, there are clear cubes with a small pedestal on each square. Columns d & e are similar, except with multiple cubes on each square. No chess pieces are visible, except for a white piece -- not clearly visible, but implicitly the white king's knight -- on the second board above the middle on b2 and a black pawn on the top board on f3. Below the chessboards is a caption] [Caption below the panel]: The problem with N- dimensional chess is that N is a constant across the board. In my new variant, every row has one more dimension than the one behind it.

In Your Classroom

In Your Classroom

https://www.xkcd.com/2466

https://www.explainxkcd.com/wiki/index.php/2466:_In_Your_Classroom

[Caption above scatter plot with labeled axes] Caption: The thing you study just showed up in your classroom! That's... Upper y-axis label: Good Lower y-axis label: Bad Upper x-axis label: Normal Lower x-axis label: Weird [First quadrant (left to right, top to bottom):] 20th century authors Exobiology 21st century authors 19th century authors Robotics Paleontology Martian soil chemistry Child psychology Tourism [Second quadrant] Atmospheric physics Ethics Education Bibliography Human physiology Public speaking Architecture Library science Furniture design Culinary arts Ergonomics Botany [Third quadrant] Entomology Occupational therapy Hydraulic engineering Pest control Foodborne illness Criminal law Physiology of stress Oncology [Fourth quadrant] Ornithology Animation Petroleum geology Highway engineering Toxicology Hematology Hostage negotiation History of siege warfare Trauma surgery Volcanology Quasar astronomy

Randall has created a thought experiment and corresponding chart about school courses. The idea is, "the subject of the class appears in the classroom" and the chart compares how dangerous and how unusual that would be. In the title text two points that are off the chart to the left and right are also mentioned. See details about all the subjects in the table below. Note that Randall uses similar diagrams in each of 388: Fuck Grapefruit , 1242: Scary Names and 1501: Mysteries , which also contain different items. They also have extra points mentioned in the title text. In the first two comics the points are also off the chart, whereas for the last the description of the point is too long to fit on the chart. Extra info outside the chart is also used in the title text of 1785: Wifi , but this is a line graph. [Caption above scatter plot with labeled axes] Caption: The thing you study just showed up in your classroom! That's... Upper y-axis label: Good Lower y-axis label: Bad Upper x-axis label: Normal Lower x-axis label: Weird [First quadrant (left to right, top to bottom):] 20th century authors Exobiology 21st century authors 19th century authors Robotics Paleontology Martian soil chemistry Child psychology Tourism [Second quadrant] Atmospheric physics Ethics Education Bibliography Human physiology Public speaking Architecture Library science Furniture design Culinary arts Ergonomics Botany [Third quadrant] Entomology Occupational therapy Hydraulic engineering Pest control Foodborne illness Criminal law Physiology of stress Oncology [Fourth quadrant] Ornithology Animation Petroleum geology Highway engineering Toxicology Hematology Hostage negotiation History of siege warfare Trauma surgery Volcanology Quasar astronomy

Wikipedia Caltrops

Wikipedia Caltrops

https://www.xkcd.com/2467

https://www.explainxkcd.com/wiki/index.php/2467:_Wikipedia_Caltrops

[Cueball drives a car, followed by another car driven by Hairy. Cueball is leaning on the open window looking back as 24 large paper slips with Wikipedia links are flying out of the open trunk of the car. They extend to the front of Hairy's car, obscuring that all the way up to Hairy's position in the car. None of the links can be read in full, and only on a few can parts of the actual link be seen. Many has only part of the pages title visible, some parts are obstructed partly by other slips in front of them or they have not entirely left the trunk. In once case the link is so long that it has been split on two lines on a thicker slip. There is a large part of the link that cannot be seen after the first line, but the end of the second line can be seen as well. Here the (fairly) readable parts are give, roughly in normal reading order.] a.org/wiki/Elsagate wiki/Bubbly_Creek wiki/Pheasant_Island a.org/wiki/American_death_triangle List_of_fictional_colors /wiki/Future_of_Earth#Introversion pedia.org/wiki/Fastest_animals#Invertebrates ki/Defence_Scheme_No._1 i/Boeing_YAL-1 ki/Bald-hairy /Walkalong_glider Burned_house_horizon /wiki/AVE Mizar Flying_ice_cube Time in Australia#Anomalies: Unexplained_sounds Talk:List_of_U.S._states_and_ Ebright_Azimuth Mosquito_laser January_0 /1808_mystery_eruption /Hairy_Hands Cumberland_vs._Georgia_Tech_football_game Timeline_of_the_far_future /wiki/1994_Caribbean_Cup#Anomaly [Caption below the panel:] I have a collection of Wikipedia links to throw behind my car if I'm ever being chased by someone as easily distracted as me.

Cueball's car has a collection of Wikipedia links spilling out of the trunk, meant to stop Hairy who's in the following car. The idea is that by dropping a series of interesting links, one could stop someone else's movement as they take the time to go through them all, provided that they are also easily distracted. This is analogous to the caltrops mentioned in the title; caltrops are small, spiked implements that are scattered on a road to slow down someone pursuing you. Hence the title of Wikipedia Caltrops . Wikipedia is also a website that is notorious for having many links to other pages, which may result in a "wiki walk", a dilemma for Randall that has been discussed previously in 214: The Problem with Wikipedia (and separately with TV Tropes in 609: Tab Explosion ). This strategy is similar to a weaponized version of 356: Nerd Sniping , using the high levels of focus that tend to come along with nerdy interests against someone. Munroe apparently reasons that, because these links would stop him in his tracks, they might do the same for a given target. The Wikipedia links include: Mentioned in the title text, a " Czech hedgehog " is an anti-tank obstacle made of metal, essentially a large caltrop. It would be an effective roadblock, however a sign describing it would not impede most traffic, [ citation needed ] only for those distracted as easily as Randall. [Cueball drives a car, followed by another car driven by Hairy. Cueball is leaning on the open window looking back as 24 large paper slips with Wikipedia links are flying out of the open trunk of the car. They extend to the front of Hairy's car, obscuring that all the way up to Hairy's position in the car. None of the links can be read in full, and only on a few can parts of the actual link be seen. Many has only part of the pages title visible, some parts are obstructed partly by other slips in front of them or they have not entirely left the trunk. In once case the link is so long that it has been split on two lines on a thicker slip. There is a large part of the link that cannot be seen after the first line, but the end of the second line can be seen as well. Here the (fairly) readable parts are give, roughly in normal reading order.] a.org/wiki/Elsagate wiki/Bubbly_Creek wiki/Pheasant_Island a.org/wiki/American_death_triangle List_of_fictional_colors /wiki/Future_of_Earth#Introversion pedia.org/wiki/Fastest_animals#Invertebrates ki/Defence_Scheme_No._1 i/Boeing_YAL-1 ki/Bald-hairy /Walkalong_glider Burned_house_horizon /wiki/AVE Mizar Flying_ice_cube Time in Australia#Anomalies: Unexplained_sounds Talk:List_of_U.S._states_and_ Ebright_Azimuth Mosquito_laser January_0 /1808_mystery_eruption /Hairy_Hands Cumberland_vs._Georgia_Tech_football_game Timeline_of_the_far_future /wiki/1994_Caribbean_Cup#Anomaly [Caption below the panel:] I have a collection of Wikipedia links to throw behind my car if I'm ever being chased by someone as easily distracted as me.

Inheritance

Inheritance

https://www.xkcd.com/2468

https://www.explainxkcd.com/wiki/index.php/2468:_Inheritance

[Ponytail, White Hat, Megan, and Cueball are playing a board game. There are drinks on the table. Ponytail is writing something] Ponytail: Let's see...I got 31, you have 28, 35 for you, and- Cueball: -I've got 10,019. Ponytail: *Sigh* Cueball: Hey, add another 20 to everyone, on me! White Hat: I hate this . [Caption beneath the panel:] No one wants to play board games with me ever since I inherited 4,000,000 victory points from my grandfather.

This comic is in reference to strategy board games , which often score players on some type of point system based on a variety of possible achievements. The joke in this comic is that Cueball has a massive sum of points that were not scored in the current game but rather handed down from his grandfather. Board games do not normally include an inheritance from previous sessions [ citation needed ] , in contrast to real life where some people become wealthy by inheriting vast sums of money from ancestors. Such inheritances tend to lead to 'successes' in life for those who have done little to earn their wealth. Cueball offers to distribute a trifling fraction of his points to the other players, teasing them, but he will still have an insurmountable advantage. Despite his 'generosity', no one wants to play a game that they have no chance of winning. The value of his score, 10,019, seems to indicate that he "earned" 19 points during the course of the game (less than his competitors) and then added 10,000 from his 'inheritance'. The comic may be a reference to economic simulation board games like Monopoly , which was created as a critique to capitalism; in this case, no one can win the game against people who start out with a large amount of accumulated wealth. See also the ' Small Loan of a Million Dollars ' trope of a profile in which the author or subject discusses the simple tricks they used to retire early or buy a house, often involving a hurried admission of financial assistance from a family member. The title text asks Cueball if he has any moral qualms over the source of these points, then indicates his grandfather's fortune was made through factory farming in the farm-themed board game Agricola . Factory farming is a broad term for applying mass-production techniques to agriculture, treating both plants and animals as commodities to be processed as efficiently as possible. These techniques are condemned, at least in some circles, as being cruel to livestock, in addition to having serious environmental and land-use implications, among other criticisms. The implication is that Cueball's grandfather somehow managed to introduce an immoral and/or socially harmful mechanic into a board game, greatly enriching himself and his heirs. This echoes another concern about inherited wealth: that the source of the money may have been unethical, but the heirs still get to enjoy the advantages, without considering themselves accountable for the harm. Cueball brushes off this criticism with the claim that the change was inevitable, which is a common response to analogous real-life concerns. The game Agricola was previously mentioned in 696: Strip Games and 778: Scheduling . [Ponytail, White Hat, Megan, and Cueball are playing a board game. There are drinks on the table. Ponytail is writing something] Ponytail: Let's see...I got 31, you have 28, 35 for you, and- Cueball: -I've got 10,019. Ponytail: *Sigh* Cueball: Hey, add another 20 to everyone, on me! White Hat: I hate this . [Caption beneath the panel:] No one wants to play board games with me ever since I inherited 4,000,000 victory points from my grandfather.

Astronomy Status Board

Astronomy Status Board

https://www.xkcd.com/2469

https://www.explainxkcd.com/wiki/index.php/2469:_Astronomy_Status_Board

[Ponytail is looking through a telescope, while Cueball is pressing buttons, which makes noises, on a remote control connected with a wire to a large board to their right. He controls the messages shown on this board.] Remote: Beep beep [The board has a black screen, with a label in a white section above the screen:] Astronomy Status Board: [The black screen has five rows with text in three columns. The first column is with white text. The second is in glowing green text and the last are in faded grey red text.] Astronomers do regularly observe occultations of stars by other celestial bodies, and sometimes also search through archived images for missed occultations. This can provide information on the size and orbit of an asteroid too small to observe directly, or other useful scientific knowledge, but occulted stars are not "gone", merely hidden. There are also a few astronomers who are searching image archives for stars that really have completely vanished without a trace (or suddenly appeared), as this would be a sign of truly novel physics -- perhaps even a sign of extraterrestrial intelligence -- but no such vanishings have yet been identified. This comic appeared at the time the VASCO project is receiving media attention, claiming that 800 stars visible in 70 years old photos are not seen anymore . Small stars which have exhausted their hydrogen fuel without building enough heat to fuse carbon or oxygen, are theorized to eventually collapse into faint " white dwarf stars" which are of such low luminosity that they are unlikely to remain visible to the naked eye from the Earth's surface except at very close proximities. The Earth's sun, Sol, is generally expected to follow this progression as a low-mass main sequence star, during the latter period of its stellar evolution . Although some stellar models predict that relatively rapid collapses are possible, the long time scale over which stellar evolutions are believed to occur decreases the odds of observing any one specific star both before and after this transition. In this comic, individual stars are not listed; therefore "gone" is unlikely to be useful for the stars, because a great number of stars would be "still there" until well after the expected collapse of our own sun. One of the proposed outcomes of the ultimate fate of the universe is the Big Rip . If it's correct, all the items on the status board will eventually move from Still There to Gone, beginning with the most distant galaxies and proceeding to the the objects in our own solar system (although there will be hardly any time for the board to show Gone for the closest, especially the Moon). This scenario is dramatized in the short story " Last Contact " by Stephen Baxter. Collisions between celestial bodies are commonly postulated as a fundamental part of the formation of planetary nebula . Since most mass in the known universe is observed to have a relatively low albedo , the presence of numerous unlit, massy bodies of planetary scale and smaller is strongly indicated. This is corroborated by measurements of orbital deflection detected in many visible stars, hinting at the possibility of large planets orbiting around them, unseen due to distance & low luminosity. The possibility of one or more local planets being "gone" could be attributed to unpredicted collision with another object of similar mass or equivalent velocity. Such a collision is one possible explanation for the sudden & catastrophic disintegration of Earth's moon, Luna, in the novel Seveneves by Neal Stephenson. This hypothetical event forms the premise of this book, during which Earth's whole sky becomes occluded by dust raised by millions of impacts across its surface & eventually by the constant incandescent descent of lunar debris itself. Again however, a single collision with any planet besides the Earth would not remove all the "Planets" from the Earth's visible night sky, so "gone" remains unlikely to be used for that category of celestial objects. Occlusion of Earth's entire sky, due to airborne dust, volcanic ash, increased cloud cover, light pollution , or sufficiently dense layers of high-albedo material in orbit, may be the least unlikely potential reason for all of these celestial phenomena to be flagged as "gone". Notably, the phenomena in question would remain; only our view of them would be gone.

Ponytail is staring at the sky through a telescope while Cueball is operating a checklist, visible on a large screen on what looks like a large billboard. Since they are junior astronomers, they appear to have been tasked with simply verifying whether normal celestial objects are still present in the sky, such as the Sun and the Moon. Only large objects that are clear in the sky (at least at night for those not the Sun). Although all of these objects will eventually disappear it is not expected to happen within the life of the status board. [ citation needed ] This is likely a reference to the many "status boards" for online services ( example , another example , a different example , a funnier example ). The joke is that it would be funny if there was a status board to check that all the celestial bodies are still there, and that with our modern culture few people are looking directly at the real sky, even though anyone with a telescope and an unobstructed view could just look at the sky to verify for themselves without referencing such a status board. This is compounded by the fact that the listed celestial bodies have existed for billions of years, and are expected to last for billions more, leading one to wonder why astronomers would bother checking and rechecking just to see if they're "still there" with any sort of regularity. This comic may also be an oblique reference to the study of the projected future of celestial objects given our current understanding of physics. At various points in the future the objects on the billboard may become unobservable from Earth. The Moon is gradually receding from Earth, and when the Sun enters its red giant phase the Moon might be broken up. [1] Eventually the Sun itself will run out of usable fuel and will go dark as will other stars. Moreover, if current theories of dark energy and universal expansion hold, the acceleration of the universe could push galaxies beyond the "Hubble Horizon" , meaning they would no longer be observable. Matter itself could even cease to exist under some hypothetical scenarios, such as proton decay or the Big Rip . The joke of the comic here would be that all these scenarios are only possible in the unimaginably far future (exception: False Vacuum Decay ) and do not need constant monitoring by astronomers. [Ponytail is looking through a telescope, while Cueball is pressing buttons, which makes noises, on a remote control connected with a wire to a large board to their right. He controls the messages shown on this board.] Remote: Beep beep [The board has a black screen, with a label in a white section above the screen:] Astronomy Status Board: [The black screen has five rows with text in three columns. The first column is with white text. The second is in glowing green text and the last are in faded grey red text.] Astronomers do regularly observe occultations of stars by other celestial bodies, and sometimes also search through archived images for missed occultations. This can provide information on the size and orbit of an asteroid too small to observe directly, or other useful scientific knowledge, but occulted stars are not "gone", merely hidden. There are also a few astronomers who are searching image archives for stars that really have completely vanished without a trace (or suddenly appeared), as this would be a sign of truly novel physics -- perhaps even a sign of extraterrestrial intelligence -- but no such vanishings have yet been identified. This comic appeared at the time the VASCO project is receiving media attention, claiming that 800 stars visible in 70 years old photos are not seen anymore . Small stars which have exhausted their hydrogen fuel without building enough heat to fuse carbon or oxygen, are theorized to eventually collapse into faint " white dwarf stars" which are of such low luminosity that they are unlikely to remain visible to the naked eye from the Earth's surface except at very close proximities. The Earth's sun, Sol, is generally expected to follow this progression as a low-mass main sequence star, during the latter period of its stellar evolution . Although some stellar models predict that relatively rapid collapses are possible, the long time scale over which stellar evolutions are believed to occur decreases the odds of observing any one specific star both before and after this transition. In this comic, individual stars are not listed; therefore "gone" is unlikely to be useful for the stars, because a great number of stars would be "still there" until well after the expected collapse of our own sun. One of the proposed outcomes of the ultimate fate of the universe is the Big Rip . If it's correct, all the items on the status board will eventually move from Still There to Gone, beginning with the most distant galaxies and proceeding to the the objects in our own solar system (although there will be hardly any time for the board to show Gone for the closest, especially the Moon). This scenario is dramatized in the short story " Last Contact " by Stephen Baxter. Collisions between celestial bodies are commonly postulated as a fundamental part of the formation of planetary nebula . Since most mass in the known universe is observed to have a relatively low albedo , the presence of numerous unlit, massy bodies of planetary scale and smaller is strongly indicated. This is corroborated by measurements of orbital deflection detected in many visible stars, hinting at the possibility of large planets orbiting around them, unseen due to distance & low luminosity. The possibility of one or more local planets being "gone" could be attributed to unpredicted collision with another object of similar mass or equivalent velocity. Such a collision is one possible explanation for the sudden & catastrophic disintegration of Earth's moon, Luna, in the novel Seveneves by Neal Stephenson. This hypothetical event forms the premise of this book, during which Earth's whole sky becomes occluded by dust raised by millions of impacts across its surface & eventually by the constant incandescent descent of lunar debris itself. Again however, a single collision with any planet besides the Earth would not remove all the "Planets" from the Earth's visible night sky, so "gone" remains unlikely to be used for that category of celestial objects. Occlusion of Earth's entire sky, due to airborne dust, volcanic ash, increased cloud cover, light pollution , or sufficiently dense layers of high-albedo material in orbit, may be the least unlikely potential reason for all of these celestial phenomena to be flagged as "gone". Notably, the phenomena in question would remain; only our view of them would be gone.

Next Slide Please

Next Slide Please

https://www.xkcd.com/2470

https://www.explainxkcd.com/wiki/index.php/2470:_Next_Slide_Please

[A list of 12 quotes is given. Above is a large header with a question, and then a description, before the quotes follows. The text above the quotes is centered:] Did you know? Transcripts of famous quotes often leave out the slideshow instructions. Here’s how these lines actually sounded: [The first six quotations, are written so they fit around an image of Ronald Reagan standing next to his slide showing six segments of the Berlin Wall. A large arrow points down on to the middle segment of the wall. There is something on the ground in front of the wall, could be puddles or debris. The image is to the right, and the two first and last quote goes above and below the image, while the other three stops to the left of the image:] "Give me liberty or give me—Next slide, please—death!" "Mr. Gorbachev, tear down—Next slide, please—this wall." "It was the best of times—Next slide, please—It was the worst of times." "We have nothing to fear but—Next slide, please—fear itself." "To be or—Next slide, please—not to be, that is the question." "Shall I compare thee to a summer’s day? Thou art—Next slide, please—more lovely and—Next slide, please—more temperate." [Below those five quotations is three more quotes to the right of an image showing Winston Churchill standing next to his slide showing a beach. The sun and three small clouds are over the ocean which has white waves on the black water. Ponytail is sitting under a parasol to the left, Cueball is sitting on the sand to the right with a drink in his hands, and behind him is a kid running after a large beach-ball.] "We shall fight—Next slide, please—on the beaches, we shall fight on—Next slide, please—the landing grounds..." "Read my lips—Next slide, please—no new taxes." "That's one small step for man—Next slide, please—one giant leap for mankind." [Below this picture is the last three quotations, without any pictures:] "Friends, Romans, Countrymen, lend me your ears! Next slide, please. I come to bury Caesar, not to praise him." "It is a truth universally acknowledged, that a single man in possession of—Next slide, please—a good fortune, must be in want of—Next slide, please—a wife." "Veni, vidi—Velim, pictura proxima—vici."

This comic presumes that many famous quotes are actually excerpts from slideshow presentations , and the text they were reading was split across multiple slides. Splitting sentences across multiple slides can often be a useful tool if there are images accompanying it, which could explain the specific placement of many of "next slide, please" comments. For example, in the quote "It was the best of times, it was the worst of times," one can imagine the speaker starting with a slide that showed the prosperity of some people then, in the middle of the sentence, switching to a slide of many people's destitution. When using images this way, it is often better for timing purposes to have control of your own slides. However, Randall claims that, in these speeches, the person making the speech wasn't controlling their slide presentation, so they had to ask the operator to go to the next slide. A common way to ask this is to say "next slide, please", but these requests would have been edited out of the historical transcripts. The comic imagines the places where the slide breaks might have been, and inserts that request. Most of these quotes are drawn from speeches, which could conceivably have been accompanied by slides or other stage directions ("pause for laughter"), but the list is quite ridiculous as it includes works of literature, where the reader is the one who turns pages as necessary, and speeches from periods of history, such as the American Revolution and Caesar's Veni, vidi, vici speech, which predated slide projectors [ citation needed ] . Even in the quotations that take place in an era with slide projectors, every single one is an instance where the speaker was, quite famously, recorded live — said recordings would show there were in fact no edits, and certainly not any instructions for a slide projector operator. See details in the table below, including the quote in the title text. The phrase "Next slide, please" is perhaps in a sweet-spot of utility and performance. A rehearsed presentation, with speaker and 'slide handler' working with a tight script, could probably do without off-stage prompting at all, or the better lecturers with an oft-repeated talk could set it all on timings knowing they can keep the changes synchronised with their speech, or vice-versa. But when a cue is necessary, an unambiguous signal should be used, and an audible 'clicker' (or a small and briefly flashed light) has been used historically, especially with pre-electronic slide-shows where the slide-operator at the back of an auditorium needed to clearly discern the intent of the person at the lectern. In the United Kingdom, England's Chief Medical Officer caused some amusement on social media with the constant use of the phrase in coronavirus presentations, culminating in the availability of many mugs and cards with his image and this slogan on, and a campaign [1] to purchase an automatic clicker for him instead. [A list of 12 quotes is given. Above is a large header with a question, and then a description, before the quotes follows. The text above the quotes is centered:] Did you know? Transcripts of famous quotes often leave out the slideshow instructions. Here’s how these lines actually sounded: [The first six quotations, are written so they fit around an image of Ronald Reagan standing next to his slide showing six segments of the Berlin Wall. A large arrow points down on to the middle segment of the wall. There is something on the ground in front of the wall, could be puddles or debris. The image is to the right, and the two first and last quote goes above and below the image, while the other three stops to the left of the image:] "Give me liberty or give me—Next slide, please—death!" "Mr. Gorbachev, tear down—Next slide, please—this wall." "It was the best of times—Next slide, please—It was the worst of times." "We have nothing to fear but—Next slide, please—fear itself." "To be or—Next slide, please—not to be, that is the question." "Shall I compare thee to a summer’s day? Thou art—Next slide, please—more lovely and—Next slide, please—more temperate." [Below those five quotations is three more quotes to the right of an image showing Winston Churchill standing next to his slide showing a beach. The sun and three small clouds are over the ocean which has white waves on the black water. Ponytail is sitting under a parasol to the left, Cueball is sitting on the sand to the right with a drink in his hands, and behind him is a kid running after a large beach-ball.] "We shall fight—Next slide, please—on the beaches, we shall fight on—Next slide, please—the landing grounds..." "Read my lips—Next slide, please—no new taxes." "That's one small step for man—Next slide, please—one giant leap for mankind." [Below this picture is the last three quotations, without any pictures:] "Friends, Romans, Countrymen, lend me your ears! Next slide, please. I come to bury Caesar, not to praise him." "It is a truth universally acknowledged, that a single man in possession of—Next slide, please—a good fortune, must be in want of—Next slide, please—a wife." "Veni, vidi—Velim, pictura proxima—vici."

Hippo Attacks

Hippo Attacks

https://www.xkcd.com/2471

https://www.explainxkcd.com/wiki/index.php/2471:_Hippo_Attacks

[Cueball is sitting in an office chair at his desk. He has lifted both arms with palm up towards the screen of his laptop in front of him. Megan stands behind him to the right, looking over his shoulder at the screen.] Cueball: I hate unsourced statistics. Cueball: This viral post says hippos kill 2,900 people a year, but this random listicle says 500. Megan: Makes sense. Megan: Publishing the real number would be a HIPPO violation.

The first part of this comic deals with unreliable sources on the internet. Neither "viral posts" nor "random listicles " are usually very reliable sources of information. They rarely cite their sources, [ citation needed ] and they are often published without much fact-checking, as published volume and impressive-sounding numbers are far more important for ad-revenue than actual facts. The viral post appears to be this Facebook post. The relevant source is unknown (and may very well be made up, since the source is ClickHole, a satirical website formerly owned by The Onion ). There are a number of listicles Cueball may be referring to, but they all appear to be citing the Bill & Melinda Gates Foundation , however, even they do not seem to provide source for the number of fatalities caused by hippopotamus. The Health Insurance Portability and Accountability Act ( HIPAA , pronounced HIP-uh ) is an American healthcare law enacted in 1996. One of the most commonly cited provisions from HIPAA is the HIPAA Privacy Rule, which regulates the use and disclosure of protected health information. In this comic, Cueball and Megan are discussing the number of hippopotamus attacks, which is unverified. Megan proposes an alternative explanation as to why this particular number is hard to come by: it would be violating the patients' privacy to create statistics of a very specific and unusual cause of death. The punchline comes with the pun on "hippo violation" ("HIPAA violation"). The title text amplifies the criticism of listicles. They sometimes provide factoids with regards to ill-defined, hard-to-measure numbers, and these factoids might end up in common circulation between such articles. One extreme example would be the number of waves in the ocean. Some problems with this definition would be: With different replies to these questions, wildly different answers could be reached. But, counting every body of water on the planet, 850 trillion waves works out as around 2.354 (unique) waves per square meter. [Cueball is sitting in an office chair at his desk. He has lifted both arms with palm up towards the screen of his laptop in front of him. Megan stands behind him to the right, looking over his shoulder at the screen.] Cueball: I hate unsourced statistics. Cueball: This viral post says hippos kill 2,900 people a year, but this random listicle says 500. Megan: Makes sense. Megan: Publishing the real number would be a HIPPO violation.

Fuzzy Blob

Fuzzy Blob

https://www.xkcd.com/2472

https://www.explainxkcd.com/wiki/index.php/2472:_Fuzzy_Blob

[Cueball takes picture of his house from a distance great enough to get the whole house in the picture. He holds the camera (or smartphone) in both hands. The shutter makes a sound:] Click [The picture he has taken is shown below. The picture is lying tilted compared to the panel, and shows the house but with a fuzzy light brown blob covering the left part of the picture, just touching the left side of the house. Above and partly over the picture is a small frame with Cueball's response when he sees the picture:] What the... [White Hat gestures towards Cueball with one hand, while Cueball holds his camera in one hand towards White Hat, with the picture shown on the screen, too small to see though.] White Hat: What's that fuzzy blob next to your house? It's huge! Cueball: I don't know! I looked up and it was gone! White Hat: How can a giant structure vanish? Cueball and White Hat: ...Cloaking device?!! [Blondie is standing at the front of the panel with a microphone in her hand speaking towards the viewer. Behind her is a close up of the Blob (in black and white) on a screen. To the left of the screen is an almost bald man with hair behind his ears, holding a hand to his chin. To the right is Megan, who is holding one hand out palm up, towards the picture, which they are both looking at.] Blondie: The fuzzy blob, dubbed "flob" by internet sleuths, has city planners stumped. Man: No, that's not any type of building I'm familiar with. Megan: Could be an experimental military dome. [Hairbun is standing on a podium behind a lectern with a microphone on it. She addresses three people in front of the stage, Cueball, Megan and White Hat. Behind them Blondie is turned the other way speaking to a camera, on a tripod. She has a microphone in her hand.] Hairbun: The zoning board investigation has found no evidence of a cloaked dome structure. Hairbun: The historical commission will be joining the research into these domes and other unusual buildings, such as the historic 4th Ave Church... Blondie: This only raises more questions.

Cueball is taking a picture of his house, but sees a large fuzzy blob on the side of the picture. This blob seems to come from Cueball making the mistake of putting one of his fingers partially in front of the lens. This is a common enough occurrence with smartphones or compact cameras that an ordinary user should immediately be able to identify the problem; however, the comic derives humor from having no one in the comic come to this conclusion, and accordingly taking it very seriously as a perplexing mystery. Likely, this comic stems from the resurgent talk of Unidentified Flying Objects (UFO) now dubbed " Unidentified Aerial Phenomena " (UAP) The topic regained popularity after the Department of Defense (DoD), recently confirmed the authenticity of 3 videos taken by US Naval personnel. It has been much discussed in mainstream news, not just among extraterrestrial enthusiasts or conspiracy theorists , some of whom have created QAnon spin-off theories. Randall has previously expressed skepticism about claims of witnesses who claim to have seen unproven phenomena (including 'flying saucers', as well as supernatural events and cryptozoological specimens) based on the simple reality enough people carry cameras that they would be constantly captured in photos and videos. (See 1235: Settled ). In this strip Randall appears cases where phenomena have been caught on film, but are generally unclear and ambiguous. He appears to be suggesting that there are generally simpler explanations for what we see in the videos than objects of alien origin. Examples in the past have turned out to be things such as birds, dirt on camera lenses and lights being reflected off glass windows or bodies of water. The fact that many people seem uninterested in the more mundane and likely explanations and assume these videos are proof of alien crafts is mocked here. It's worth noting that Randall is a strong enthusiast for space exploration, and has expressed certainty that intelligent life exists elsewhere in the galaxy. This strip is likely not intended to mock belief that other intelligences exist (notably, the conspiracy theorists in the strip assume the "flob" is manmade, not alien) but instead to make fun of excessive credulity, and point out that any definitive conclusion of aliens is overhyped . The tendency to make unwarranted connections to unrelated but synchronous 'evidence' is shown in the title text. Investigation of this phenomena has brought to light 'irregularities' in the local zoning permits . Such irregularities are extremely common in most bureaucracies, and may be the result of mundane corruption, incompetence, honest mistakes in a complex system, or the result of complexities that make consistent documents difficult or impossible. To connect such irregularities to an identified image does not follow logically, as both are pretty normal occurrences. However, conspiracy theories make similar leaps all the time, insisting that some case of corruption, bad decision by a government official, or developing social problem is proof of a conspiracy, rather than a very normal government problem. An alternate intention of the word 'irregularities' might be due to the necessarily zig-zaggy nature of defining a 'circular' zone footprint by drawing best-fit boundary lines only along streets, within any established grid-based system of city 'blocks'. The interpretation of why any zone is a complex and crinkly shape, rather than a strictly utilitarian rectangle, may not be so obvious from an overview that does not take into account geological or political restrictions such as the curve of a watercourse in a valley or a mandate against hi-rise buildings within a certain radius of a monument. [Cueball takes picture of his house from a distance great enough to get the whole house in the picture. He holds the camera (or smartphone) in both hands. The shutter makes a sound:] Click [The picture he has taken is shown below. The picture is lying tilted compared to the panel, and shows the house but with a fuzzy light brown blob covering the left part of the picture, just touching the left side of the house. Above and partly over the picture is a small frame with Cueball's response when he sees the picture:] What the... [White Hat gestures towards Cueball with one hand, while Cueball holds his camera in one hand towards White Hat, with the picture shown on the screen, too small to see though.] White Hat: What's that fuzzy blob next to your house? It's huge! Cueball: I don't know! I looked up and it was gone! White Hat: How can a giant structure vanish? Cueball and White Hat: ...Cloaking device?!! [Blondie is standing at the front of the panel with a microphone in her hand speaking towards the viewer. Behind her is a close up of the Blob (in black and white) on a screen. To the left of the screen is an almost bald man with hair behind his ears, holding a hand to his chin. To the right is Megan, who is holding one hand out palm up, towards the picture, which they are both looking at.] Blondie: The fuzzy blob, dubbed "flob" by internet sleuths, has city planners stumped. Man: No, that's not any type of building I'm familiar with. Megan: Could be an experimental military dome. [Hairbun is standing on a podium behind a lectern with a microphone on it. She addresses three people in front of the stage, Cueball, Megan and White Hat. Behind them Blondie is turned the other way speaking to a camera, on a tripod. She has a microphone in her hand.] Hairbun: The zoning board investigation has found no evidence of a cloaked dome structure. Hairbun: The historical commission will be joining the research into these domes and other unusual buildings, such as the historic 4th Ave Church... Blondie: This only raises more questions.

Product Launch

Product Launch

https://www.xkcd.com/2473

https://www.explainxkcd.com/wiki/index.php/2473:_Product_Launch

[Hairy and Ponytail are standing to the left of a wrapped object. Cueball is standing on the right.] Hairy: The press is here for the product launch! Hairy: Remember, people are wary of smart devices, so we want to strike a non-threatening tone. [Pan over to just Cueball; Hairy and Ponytail are off of the left side of the panel.] Cueball: Hang on, did you say non -threatening? Hairy: Yes. Why- Cueball: Nothing. It's probably fine. [Caption: Soon...] [Cueball is standing on a platform next to the previously seen wrapped object.] Cueball: They say technology can change the world, for good or for evil. Our new product will show how true that is. Cueball: We hear the plaintive cries of our customers. We want to give them what they deserve. [Zoom in on Cueball, who has his hand up in a gesture.] Cueball: Now, let us expose our product to the atmosphere for the first time, surprising and delighting customers within a five-block radius. (Voice off-panel): I'm leaving. Cueball: No, don't worry! A staggering number of people will survive!

Three people are discussing the upcoming public announcement of their company's new product, apparently an electronic device shown on the pedestal between them. Hairy mentions that smart devices can make people uncomfortable. Common reasons include: To allay these concerns, the device should be presented as non-threatening. Cueball asks to confirm the non , implying that this was not clear to him before. In fact, it even appears he thought he was being asked to put together a threatening presentation, but does not explain. Later, Cueball presents the device on-stage, with statements that have been styled to sound positive but carry double meanings. The subtlety of the changes in tone could make them harder to discuss for many. In the title text, someone is saying that the actual reveal was uneventful. Cueball interrupts, implying that there is one last feature to demonstrate, at which point the first speaker assumes the worst (that the product's most threatening aspect was saved for last). Besides the main joke of a product that is likely so unsafe as to be illegal, the comic could also be poking fun at the desire of tech companies to make their products sound important, which can undermine the message of benign safety. This comic was released on the day of Apple's 2021 WWDC (Worldwide Developer Conference) keynote, at which the company traditionally announces new features and products. "One more thing" is a tagline famously associated with Steve Jobs' product announcements and something of an Apple tradition. [Hairy and Ponytail are standing to the left of a wrapped object. Cueball is standing on the right.] Hairy: The press is here for the product launch! Hairy: Remember, people are wary of smart devices, so we want to strike a non-threatening tone. [Pan over to just Cueball; Hairy and Ponytail are off of the left side of the panel.] Cueball: Hang on, did you say non -threatening? Hairy: Yes. Why- Cueball: Nothing. It's probably fine. [Caption: Soon...] [Cueball is standing on a platform next to the previously seen wrapped object.] Cueball: They say technology can change the world, for good or for evil. Our new product will show how true that is. Cueball: We hear the plaintive cries of our customers. We want to give them what they deserve. [Zoom in on Cueball, who has his hand up in a gesture.] Cueball: Now, let us expose our product to the atmosphere for the first time, surprising and delighting customers within a five-block radius. (Voice off-panel): I'm leaving. Cueball: No, don't worry! A staggering number of people will survive!

First Time Since Early 2020

First Time Since Early 2020

https://www.xkcd.com/2474

https://www.explainxkcd.com/wiki/index.php/2474:_First_Time_Since_Early_2020

[Heading:] "This is actually the first time I've _____ since early 2020." [Below is a long vertical arrow with the words "normal" and "alarming" at the top and the bottom of the arrow respectively. To the right side of the arrow is a list of text, with each item starting with a triangle.] ◀ been to a birthday party ◀ eaten at a restaurant ◀ seen my family ◀ been on a plane ◀ gone to a movie ◀ gone to a store ◀ installed software updates ◀ eaten a vegetable ◀ opened the fridge ◀ paid taxes ◀ washed my hands ◀ seen another person ◀ seen a ghost ◀ served as a decoy ◀ sighted land ◀ checked the news ◀ checked on the customers in the escape room ◀ contracted a novel bat virus On July 6, 2021, four weeks after the release of this comic, an emergency patch update was released for Windows 7. Since support for Windows 7 had otherwise ended in mid-January 2020, this means that people whose computers ran Windows 7 could have installed software updates for the first time since early 2020.

This is yet another comic part of the series of comics on the COVID-19 pandemic . This comic is a chart that orders things based on the level of alarm that would occur if it were revealed that someone had not done a given thing since early 2020. Many of the items, but not all, are linked to new constraints due to the pandemic. The title text serves as another chart point, though it isn't given where it is on the chart. Been to a birthday party Going to a birthday party was a normal task before the pandemic, and it's normal to say you haven't gone to one since early 2020. Eaten at a restaurant Eating at a restaurant was also common before governments instated lockdowns, but during the lockdowns many restaurants had to limit their service to delivery and take-out. Seen my family Seeing your family was fairly common before the governments instated lockdowns. However, there were emergency visits during the lockdown period. Been on a plane Governments around the world cancelled commercial flights during the pandemic. However, businessmen like Bill Gates used private jets during the pandemic. Gone to a movie Many cinema halls around the world closed due to the pandemic. Several movies were instead released directly to TV via OTT platforms. Gone to a store Although some stores were closed during the lockdown period, others were open for essential commodities. Therefore, going to a store for the first time since early 2020 is little strange. Installed software updates Regularly installing software updates is recommended, mainly for security reasons. However, many people don't follow these recommendations (mostly by fear of software inconsistency or instability), although a delay of more than one year is quite long. Mentioning software updates is weird, because it is not directly related to the COVID pandemic. On the contrary, since many people spent much more time at home and worked at home, it was all the more important to keep software up to date, especially due to zero-day exploits. Eaten a vegetable Since vegetables are essential to a healthy diet, not eating a single vegetable in a whole year is not recommended. [ citation needed ] Anxiety due to the pandemic and disruption of social relations may have caused people to consume more junk food than usual. Opened the fridge This is quite weird, since most people use their refrigerators to store fresh food. Maybe some people became anorexic because of anxiety due to the pandemic or stopped consuming fresh food and relied more on junk food. Moreover, most food products will alter or rot if stored in a fridge for more than one year, and become dangerous to eat. [ citation needed ] Paid taxes Although some people, depending on where they live and their income, may not pay taxes in an immediately obvious way, there are some taxes, such as VAT in many countries and sales tax in the United States or Canada, which almost everyone would pay in the natural course of everyday life, though may not be 'obvious' in the paying, or even be extracted at source (withheld from payroll) in the simpler cases. (Randall lives in Massachusetts , which does not have a VAT, but does have a 6.25% sales tax.) It is therefore strange that someone could have gone a year without paying any taxes, implying they made almost no monetary transactions in the period, nor are made (directly) responsible for any residential or property-owning taxations that might otherwise be payable to one or other layer of government. If the statement refers specifically to filing income taxes (which is often the case when people refer to "taxes", because the paperwork and large sums of money transferred at once makes the income tax highly noticeable and memorable), it might describe someone who filed a tax return for 2019 early in 2020 and then waited until later in 2021 to file a return for 2020. Washed my hands One of the main pieces of advice during the pandemic was to wash one's hands, frequently. Even in normal circumstances, washing hands is a good idea to remain hygienic, [ citation needed ] and not do so for a year would be disgusting to most people, and a good way of catching diseases. Like paying taxes, it is very common to wash one's hands inadvertently as part of another activity, so someone who actually has not washed their hands since early 2020 likely also never bathed or showered. Seen another person Despite the restrictions, most people will have seen another person during the pandemic, virtually or otherwise. Seen a ghost The fact that the speaker apparently has seen a ghost, both now and presumably before early 2020 (else they would simply say it was the 'first time' they saw a ghost) is unusual. [ citation needed ] Served as a decoy Similar to the previous point, this is not a normal activity, so the specificity is unusual. Sighted land Most people live on land, [ citation needed ] so sighting land should not be unusual, even during a pandemic. The fact that someone has gone over a year without sighting land suggests they have been lost at sea for the duration. There are several reported cases of ships' crews refused permission to disembark, due to local restrictions and/or because their scheduled relief were unable to embark, but the unluckily held-on persons forced to remain beyond their originally planned obligations should never have been left permanently beyond any tantalizingly unreachable view of the shore. Taken more literally, it could simply mean that the person remained indoors and did not look outside, or that the person was temporarily blind. Checked the news If someone has not checked the news since early 2020, they will likely be in for a shock upon checking. Noting that this could possibly (if increasingly absurdly) still apply to someone like Ponytail (as portrayed in strip 2396: Wonder Woman 1984 ). Checked on the customers in the escape room The implication is that the customers in question have been trapped in the escape room since early 2020. Most escape rooms are not equipped to support a person for that length of time, so unless the customers actually escaped, they would likely not have survived. [ citation needed ] Contracted a novel bat virus As a 'novel bat virus' is what kicked off the whole pandemic, contracting another one may send the whole world into a new pandemic. Gotten the Ferris wheel operator's attention (title text) It seems that the speaker has been stuck in a Ferris wheel for a year. It is unclear how they may have survived. Alternately, it would be perfectly normal that the speaker has not been at an amusement park with a working Ferris wheel since early 2020 - but it would be unusual to focus on interacting with the operator versus enjoying the attraction. Several science fiction stories include wheel-like prisons where people stay for years, but generally they are underground and horizontal rather than in the air and vertical like Ferris wheels are. [Heading:] "This is actually the first time I've _____ since early 2020." [Below is a long vertical arrow with the words "normal" and "alarming" at the top and the bottom of the arrow respectively. To the right side of the arrow is a list of text, with each item starting with a triangle.] ◀ been to a birthday party ◀ eaten at a restaurant ◀ seen my family ◀ been on a plane ◀ gone to a movie ◀ gone to a store ◀ installed software updates ◀ eaten a vegetable ◀ opened the fridge ◀ paid taxes ◀ washed my hands ◀ seen another person ◀ seen a ghost ◀ served as a decoy ◀ sighted land ◀ checked the news ◀ checked on the customers in the escape room ◀ contracted a novel bat virus On July 6, 2021, four weeks after the release of this comic, an emergency patch update was released for Windows 7. Since support for Windows 7 had otherwise ended in mid-January 2020, this means that people whose computers ran Windows 7 could have installed software updates for the first time since early 2020.

Health Drink

Health Drink

https://www.xkcd.com/2475

https://www.explainxkcd.com/wiki/index.php/2475:_Health_Drink

[White Hat holding a bottle and standing next to Cueball] White Hat: My new health drink is packed with amino acid nanoenzymes that I designed to train your immune system to fight infections! Cueball: Can you give it to some people and see if they get sick less often? White Hat: Whoa, that sounds way too complicated.

This comic pokes fun at health fads, alternative medicine and the like. It points out that many such products will go out of their way to market themselves as legitimate and cutting-edge by using impressive-sounding scientific terms, yet fail to perform even the most basic part of actual science: running a randomized controlled trial to find out if the drink actually helps fight infections. When Cueball points this out, White Hat reacts as though this process is highly advanced and unreasonable, which clearly demonstrates that his product is either nonsensical or an active scam (or both). Enzymes are proteins that catalyze chemical reactions. For example, certain proteins aid digestion by breaking down large molecules. Every cell of the human body produces lots of enzymes; the suggestion that people may be lacking them is frequently used as a basis to peddle pseudoscientific products. Nanoenzymes are synthetic materials that perform similar functions to ordinary enzymes; although they may be useful for treating specific diseases and conditions, the average person will probably not find them beneficial. Amino acids are the chemicals that make up proteins, and therefore all natural enzymes are made from amino acids anyway. White Hat's claim use of the term is not particularly explanatory and is likely used to impress and bewilder his audience, so that they are more likely to buy the product. The comic may reference the FDA's decision three days earlier to approve a drug for Alzheimer treatment, without direct evidence of efficacy. The title text further showcases White Hat's incompetence. First, he suggests keeping track of large numbers of people in a clinical trial by storing their data in Microsoft Excel , a popular spreadsheet application. Despite the insistence of many companies and government agencies throughout the years, Excel is not a database , and it should not be used to store other people's personal and medical information. He then complains that Excel is too "fancy", and then calls himself a "simple country nanoenzyme developer" — this is a parody of the idiom "simple country lawyer," a trained professional who pretends to be an average joe to garner sympathy. Nanomaterials are developed using specialized equipment in laboratories by people who are extremely well-versed in science; the notion of comparing one of these scientists to a 'simple country' anything is ludicrous, and the idea that they would find Excel daunting and overcomplicated is equally so. It's ironic that the person with the seemingly very complicated work and production would be unable to perform the simple procedures which Cueball has suggested in order to make his claims rigorous and supported with evidence. In this, White Hat is demonstrating his complete incompetence and lack of knowledge into what his product actually does. [White Hat holding a bottle and standing next to Cueball] White Hat: My new health drink is packed with amino acid nanoenzymes that I designed to train your immune system to fight infections! Cueball: Can you give it to some people and see if they get sick less often? White Hat: Whoa, that sounds way too complicated.

Base Rate

Base Rate

https://www.xkcd.com/2476

https://www.explainxkcd.com/wiki/index.php/2476:_Base_Rate

[Cueball is standing in front of a screen that shows a bar graph with 2 bars with labels beneath. The right bar is significantly higher than the left. Cueball is holding a pointer which he points at the label of the highest bar, which has been encircled.] Cueball: Remember, right-handed people commit 90% of all base rate errors. Label: L R

The " base rate " is a type of base probability, which a statistical probability can be based on. The base rate fallacy is a type of error in which people are presented with the rate at which something occurs throughout an entire population along with more specific information about a subset of that population, and tend to ignore the whole-population information in favor of the specific information. In this case, the joke is that 90% of people are right-handed, so if there is no connection between handedness and making base rate errors, then 90% of these errors would be made by right handers. Thus while Cueball's claim that right-handers commit 90% of base-rate errors is technically true, taking that as reason to believe that "making base-rate errors" is somehow specially associated with right-handed-ness -- as would be implied by an intervention effort specific to right-handed-people -- is itself a base-rate error. Cueball may be holding the pointer in his right hand, suggesting he might be right-handed (as 90% of stick figures are [ citation needed ] ). Since Cueball has no facial features it is impossible to tell if he faces the audience, or looking at his graph. However, it seems most likely that he is looking at his audience while delivering the take home message and thus points at the graph behind him. Thus he likely belongs to the 90% that makes 90% of the base-rate errors, one of those he is just committing. In the title text, Cueball dismisses the idea of adjusting his graph to account for the difference in numbers of left-handed versus right-handed members of the population. He suggests focusing efforts on the right-handed majority to resolve that 90% of base rate errors. This is a somewhat common counterargument to statistical arguments of this stripe (often as justification for racial profiling, for example); it fails because if the target group is not in fact somehow special with regard to the issue at hand, there is generally "nothing to fix" and no special approach to discover that cannot be just as easily applied to the population of the whole. Something similar occurs in 1138: Heatmap , where Cueball makes inferences simply based on a population map of the US, instead of statistical evidence. [Cueball is standing in front of a screen that shows a bar graph with 2 bars with labels beneath. The right bar is significantly higher than the left. Cueball is holding a pointer which he points at the label of the highest bar, which has been encircled.] Cueball: Remember, right-handed people commit 90% of all base rate errors. Label: L R

Alien Visitors

Alien Visitors

https://www.xkcd.com/2477

https://www.explainxkcd.com/wiki/index.php/2477:_Alien_Visitors

[A flying saucer is hovering high above Cueball and Megan, drawn very small standing on the ground beneath it. The aliens inside speak to them from inside their saucer, indicated with zigzag lines between it and the text.] Aliens: Greetings, humans! Megan: Whoa, aliens! Aliens: We bring you technological wonders! [Zoom in on the flying saucer which has two beams below it, the left showing an outline of a pyramid and the right is shown lifting a large stone. Cueball replies off-panel.] Aliens: We will help you lift great stones and build towering monuments. Cueball (off-panel): Oh, pyramids? [Zoom in on Cueball and Megan looking up, the Aliens reply from above the panel.] Aliens (off-panel): ...Yes. Cueball: Yeah, we have those. In Egypt. Megan: And Mexico. Cueball: I think they used ramps? [Zoom back out, as in first panel] Aliens: Then we shall build a ring of stones aligned with the stars, so at the solstice- Megan: Oh, like Stonehenge? Aliens: Dammit, humans.

This is the first comic in a new series , followed in the next comic by 2478: Alien Visitors 2 . This strip satirizes the ancient astronauts hypothesis: that aliens were involved in building the pyramids and Stonehenge . This concept, popular in some circles, is based on the assumption that earlier civilizations lacked the technology to build such large structures. There are also geometric or other scientific properties to these structures, which some people assume that humans of that era would have been incapable of creating. Erich von Däniken , a Swiss author, is one of the foremost proponents of "ancient astronauts." Some say that such pseudoscience is inherently racist, as it assumes, without any proof, that other civilizations were unable to build their monuments without foreign help. Although others disagree since most races and nationalities have one or another of these monuments with similar claims. In the comic, aliens arrive with the intention of building such monuments with their highly advanced technology, including some sort of tractor beam to lift the heavy stones and another beam that can depict a pyramid. They are shocked to hear from Cueball that humans accomplished the same thing thousands of years earlier with such simple tools as ramps, and even in more than one location on Earth (Pyramids in Egypt and Mexico ). Thus they proceed to suggest a stone circle to predict the solstice, but before they can finish this sentence Megan says this is like Stonehenge. The joke of the strip is that, if aliens were interested in building such structures on earth, they'd be just as likely to show up today as thousands of years ago. And if they offered to build pyramids today, humans would be very unimpressed, as we've had the technology to do so for quite some time. The notion that an advanced, spacefaring species would come all the way to Earth (or whatever other planets they visit) to build relatively simple stone structures seems dubious, when put that way. Alternately, the aliens may have visited Earth before in the past and impressed the humans of the time with their advanced technology of pyramids and stone circles, leading them to expect the same technology to impress the humans again in the present day. This is somewhat plausible: Stonehenge is estimated to have been built around 3100BC, while the pyramids were built 500-1000 years later. Assuming both structures were indeed built by aliens in the past, the visitors would have returned to the Earth to find agricultural civilizations almost identical to the ones they encountered centuries prior. The aliens could have then been led to believe that human technology, if almost entirely unchanged in the 500 years since they last visited, would not have advanced significantly in a few thousand years. Indeed, the aliens were mostly correct in this assessment: technological advancement progressed at a crawl until the scientific revolution marked the emergence of modern science only a relatively short 600 years ago. From this perspective, the aliens would seem to be correct in their assumption that human technology would not significantly improve such that they could not impress humanity with their technological wonders. Unfortunately, the aliens have been caught off-guard by the exponential nature of technological advancement, in that advanced civilizations have the resources to advance even more rapidly. The aliens' reaction is frustration as they cannot teach us anything new; evidently, it does not occur to them to share their technologies for antigravity and interstellar travel (which, having come to Earth in floating spaceships, they clearly possess). In the title text they have regrouped and would now present another wonder - gears . This is very likely a reference to the Antikythera mechanism , an artifact dating from the 2nd century BC which used a complex, geared calculating system to predict the movement of stars and planets. As with the aforementioned structures, some fringe groups theorize that such mechanisms were beyond human technology at the time, and therefore must have been given by aliens. Once again, such technology is not impressive to humans at this point, as complex, geared mechanisms are now commonplace in most human societies. Indeed, quite a bit of intricate mechanical gearing and timing has been obsoleted by electronics. [A flying saucer is hovering high above Cueball and Megan, drawn very small standing on the ground beneath it. The aliens inside speak to them from inside their saucer, indicated with zigzag lines between it and the text.] Aliens: Greetings, humans! Megan: Whoa, aliens! Aliens: We bring you technological wonders! [Zoom in on the flying saucer which has two beams below it, the left showing an outline of a pyramid and the right is shown lifting a large stone. Cueball replies off-panel.] Aliens: We will help you lift great stones and build towering monuments. Cueball (off-panel): Oh, pyramids? [Zoom in on Cueball and Megan looking up, the Aliens reply from above the panel.] Aliens (off-panel): ...Yes. Cueball: Yeah, we have those. In Egypt. Megan: And Mexico. Cueball: I think they used ramps? [Zoom back out, as in first panel] Aliens: Then we shall build a ring of stones aligned with the stars, so at the solstice- Megan: Oh, like Stonehenge? Aliens: Dammit, humans.

Alien Visitors 2

Alien Visitors 2

https://www.xkcd.com/2478

https://www.explainxkcd.com/wiki/index.php/2478:_Alien_Visitors_2

[A flying saucer is flying high above Ponytail who is walking towards White Hat, Cueball and Megan. Those three are looking up at the spacecraft. The humans are drawn very small standing on the ground beneath it. The aliens inside speak to them from inside their saucer, indicated with zigzag lines between it and the text.] Aliens: Greetings, humans. We have returned. Aliens: Since you already have pyramids, we've brought you more advanced wonders. [Pan up to only showing the flying saucer which has two beams below it, the left showing an outline of a biplane and the right is showing an outline of a blimp. The humans reply off-panel. Given their positions before, the first is probably Ponytail, but it cannot be determined.] Aliens: These machines will let you conquer the sky! Voice 1 (off-panel): A biplane? Voice 1 (off-panel): Aren't monoplanes more efficient? Voice 2 (off-panel): Does that blimp use hydrogen? [Zoom in on the four humans looking up, the Aliens reply from above the panel. There is a chemical formula in an outline from the alien flying saucer, shown in a similar manner to the other items.] Chemical formula: (CH 3 CH 2 ) 4 Pb Aliens (off-panel): Add this elixir of lead to your gasoline and your engines will run smooth. White Hat: Lead? Isn't that stuff toxic? Aliens: Is it? Aliens: Oh no. [Zoom back out, as in first panel but the flying saucer and the humans are shown in silhouette. A beam from the saucer is showing an outline of a juice machine.] Aliens: Okay, uh. Aliens: This device's electric press can squeeze fresh fruit juice from bags of pulp! Ponytail: ...Just curious, did you build that saucer? Cueball: Maybe we shouldn't stand right under it.

This is the second comic in a series , following the previous comic 2477: Alien Visitors . The aliens now return to show us even more "advanced" inventions. As with the previous strip, the only innovations they offer are not only things that humans know how to build, but things we figured out some time ago, and are now obsolete. As with the pyramids and Stonehenge, these inventions might have been impressive in their time, but now offer nothing to humanity. Biplanes are planes with two sets of wings, which provide more of the necessary lift at slow speed than a contemporaneous monoplane , but develop increased drag and aerodynamic and air-frame issues as higher air-speeds became possible/necessary. Biplanes have been obsolete for most purposes since the 1930s, though they remain in use for agriculture and aerial sports. A blimp is a lighter than air aircraft with no internal structure. These aircraft were traditionally filled with hydrogen gas to provide the needed buoyancy, due to the lower density of hydrogen and a US monopoly on helium limiting availability for the German blimp manufacturer. Hydrogen is highly flammable and thus presents a safety issue. The famous Hindenburg disaster is widely seen as a reason hydrogen airships are unlikely to be widely accepted. However, it is still disputed whether the hydrogen or the coating of the airframe caused the fire. Blimps are still used today, but only rarely, in niche applications, such as for advertising or for aerial photography/videography. Modern airships generally use helium as a lifting gas, which is more expensive, but non-flammable. Tetraethyllead ((CH 3 CH 2 ) 4 Pb) is a chemical added to gasoline (mostly from the 1920s to the 1990s — although some countries still use it to this day ) to prevent engine knocking . Lead is toxic and bio-accumulative, and there's substantial evidence that its use in gasoline caused widespread lead exposure, impacting public health on a huge scale. The aliens seem surprised to learn of these toxic effects, and their concern implies that they may be using leaded gasoline themselves, but it's unclear whether they might think that their biology may by vulnerable to lead as well or whether they never considered that biologies alien to theirs would be. The final invention appears to be a reference to Juicero , a defunct and short-lived brand of juicer, which has become iconic of the absurdity of modern technology investment. The company produced a high-tech, internet-connected juicer which sold for $700, and only worked on the company's proprietary branded single-serving bags of pulped fruit, which were available by subscription for $5-$7 per serving. The company raised over $100 million in startup capital, but quickly went out of business because most consumers considered the expensive product to be nearly useless, coupled with a rather damning video by Bloomberg demonstrating said packets could easily be squeezed by hand. The title text singles this invention out, calling it one of the "mistakes of the past". After the latest showing of unimpressive "inventions", the humans start questioning how "advanced" the aliens really are. It's traditionally assumed that a species capable of interstellar travel would have a host of other advanced technologies, which is inconsistent with the unimpressive and not only obsolete, but also fatally-flawed inventions they're offering to humanity. The humans on the ground ask whether they actually built their own flying saucer. They also consider the wisdom of standing directly under the saucer, implying that, if the aliens did build it, it's likely to be unreliable, and may be at risk of crashing (though perhaps a bit ironically, the humans say this in response to the juicer, and while the actual device it is spoofing was a failure in many ways, one thing it was not was shoddily built (aside from the fact that you could squeeze more juice by hand than by using the machine...) - one critique of the Juicero was that it was needlessly over-engineered). [A flying saucer is flying high above Ponytail who is walking towards White Hat, Cueball and Megan. Those three are looking up at the spacecraft. The humans are drawn very small standing on the ground beneath it. The aliens inside speak to them from inside their saucer, indicated with zigzag lines between it and the text.] Aliens: Greetings, humans. We have returned. Aliens: Since you already have pyramids, we've brought you more advanced wonders. [Pan up to only showing the flying saucer which has two beams below it, the left showing an outline of a biplane and the right is showing an outline of a blimp. The humans reply off-panel. Given their positions before, the first is probably Ponytail, but it cannot be determined.] Aliens: These machines will let you conquer the sky! Voice 1 (off-panel): A biplane? Voice 1 (off-panel): Aren't monoplanes more efficient? Voice 2 (off-panel): Does that blimp use hydrogen? [Zoom in on the four humans looking up, the Aliens reply from above the panel. There is a chemical formula in an outline from the alien flying saucer, shown in a similar manner to the other items.] Chemical formula: (CH 3 CH 2 ) 4 Pb Aliens (off-panel): Add this elixir of lead to your gasoline and your engines will run smooth. White Hat: Lead? Isn't that stuff toxic? Aliens: Is it? Aliens: Oh no. [Zoom back out, as in first panel but the flying saucer and the humans are shown in silhouette. A beam from the saucer is showing an outline of a juice machine.] Aliens: Okay, uh. Aliens: This device's electric press can squeeze fresh fruit juice from bags of pulp! Ponytail: ...Just curious, did you build that saucer? Cueball: Maybe we shouldn't stand right under it.

Houseguests

Houseguests

https://www.xkcd.com/2479

https://www.explainxkcd.com/wiki/index.php/2479:_Houseguests

[Cueball and Megan are talking.] Cueball: Now that we're fully vaccinated, we can invite people over. Megan: Exciting! [Same setting, without talk. Beat panel.] [Cueball and Megan are standing in a wider panel. Megan is looking down at her torso while holding her arms out from her body.] Cueball: Which means we have to clean. Megan: ...You know, I suddenly feel only about 98% vaccinated. Cueball: Yeah, let's give it a few more days.

This comic is another entry in a series of comics related to the COVID-19 pandemic , specifically regarding the COVID-19 vaccine . With COVID-19 vaccines under distribution, more and more people are becoming fully vaccinated. Cueball and Megan have apparently become part of that group, and Cueball notes that with the vaccine in their systems, they can once again start hosting people at their house — the various local and national rules maintained to mitigate infections now allowing indoors association in such circumstances for many individuals. Megan concurs, indicating they have been looking forward to having their friends over. After a beat panel, Cueball notes that if they intend to host people, they need to clean the house. Megan promptly backtracks on her eagerness to have people over, implying that her reluctance to complete this task (possibly a rather onerous one, if they have been neglecting housework during the pandemic) may outweigh her desire to socialize. Megan claims she only feels 98% vaccinated, and thus is not completely ready for houseguests; Cueball agrees that they need to wait a few more days before they are 100% vaccinated/ready for guests. The earlier vaccination-related comic 2460: Vaccinated depicted Cueball and Megan as not very skilled at social interactions , so it's possible they may not have many "people" to invite over anyway, or may be awkward with those they do invite over. The title text continues the theme of "vaccination status = houseguest readiness" and assumes that this is an association of one state with the other that is commutative - that is, reversible, with either one implying the other. In the title text, it appears Cueball and Megan have cleaned most of their house in preparation for having guests, with the evident exception of the spare room next to the living room, which is perhaps being used to store junk from the other rooms. Thus they pretend that in that room they are not fully vaccinated, as if their vaccination status is dynamically influenced by their location in their home rather than, for instance, by the memory of their adaptive immune system . [Cueball and Megan are talking.] Cueball: Now that we're fully vaccinated, we can invite people over. Megan: Exciting! [Same setting, without talk. Beat panel.] [Cueball and Megan are standing in a wider panel. Megan is looking down at her torso while holding her arms out from her body.] Cueball: Which means we have to clean. Megan: ...You know, I suddenly feel only about 98% vaccinated. Cueball: Yeah, let's give it a few more days.

No, The Other One

No, The Other One

https://www.xkcd.com/2480

https://www.explainxkcd.com/wiki/index.php/2480:_No,_The_Other_One

[A typical line-drawn map projection of the United States, with discontiguous Alaska and Hawaii moved into a convenient corner.] [Coastlines and national borders are in a firm half-tone.] [Non-coastal state boundaries are shown in a lighter tone and feature the standard two-letter abbreviations.] [Location dots and labels of the settlements they represent are overlaid in solid black.] [Within each of the states, expanded here for readability, are the following placenames...] AK [Alaska] Houston AL [Alabama] Detroit Houston Jackson AR [Arkansas] Nashville AZ [Arizona] Miami Peoria CA [California] Beaumont Jamestown Lincoln Mesa Plymouth CO [Colorado] [An unlabelled dot, between text for Louisville, CO and Atlanta, NE; probably the actual Mesa, CO.] Louisville Mesa [Appears to be the incorrectly-labeled town of Orchard Mesa, CO.] CT [Connecticut] Salem DE [Delaware] Atlanta Newark FL [Florida] Bowling Green Houston GA [Georgia] Albany Columbus Dallas Roswell HI [Hawaii] Mountain View IA [Iowa] Indianapolis Knoxville ID [Idaho] Atlanta Princeton IL [Illinois] Beverly Hills Lincoln Plano IN [Indiana] Houston Plymouth KS [Kansas] Detroit Manhattan Ottawa KY [Kentucky] Anchorage New Haven LA [Louisiana] Alexandria MA [Massachusetts] Princeton MD [Maryland] Pasadena Phoenix ME [Maine] Lisbon Portland Vienna MI [Michigan] Atlanta Saint Louis MN [Minnesota] Albany Austin Bloomington Grand Rapids MO [Missouri] Boston Houston Savannah MS [Mississippi] Philadelphia MT [Montana] Lincoln Manhattan NC [North Carolina] Dallas Washington ND [North Dakota] Jamestown New England NE [Nebraska] Atlanta Cedar Rapids Memphis NH [New Hampshire] Lisbon NJ [New Jersey] Long Beach NM [New Mexico] Des Moines Las Vegas NV [Nevada] Dayton NY [New York] North Pole Philadelphia Texas [Further subtitled as...] (Texas, Mexico) OH [Ohio] Bowling Green Cambridge Gettysburg Houston OK [Oklahoma] Disney Orlando Saint Louis OR [Oregon] Dallas Oakland Phoenix PA [Pennsylvania] Jersey Shore RI [Rhode Island] Lincoln SC [South Carolina] Baton Rouge SD [South Dakota] Dallas Gettysburg TN [Tennessee] Fayetteville White House TX [Texas] Atlanta Beverly Hills Buffalo Los Angeles Miami New York Pasadena San Diego Santa Fe South Bend UT [Utah] Cleveland VA [Virginia] Key West VT [Vermont] Richmond WA [Washington] Des Moines WI [Wisconsin] Atlanta WV [West Virginia] Bridgeport WY [Wyoming] Albany Atlantic City Buffalo

This is a map of the United States, showing cities or towns with the same name as other more famous places. For example, the map has a dot for a relatively unknown place called Los Angeles, located in Texas, not to be confused with the very well known Los Angeles that is in California. Few place names are unique, and there may be many places with the same name . Multiple American towns have been named after the same British town, famous person, or geographic feature. However, names can become associated with specific places on a national level, where the best-known example is usually the biggest or otherwise the most significant. The name of this comic indicates the contextualization required to specify one of the less-famous exemplars of a given name. Someone might say they are from "Los Angeles" and would have to say "no, the other one" since the listener would assume they are from Los Angeles, California. The title text references Key, West Virginia and Key West, Virginia , two places that, when spoken aloud, are only distinguishable by the pause (comma) location. Neither are to be confused with Key West, Florida , which is a location well-known nationally. [A typical line-drawn map projection of the United States, with discontiguous Alaska and Hawaii moved into a convenient corner.] [Coastlines and national borders are in a firm half-tone.] [Non-coastal state boundaries are shown in a lighter tone and feature the standard two-letter abbreviations.] [Location dots and labels of the settlements they represent are overlaid in solid black.] [Within each of the states, expanded here for readability, are the following placenames...] AK [Alaska] Houston AL [Alabama] Detroit Houston Jackson AR [Arkansas] Nashville AZ [Arizona] Miami Peoria CA [California] Beaumont Jamestown Lincoln Mesa Plymouth CO [Colorado] [An unlabelled dot, between text for Louisville, CO and Atlanta, NE; probably the actual Mesa, CO.] Louisville Mesa [Appears to be the incorrectly-labeled town of Orchard Mesa, CO.] CT [Connecticut] Salem DE [Delaware] Atlanta Newark FL [Florida] Bowling Green Houston GA [Georgia] Albany Columbus Dallas Roswell HI [Hawaii] Mountain View IA [Iowa] Indianapolis Knoxville ID [Idaho] Atlanta Princeton IL [Illinois] Beverly Hills Lincoln Plano IN [Indiana] Houston Plymouth KS [Kansas] Detroit Manhattan Ottawa KY [Kentucky] Anchorage New Haven LA [Louisiana] Alexandria MA [Massachusetts] Princeton MD [Maryland] Pasadena Phoenix ME [Maine] Lisbon Portland Vienna MI [Michigan] Atlanta Saint Louis MN [Minnesota] Albany Austin Bloomington Grand Rapids MO [Missouri] Boston Houston Savannah MS [Mississippi] Philadelphia MT [Montana] Lincoln Manhattan NC [North Carolina] Dallas Washington ND [North Dakota] Jamestown New England NE [Nebraska] Atlanta Cedar Rapids Memphis NH [New Hampshire] Lisbon NJ [New Jersey] Long Beach NM [New Mexico] Des Moines Las Vegas NV [Nevada] Dayton NY [New York] North Pole Philadelphia Texas [Further subtitled as...] (Texas, Mexico) OH [Ohio] Bowling Green Cambridge Gettysburg Houston OK [Oklahoma] Disney Orlando Saint Louis OR [Oregon] Dallas Oakland Phoenix PA [Pennsylvania] Jersey Shore RI [Rhode Island] Lincoln SC [South Carolina] Baton Rouge SD [South Dakota] Dallas Gettysburg TN [Tennessee] Fayetteville White House TX [Texas] Atlanta Beverly Hills Buffalo Los Angeles Miami New York Pasadena San Diego Santa Fe South Bend UT [Utah] Cleveland VA [Virginia] Key West VT [Vermont] Richmond WA [Washington] Des Moines WI [Wisconsin] Atlanta WV [West Virginia] Bridgeport WY [Wyoming] Albany Atlantic City Buffalo

1991 and 2021

1991 and 2021

https://www.xkcd.com/2481

https://www.explainxkcd.com/wiki/index.php/2481:_1991_and_2021

[Cueball (with an aura) is talking to White Hat.] White Hat: Welcome to 1991! White Hat: So you're from 2021? What happens with technology over the next 30 years? [Same scene, except Cueball has his palm out.] Cueball: We passed a federal law to combat laser attacks on airliners, and there are TV shows where robots battle. Cueball: Also, cordless phones are longer range now, and it's really easy to send news stories to your friends. White Hat: Wow, okay. [Same scene.] Cueball: Now, try to guess which of those things turn out to be important. White Hat: ...is it not the lasers? Cueball: It is not the lasers. On release, the title text was not actually included as such. It was instead included as the text of a "see also" link, which is often invisible to readers and is activated by clicking the comic. Such links have been used in the past for larger versions of the comic or for related information on other sites. Here, it linked back to the comic itself, and was evidently a mistake.

This comic shows a Cueball from 2021 who is once again discussing the future's technology with White Hat, this time in 1991 instead of 2010. White Hat is awed by the advances in technology, but is not expecting that the law combating laser attacks on passenger aircraft is not the most important thing mentioned. "Laser attacks on airliners" sounds dramatic and important, and White Hat probably thinks that laser weapons have been developed and used to attack aircraft. Given that "a [US] federal law" has been passed to combat such attacks, White Hat may be envisioning a future where US citizens have access to laser guns, and some reckless individuals have been firing them at airplanes. (If it were some other group like terrorists or foreign militaries, a federal law would be unlikely to dissuade them.) In reality, the "lasers" in question are low-powered laser pointers, which some people aim at passenger airliners as a (dangerous) prank. When the beam hits the airplane, it cannot damage the plane itself, much less shoot it from the sky; [ citation needed ] it can, however, blind the pilot, which poses a threat to them and their passengers. A law ( 18 USC §39A ) was thus passed in 2012 to criminalize this. The robot fighting TV shows mentioned include BattleBots , Robot Wars , and MegaBots , the earliest of which started in 1998. In them, machines armed with a variety of weapons fight in an arena. These are not technically robots or drones in the traditional sense of operating autonomously; for the most part, they are either remote controlled or piloted by humans, and have only rudimentary on board computer systems. They are certainly not controlled by AI. Also, while these shows have been popular enough to return to the air after periods of hiatus, they are not nearly as popular as sports involving humans. In this comic, "cordless phone" may be meant literally, meaning any wireless phone without a cord. That's distinct from common parlance where "cordless phone" is distinct from a cellular phone, and is a wireless extension of a landline, typically of limited range, i.e. within a home. It seems likely that Cueball was using a term he believed a 1991 citizen would more easily relate to. Although cell phones had been in use for over a decade by 1991, they were most commonly depicted as a foible of a stereotypical "businessman", typically accompanied by displays of distraction, classism, & self-importance. The term "cell phone" was at that time frequently used to refer to older analog cellular networks, with many mobile users proud of their new CDMA or GSM " digital " phones, as distinct from true "cellular" systems which have been deprecated since that time (this distinction has since disappeared from common usage). A more general term used in modern parlance, such as "mobile phone" or "wireless phone" may have been less recognizable to the average person in 1991. Describing a cell phone as "a cordless phone [where you can] send news stories to your friends" would be a reasonable way of describing a cell phone to a person of that era. Additionally, cellular phones today do not have much longer range than cellular phones of 1991 (in fact most have less range, due to their lower transmission power & use of higher frequencies, as well as indirectly due to increasing crowding on most wireless frequencies). Cordless phones reliant on a land-line, may exhibit somewhat longer range than they did in 1991, due to improvements in digital error correction & audio compression, although the effective range of a single transmission at a given power & frequency would otherwise be reduced by interference from the proliferation of other wireless devices outside functional range &\or operating independently. Satellite phones also offer more terrestrial range than cellular or cordless landline phones, however their functional range has not greatly increased since 1991 either (being already sufficient to reach a satellite within line-of-sight above). A possible explanation for a perceived "longer range" is that cellular phone towers are much more omnipresent than in 1991, granting cellular devices much greater functional area even though their functional range from one tower is typically less than in 1991. Sharing on social media has distorted what news stories people encounter. Instead of a curated selection of important [ citation needed ] news fact-checked by a newspaper or tv/ radio broadcast from a large corporate media conglomerate , we see only what people similar to us found interesting. By most reasonable measures, the most important technologies on the list could be seen as the rise of mobile phones, and the ability to easily share news stories (aside of course, from any perceived advent of high-powered laser weapons or televised robotic warfare). The first of these, mobile phone usage (& smartphones in particular) has led to a dramatic change in how people communicate, with a large amount of communication now remote, which was not as convenient in the 90s (requiring, for example, setting up roaming at the carrier's office before taking the phone to another city) and impossible for most people a few decades prior: Low frequency wireless for personal communication was relatively uncommon in the early '90s & remains so today. Sharing of news stories person-to-person is partly blamed for the spread of fake news ; misinformation has become more and more politically, legally, & socially significant in the past few years. While wireless communication has certainly had enormous & wide-ranging effects, the factuality of the data communicated is arguably of greater importance than the means of its communication. The joke is that the impact of a technology on society isn't really about how exciting or dangerous it might look at first glance. The title text horrifies 90s White Hat , as it not only refers to a pandemic serious enough to induce lockdowns, but mentions it casually, in reference to the existence of computer webcams. COVID-19 is already a hugely impactful deadly disease, but by mentioning it without details, it leaves White Hat to guess as to the details. Cueball doesn't specify whether there have been one or more pandemics (the plural use of 'lockdowns' could be taken to imply that there were more than one), or how serious they were, how long-lasting, or how many lives were lost to them. In consequence, White Hat could easily be assuming a dystopian future even worse than what really happened. [Cueball (with an aura) is talking to White Hat.] White Hat: Welcome to 1991! White Hat: So you're from 2021? What happens with technology over the next 30 years? [Same scene, except Cueball has his palm out.] Cueball: We passed a federal law to combat laser attacks on airliners, and there are TV shows where robots battle. Cueball: Also, cordless phones are longer range now, and it's really easy to send news stories to your friends. White Hat: Wow, okay. [Same scene.] Cueball: Now, try to guess which of those things turn out to be important. White Hat: ...is it not the lasers? Cueball: It is not the lasers. On release, the title text was not actually included as such. It was instead included as the text of a "see also" link, which is often invisible to readers and is activated by clicking the comic. Such links have been used in the past for larger versions of the comic or for related information on other sites. Here, it linked back to the comic itself, and was evidently a mistake.

Indoor Socializing

Indoor Socializing

https://www.xkcd.com/2482

https://www.explainxkcd.com/wiki/index.php/2482:_Indoor_Socializing

[White Hat and Cueball are having a conversation.] White Hat: How are you? Cueball: Excruciatingly aware of how much of each other's gross lung air we're breathing. Cueball: I mean, fine! How are you?

Cueball is meeting White Hat , who is probably not in the same household. White Hat asks how Cueball is, which is normal small talk, but Cueball responds by expressing his anxiety that they're inhaling one another's "gross lung air". Cueball then repeats a common joke regarding how impossible it is to connect with people when our conversation norms discourage honest communication, switching to a more socially acceptable "fine". "Gross" here may be a pun on the term gross anatomy (i.e. anatomy at the macroscopic level) and "gross" as a synonym for "disgusting." A recurring theme in xkcd is characters expressing an uncomfortable awareness of realities that most people tend to ignore, particularly for experts in a particular field (examples include 2057: Internal Monologues , 913: Core , 203: Hallucinations , and 1839: Doctor Visit ). In this strip, likely as a result of being primed by awareness of the COVID-19 pandemic , Cueball finds it difficult to be in the same building with other people without being aware of the fact that they're breathing the same air, meaning that particles of biological material are being freely exchanged. In an earlier era, such concerns might have been dismissed as being extreme, but the pandemic has demonstrated that there's very real reason to be concerned. Even if everyone involved is vaccinated, that doesn't entirely remove the risk, nor does it protect against other diseases, which can spread in similar ways. The title text reinforces the idea that knowing more about any subject increases the likelihood that you'll become disturbed by some constant and basic reality of life. In this case, studying biology tends to be disturbing, since the field involves in depth knowledge of our own bodies, as well as all other organisms we encounter, and which makes one uncomfortably aware of all the risks and flaws basic to being alive. Normally, inhaling unfamiliar biological organisms from the bodies of others is one way the immune system learns its environment, to prepare for possible diseases like seasonal colds. With the advent of common distant travel, culture has adapted to the onslaught of new organisms people are exposed to, giving us strong senses of hygiene to protect our health beyond the adaption of our immune systems. Diverse cultures of hygiene have evolved deadly superbacteria, produced sets of people with very good hygiene and very weak immune systems, as well as saving millions of lives, providing for treatments like safe open surgery and normalising novel piercings. Often learning of the realities of the pervasiveness of micro-organisms and the details of biology can clash with one's culture of hygiene. [White Hat and Cueball are having a conversation.] White Hat: How are you? Cueball: Excruciatingly aware of how much of each other's gross lung air we're breathing. Cueball: I mean, fine! How are you?

Linked List Interview Problem

Linked List Interview Problem

https://www.xkcd.com/2483

https://www.explainxkcd.com/wiki/index.php/2483:_Linked_List_Interview_Problem

[Cueball is writing on a whiteboard with a blue pen with Ponytail looking over his shoulder. The text on the board is unreadable, but it is is written in blue above them. It is a piece of code and it reads:] Ponytail: Hey. [Caption beneath the panel:] Coding interview tip: Interviewers get really mad when you try to donate their linked lists to a technology museum.

This is another one of Randall's Tips , this time a Coding interview Tip. In computer programming, a linked list is a type of data structure that stores data throughout memory accompanied with memory addresses of the next, and potentially previous data point, establishing a relative ordering for a collection of data. Several common software engineering interview questions involve manipulating or otherwise interacting with linked lists. Possibly because programmers in the current day rarely work with linked lists directly, Randall suggests that such structures belong in a "technology museum," and thinks it would be more beneficial to mankind to email the list to such a museum rather than perform any useful work with it. A linked list is a way to store sequential data in computer memory. Each piece of data is stored with a pointer to the next piece. This makes it very easy to add new data in the middle, since only one existing pointer must change to point to the new data. The drawback of a naive implementation can be that finding data may require following the entire chain. Technical programming interviewers like to see if applicants are familiar with the structure and the computational complexity concept itself. Linked lists are, historically, one of the two main data structures that represent sequential data, along with arrays. Unlike arrays, they have the theoretical advantage of O(1) insertions and deletions thanks to not needing to reallocate the entire structure, but have O(n) random access (see comparisons ). However, modern processors' cache structure favors data that are located next to each other, pre-fetching the adjacent items, and modern processors can perform bulk memory moves, making resize operations faster. Finally, using linked lists usually implies dynamic allocation of each list member as opposed to reserving memory for a bunch of items in a bulk and then using that memory once an item has to be added. Memory allocation tends to be slow on modern systems and adds overhead for managing the information, which byte is allocated for what item, which can be significant, particularly for smaller data items; many small allocations also tend to fragment memory, which can lead to it being wasted and unavailable to the app later, particularly in long-running processes such as web servers. These properties tend to make linked lists poorly suited for most system programming applications in which a programmer might write algorithms to manipulate data structures, instead of using existing libraries. Modern programming languages usually provide abstractions (often named "array," "vector" or "list") which interact with the sequential data at the memory level, providing access to this data while using arrays, linked lists, hybrids of the aforementioned technologies, or other approaches, and the programmer doesn't necessarily need to care one way or another. Knowing the underlying concepts is still useful, however, when creating fast running code which scales well to large data, avoiding (e.g.) traversing the list over and over again, or performing particularly inefficient operations. Cueball's code implements a routine whose name implies that it does a mundane task, specifically traversing a linked list, but in fact emails the contents of the list to a technology museum. This could reveal private data that might be stored in a linked list, such as bank account numbers, medical information, passwords, etc., and would thus be a terrible idea. This is why interviewers - presumably job interviewers - would "get really mad". In the title text, a singly linked list contains pointers to traverse the list in only one direction; namely, from the head to the end. By contrast, each element in a doubly linked list contains pointers to both the "next" and "previous" elements, enabling traversal in either direction. Randall continues the implication that such lists are obsolete by implying that traversing such a list would be akin to time travel. Without the "previous element" pointers, Randall is concerned he would not be able to reverse the time travel, as he could not traverse the list in the reverse direction. [Cueball is writing on a whiteboard with a blue pen with Ponytail looking over his shoulder. The text on the board is unreadable, but it is is written in blue above them. It is a piece of code and it reads:] Ponytail: Hey. [Caption beneath the panel:] Coding interview tip: Interviewers get really mad when you try to donate their linked lists to a technology museum.

H-alpha

H-alpha

https://www.xkcd.com/2484

https://www.explainxkcd.com/wiki/index.php/2484:_H-alpha

[In a slim panel Black Hat is seen holding a small black device up in his left hand.] Black Hat: I got an H-Alpha filter for looking at the sun. [In a broad frame-less panel Black Hat, holding the device down in his left hand while standing behind Cueball who is sitting in an armchair reading on his tablet.] Black Hat: It also works for nebulae. But that's about it. There just aren't that many hot blobs of hydrogen to look at, I guess. [Back to a slim panel, Black Hat is seen holding his left hand to his chin, while he holds the device down in his right hand.] Black Hat: ...Unless... [Another two slim panels follows. In the first Black Hat turns around and leaves, his head already partly outside the panel already, and he no longer holds the device in his hands. And then follows an empty beat panel.] [In a broad panel Black Hat re-enters with the device held down in his hand. He is walking towards Cueball in his armchair. His black hat is somewhat out of shape. Cueball is still reading but is now hunched further forward and he has lifted his tablet so it is very close to his face.] Black Hat: Huh, did you know blimps all use helium now? You learn something new every day! By the way, we're out of fireworks. Black Hat: And some advertising company is real mad.

Black Hat has acquired an H-alpha filter. This is a special kind of optical filter used for scientific observations of the Sun's chromosphere . It is different from an ordinary solar filter, which is used to protect one's eyes or camera, as looking at the Sun bare-eyed will do damage to one's eyes. A camera using an ordinary (not H-alpha) solar filter was seen in 1828: ISS Solar Transit , and the consequences of not using such a filter were explored in 2227: Transit of Mercury . Black Hat points out that the filter can also be used to look at nebulae , but doesn't see much further use for it; since the filter only transmits a very narrow bandwidth of light, one generated by hot hydrogen, it is not useful for looking at much else. This gives him an idea, and he leaves. WARNING!!! A deep sky nebula H-alpha filter has a wider bandwidth than a solar H-alpha filter and WILL hurt the eyes if used to observe the sun! Upon returning, his hat looks damaged. He casually shares with Cueball three seemingly unrelated observations which suggest what he was up to in the meantime: that most modern blimps use helium to keep them aloft, that their household is out of fireworks, and that an advertising company (or several, going by the title text) is upset. Early in the 20th century, most airships such as blimps and zeppelins used hydrogen as the lifting gas. There were several incidents in which this gas ignited while the ships were in flight, resulting in spectacular and catastrophic fireballs, most famously the Hindenburg disaster . Taken together, the implication is that Black Hat tried to set someone's advertising blimp alight using fireworks; so he could use his H-alpha filter to look at the burning hydrogen. In modern times, one of the most well-known uses of airships is blimps for advertising, as they are an unusual and hence attention-getting sight in the sky, offer a large surface area that can be used to show a slogan or logo, and can stay aloft for a long time at comparatively little cost. Modern blimps almost exclusively use helium as a lifting gas. While helium is significantly more expensive than hydrogen (and a non-renewable resource), it has similar weight and therefore similar lifting power to hydrogen, but is not flammable. (In fact, as a noble gas, helium is totally non-reactive under normal conditions). Any attempt to cause a hydrogen fireball would, therefore, be doomed to failure. Nonetheless, if Black Hat managed to set off sufficiently powerful fireworks near the blimp, it could potentially damage the skin, risking a loss of helium and possibly putting people in danger, which is likely why the advertising company is "real mad". The joke is that Black Hat would do something as destructive as attempting to destroy a blimp in flight, potentially killing people aboard or on the ground, merely to have the opportunity to use his H-alpha filter. Cueball "responds" by holding whatever he's reading closer to his face, apparently hoping to avoid further conversation (or consequences). The title text references the insurance company MetLife, which until 2016 used the cartoon character Snoopy as an advertising mascot. In the Peanuts comics, Snoopy would frequently imagine himself as a fighter pilot in World War I in an aerial battle with the Red Baron , a battle he would frequently lose. The detail that Black Hat "dressed up as the Red Baron" might help explain another point: advertising blimps typically fly higher than the effective range of most fireworks. It would be entirely consistent with Black Hat's history to modify the stolen triplane mentioned in 496: Secretary: Part 3 to allow him to launch fireworks from the air, in mockery of an old-fashioned dogfight. This comic was published shortly before Independence Day 2021, a US holiday that is often commemorated with fireworks. This may explain why Black Hat and Cueball originally had some fireworks around. [In a slim panel Black Hat is seen holding a small black device up in his left hand.] Black Hat: I got an H-Alpha filter for looking at the sun. [In a broad frame-less panel Black Hat, holding the device down in his left hand while standing behind Cueball who is sitting in an armchair reading on his tablet.] Black Hat: It also works for nebulae. But that's about it. There just aren't that many hot blobs of hydrogen to look at, I guess. [Back to a slim panel, Black Hat is seen holding his left hand to his chin, while he holds the device down in his right hand.] Black Hat: ...Unless... [Another two slim panels follows. In the first Black Hat turns around and leaves, his head already partly outside the panel already, and he no longer holds the device in his hands. And then follows an empty beat panel.] [In a broad panel Black Hat re-enters with the device held down in his hand. He is walking towards Cueball in his armchair. His black hat is somewhat out of shape. Cueball is still reading but is now hunched further forward and he has lifted his tablet so it is very close to his face.] Black Hat: Huh, did you know blimps all use helium now? You learn something new every day! By the way, we're out of fireworks. Black Hat: And some advertising company is real mad.

Nightmare Code

Nightmare Code

https://www.xkcd.com/2485

https://www.explainxkcd.com/wiki/index.php/2485:_Nightmare_Code

[A Cueball-like person is giving a presentation while wearing futuristic gear, including a visor with an antenna rising from it, a backpack-like appliance of some kind, and a futuristic pointer. The audience is not pictured. The presenter is floating rather than standing. The presentation is projected from a small device near the bottom of the frame, and the appearance of the presentation suggests it is a hologram. The content of the slide shows the names of the first four letters of the Greek alphabet:] Alpha Beta Gamma Delta Presenter: We all know the Nightmare Code , used to assign neutral names to scary ongoing lists, such as hurricanes, virus variants, and nanobot swarms. Presenter: But did you know it actually originated as the letters of an ancient Earth language?

Although the pandemic is not directly mentioned, this comic is another in a series of comics related to the COVID-19 pandemic . A person using futuristic technology is giving a presentation or lecture. The content of his projected screen includes the names of the first four letters of the Greek alphabet , which he refers to as the Nightmare Code. The presenter expects that the list is familiar to his audience, but that it is novel information to them that it used to have a purpose other than providing arbitrary names to hurricanes, virus variants, and nanobot swarms. The presenter refers to Greek as a language from Earth: this implies that the audience is mostly extraterrestrial - on Earth, everything is Earth implicitly. This may be the reason that they're unaware of the Greek language: the nightmare code may have spread beyond Earth, but a rather small Earth language may not be common knowledge. Atlantic hurricanes and tropical storms are named once they have sustained wind speeds of 33 knots (61 km/h; 38 mph) or more. The names for these storms go from A-W each year (each letter has a name randomly chosen from a predefined list), with 21 names allocated each yearly period . When the 21 names are exhausted, Greek letters were once used to continue naming storms as needed, although the World Meteorological Organization decided not to use Greek letters when naming storms from 2021 onward. Perhaps in this vision of the future, the naming lists have given way to using the Greek alphabet exclusively. Virus variants may also be given names once they are deemed sufficiently nightmarish. At the time of this writing, eleven variants of SARS-CoV-2 have been labeled with Greek letters. Previously, variants were named informally for the region in which they were identified (as were many viruses themselves), but this practice has ceased due to risks of discrimination and the perverse incentive of countries to suppress health information for the sake of saving face. A place may become (in)famously known as the origin of a disease by such a name, even if it originated elsewhere; an example is Spanish flu , which was actually first observed in the US state of Kansas. Nowadays vague names such as 'bird flu' or partly-informed geographic names tend to be better referenced by their hemagglutinin and neuraminidase subtypes, such as "H1N1" and "H9N2". The more technical coronavirus identification system uses a term such as "lineage B.1.617.2", whose awkwardness makes it unlikely to replace better-known names such as the "Kent variant" or "Indian variant". Another set of historic nightmares the audience clearly knows about, which are still in our own future, are nanobot swarms, presumably nanoengineering failures and/or deliberate misuses of nanotechnology of the Gray goo type. Significant recurring or sequential events have seemingly earned the need to differentiate their outbreaks, and Greek letters have been used to do this. One may even be tempted to speculate that the futuristic figure and his presentation equipment float in space because the Earth has been rendered uninhabitable as a result of one or more of said nanotechnology disasters. The cultural forgetfulness about the neutral basis of the old letters, after perhaps who-knows-what nanobot disasters that may have scoured the Earth clean of all things Greek, has led to no other common use for them except for their use in identifying far too many crises. The words themselves thus are instantly associated to bad times for almost everyone. The title text indicates that future people stopped using the term "alphabet" (which derives from the first two letters of the Greek alphabet, alpha and beta ) due to the negative associations of the words caused by them being used to describe nightmarish occurrences. The "alphabet" is now called "charset", for "character sets". [A Cueball-like person is giving a presentation while wearing futuristic gear, including a visor with an antenna rising from it, a backpack-like appliance of some kind, and a futuristic pointer. The audience is not pictured. The presenter is floating rather than standing. The presentation is projected from a small device near the bottom of the frame, and the appearance of the presentation suggests it is a hologram. The content of the slide shows the names of the first four letters of the Greek alphabet:] Alpha Beta Gamma Delta Presenter: We all know the Nightmare Code , used to assign neutral names to scary ongoing lists, such as hurricanes, virus variants, and nanobot swarms. Presenter: But did you know it actually originated as the letters of an ancient Earth language?

Board Game Party Schedule

Board Game Party Schedule

https://www.xkcd.com/2486

https://www.explainxkcd.com/wiki/index.php/2486:_Board_Game_Party_Schedule

[Caption above:] Board Game Party Schedule [A timeline is shown, from about 6PM at the top to about 11PM at the bottom. Events are displayed as white rectangles, labeled as follows:] before 6PM: people filter in 6:00–6:25: small talk 6:25–6:55: debate which game to play 6:55: remember that you need to order food 6:55–7:15: debate where to order from 7:15: pick a place, order 7:15–7:40: pick a game and start setting up 7:40–8:20: explain rules to new people 8:20: food arrives 8:20–9:00: eat food 9:00–9:27: resume setting up 9:27–9:52: more explanation 9:52–10:13: restless faction tries to start simpler game 10:13–10:38: general debate 10:38–10:57: “It will make sense once you play” 10:57–11:10: finish setting up after 11:10 PM: people head home

This comic shows a timeline of a gathering to play some sort of fairly complex board game. These games often have many pages of rules, and a long setup time. Often the very complex rules must be explained in detail, which can be extremely dull in a group environment. Conversely, just beginning like at the time entry point "it will make sense once you play" without explanation often leads to new player frustration that, had they had a complete understanding, they would have made different choices and had a more reasonable chance at victory, or even worse, avoided constantly being informed of "illegal moves". In addition, since it's a party, there are other activities that take place in addition to playing the game, notably ordering and eating food. By the time you eat, prepare the game, and teach the new players, little time is left to actually play the game. This comic exaggerates this dynamic, for in the timeline, no one gets to play the game at all. Often during these gatherings the frustration with the factors above cause people to suggest settling on a simpler or more well known game. The title text observes some of the guests supposedly playing a fictional [ citation needed ] board game, Meta Board Game Party – a game about board game parties. Because the quoted rule states that arguing in the "breakaway faction" is worth more victory points, it would be optimal strategy for them to do just that, for as long as possible. This seems to be a sarcastic explanation as to why they tried to get the whole group to play some other game and turned the ensuing debate into 45 minutes of bickering. [Caption above:] Board Game Party Schedule [A timeline is shown, from about 6PM at the top to about 11PM at the bottom. Events are displayed as white rectangles, labeled as follows:] before 6PM: people filter in 6:00–6:25: small talk 6:25–6:55: debate which game to play 6:55: remember that you need to order food 6:55–7:15: debate where to order from 7:15: pick a place, order 7:15–7:40: pick a game and start setting up 7:40–8:20: explain rules to new people 8:20: food arrives 8:20–9:00: eat food 9:00–9:27: resume setting up 9:27–9:52: more explanation 9:52–10:13: restless faction tries to start simpler game 10:13–10:38: general debate 10:38–10:57: “It will make sense once you play” 10:57–11:10: finish setting up after 11:10 PM: people head home

Danger Mnemonic

Danger Mnemonic

https://www.xkcd.com/2487

https://www.explainxkcd.com/wiki/index.php/2487:_Danger_Mnemonic

[Miss Lenhart is holding a finger up in front of two children: a boy with spiky hair and Science Girl.] Miss Lenhart: Now, remember: Miss Lenhart: If red touches yellow amid leaves of three under a red sky at morning, Miss Lenhart: You should probably just get out of there.

The teacher Miss Lenhart warns two small kids using a danger mnemonic . However, this is actually a mash-up of three different common danger mnemonics, each of which warn about different hazards. This mnemonic is intended to help recognize a venomous coral snake , which has red, black, and yellow stripes, with the red and yellow stripes adjacent. Nonvenomous king snake species also have red, black, and yellow stripes, but the black stripes separate the red and yellow ones. Note that this identification is accurate only in eastern North America; coral snakes in other parts of the world sometimes have black stripes touching red stripes. The safest course of action is to avoid any snake with the warning colors of red, yellow/white, and black stripes. Another corruption of same warning features in 1604: Snakes . This mnemonic is used to identify poison ivy and poison oak throughout much of North America. These plants both produce an oily surface resin called urushiol, which causes an allergic reaction in the majority of people. Touching either plant can result in contact dermatitis, which can be severely itchy or painful. If burned, the urushiol can be inhaled, causing lung irritation. While rarely serious, these reactions are often severely unpleasant and can last for weeks, so avoiding the plants is well advised. Both plants generally grow three leaves at the end of each branch, and grow berries that turn white when ripe. The mnemonic helps in remembering this characteristic to distinguish them from similar-looking but harmless vines. See 443: Know Your Vines . This mnemonic predicts bad/good weather conditions based on a particularly red sunrise/sunset. It is predictive at middle latitudes where the prevailing winds go from west to east. Regions of higher air pressure will cause a particularly red sky at sunrise/sunset, so a red sky in the evening indicates a high pressure system is coming in from the west with its calmer weather, while a red sky in the morning indicates a low pressure front coming in (usually with rain and rougher weather). In some countries (such as the United Kingdom), the saying mentions shepherds rather than sailors. Randall actually wrote a newspaper article explaining this phenomenon. Combining all three sayings sounds particularly ominous. It implies that a person is involved with a situation simultaneously involving coral snakes, poison ivy, and potentially nasty weather. In such a case, Miss Lenhart advises the children to "just get out of there", implying that the situation is too dangerous to try to deal with. The title text refers to another mnemonic: 'Beer before liquor, never been sicker; liquor before beer, you're in the clear.' Unlike the first three mnemonics, which are genuinely useful for avoiding danger, this one is largely a myth , as the order in which you drink alcohol is unlikely to impact how sick you become. However, whether the mnemonic is true or not, testing it would involve multiple drinks of alcohol, which would be ill-advised when facing a dangerous situation, particularly one as bizarre and complex as implied in this strip. See also 2422: Vaccine Ordering for the previous time xkcd referenced the latter mnemonic. See also 2038: Hazard Symbol for another combination of danger warnings. [Miss Lenhart is holding a finger up in front of two children: a boy with spiky hair and Science Girl.] Miss Lenhart: Now, remember: Miss Lenhart: If red touches yellow amid leaves of three under a red sky at morning, Miss Lenhart: You should probably just get out of there.

Board Game Argument Legacy

Board Game Argument: Legacy

https://www.xkcd.com/2488

https://www.explainxkcd.com/wiki/index.php/2488:_Board_Game_Argument:_Legacy

[White Hat, Megan, Ponytail, and Cueball are sitting around a table that is covered with board game boxes. White Hat is pointing at Ponytail. Both Ponytail and Cueball are holding boxes.] Ponytail: You may reallocate up to five tokens to your top choice from last week. Remember, the game with the least support tonight will go to the thrift store. Ponytail: Next, we'll resume the debate over ordering expansion packs. [Caption beneath the panel:] We got tired of having the same repetitive arguments every week over which game to play, so we developed Board Game Argument: Legacy .

This comic continues the joke from comic 2486: Board Game Party Schedule , released the previous week, about the difficulty some gaming groups have actually playing any game at all once they get together. In this scenario the group have leveraged the difficulty of choosing a game into a game itself. It seems to be that each player has a certain number of votes, or tokens, that they can use to decide which game to play, with the added element that they permanently dispose of the losing game. This can lead to strategic play where a player might vote for a game, even if they don't want to play it that night, so that they could still play it at some future resolution of the choosing. Once the voting is finished, the next phase of the game is to debate which expansion packs they should collectively buy for which game. A legacy board game is one where players change the game itself in the course of play, such as by writing on certain cards and ripping up others, causing future sessions to be modified. A legacy game thus avoids the tendency of some games to become repetitive if they are played every week, which is a common tradition among friends or families. The meta-game this comic describes fits this definition, because the available pool of games (and expansion packs) changes based on the players' decisions. Randall refers to the “game” of choosing what to play having become repetitive. Although official legacy games are sold by the manufacturers of the original game, some players may create their own legacy versions of a game. The title text refers to how many board and card game owners are bothered by legacy games because they destroy game pieces. A legacy game, of course, is meant to be permanently altered, but many players find it hard to perform destructive actions like cutting or tearing up cards. At an extreme, some owners wish to keep their games in as-new condition, going as far as refusing to shuffle cards in ways that bend them, or not punching tokens out of their cardboard frames. Even some games not classed as "legacy" games may have elements such as blank cards to be filled in by the players. For those who are reluctant to make changes, these items may remain blank forever. An additional layer of humour comes from the fact that it sounds like the speaker is chastising a game owner who does not want to engage with ordinary elements of the game, but instead urges them to pour soda on the game (something that would usually be an unfortunate accident). "2d6" is standard notation for games that involve rolling several different types of dice, where the first number refers to the number of dice to be rolled (in this case 2), and the second number referring to the style of dice (in this case 6-sided). That means that the player could end up pouring between 2 and 12 ounces of soda (inclusive) into their game box, depending on the total value rolled on the two 6-sided dice and assuming the dice roll directly translates to ounces. The board game boxes visible in this comic are real board games (from left to right): [White Hat, Megan, Ponytail, and Cueball are sitting around a table that is covered with board game boxes. White Hat is pointing at Ponytail. Both Ponytail and Cueball are holding boxes.] Ponytail: You may reallocate up to five tokens to your top choice from last week. Remember, the game with the least support tonight will go to the thrift store. Ponytail: Next, we'll resume the debate over ordering expansion packs. [Caption beneath the panel:] We got tired of having the same repetitive arguments every week over which game to play, so we developed Board Game Argument: Legacy .

Bad Map Projection The Greenland Special

Bad Map Projection: The Greenland Special

https://www.xkcd.com/2489

https://www.explainxkcd.com/wiki/index.php/2489:_Bad_Map_Projection:_The_Greenland_Special

Bad Map Projection #299: The Greenland Special Equal-area map preserves size everywhere except Greenland, which uses the Mercator projection. [A drawn world map, perhaps the Tobler hyperelliptical projection, except for Greenland which is of a typical Mercator appearance and sized at almost the size of Africa, to almost entirely fill the space between Canada and Iceland. It extends up well beyond the nominal location of the North Pole, while its southern tip has an apparent latitude comparable to that of Spain or the vicinity of Virginia.]

This is the fourth comic in the series of Bad Map Projections displaying Bad Map Projection #299: The Greenland Special. It came one and a half year after the third 2256: Bad Map Projection: South America (#358), and was followed about 10 months later by 2613: Bad Map Projection: Madagascator (#248). Map projections are different methods of representing the curved surface of the Earth on a two-dimensional map. There's no perfect way to do so. Because the Earth is not flat, any 2D map projection of it will always distort in a way the spherical reality, and a map projection that is useful for one aspect (like navigation, geographical shapes and masses visualization, etc.) will not be so for all the others. Typically a projection can represent only distances, areas or angles correctly, or at best imperfectly compromise two of these. The map choice should reflect the purpose you need to put it to, as it will necessarily distort (perhaps by twisting, skewing and/or resizing) those aspects it was not designed to show intact. One such projection is the Mercator projection , which is designed so that all north-south lines of longitude are parallel to each other and all rhumb lines are consistent, which is most important in the time of map-based navigation. In reality, apart from the direct east-west directions, all the imaginary straight lines eventually meet at the poles - even if they look parallel. The apparent distance between lines of latitude at the more extreme latitudes expands and the vicinity around each pole can never be drawn, as Mercator maps show geographic features plotted over ever larger map areas and distances than they should, for those nearer the poles, compared to those more equatorial. It is not possible to accurately compare the sizes of features across the globe using this projection, although the distortions can be effectively ignored for more local maps that do not plot a significant area of the globe (other than very close to the poles, historically not an issue) and along or between any given narrow strips of latitude away from the equator the comparison is between near equal scalings. Greenland is a large [ citation needed ] island in the Arctic ocean and one of the nearest pieces of land to the north pole. The Mercator projection shows it to be significantly larger than it really is, compared to equator-straddling features such as Africa. It is therefore one of the most obvious inaccuracies of Mercator's map, if used (e.g.) in the classroom to teach physical geography (which perhaps would best use a representation that was consistent to area) rather than navigation. The equal-area projections such as Mollweide or Tobler Hyperelliptical , the latter of which seems to extremely closely match the majority of the features evident upon the hand-drawn map, ensure that shapes contain the same relative proportion of area as they would upon the original spherical (or slightly spheroidal ) surface, across all latitudes, but only by bending the directions and rescaling the distances ever more drastically the closer to the map edge (the anti-meridian to that the map is centred upon) you go. Unlike the Mercator projection, you can show the poles (as the extreme upper and lower limits of the rim) from an equatorially-centred view, and every point of the Earth is given one definite position (or two, where they lie exactly upon the crossing point between the left/right extremes of the map). This comic's projection has retained this singular inaccuracy as a deliberate feature, though avoiding all other such inaccuracies of the Mercator projection by using a different projection elsewhere that is designed explicitly to avoid them. For example, a traditional Mercator map would show other polar areas such as Antarctica, southern South America, or even New Zealand as larger, but this map does not. Although it may not be obvious, due to no land-masses being normally shown at/close-enough to the North Pole, the Mercatorish Greenland actually extends beyond the Elliptic map's northern limits into positions that do not even exist in reality - it does not even 'wrap around and over' the pole (like a bad toupée) but passes through it and the arbitrary back-edge meridian line and into purely imaginary space that does not exist upon the surface of the Earthly sphere. (For a flipped comparison, the lower 'curve' of Antarctica is not its coast, but merely the map's 'wrap-around' edge where a further step would have you stepping back onto the continent at a second point of this nominal edge. The true coast of Antarctica is only the rough upper edge, passing between the two points which each represent the one arbitrary 'wrap-around' coordinate that is opposite-but-adjacent on the map's oval edging, i.e. at ±180°E/W, but which otherwise has no particularly special quality 'on the ground'.) The title text suggests that this map was created for people who believe Greenland should be larger. Whether these people believe it should be physically increased in size in some manner or should simply receive a greater share of the attention is unclear. One method for increasing its size would be to increase the coverage of its ice cap, which is currently decreasing in size due to increases in temperature. However, increasing Greenland's ice coverage to the size it appears on a Mercator map would involve covering the entire island and surrounding ocean with ice, which would be very problematic for Greenland's population [ citation needed ] . Bad Map Projection #299: The Greenland Special Equal-area map preserves size everywhere except Greenland, which uses the Mercator projection. [A drawn world map, perhaps the Tobler hyperelliptical projection, except for Greenland which is of a typical Mercator appearance and sized at almost the size of Africa, to almost entirely fill the space between Canada and Iceland. It extends up well beyond the nominal location of the North Pole, while its southern tip has an apparent latitude comparable to that of Spain or the vicinity of Virginia.]

Pre-Pandemic Ketchup

Pre-Pandemic Ketchup

https://www.xkcd.com/2490

https://www.explainxkcd.com/wiki/index.php/2490:_Pre-Pandemic_Ketchup

[Cueball is standing in a kitchen, looking at bottle with label which he is holding in his hand. He is talking to a person off-panel behind him, who replies. There is a cupboard above him, with stuff protruding from the shelves. Below that is a counter, with a drawer and a cupboard. There is an bottle with fluid, a can and a jar on top. Only the latter two has labels.] Cueball: Oh wow, pre-pandemic ketchup! Cueball: We haven't bought this kind since before. Cueball: I'm gonna toss it. (off-screen): Eww, yes. [Caption below the panel:] Spring 2020 forms a weird dividing line in my kitchen.

This comic is another in a series of comics related to the COVID-19 pandemic . Just like 2474: First Time Since Early 2020 , Randall compares the pre-pandemic life and the post-pandemic life in this comic. Life has changed dramatically due to the COVID-19 pandemic and the subsequent lockdowns and restrictions by governments around the world. In this comic, Cueball bought a bottle of ketchup before the pandemic and they have not bought that kind of ketchup since, possibly due to supply chain disruptions or that brand not being available to order online. It may be a reference to the shortage of ketchup packets caused by an increase in takeout orders and restaurants replacing the ketchup bottle on the table with single serving units [ dubious ] . Cueball is now cleaning out his cupboard, perhaps as a form of "pandemic spring cleaning" to make way for the future, and considers throwing it away. An offscreen character encourages him to toss it. In the title text, Cueball (or possibly Randall ) is wondering in which year he would discard the last weird food item that he bought online in early 2020. If he's going for the Expiration Date High Score to beat 24.3, he should probably wait until 2045 or so. [Cueball is standing in a kitchen, looking at bottle with label which he is holding in his hand. He is talking to a person off-panel behind him, who replies. There is a cupboard above him, with stuff protruding from the shelves. Below that is a counter, with a drawer and a cupboard. There is an bottle with fluid, a can and a jar on top. Only the latter two has labels.] Cueball: Oh wow, pre-pandemic ketchup! Cueball: We haven't bought this kind since before. Cueball: I'm gonna toss it. (off-screen): Eww, yes. [Caption below the panel:] Spring 2020 forms a weird dividing line in my kitchen.

Immune Factory

Immune Factory

https://www.xkcd.com/2491

https://www.explainxkcd.com/wiki/index.php/2491:_Immune_Factory

[Cueball walks in from the left, hand held up in front of him, to where Hairy is sitting in an armchair facing away, sick from a second vaccination. Hairy is wrapped in a blanket and holding a steaming mug, and his hair is messy.] Cueball: I guess the first shot made your body build defenses, and now it's ramping up production. Hairy: So I've become an antibody factory. [Cueball has walked around the chair and is now facing Hairy, whose mug continues to steam just as much.] Hairy: I don't feel great. I think my factory has some OSHA violations. Hairy: My lymphatic system is protesting brutal working conditions. [In a frame-less panel, Cueball continues to stand in front of Hairy, whose mug is steaming less.] Hairy: Update: my immune cells have unionized. Cueball: Common side effect. Helps maintain a healthy balance. [Cueball has raised a finger into the air, while Hairy is pointing in Cueball's direction. Hairy's mug is no longer steaming.] Cueball: Immune system unions are actually why we stopped doing variolation. Hairy: Oh? Why? Cueball: They don't like scabs. Hairy: Ugh. Leave.

This comic is another entry in a series of comics related to the COVID-19 pandemic , specifically regarding the COVID-19 vaccine . When Hairy received his first dose of a COVID-19 vaccine, his body began building a defense in the form of antibodies. He has now received his second shot, and is feeling even more unwell than the first time, since his body has ramped up the production of antibodies, as Cueball states. Hairy and Cueball then begins to make comments that metaphorically compare Hairy's immune system to a factory, hence the title Immune Factory. Vaccines in general work by giving the body's immune system a chance to respond to a pathogen without actually being infected. The immune system responds by producing antibodies, proteins customised to attach to the pathogen, either disabling it directly or marking it for attack by immune cells. After the vaccine (or after an actual illness), the immune system remembers how to make the antibodies and can more quickly respond to future infections. This is why Hairy describes his body as an "antibody factory". However, many common symptoms of illness (such as fever, soreness, diarrhea and nausea) are actually caused by the body's immune response rather than the infection itself. As a result, vaccines can result in similar symptoms to an illness, albeit milder and of shorter duration. Hairy extends the "body as factory" metaphor by complaining that, since he feels unwell, the factory must be violating OSHA regulations—that is, rules that protect workers from unsafe work conditions. Hairy says his lymphatic system (a major component of the immune system) is protesting the "brutal" work of responding to the vaccine, as human workers might protest a dangerous workplace. In real workplaces, one possible response to worker dissatisfaction is for them to unionize , forming an organization that can use their solidarity to bargain for improvements to working conditions. Hairy says that this is what his immune cells have done. It is not clear whether this corresponds to any actual part of the immune response, or whether it is simply a humorous expansion on the "factory" metaphor. Cueball uses the "union" statement to set up a pun on two meanings of the word "scab". If unions make demands that an employer refuses, their workers may strike , or refuse to work. Employers may keep the workplace running by hiring strikebreakers , non-union workers (or union workers who break ranks with their colleagues). Union members may refer to strikebreakers by the pejorative term "scabs". Another meaning of "scab" is the hard coating the body produces to cover a bleeding or seeping wound while it heals. Smallpox is a dangerous illness that causes ulcers upon the skin, leading to many small scabs forming as those ulcers heal. Prior to modern vaccination techniques, people were sometimes deliberately infected with smallpox—typically from a person with a mild case—while they were healthy. This process, now called variolation (after Variola , the virus that causes smallpox), could be done in various ways. Some methods used pus or fluid from smallpox ulcers, but others used scabs from the ulcers, dried and powdered. This powder might be rubbed into a cut in the skin, or insufflated (blown up the person's nose). The pun therefore is that members of the immune system union would not like either kind of scab. Hairy finds the pun appalling, and tells Cueball to leave . The title-text parodies the trend for recent incarnations of unions to rebrand or form anew with a descriptively apt name (possibly with a forced acronym, or styled as one for branding purposes), rather than the (Extended/ Very Extended /etc) Three Letter Acronyms of times past. In this case making a portmanteau of "immune union" - Immunion. The cleverness of this name apparently convinced some of Hairy's immune cells that were previously opposed to the union to change their minds. [Cueball walks in from the left, hand held up in front of him, to where Hairy is sitting in an armchair facing away, sick from a second vaccination. Hairy is wrapped in a blanket and holding a steaming mug, and his hair is messy.] Cueball: I guess the first shot made your body build defenses, and now it's ramping up production. Hairy: So I've become an antibody factory. [Cueball has walked around the chair and is now facing Hairy, whose mug continues to steam just as much.] Hairy: I don't feel great. I think my factory has some OSHA violations. Hairy: My lymphatic system is protesting brutal working conditions. [In a frame-less panel, Cueball continues to stand in front of Hairy, whose mug is steaming less.] Hairy: Update: my immune cells have unionized. Cueball: Common side effect. Helps maintain a healthy balance. [Cueball has raised a finger into the air, while Hairy is pointing in Cueball's direction. Hairy's mug is no longer steaming.] Cueball: Immune system unions are actually why we stopped doing variolation. Hairy: Oh? Why? Cueball: They don't like scabs. Hairy: Ugh. Leave.

Commonly Mispronounced Equations

Commonly Mispronounced Equations

https://www.xkcd.com/2492

https://www.explainxkcd.com/wiki/index.php/2492:_Commonly_Mispronounced_Equations

[Each equation is bordered, with a pronunciation guide beneath.] Commonly Mispronounced Equations Row 1 F = G m₁m₂/r² FUH- JAM -ER E = mc² EM -CAH-TOO a² + b² = c² AT- BOOT -COOT Row 2 A = πr² APP -ER-TOO H = −Σpᵢlog pᵢ HA- SPLOG -PEE PV = nrt PAV -NURT Row 3 e iπ = −1 EYE -PIN F = ma FEE -MAH ∂²u/(∂t²) = c ∂²u/(∂x²) DOOT CAH- DOOX Row 4 f'(x) = lim h→0 f(x+h) − f(x) / h FAX -LIM-OH FAX -UH-FOX x = −b ± √(b² − 4ac) / (2a) ZA- BO -BA FAK- TOH -AH

This comic is a collection of very commonly used physics and mathematical equations, along with their "correct" pronunciations. Equations are normally voiced out loud either by their names ("mass-energy equivalence") or by saying the parts out loud using normal linguistic rules ("E equals m c squared"). This comic instead asserts that equations are meant to be said out loud like words, using their own set of phonic rules. Though the premise may initially seem absurd, some nerds have both the trait of using equations as commonly as others might chat and that of finding it entertaining to coin amusing new words ("input", "pwn"). Saying the equations more rapidly can speed up work or make work seem more enjoyable. This phenomenon is called clipping . Using clipped or verbalized forms of equations is sometimes standard practice within a given field. The equation for continuously compounding interest A=Pe rt is commonly taught and discussed as the "pert" equation, while the definitions of the main trigonometric functions is similarly taught and discussed as SOH-CAH-TOA: sine = opposite/hypotenuse, cosine = adjacent/hypotenuse, and tangent = opposite/adjacent. These particular "corrections" are all nonstandard, however, occasionally conflicting with more normal readings like "pivnert" for the ideal gas law. The "corrections" are also internally inconsistent, with equal signs and exponents sometimes omitted and sometimes included and intermediate vowels. [Each equation is bordered, with a pronunciation guide beneath.] Commonly Mispronounced Equations Row 1 F = G m₁m₂/r² FUH- JAM -ER E = mc² EM -CAH-TOO a² + b² = c² AT- BOOT -COOT Row 2 A = πr² APP -ER-TOO H = −Σpᵢlog pᵢ HA- SPLOG -PEE PV = nrt PAV -NURT Row 3 e iπ = −1 EYE -PIN F = ma FEE -MAH ∂²u/(∂t²) = c ∂²u/(∂x²) DOOT CAH- DOOX Row 4 f'(x) = lim h→0 f(x+h) − f(x) / h FAX -LIM-OH FAX -UH-FOX x = −b ± √(b² − 4ac) / (2a) ZA- BO -BA FAK- TOH -AH

Dual USB-C

Dual USB-C

https://www.xkcd.com/2493

https://www.explainxkcd.com/wiki/index.php/2493:_Dual_USB-C

[A power cord like plug with two prongs is shown, but each prong is in the shape of USB-C connectors. Above is a title and below is a label.] Cursed Connectors #187 Dual USB-C

This comic was the first in what became a new series of Cursed Connectors and presents Cursed Connector #187: Dual USB-C. The series continued two comics later with 2495: Universal Seat Belt (#65) and was followed three weeks after that by 2503: Memo Spike Connector (#102). Starting roughly around 2016, the word "cursed" has become slang for something that makes the user feel uncomfortable (unlike the classic definition, nothing supernatural needs to cause the discomfort). USB-C connectors are the newest version of the USB standard , and Randall showcases a new type of connector which would see two USB-C plugs side-by-side able to be inserted simultaneously by housing them inside a NEMA 1-15P plug, more commonly known as a Type A plug, that is usually used in some countries to connect electrical devices to AC current. This does not seem to offer any advantages over the current implementation. Further, the plug introduces several disadvantages, including, but not limited to The connector therefore is considered cursed. Notably, there's an existing dual USB-C plug in use for Macbook-compatible high-performance dongles, among other things, which is remarkably similar but avoids all the above disadvantages. It instead invites confusion with the NEMA 6-15 connectors. The title text indicates that an equivalent for the 3-pronged NEMA 5-15P plug (a.k.a the Type B plug) for AC current could be created easily by incorporating a USB-B plug, which are small and square-shaped and could therefore function as the ground prong. There appears to be no reason to do this other than because both names contain the letter 'B'. Unconventional uses for electric plugs are a recurring topic in xkcd (see 1293: Job Interview and 1395: Power Cord ). Combining them with USB was previously explored in 1406: Universal Converter Box among other combinations. [A power cord like plug with two prongs is shown, but each prong is in the shape of USB-C connectors. Above is a title and below is a label.] Cursed Connectors #187 Dual USB-C

Flawed Data

Flawed Data

https://www.xkcd.com/2494

https://www.explainxkcd.com/wiki/index.php/2494:_Flawed_Data

[Cueball is pointing a stick at a poster hanging behind him while addressing an unseen audience. There are two graphs on the poster with data points and fitting curves.] Cueball: We realized all our data is flawed. [The three next panels all have a label in a frame going over the top of each panels frame. The poster can no longer be seen in the rest of the panels. Cueball has taken the stick down.] Label: Good Cueball: ...So we're not sure about our conclusions. [Cueball holds the pointer almost as in the first panel.] Label: Bad Cueball: ...So we did lots of math and then decided our data is actually fine. [Cueball holds the pointer so it point upwards. Also he lifts his other hand a bit up.] Label: Very bad Cueball: ...So we trained an AI to generate better data.

This is another comic about what is the right or wrong way to perform research when data is not adequate. In the first frame, Cueball presents a report on a poster (two graphs with data points and possible fitted curves), admitting that all of the data is actually flawed. He doesn't explain if it's contrary to some outcome or revelation, or perhaps a systematic error in the data-gathering process. From there, three different reactions to this is displayed in order of how good a decision they make based on this realization. Good In the first scenario Cueball states they are no longer sure about the conclusions they had drawn from the flawed data. This is, of course, the scientifically appropriate decision. The less reliable data is, the less reliable the conclusions that can be drawn. Ideally, flawed data would be discarded altogether, but there are situations in which better data is not available, so a compromise may be to draw tentative conclusions, but make clear that those are uncertain, due to issues with the data. Bad In the second scenario Cueball then explains that after heavy manipulation ("doing a lot of math") of their flawed data, they decided they were actually fine. There are a number of methods that can be used to manipulate or "clean" data, with varying levels of complexity and reliability. Some of these methods may be valid in certain situations, but applying them after the initial analysis failed is highly suspect. The likelihood, in such a case, is that the researchers tried different methods of data manipulation, one after another, until they found one that gave the results they wanted. This is clearly highly subject to the biases of the researchers (both conscious and unconscious) and is much less likely to result in accurate conclusions. Hence, this approach occurs in research more often than it should, and Randall is making clear that it's "bad". Very bad In the third and final scenario, Cueball explains that they scrapped all the flawed data. However, instead of trying to make some new data by correctly redoing research/measurements/tests, they instead trained an Artificial Intelligence (AI) to generate better data from nothing but a desire to match a target outcome. This is of course not real data, but just a simulation of data, selectively sieving statistical noise for desirable qualities. And since they are probably looking for a specific result, they are training the AI to generate data that supports this. This approach is "very bad", as it not only produces no useful science, but means that future researchers will be working from entirely artificial data. Doing so would be destructive to science and would be considered incredibly unethical in any research body or association. The only purpose of such a method would be to convince others that you'd proven something interesting, rather than determining what's true (and possibly gain some experience in AI programming). AI is a recurring theme on xkcd. In the title text, the results from the very bad approach are mentioned and the fact that they got the data they were looking for is made clear when they state that We trained it to produce data that looked convincing, and we have to admit, the results look convincing! The AI was of course trained to provide data that looks convincing, which is why they are so convinced of the results. [Cueball is pointing a stick at a poster hanging behind him while addressing an unseen audience. There are two graphs on the poster with data points and fitting curves.] Cueball: We realized all our data is flawed. [The three next panels all have a label in a frame going over the top of each panels frame. The poster can no longer be seen in the rest of the panels. Cueball has taken the stick down.] Label: Good Cueball: ...So we're not sure about our conclusions. [Cueball holds the pointer almost as in the first panel.] Label: Bad Cueball: ...So we did lots of math and then decided our data is actually fine. [Cueball holds the pointer so it point upwards. Also he lifts his other hand a bit up.] Label: Very bad Cueball: ...So we trained an AI to generate better data.

Universal Seat Belt

Universal Seat Belt

https://www.xkcd.com/2495

https://www.explainxkcd.com/wiki/index.php/2495:_Universal_Seat_Belt

[The two ends of a seatbelt are shown next to each other, but the seatbelt connectors are replaced with a USB-A plug and port. Above is a title and below is a label.] Cursed Connectors #65 the Universal Seat Belt

This became the second installment in the series of Cursed Connectors and presents Cursed Connectors #65: The Universal Seat Belt. The series began two comics earlier with 2493: Dual USB-C (#187) and was followed three weeks later by 2503: Memo Spike Connector (#102). The comic shows another of Randall's "Cursed Connectors", the "Universal Seat Belt " — a pun on the Universal Serial Bus ( USB ) connector — which would have the same abbreviation of USB. USB connectors are mostly designed for free and unrestricted insertion and removal. There may be a slight use of the internal and external bumps and dimples to provide a tactile indication of being engaged or disengaged, but there are usually no facilities to prevent a connector being easily pulled out of even a port being actively used - the OS can do no more than complain that a device has been removed without first ensuring proper logical unmapping of the resource (which in turn may have to await a current session of data transfer being completed or aborted) or warn that a "delayed write" has failed. Anyone who has used USB in a frequently-jostled environment knows the connectors can't withstand much jerking around without their connection to their mainboard permanently failing. Car seat-buckles, on the other hand, have very definite requirements to not come loose unless intentionally and mechanically released, in order to keep the passenger safely anchored to the seat. The title text claims that the seat belt is secure in the case of a crash. This is another pun, as seat belts protect passengers in a car crash while USB standard is designed to protect the computer in the event of a device hardware malfunction. Another similarity between seat-belts (especially on back seats) and USB-plugs is that they can be a bit fiddly to insert. A seat-belt lock with the asymmetric design of a USB-A plug would be even more fiddly and thus "cursed". One possible use for the USB data connector might be to give a certain degree of 'proof' that the belt is plugged in, although that functionality is fairly well covered by current anchor-point sensors that (combined with seat-occupancy sensors that may respond to the weight of a seated person) can trigger dashboard lights and possibly warning sounds in vehicles as necessary to prompt correct usage of restraining belts. That system does not usually need an electronic data connection between anchor and belt, an anchor-side switch should suffice, and it would still require a mechanical gripping/hooking method to make it of any use to be engaged in the first place. The USB specification is designed such that USB connectors fit snugly from pressure. This means they usually need no button, like seatbelts have, to lock them in place. If one hacks a USB connection to increase the tightness, so that it can withstand more force applied to it and still hold its function, it becomes much harder, or even impossible, to insert and remove. Randall has removed the button, such that the connectors are a "cursed" misleading and dangerous use of similar form. [The two ends of a seatbelt are shown next to each other, but the seatbelt connectors are replaced with a USB-A plug and port. Above is a title and below is a label.] Cursed Connectors #65 the Universal Seat Belt

Mine Captcha

Mine Captcha

https://www.xkcd.com/2496

https://www.explainxkcd.com/wiki/index.php/2496:_Mine_Captcha

[A Minesweeper game in a 4x4 grid is shown beneath a blue rectangle. There is an explanation in white text in the blue field:] To proceed, click all the pictures of Mines [The Minesweeper field has six cells with revealed numbers on a light gray background. The other 10 fields are empty and dark gray. The three ones are blue, the single two are green and the two threes are red. On top of this each number is drawn in a different font/style. The ones changes how bold they are. The two is drawn in a 3D format, the one three is very thin and the other is drawn with two lines and no filling in between (hollow). The grid looks like this:]

This comic, like 1897: Self Driving , references the approach of using human-entered CAPTCHA inputs to solve machine learning problems, particularly those involving image classification. In order to prevent automated programs from using web services, Google offers a protection called reCAPTCHA , which performs various tests to see if a user is human or machine. (One of these tests is a "I'm not a robot" checkbox which must be checked in order to proceed, although ticking the box is merely a formality, and later versions of reCAPTCHA can simply perform the tests quietly in the background without needing user consent). If the reCAPTCHA system suspects that the user may be an automated bot, it presents an image recognition challenge that only humans should be able to pass. This has the desired effect of denying access to robots, but it also has a side benefit that the human input can be used to train Google's image recognition software. The challenge usually features a square grid of images, typically things one might see while driving - eg. "check all squares containing a STOP SIGN". If the user clicks the correct squares, they are permitted to continue. Minesweeper , on the other hand, is a logic puzzle game in which the player is presented with a grid of unrevealed squares, and must deduce the location of mines that have been secretly hidden on random squares. The game provides clues by marking some squares with the number of mines (up to a maximum of 8) that are adjacent to that square; by carefully considering the possibilities, a player can deduce which squares must contain mines, and mark them with flags to avoid clicking on them. Revealing a mine loses the game. In this comic, Randall combines the two concepts to create a "Mine Captcha", which is presented in the form of a reCAPTCHA challenge but actually appears to be a mini game of Minesweeper. (To be more precise, it is actually the opposite of regular Minesweeper, since the challenge invites the user to click on the mines - in Minesweeper, you are supposed to not click the mines. Furthermore, on its own terms it is unsolveable as a reCAPTCHA, since the user is asked to click on all pictures of mines. However, as in the real Minesweeper, there are no pictures of mines displayed (in Minesweeper, these only appear when the game is over). Taking the game as playable, however, in both cases you still need to know where the mines are, so it is still solved the same way). A real-world Mine Captcha would be somewhat ineffective for a variety of reasons. Firstly, not every human would recognize a game of Minesweeper and therefore wouldn't understand what they are being asked to do. Even if they do recognize the game, they may not know the logical method for deducing the locations of mines. Additionally, even for skilled players, there is a trap in that the Captcha's objective is the reverse of regular Minesweeper; they might therefore get tripped up by muscle memory and click on something that is not a mine, which would fail the challenge. Another issue is that games of Minesweeper can sometimes involve a degree of luck, as it is possible to generate a puzzle which does not give sufficient information to unambiguously deduce the location of every mine (Though this may not be a problem since Randall's Minesweeper is only a 4x4 grid). In these situations, the most a player can do is click the uncertain square and hope for the best. If the Mine Captcha is poorly implemented in this way, this would increase false negatives in human detection due to some humans failing the captcha purely due to bad luck. (Some variants attempt to eliminate this problem: Mine Detector , for example, is a variant game which provides better information, such that it's almost always solvable without guessing except at the highest difficulty level). Finally, a Mine Captcha would actually be fairly easy for an artificial intelligence (AI) to solve, since it is a logic puzzle - as long as the AI can read the numbers, it can simply use an algorithm to eliminate all impossibilities until it has the correct answer. (Indeed, for a 4x4 grid, it's even easier than that; a computer could quickly brute-force the problem by trying every possible arrangement of mines until it has the correct one). It seems that Randall predicted that an AI might try to solve the captcha itself, as he rendered each numeral in a different style; this is similar to obfuscation methods used in text-based captchas to prevent automatic text recognition software from reading the captcha. However, it would not be very effective in this case as the same numbers have the same color; an AI could simply recognize the color instead, which is even easier for an AI than trying to read a number. The title text is similar to 1897: Self Driving where the CAPTCHA solver is asked to answer quickly, implying that the training data is actually a real-world situation being experienced by a self-driving vehicle at that very moment. The joke here is that real-life minefields do not have large numbers indicating which of the surrounding land contains mines [ citation needed ] . Assuming that columns are denoted by letters A, B, C, D, left to right, and rows are denoted by 1, 2, 3, 4, top to bottom, one way to solve the captcha is as follows: The leftmost red 3 at A3 is surrounded by four squares (A2, B2, B3, A4), of which we know three are mines. Therefore, one of these squares is not a mine. However, because of the blue 1 at B4, we know that only one of B3 and A4 can be a mine, otherwise, there would be more than one mine adjacent to B4; therefore, A2 and B2 must be mines. Otherwise, there could only be two total mines adjacent to A3. Since A1 is a green 2 and is adjacent to two squares that we now know are mines (A2 and B2), this means that B1 is not a mine. If it was, there would be 3 adjacent mines to A1. Furthermore, since there is a blue 1 at C1, and we know that the adjacent B2 is a mine, this means that D1 and D2 are also not mines, since if any of them were, there would be more than one mine adjacent to C1. We also know that C3 and C4 are not mines, since we already know that the blue 1 at B4 is next to exactly one mine (on either B3 or A4). Since this eliminates two of the three possible neighbors of the blue 1 at D4, this means that D3 must be a mine. Finally, since we now know the locations of two of the mines around the red 3 at C2, and we have eliminated all other possibilities, B3 must be a mine. Therefore, the mines are at A2 , B2 , B3 , and D3 . This solves the puzzle. [A Minesweeper game in a 4x4 grid is shown beneath a blue rectangle. There is an explanation in white text in the blue field:] To proceed, click all the pictures of Mines [The Minesweeper field has six cells with revealed numbers on a light gray background. The other 10 fields are empty and dark gray. The three ones are blue, the single two are green and the two threes are red. On top of this each number is drawn in a different font/style. The ones changes how bold they are. The two is drawn in a 3D format, the one three is very thin and the other is drawn with two lines and no filling in between (hollow). The grid looks like this:]

Logic Gates

Logic Gates

https://www.xkcd.com/2497

https://www.explainxkcd.com/wiki/index.php/2497:_Logic_Gates

[The comic shows a chart with twelve electronic logic gates arranged in three rows of four. Each gate is depicted as a schematic symbol, with a label underneath. Above them is a header:] Common logic gate symbols [Here below follows a description of the 12 gates in the three rows, with their label given beneath each description:] [A standard gate symbol used in real life. Two inputs on the left lead to the vertical left edge of a solid D-shaped symbol. From the right side of the D there is one output.] AND gate [A standard gate symbol used in real life. Two inputs on the left lead to a convex-crescent left edge of a crescent-shaped symbol. The right side of the crescent symbol's shape forms a point at its output. From the right side of the crescent there is one output.] OR gate [A standard gate symbol used in real life. One input leads to a triangular symbol pointing to the right. There is a small bubble symbol connected to the triangle on the output, which leads right.] NOT gate [A standard gate symbol used in real life. This is identical to the OR GATE, except the output has a bubble attached, like the NOT GATE's output.) NOR gate [A standard gate symbol used in real life. This is identical to the OR GATE, except the left-hand arc at the input has a double-stroked line.] XOR gate [A standard gate symbol used in real life. This is identical to the AND GATE, except the output has a bubble attached, like the NOT GATE's output.] NAND gate [An unusual symbol. This symbol has one input on the left leading to a convex-crescent left edge, like the OR GATE. The output side as a smooth crescent like the AND GATE but has two outputs.] NORX gate [An unusual symbol. This symbol has two inputs on the left leading to a vertical left edge input, like the AND GATE. The output side has a convex-crescent double-stroked output like the mirror image of the XOR GATE's input. There are two outputs.] GAND ate [An unusual symbol. This resembles the NOT GATE except there are two inputs instead of one leading into the left side.] XAND gort [An unusual symbol. This has a double-stroked convex-crescent input like the XOR GATE, but the two inputs have bubbles attached. The single output has a smooth crescent shape with a bubble, like a NAND GATE.] NORG xort [An unusual symbol. Two inputs lead to a convex-crescent edge, and the two lines of this symbol now enter a double-stroked convex-crescent input like the XOR GATE. The two lines of -this- symbol have bubbles placed half way across their horizontal length, and are presumably the outputs.] ANDORX gant [An unusual symbol. The symbol is identical to the NOR GATE, except the upper and lower horizontal parts of the symbols hull have a NOT GATE placed on them - one pointing to the left on the upper line, and to the right on the lower line. There is one output to the symbol, with a bubble attached.] NORXONDOR gorgonax

The comic lists logic gates . The first six are real but the last six are made up and get increasingly absurd. The names for these last six use the same letters and syllables as the first six so as to appear at a glance to be consistent with their naming conventions. Some of the ways the gate parts are combined seemingly-impossibly can raise ideas in the mind of the reader of how quantum computing involves processing multiple possibilities at once, or how machine learning involves solving systems backward from their outputs to their inputs. The names ring of calling more and more profoundly to some mythological catastrophe. The only real-life logic gate that was omitted is the XNOR gate (short for "eXclusive Not OR"; it compares the inputs, and if and only if they are equal, it outputs true). Note that the "NORG XORT" gate would be logically equivalent to it, if it were tipped to match its uniquely XOR-style tail, since it would then be an XNOR gate with NOT on both inputs, a modification that has no ultimate effect on the logic as it merely switches the case of which exclusivity it needs to be, and does not care which version of same-input it might be responding to. A double-NOT on an input would produce the identical output again (...if the input is not not true). Two NOTs preapplied to a (N)AND or (N)OR would produce the same output as a (further-)NOTed version of the (N)OR or (N)AND, conversely (...if not -1 and not -2 then this also means that neither 1 nor 2). Normally this would be shown, if necessary, as full NOT gates on the lead-in inputs but (see Transcript, below, and the NORG XORT description above) the shortcut element is occasionally used in further mix'n'match symbology (together with reinterpreting connectivity lines as partial shape-edges and vice-versa) in 'understandable' but definitely non-standard ways. Along with the deliberate confusion of connector and shape-edge lines, directionality is also played with in several cases, with input 'ends' perhaps also at the (implied) output end and reversed sub-symbols implying a composite gate with substructural feedback or perhaps diode-rectification upon a bidirectional logic path. Much like 2360: Common Star Types , as the list progresses, the names start to sound more like mythical creatures, closing with the "Norxondor gorgonax". As with the symbology, the names appear to be nonsensical recombinations of the standard ones (perhaps with off-subject inspirations, in some cases) but often do not match up with the symbolic (mis)use, such as an X in the name not implying/being implied by an XOR's unique drawn feature. In the title text Randall claims that in the programming language C the multiocular O (ꙮ) character, an exotic glyph variant of the Cyrillic letter O, is used to represent the bitwise version of the last operator Norxondor gorgonax (presumably ꙮꙮ represents the non-bitwise version), fitting as the multiocular O is used to refer to "many-eyed seraphim " (angels) in some religious literature. Gorgons ( beige or otherwise) have heads covered with snakes instead of hair, and so possess multiple eyes, the most famous was known as Medusa (she was depicted in 1608: Hoverboard ). The ꙮ character abstractly inspires ideas of great otherworldly demons like those of the Cthulhu mythos. C is a low-level programming language, and as such, it has many operations that correspond to logical (i.e. bitwise) operations. These contrast with operations that work in a non-bitwise way. For example, "&&" is the non-bitwise "AND" operator that takes the operands as a whole, while "&" is the bitwise "AND" that combines the respective bits of its two inputs independently before spitting out the new single composite value the output bits represent. In non-bitwise operations, 0 always represents "FALSE", while any non-zero value means "TRUE" for inputs, and 1 is used to represent TRUE for outputs. Thus, "14 && 3" gives the result 1: TRUE AND TRUE -> TRUE. In the bitwise operation, using the same values, the decimal value 14 has the binary value 1110 and the decimal value 3 has the binary value 0011, and for this example we get: [The comic shows a chart with twelve electronic logic gates arranged in three rows of four. Each gate is depicted as a schematic symbol, with a label underneath. Above them is a header:] Common logic gate symbols [Here below follows a description of the 12 gates in the three rows, with their label given beneath each description:] [A standard gate symbol used in real life. Two inputs on the left lead to the vertical left edge of a solid D-shaped symbol. From the right side of the D there is one output.] AND gate [A standard gate symbol used in real life. Two inputs on the left lead to a convex-crescent left edge of a crescent-shaped symbol. The right side of the crescent symbol's shape forms a point at its output. From the right side of the crescent there is one output.] OR gate [A standard gate symbol used in real life. One input leads to a triangular symbol pointing to the right. There is a small bubble symbol connected to the triangle on the output, which leads right.] NOT gate [A standard gate symbol used in real life. This is identical to the OR GATE, except the output has a bubble attached, like the NOT GATE's output.) NOR gate [A standard gate symbol used in real life. This is identical to the OR GATE, except the left-hand arc at the input has a double-stroked line.] XOR gate [A standard gate symbol used in real life. This is identical to the AND GATE, except the output has a bubble attached, like the NOT GATE's output.] NAND gate [An unusual symbol. This symbol has one input on the left leading to a convex-crescent left edge, like the OR GATE. The output side as a smooth crescent like the AND GATE but has two outputs.] NORX gate [An unusual symbol. This symbol has two inputs on the left leading to a vertical left edge input, like the AND GATE. The output side has a convex-crescent double-stroked output like the mirror image of the XOR GATE's input. There are two outputs.] GAND ate [An unusual symbol. This resembles the NOT GATE except there are two inputs instead of one leading into the left side.] XAND gort [An unusual symbol. This has a double-stroked convex-crescent input like the XOR GATE, but the two inputs have bubbles attached. The single output has a smooth crescent shape with a bubble, like a NAND GATE.] NORG xort [An unusual symbol. Two inputs lead to a convex-crescent edge, and the two lines of this symbol now enter a double-stroked convex-crescent input like the XOR GATE. The two lines of -this- symbol have bubbles placed half way across their horizontal length, and are presumably the outputs.] ANDORX gant [An unusual symbol. The symbol is identical to the NOR GATE, except the upper and lower horizontal parts of the symbols hull have a NOT GATE placed on them - one pointing to the left on the upper line, and to the right on the lower line. There is one output to the symbol, with a bubble attached.] NORXONDOR gorgonax

Forest Walk

Forest Walk

https://www.xkcd.com/2498

https://www.explainxkcd.com/wiki/index.php/2498:_Forest_Walk

[Megan and Beret Guy are walking through a landscape with spread-out trees and grass and puddles on the ground.] Megan: Wow, this is all yours? Beret Guy: Yeah! All the way back to the river! Beret Guy: I walk here every day. [Megan still walks towards Beret Guy who has now stopped and is looking up while speaking to a man hanging in a tree in front of them. The man has long wild hair and a large beard. He hangs from his parachute which has been folded around a large branch sticking out from beneath the top of the tree. He is holding a long stick of some sort, seemingly attempting to threaten Beret Guy, as the stick and his legs are vibrating as indicated with small lines.] Beret Guy: Morning, Mister Cooper! Cooper: You help me down this instant! [Pan down to show only Beret Guy and nothing else. Cooper replies from off-panel from the top corner.] Beret Guy: Do you promise to give back all the money you took? Cooper [off-panel]: Never! Beret Guy: Okay! See you tomorrow! [Megan and Beret Guy continue walking through the landscape with three small trees behind them, as well as grass, rocks, and a small puddle. Megan looks back over her shoulder towards where Cooper is hanging.] Megan: Was that D.B. Cooper? Beret Guy: Yeah, and up ahead there's an owl nest! Beret Guy: There's so much neat stuff here.

Megan is walking through a wide landscape with Beret Guy who owns a big part of it. Megan is surprised that he owns such a big property, however, Beret Guy is known for his inexplicable businesses such as in 1493: Meeting and from 1032: Networking ; we know he probably has enough resources to be able to buy it. Alternatively, he might have simply inherited it from his mom (see 502: Dark Flow ), or may not understand the concept of owning it. Nevertheless, he walks here every day, and from the context of the comic, it seems pretty much no one else comes here. They meet a rather disheveled-looking bearded man hanging from a parachute caught in a tree. The man shakes a stick at them and demands to be helped down to the ground. Beret Guy simply addresses him as "Mister Cooper" and asks if he promises to return the money he took. The man angrily refuses, and Beret Guy casually says he'll see him again tomorrow, suggesting that this conversation has become a daily routine. Megan asks if the man was D. B. Cooper, which Beret Guy immediately confirms. He then comments on an owl nest as another bit of "neat stuff" found on his land, suggesting that he finds Cooper's presence to be just another mildly interesting part of this land. D. B. Cooper is the identity given to a man who hijacked a Boeing 727 aircraft in 1971. He collected a $200,000 ransom (equivalent to $1,250,000 in 2020) and famously donned a parachute and jumped from the plane over the state of Washington. He was never seen or heard from again. Despite lengthy FBI investigations and nationwide publicity, the hijacker was never identified. A few thousand dollars of the ransom money was found in a river, nearly 10 years after the hijacking, but the remainder has never been recovered. The only things known about him are a police composite drawing and the name "Dan Cooper", under which he had purchased his airline ticket (he was called "D.B." as a result of a miscommunication with the media, and the name stuck). The high-profile case followed by the never-solved mystery has led to a massive amount of speculation as to his identity, background, and what became of him. Many consider the most likely scenario to be that he didn't survive the parachute jump, and simply crashed somewhere that his body was never found. Others imagine that he escaped with the money and simply managed to evade capture. The comic is insinuating that, after leaping from the plane, he got entangled in a tree in Beret Guy's land, and has been there ever since. Uncanny situations are nothing new to Beret Guy since he possesses many strange powers . Hence, the concept of a famous criminal hanging from a tree for nearly 50 years doesn't seem any more interesting to him than an owl's nest. In keeping with the typical bizarre-ness of Beret Guy's life, it isn't explained how a man could survive for half a century hanging from a tree, why he'd choose to remain trapped there for his entire life rather than return money that he's in no position to spend, or why Beret Guy wouldn't simply report his whereabouts to the police. All of these are simply accepted as unremarkable realities of life, for him. D. B. Cooper was already referenced by Randall in 1400: D.B. Cooper , 1501: Mysteries and 2452: Aviation Firsts . The title text may refer to the linguist from 2390: Linguists who is more interested in the linguistic nuances that people use than in actually responding to their call for assistance. It is not known how many others have walked through Beret Guy's land, in the interim, or whether it is their nature or the general aura from Beret Guy, but the linguist did not much more than ponder the phrase "help me down". Megan also seems in no particular hurry to intervene. [Megan and Beret Guy are walking through a landscape with spread-out trees and grass and puddles on the ground.] Megan: Wow, this is all yours? Beret Guy: Yeah! All the way back to the river! Beret Guy: I walk here every day. [Megan still walks towards Beret Guy who has now stopped and is looking up while speaking to a man hanging in a tree in front of them. The man has long wild hair and a large beard. He hangs from his parachute which has been folded around a large branch sticking out from beneath the top of the tree. He is holding a long stick of some sort, seemingly attempting to threaten Beret Guy, as the stick and his legs are vibrating as indicated with small lines.] Beret Guy: Morning, Mister Cooper! Cooper: You help me down this instant! [Pan down to show only Beret Guy and nothing else. Cooper replies from off-panel from the top corner.] Beret Guy: Do you promise to give back all the money you took? Cooper [off-panel]: Never! Beret Guy: Okay! See you tomorrow! [Megan and Beret Guy continue walking through the landscape with three small trees behind them, as well as grass, rocks, and a small puddle. Megan looks back over her shoulder towards where Cooper is hanging.] Megan: Was that D.B. Cooper? Beret Guy: Yeah, and up ahead there's an owl nest! Beret Guy: There's so much neat stuff here.

Abandonment Function

Abandonment Function

https://www.xkcd.com/2499

https://www.explainxkcd.com/wiki/index.php/2499:_Abandonment_Function

[A multi-Rotor drone is seen flying though the air from left to right. Tied below the drones main body is the drone's own remote controller. Movement lines behind drone indicate a wavery flight path. A voice emanates from the drone:] Drone: Hi, I'm yours now! Please charge me! Drone: Hi, I'm yours now! Please charge me! [Caption below the panel:] Tech Tip: If you ever get tired of a toy drone, tie the controller to it and set it outside. Its abandonment function will activate and it will find a new home.

This is another one of Randall's Tips , this time a Tech Tip. Pet abandonment is a situation of concern among biological pets, and is part of the reason there are animal rescue organizations providing for adoption in most regions. Since drones are automated, they can be programmed to have an automatic abandonment function. In reality, this "abandonment function" is the norm that things left outside homes are often considered gifts for any passersby who would like them. Hence, following the instructions in the webcomic may result in one's drone disappearing for a new owner, but not for the reason depicted. With the drone responsible for flying to find its own new owner, one can possibly imagine it becoming more and more "fervent" as its charge runs down, to prevent the accumulation of derelict drones in the streets. Triggering abandonment based on extended close proximity to the device's own controller could produce issues such as accidental activation, or malicious activation by a party who could send the proximity signal from a great distance, possibly to many drones at once, via software defined radio . It is, however, more likely that being left consciously uncontrolled for an extended period is the actual trigger, with the attachment of the controller being more a direct courtesy to the next adoptive-owner, and/or preventing the loss of carrier signal that would instead activate whatever auto-homing (i.e. return-to-launch-point) behavior the more sophisticated drones may use if ever beyond their pre-programmed flight parameters. The concept of there being "wild" vs "domesticated" drones rings again both of wildlife and pets, and of new intelligent software providing for drones acting on their own. In the latter case, protection for "wild" drones could imply many things about the role of artificial intelligence in society. Did we organize the wild drones to obey our laws, or are we protecting them in fear of being punished by their superior power? A foreign military drone could also be considered a wild drone. But more likely Randall is imagining flocks of abandoned drones, fending for themselves, traveling distances as they survive off of seasonally-dependent charging resources. This is similar to the behavior of birds, which are protected (in the U.S.) by the real-world Migratory Bird Treaty Act of 1918 . Aggressive flocks of drones was used in 1630: Quadcopter and drones has become a recurring theme on xkcd, where also training of drones as a pet has been the subject in 1881: Drone Training . This idea of protecting drones is analogous to the anomaly that misbehaving drones have not been well tracked by law enforcement: https://observer.com/2020/01/drone-flock-mystery-baffling-authorities/ . If computer viruses continue to evolve, wild drones could indeed evolve too, as they are directed by software, but usually a human being or organization is considered to be somewhere at the helm (separately) of both computer viruses and drones. The idea that a drone may choose of its own volition whether to find a new owner or join a wild flock is a little similar to the situation for abandoned pets. [A multi-Rotor drone is seen flying though the air from left to right. Tied below the drones main body is the drone's own remote controller. Movement lines behind drone indicate a wavery flight path. A voice emanates from the drone:] Drone: Hi, I'm yours now! Please charge me! Drone: Hi, I'm yours now! Please charge me! [Caption below the panel:] Tech Tip: If you ever get tired of a toy drone, tie the controller to it and set it outside. Its abandonment function will activate and it will find a new home.

Global Temperature Over My Lifetime

Global Temperature Over My Lifetime

https://www.xkcd.com/2500

https://www.explainxkcd.com/wiki/index.php/2500:_Global_Temperature_Over_My_Lifetime

Graph of temperature over time, titled: "Global average temperature Over my lifetime (60-month running june average, NOAA NCEI time series)" The X axis is in years, going from 1980 to a little after 2020. Each decade is marked. The Y axis in in °C, with the "20th century average" at the bottom, up to +1°C (from the average), labelled every 0.2°C. Certain points and periods on the graph are marked and contain descriptions of events and actions that occurred in Randall's life. November 1982 Exxon International report predicts that fossil fuel use will raise global temperatures to about 1°C above their normal levels within 40 years October 1984 I’m born in Easton, PA Summer 1991 I learn to ride a bike Spring 1992 My elementary school celebrates Earth Day and I learn about the greenhouse effect 1993-1996 I get very into Star Wars and Animorphs Fall 1996 I stand around awkwardly at my first middle school dance Spring 2002 I get accepted into college Spring 2006 I somehow graduate despite spending most of my time playing Mario Kart Summer 2006 I see An Inconvenient Truth in the theater and feel anxious Fall 2011 I get married Summer 2012 I read headlines about a global warning “pause” and hope that maybe things aren’t so bad 2013-2021 I read more about climate science and get steadily more alarmed Spring 2016 I read the 1982 Exxon report June 2020 Global 60-month average reaches +0.94°C, Easton, PA is 2°C hotter than normal for the fifth year in a row Today (no description) 2022 (near future) [Large X within a circle] 1982 Exxon Prediction

This is Randall Munroe in his role as a meticulous, conscientious presenter of scientific data. The activities shown in Randall's lifeline, whether learning to ride a bike or even getting married, pale into insignificance when the consequences of unprecedented global average temperature rise are understood and accepted. In particular, he shows that back in 1982, two years before Randall was born, Exxon wrote an internal report predicting the rise of global temperatures due to fossil fuel use, and 40 years later their prediction (shown as the X in a circle at the top-right) is being shown to be right on track. Unfortunately, that report was hidden and not seen until much later, and the world has been slow to respond with the urgency needed to reverse the damage being done to the planet. The Wikipedia article global temperature record has some telling graphs to supplement Randall's. This one: Global Average Temperature is the global average temperature change for the modern era, since data started being collected regularly in 1850. This one: 2000 Year Temperature Comparison reconstructs 2000 years of temperatures. And this comic is a small segment of another comic 1732: Earth Temperature Timeline . The comic itself links to the referenced Exxon document about CO2 emissions . The comic was published on the same day that the U.N. Intergovernmental Panel on Climate Change released its 2021 Assessment Report One of the entries is I somehow graduate despite spending most of my time playing Mario Kart. Mario Kart is a popular video game series developed by Nintendo , and has been a recurring theme on xkcd. Hewing close to the comic's timeline, 127: The Fast and the Furious , which contains an early Mario Kart joke, was released in July 2006. The title text refers to the fact that Exxon, being a fossil fuel company, is likely to make better predictions on fossil fuel use as they are involved in fossil fuel production themselves. Graph of temperature over time, titled: "Global average temperature Over my lifetime (60-month running june average, NOAA NCEI time series)" The X axis is in years, going from 1980 to a little after 2020. Each decade is marked. The Y axis in in °C, with the "20th century average" at the bottom, up to +1°C (from the average), labelled every 0.2°C. Certain points and periods on the graph are marked and contain descriptions of events and actions that occurred in Randall's life. November 1982 Exxon International report predicts that fossil fuel use will raise global temperatures to about 1°C above their normal levels within 40 years October 1984 I’m born in Easton, PA Summer 1991 I learn to ride a bike Spring 1992 My elementary school celebrates Earth Day and I learn about the greenhouse effect 1993-1996 I get very into Star Wars and Animorphs Fall 1996 I stand around awkwardly at my first middle school dance Spring 2002 I get accepted into college Spring 2006 I somehow graduate despite spending most of my time playing Mario Kart Summer 2006 I see An Inconvenient Truth in the theater and feel anxious Fall 2011 I get married Summer 2012 I read headlines about a global warning “pause” and hope that maybe things aren’t so bad 2013-2021 I read more about climate science and get steadily more alarmed Spring 2016 I read the 1982 Exxon report June 2020 Global 60-month average reaches +0.94°C, Easton, PA is 2°C hotter than normal for the fifth year in a row Today (no description) 2022 (near future) [Large X within a circle] 1982 Exxon Prediction