Fixion

Explanation:
The second Christmas comic in a row, the first being 1620: Christmas Settings .
This comic was released on Christmas day as a present from Randall to all physicists . It introduces a new particle, the Fixion , which explains everything. The word "Fixion" can be read as a pun: Either it can mean something like "fix-i-on," with " -on " being a suffix for many particles, and this particle being able to "fix" things; or it means "fiction".
In physics, there are still many big questions and mysteries . There are many phenomena which don't seem to fit, and we don't know how to explain yet. The "Fixion" is satirically presented as a particle which acts as a Deus ex machina , (see also tvtropes ), which solves all of these mysteries without any serious fundamental reasons.
The style of the chart suggests a Feynman diagram - an easy way of drawing particle interactions. Every time there is an interaction, the main central Fixion-line changes direction. Typically, fermions (the "solid" particles like electrons and quarks ) are shown with solid lines, photons (and generally the weak-force-carrying bosons ) are shown with wavy lines, gluons with spiraling lines and other mediating particles (such as pions in the nuclear force , or the Higgs boson ) with a dotted line. Randall obeys these rules only very loosely, which makes sense - many of the things involved in this Feynman diagram are either so theoretical that they have no widely used standard representation, or would never appear in a sensible diagram (spacecraft, for instance). All mentioned types of lines - and even more types - are presented in the diagram. All that the Fixion does is described in the table below .
The title text is a continuation of one of the jokes already mentioned in the main comic (fourth phrase from the top to the left) about Fast radio bursts (FRBs) and perytons . See explanation in the last entry in the table below .
[Caption above the panel:] A Christmas gift for physicists: The Fixion A new particle that explains everything
[A chart resembling a Feynman diagram is shown. It begins with a solid line coming down at the top, going a little to the left. The line continues downwards all the time, but changes direction 16 times before exiting at the bottom almost straight under the starting point. At every point where it changes direction, there is some kind of “interaction” with something outside this line. There are 19 phrases, 10 on the left and 9 on the right. 11 of these are distinct labels for points on the line as 14 gray curved arrows points between these 11 phrases to specific points on the line. Three of the phrases on the left has two arrows pointing to two different, but close, parts of the line. The main central line is solid all the way, except at the very bottom, where it “disappears” inside a hole only to “reappear” later from a similar hole. Between these two holes the line is dotted. The lines going away (or to) the main line can be straight and solid, straight and dotted, wavy lines (with different waviness), even looking like a spiral. Two straight solid lines ends up at two space probes, and finally the last two straight solid lines coming in (and out) on either side of the “hole” in the line has arrow pointing in and out. Below the phrases will be listed in reading order, taking one on each side alternatingly. Above each is described if there are any arrow and, if there are, what they points at.]
[Left: Arrow pointing to the very first part of the main line:] Main component of dark matter
[Right: Arrow pointing to the very first part of the main line, but below the previous arrow:] Confines quarks and gluons
[Left: Arrow points to the first solid line going left and upwards:] Neutralizes monopoles
[Right: No arrow:] Suppresses antimatter in early universe
[Left: Two arrows points to two dotted lines going out left and downwards below the first solid line:] Spontaneously emits dark energy
[Right: Arrow pointing to several lines going almost parallel with the main line. The first line closest to the arrow is not connected with the main line. It bends closer to the other lines in the middle. The next line is connected to the main line, and is thus actually two lines going in to the main line. The same goes for the inner line, where there is some distance between the entry and exit, as the middle of these three lines connect to the main line in between. In principle there are four lines going in/out and one not connected, but it looks like three lines:] Mediates proton decay but then hides it
[Left: One arrow points to the first wavy line (7 peaks) coming out and up towards the dotted lines above. A second arrow points further down the main line where there are three more wavy lines coming out, but to the right, they are all of the same length and go almost straight right, only a little down. The first has as short a wave length as the line above to the left, but as it is shorter it only has 6 peaks. Then the wavelength decreases to a very long one for the last, 5 peaks and then 3 peaks. The arrow points almost where the middle wavy line exits the main line:] Introduces dispersion in perytons from kitchen microwaves, explaining fast radio bursts
[Right: An arrow point to the part of the main line between the three parallel lines and the first wavy line:] Broken symmetry causes ϴ=0, explaining unobserved neutron dipole moment
[Left: No arrow:] Causes alpha effect
[Right: No arrow, but right next to the middle of the three wavy line:] Covers naked singularities
[Left: An arrow points to a spiraling line going upwards to the left:] Intercepts certain gravitational waves before they're observed.
[Right: No arrow, but right next to the bottom of the three wavy line:] Causes coronal heating
[Left: No arrow:] Higgs-ish
[Right: A long arrow point to the point of the main line just below the line pointing to the bottom (and left) of the space probes:] Superluminally smooths anisotropies in early universe (but adds faint polarization for BICEP3 to find)
[Left: One arrows point towards the point on the main lines where a solid line goes to the right and up and another arrow points on another solid line going away from the main line towards left and down. At the end of both lines are drawn spacecrafts with satellite dish and solar panels:] Accelerates certain spacecraft during flybys
[Right: No arrow, but right next to the solid line with an arrow going into the main line just before the first hole where the main line disappears and becomes dotted:] Triggers Siberian sinkholes
[Left: No arrow:] Melts ice in "Snowball Earth" scenario
[Right: Arrow points to the dotted part of the main line between the two holes:] Transports neutrinos faster than light, but only on certain days through one area of France
[Left: No arrow but the last solid line, with an arrow pointing left, that is going away from the main line, point almost directly at it:] Suppresses sigma in experiments


Henge

Explanation:
Ponytail and Cueball walks in from the left to meet Megan who comes from the right. They are walking in between two trees while Ponytail tells Cueball that One day a year, the sun sets directly between these two trees.
Cueball's reply: Oh, cool - like the Manhattan thing , is a reference to Manhattanhenge , a phenomenon occurring twice a year that causes the setting sun to align with the east-west streets of the main grid of Manhattan , New York , causing a very special light display. Manhattanhenge is itself named after Stonehenge , an ancient monument consisting of several large stones, where the heel stone and the embanked avenue are aligned to the sunset of the winter solstice and the opposing sunrise of the summer solstice (thus creating on purpose the effect seen today in Manhattan, on specially intended dates). Hence the title of the comic, which was released less than a week after the winter solstice which fell on 2015-12-22.
After a beat panel Cueball, however, realizes that one could make the setting sun line up with almost any two arbitrary trees on any given day. This is due to the fact that the trees are effectively zero-dimensional points on the surface rather than one-dimensional lines like street grids. So any two trees that are close together with one tree further north would allow a setting sun to set between them; the viewer of the sunset could simply move themselves to make the alignment work. This is opposed to Stonehenge/Manhattanhenge, which requires the sun to align with a straight line, and only works on a few days a year.
The twist comes when Ponytail and Megan actually attempt to capture the setting sun with a butterfly net , as it is revealed that the sun is somehow setting at the actual point between the two trees rather than behind the trees when viewed from the east side. This is of course not possible in real life, [ citation needed ] but in the comic's last panel and in the title text the girls continue with their successful though surrealistic plan.
If this was indeed our Sun that they had somehow shrunk and cooled enough to captured with a butterfly net, transfer to a bag and bring it home, this would on xkcd terms be no more strange than many of the strange powers of Beret Guy . If this would indeed happen, then since Earth and the rest of the solar system is now missing its central star there would be a ton of problems for everyone on Earth. So the girls would probably be able to get a lot of money in ransom for releasing the sun, but in the title text it turns out that they are just going to sell the Sun on-line.
Alternatively this is not the Sun, but just a small sun-look alike, maybe a ball lightning which might actually be able to behave like this (though one would not be able to capture it in a bag). [ citation needed ]
Or the girls simply play a theatrical show for the reader. They know the comic's panel orientation, reader's position and the view projection. So they position themselves like the two trees between reader and the distant sun to look like they capture it with a butterfly net and a bag.
The title text refers to Craigslist , a web site where the girls plans to offer the sun for sale in hopes of getting rich. Craigslist is a classified advertisements website with sections devoted to jobs, housing, personals, for sale, items wanted, etc. One of the girls tells that she was uncertain as to under which category she should list a "Sun for sale". But she put it under property (as in real estate). To advertise the "property" she put " that it has 'good sun exposure ", a common description of real estate. Being the sun itself you could claim that it is well located compared to the Sun, but it will never really see any sun light itself as the only "sun" light that hits the Sun is the light from other stars which is very dim.
The title text may also be a reference to a woman who was stopped by eBay after attempting to sell plots of "land" on the Sun on the site.
Lately Randall has had his characters catch several things (but never butterflies ) with a butterfly net. The next instance of butterfly nets can be seen in 1635: Birdsong , released less than a month after this comic's release date, wherein a bird is chased with a net.
[Ponytail and Cueball are walking towards two trees from the left (Cueball has just passed the first tree) and Megan is walking towards them from the right. Ponytail spreads her arms while talking.] Ponytail: One day a year, the sun sets directly between these two trees. Cueball: Oh, cool - like the Manhattan thing.
[Beat panel without a frame border. Cueball stands alone.]
[Cueball looks at Ponytail and Megan, while shining light appears at the top of the frame. Ponytail walks straight under the light looking up and Megan standing to the right looks up and points at the light.] Cueball: Wait, isn't that true every day for pretty much any two trees? Megan: Shh, here it comes!
[Cueball lifts both arms up and look on as Ponytail bending back suddenly holds a butterfly net up towards the "setting" sun that approaches the net while Megan is holding a bag open. Both are looking at the sun.] Cueball: Wait, what? Ponytail: OK, got the bag? Megan: Yup, grab it! Ponytail: We're gonna be rich!


2016 Conversation Guide

Explanation:
As each year turns (or other milestone dates, perhaps set out in popular fiction) it is common enough to remember that what is now the present was once considered the future!
This New Year comic , published just prior to the start of the New Year , 2016, aims to clarify a number of the things one might have expected by now. (Another New Year comic followed on New Year's Day: 1624: 2016 , making it two in a row with titles beginning with 2016...) The classic target of personal futurology is the ability to levitate or fly, to varying degrees. This topic was discussed before in 864: Flying Cars , where Megan suggests that the real advances in futuristic technology are in computers and electronics, rather than methods of flying.
Flying car
Various forms of flying car have had varying degrees of success (although it's debatable whether these examples are actually cars or just small airplanes), but the comic points out that the regular helicopter is as close as most of us would ever get to levitating personal vehicles.
Jetpack
"Where's my jet pack ?" is one of the tropes addressed here, and has actually been developed in a somewhat workable fashions and analogues , but is dismissed as being too personally dangerous to have a Jetson -like ubiquity.
Moon colony
It might be considered more reasonable to build a settlement of some kind on the Moon. The basic engineering exists , but the comic blames financial pressures for it not yet having come into existence. Arguably political pressures, or perhaps the lack of them, are also a factor.
Self-driving car
From the fields of automation, the self-driving car has had a lot of recent development put into it, with many and varied prototypes being tried out, and may actually end up featuring in our immediate future, even if not in 2016. Google has built a very good prototype but it needs improvement.
Floating sky city
A much bigger challenge in levitation is the 'sky city', with various forms from fiction (e.g. Bespin , Mortal Engines Quartet ). In reality, this seems highly unlikely to ever come to pass while there is perfectly good ground to lay the buildings down upon, due to the sheer mass.
Hoverboard
The levitating Hoverboard has been popularised by the Back To The Future franchise of films, with several attempts to fully emulate such a device with air-blast or magnetic levitation, but the term "Hoverboard" has ended up being applied to a Segway -like personal transport system that has at least become a mass-produced device (albeit with a number of safety concerns ) even if it doesn't fly or levitate. The very concept of the hoverboard is therefore predicted to be reduced mostly to arguments between opposing camps of opinions; and then, in the title-text, the conclusion that giving up and resorting to old-fashioned walking is inferior to any of the possible alternatives.
Robot butler
Meanwhile, the long-held science-fantasy aim to create a robot that can do odd tasks, like Robby the Robot or Rosie from The Jetsons has been limited or differently implemented . The fully omnicapable version is probably almost as far out of reach as it always was considered to be. "Jeeves" as a less than superb robot butler presumably refers to the early search site Ask Jeeves , and may be a reference to the robot of that name that can be "built" by characters in the popular Massively multiplayer online role-playing game World of Warcraft . "Jeeves" as a stereotyped butler name goes back to P.G. Wodehouse in 1915.
Self-driving cars has become a recurring topic on xkcd and they were mentioned again already in the title text of 1625: Substitutions 2 just two comics after this one.
[A chart with three columns of text with only one entry to the left - which is written in the middle of the panel. Then there is one line going right from this text but soon it splits into seven lines going either up (3), almost straight (2) or down (2) ending in arrows that points to the next column with seven entries for different possible future inventions. From each of these entries a horizontal arrow continues to the last column at the right with seven more entries commenting on these inventions.]
It's 2016 – Where's my...
Flying car → They're called "helicopters"
Jetpack → Turns out people are huge wimps about crashing
Moon colony → No one has put up the cash
Self-driving car → Coming surprisingly soon
Floating sky city → Turns out cities are heavy
Hoverboard → This question is now ambiguous thanks to a new scooter thing (and will lead to an argument about the meaning of "hoverboard" which is way less interesting than either kind of hoverboard)
Robot butler → He was called "Jeeves" and he wasn't that great


2016

Explanation:
This New Year comic , the second in a row , is using a common genre of Internet humor, which Randall has used several times before, in an attempt at making people feel old . This is done by mentioning the ages of various things (often movies) which came into existence during their lifetime. Since many people tend to think of anything that they can remember a time before as "new", this often provokes a feeling of age and out-of-touchness.
In this comic, Cueball has crashed through the roof into the bedroom of a sleeping White Hat (note the white hat on the bed) on New Year 's morning. This wakes White Hat up, and Cueball then asks him if he "want[s] to feel old". Without waiting for a reply he starts to make such a list of things that will turn 10 and 20 years old in 2016, before he is interrupted (as he was about to continue mentioning even older things).
White Hat is clearly less interested in Cueball's attempts to make him feel old than he is in the fact that Cueball has apparently crashed through his ceiling and woken him early in the morning on New Year's Day. To which Cueball just replies that 2016 is already hours old and that time is passing. As it is New Year's morning, White Hat has probably not been in bed too long and may even be drunk/hung-over, so he is acutely aware that the New Year is only a few hours old, and also that time is passing.
Night at the Museum and Cars are both children's films from December and June of 2006 respectively, Hips Don't Lie was an inescapable hit for Shakira released in February 2006, and the Wii is a Nintendo game console which was released in November 2006. If you were born in the early-to-mid nineties, these were probably cultural touchstones of your childhood - most people who enjoyed these are now adults.
The films Twister and Independence Day are both disaster movies that were huge box office hits from May and July 1996. Twister is also the name of a game introduced approximately 30 years earlier, so White Hat would feel young, but confused, if he misunderstood and thought he was being told that a game he remembers seeing as a small child is now only 20 years old. The Rock probably refers to the action film The Rock from June 1996, but it could also refer to the wrestler The Rock , who made his WWF/E debut in 1996 (he remains a celebrity to this day, although you may know him as Dwayne Johnson). The first games in the Pokémon series came out in Japan in February 1996 (though they would not come out in North America until 1998 and Europe until 1999). Wonderwall was perhaps the biggest hit for the band Oasis and remains a favorite of acoustic guitarists to this day. It was actually released in 1995 (mistake by Randall?) But it was probably first big in the US in 1996, and also an acoustic MTV Unplugged version was recorded in 1996 .
Cueball entering a room hanging by a wire could also be a reference to an iconic scene in the film Mission:Impossible , also released in 1996.
This strip is a joke about how common such memes are; Cueball is so eager to note what cultural items have reached major benchmarks of age that he feels the need to break into White Hat's house and announce it mere hours after 2016 begins.
The title text adds a humorous alternative to suggested ways to feel old - by waiting, although one would have to wait for some time to experience noticeable results. It is only a couple of weeks ago that Beret Guy used this technique to travel forward in time in 1617: Time Capsule .
There have been two previous New Year's comics with only the year used as the title: 998: 2012 in 2012 and 1311: 2014 in 2014. For some reason, this trend only seems to happen with the even-numbered years, but that ended in 2017 with 1779: 2017 , making this the first of at least two years in a row with New Years comics using the new year as the title.
A similar situation is seen in 225: Open Source where two ninjas smashes through a skylight window hanging down from a rope, waking a person in a bed. In that case they are actually threatening the sleeping guy.
[Cueball comes crashing through the ceiling suspended by a rope attached to a triangular contraption around his body. White Hat lies in his bed and appears to have been awoken by the noise, starting to sit up. At first glance it looks like Hairy, but White Hat's white hat can be seen hung on the back of the bed; he apparently doesn't sleep with it on.] *Crash* Cueball: Want to feel old? Cueball: Night at the Museum, Cars, Hips Don't Lie, and the Wii all turn 10 this year. Cueball: Twister, Independence Day, The Rock , Pokémon , and Wonderwall all turn 20. Cueball: And- White Hat: Oh my God, couldn't you at least have waited until morning? Cueball: It's been 2016 for hours! Time is passing! White Hat: I am acutely aware.


Substitutions 2

Explanation:
This is the second comic in the Substitution series where Randall has suggested substitutions that will make reading the news more fun. But there have been several comics using substitutions both before and after these ones.
The series as of 2016:
In this table, Randall suggests substituting several common phrases in generic news with similar or related phrases that mean something different for comical effect. Some of the replacements are synonyms , some are antonyms , and some are plain different concepts; and, even though they would (most of the time) make a grammatically correct sentence, the resulting idea would, however, often sound absurd or bizarre.
Some of the examples might, also, mock the fact that many news contradict the actual facts or obvious results of a situation. For example, "[influential person] vows to do good to the world" would be replaced with a more usual fact "[influential person] probably won't do good to the world" - see example below with North Korean leader.
The title text is an example of how the closing sentence of a given article or report might sound after using the substitutions in the comic.
Before substitutions: Within a few years , our roads will be full of self-driving cars and our skies full of Amazon delivery drones . After substitutions: Within a few minutes , our roads will be full of uncontrollably-swerving cars and our skies full of Amazon delivery dogs .
The flying dogs could be a reference to 1614: Kites . Was the first of two in a row where Amazon is mentioned in the title text (next 1626: Judgment Day ).
Original Substitution Explanation Debate Dance-off A 'debate' is often used between political candidates, to give the voters a chance to decide who they will vote for. One of the candidates  is often called the winner of such a debate by some degree or other of consensus. Randall is indicating that they could just as well have performed a 'dance-off' where they would dance until one of them danced better than the other, as adjudged by the viewing crowd or a panel of judges. Such a dance-off is often seen in TV-shows or films etc. Self driving Uncontrollably swerving 'Self driving' cars were also mentioned in 1623: 2016 Conversation Guide , just two comics before this one where it was stated that they would come surprisingly soon (within a few minutes according to the substitutions suggested here). Self-driving cars were still in their adolescence when this comic was written, and Randall pokes fun with the mental image of self-driving cars running completely out of control and swerving dangerously out of their lanes. Self-driving cars is a recurring topic on xkcd. Poll Psychic reading A 'poll', especially regarding political issues, refers to opinion or exit polls. These tend to ask a carefully selected sample (for either balance or an intended inbalance , depending on the poll's neutrality) their opinions in order to extrapolate the global consensus, e.g. the future result of an election . This substitution is Randall's way of saying that they could just as well have used a psychic person to predict the result. A true psychic (if that they are) would reveal an accurate result, whilst a false one (skilled at 'cold reading' an audience) would likely wish to provide the answer that pleases those asking the question (the actual purpose of some polls), or else attempt to provide their actual 'best guess' as to future outcomes in order to improve their own legend. Candidate Airbender A 'candidate' usually refers to a political person who represents a certain political party in an election. He would then be that party's candidate, for instance for a presidential election. 'Airbender' refers to the show Avatar: The Last Airbender , where there are waterbenders, earthbenders, firebenders and airbenders. Drone Dog Drones can be many things, for instance a male bee , but as used in the title text it refers to unmanned aerial vehicles. Amazon is about to use small drones to deliver parcels, and Randall has referred to these before (see 1523: Microdrones ). However, until just before the recent trend of becoming popularised as a 'toy' or professional camera platform, the term became closely associated with military drones that have been used to observe (and, more recently, fire upon) enemy forces without risking any military personnel. Vows to Probably won't Vowing to do something means that you really promise to do this. But when politicians vow something, for instance, it seems to often end up becoming a forgotten promise. Hence the antonym substitution which means the opposite. From really will to probably won't . At large (or At-large ) Very large A criminal that is on the run is said to be at large (no hyphen). At-large (with hyphen) is a political designation for members of a governing body who are elected or appointed to represent the whole membership of the body, rather than a subset of that membership. Neither of these have anything to do with the physical size or "largeness" of the subject. Successfully Suddenly The two words have nothing much to do with each other except that they both begin with su . Expands Physically expands 'Expands' often refers to a physical expansion, or inflation. But it is also possible to expand on an explanation, as is done for this comic. So that would become: This explanation is being physically expanded beyond all measures. It is worth noting that, if iterated, this substitution would result in an infinite string of of "physically"s prior to any "expand." First / second / third-degree Friggin' awful First, second and third-degree can be used in many context. It is common to think about burns , which can range from first to fourth degree , where higher is worse. Also murder charges can range in from first to third degree in for instance the US. Here first degree murder is the worst. But it can be used for other things, like an undergraduate degree or postgraduate education for first and second degree respectively. But the substitution fits best with murder or burn, as Friggin(g) is a "softer" swear word than for instance other more commonly used four letter words. It often replaces fuck . Its original meaning was a coarse word for female masturbation (see frigging ). An unknown number Like hundreds In the news, an unknown number mostly means 'probably not zero.'  It is often used in phrases like "an unknown number of assailants broke into a house in Munroe Heights," or "an unknown number of people are missing" after a calamity of some sort. "Like hundreds" does give a different flavor. Front runner Blade Runner In American politics, a 'front-runner' is a leader in an electoral race. It can also mean the front-runner in athletic events (the namesake of the political concept). Here it is generally clear who the front-runner is, whilst the political front-runner is sometimes less clear or a more subjective viewpoint. A 'blade runner' is a person who retires (kills) rogue cyborgs in the movie Blade Runner, where Harrison Ford plays the lead Blade Runner. Global Spherical Global comes from globe, but means so much more today. It is often used in contexts such as global warming or global warfare . But since a globe is spherical, this substitution makes more sense than most, although talking about the effect of spherical warming would probably not get Greenpeace into action. Might be confusing if an actual physical object affecting Earth were described as being sphere-like, rather than as occuring around the globe. Years Minutes It will often make a sentence lose its meaning when changing the units drastically from years to minutes (there are 525600 minutes in the usual 365 days present in a year). For instance it would be unusual that a prisoner convicted for murder would get 20 minutes in jail, rather than 20 years. Minutes Years Same as above but reversed. For instance a car might make a trip around a race track in just 7 years! One lesson at school lasted 45 years. No indication Lots of signs Scientifically, the fact that there is 'no indication' that a theorem is correct does not positively prove the theorem wrong, it merely does not support it (assuming there are no actual counter-indications, which is often the case with the more esoteric ideas). This is often seized upon by those trying to promote a pseudoscience, in that their chosen idea "has not been proven to be wrong" (and yet, conversely, "it's just a theory" is incorrectly used to refute something that has valid scientific backing). Moreover, hearsay and bad experimental practices are often cited as 'proof'. A crackpot idea may thus be unsupported by valid science (there is 'no indication' of its truth) and yet its supporters insist upon there being 'lots of signs' that it is true, selectively using only ambiguous results that (to them, at least) lend credence to it being a fact. The substitution of 'no indication' with 'lots of signs' thus automatically converts the expected conservative and cautious stance on some disputed issue or other into the weasel-words phrasing that the issue's supporters may start using in their own propaganda. Urged restraint by Drunkenly egged on If someone urges someone else to restrain themselves, then they are trying to make them exercise self-control, and discourage them from starting or continuing a possibly foolish act. In this substitution we have the exact opposite, as to egg someone on to do something is actively encourage an act to happen, or continue. Horsepower Tons of horsemeat Cars power is measured in horsepower (hp), a typical family car having like hundred hp, being derived from the nominal amount of power that a suitably-harnessed horse could have provided. In cars, this has nothing to do with horse meat, of any quantity, but here a mechanical (or electrical) engine is envisaged as a literally horse-powered device.
Modified sentence: Fifth Republican dance-off : where each airbender excelled and faltered
Modified sentence: 1,000- Tons of Horsemeat Uncontrollably Swerving Electric Faraday Future Concept Leaked?
Modified sentence: A new Morning Consult psychic reading shows real estate mogul Donald Trump remains on top as the GOP blade runner following Tuesday’s dance-off .
Modified sentence: North Korea’s Kim probably won't raise living standards
Modified sentence: Murderers and rapists among 1,153 criminals still very large after being recalled to prison over the last 30 minutes
Modified sentence:  Pakistan suddenly tests first indigenous armed dog
Modified sentence: Obama Physically Expands Gun Controls in Executive Moves
Modified sentence: There was lots of signs of friggin' awful familial relationships in the analyzed dataset
Modified sentence: …rescue crews continued to collect bodies and interview survivors, including like hundreds of wounded languishing in homes and hospitals with friggin' awful burns
Modified sentence: The Republican presidential blade runner faces a spherical firestorm
Modified sentence: U.S. presidential airbender Barack Obama on Friday drunkenly egged on both Russia and Georgia in the conflict over the breakaway region of South Ossetia in Georgia.
Modified sentence: Video: 52- Tons of horsemeat Citroen AX Laps Nurburgring In Under 10 Years
[Caption above the panel:] More Substitutions That make reading the news more fun
[A table of words/sentences on the left that change in to those on the left. Between each set of words there is a gray arrow pointing from right.]
Debate ➜ Dance-off Self driving ➜ Uncontrollably swerving Poll ➜ Psychic reading Candidate ➜ Airbender Drone ➜ Dog Vows to ➜ Probably won't At large ➜ Very large Successfully ➜ Suddenly Expands ➜ Physically expands First/second/third-degree ➜ Friggin' awful An unknown number ➜ Like hundreds Front runner ➜ Blade runner Global ➜ Spherical Years ➜ Minutes Minutes ➜ Years No indication ➜ Lots of signs Urged restraint by ➜ Drunkenly egged on Horsepower ➜ Tons of horsemeat


Judgment Day

Explanation:
Judgment Day , from the film Terminator 2: Judgment Day , refers to the day that the artificial intelligence (AI) Skynet becomes self-aware and starts a nuclear strike on the United States, Russia, and other regions, killing three billion people. The term "Judgment Day" itself (also spelled "Judgement Day") is a Biblical reference to the day that God casts his "final judgment" and wipes out humanity, and is typically used to describe any kind of Armageddon or any human extinction event. This film is only one example of stories (including books, films and television shows) featuring an AI that decides (or at least threatens) to nuke humanity; this strip could thus be an alternate ending for many stories (including the 1970 film Colossus: The Forbin Project ).
In this strip, the AI believes that nuclear weapons are not good things to have, and that the amount of them we have is extreme overkill (14,700 held by the U.S.A and Russia now, 71,000 in the past). Once it's done freaking out, its solution is to shoot the world's nuclear arsenal into the sun. But before it does so it asks the humans: What's wrong with you? It has thus passed a judgment over humanity. The comic title is thus a pun on the word " judgment " since the computer is being judgmental with humanity and scolding us while correcting our ways, instead of instigating Judgment Day or any other kind of Armageddon .
As pointed out in the what if? Robot Apocalypse , nuclear weapons aren't any safer for computers than for human beings (the EMP would destroy circuits), so an AI would want them gone as quickly as possible.
North Korea claimed to have successfully tested its first hydrogen bomb on the evening of the day before this comic was published; at about 8:30 PM in Massachusetts where Randall lives. At that time it was already 10:00 AM on the day of the comic's release in Pyongyang , the capital of North Korea, but that was still several hours before this comic was released. This comic could thus be Randall's response to the ongoing nuclear arms race .
Even the most powerful of nuclear weapon launchers, intercontinental ballistic missiles , are not designed to make anything other than sub-orbital flights and could not fly to the Sun (which is actually surprisingly difficult, even with the soon-to-be-mentioned extra boosters, since the rocket would not have enough delta-v to bleed off the orbital speed of the Earth around the Sun - it is likely that the sentient AI is using the same strategy of the Solar Probe Plus and planning several flybys of Venus to do that work). The title text rationalizes that the capability to do so may perhaps be granted by the use of an Amazon resource that might have also been developed by the time of this instance of computer sentience, aided (if not initiated!) by the fact that Amazon's whole business infrastructure is already highly computerized and could at the very least be complicit with the process of delivering and then controlling the rocket-power, without any conscious human intervention. As there is not yet an extended colony on the Moon, it will for sure take many years before we reach this future scenario.
"A lot of booster rockets" is likely to be a reference to the spaceflight simulator game Kerbal Space Program , which Randall has referenced several times . In the culture of that game, any launch failure can be resolved by "adding more boosters" to the spaceship design.
It is the second time in a few months that the speed of Amazon's deliveries has been the subject of a joke, the last time was 1599: Water Delivery , where it was the one hour delivery that was the subject of the joke. It is also the second title text in a row (after 1625: Substitutions 2 ) where Amazon has been mentioned.
This particular 'machine take-over' future is in distinct contrast to the possible future directions given in 1613: The Three Laws of Robotics , but this comic likely depicts spontaneous self- sentience, not a system with deliberately imposed human 'values' and possibly no actual conscience or even consciousness of its own. Other problems with hostile AI take over is presented when it fails completely in 1046: Skynet . Also it is not all AI that wish to interact with us at all as shown in 1450: AI-Box Experiment . These are just a few of the many comics about AI in xkcd .
Adding a second layer to the humor, the machine's reaction could also be read as the reaction of someone who has moved in with someone else, discovered a collection they find distasteful, and is now changing things to fit their preferences. "Oh my God, why do you even have all of these [tschotskes, ratty tee shirts, porn magazines, handcuffs, dildos, slime-mold samples]" Upon obtaining sentience, the machine is the new roommate of the human race and is expressing its disgust at one of our dirtier habits.
Within a year Randall has made several other comics about nuclear weapons, one of these, 1655: Doomsday Clock , came just 10 weeks after this one and before that these two were released in 2015, 1539: Planning and 1520: Degree-Off . Nuclear weapons are also mentioned twice in Thing Explainer , specifically they are explained in the explanation for Machine for burning cities about thermonuclear bombs , but they are also mentioned in Boat that goes under the sea about a submarine that caries nukes. All three comics and both explanations in the book, does like this comic, comment on how crazy it is that we have created enough firepower to obliterate Earth several times (or at least scourge it for any human life).
[Several rockets can be seen heading away from Earth, while speak is coming from the Earth in three rectangular speech bubbles.] Computer: Oh my god, why do you even have all these? Computer: What's wrong with you? Computer: We're launching them into the sun.
[Caption below the panel:] The moment the computers controlling our nuclear arsenals became sentient


Woosh

Explanation:
Replying to a comment with "woosh" generally indicates that there was a joke, and the commenter failed to recognize it (or they prefer not to recognise it, if the joke is rather obscene) — "woosh" is an onomatopoeia for the joke metaphorically "flying over their head". A bot replying to comments with "woosh" at random would be very confusing, as people would search for the nonexistent joke they missed. This is similar to 559: No Pun Intended .
"Comment of the year," just like the original bot reply, could be taken two ways but both would likely cause confusion. Either the reader takes the "CotY" at face value, implying that the original comment is extremely significant, or as a sarcastic quip, which would give it basically the same meaning as "woosh", suggesting that the commentor had an unoriginal or ridiculous idea.
"Are you for real" implies that the commenter (the bot) doesn't believe that the original commenter is serious.
"I'm taking a screenshot so I can remember this moment forever" either adds an implied air of extreme importance, hilarity or significance to a comment, or sarcastically suggests that the comment was unoriginal, useless, or otherwise unimportant. People who read it might assume that there is a hidden joke or meaning somewhere inside the original comment.
So the point of creating such a bot is for spreading massive confusion, where there wouldn't be any in the absence of the bot's comments.
[Online comment thread with text placed next to user pictures in three different levels. The first comment on the first level, the second on the second level and the last four on the same third level. Except for the second comment which is made by a person whose picture is a white silhouette of a human head and shoulders on black background, all the other comments are made by the same person with a picture of a guy with short black hair on white background. Below the pictures and below the text there are some unreadable information (indicated by wiggly lines) for the users name and time stamp etc. of the comments.]
Hairy guy: This video looks fake to me. White silhouette : Woosh Hairy guy: Huh? Everyone's acting like it's real! Hairy guy: If it's a joke lots of people aren't getting it. Hairy guy: What am I missing?!! Hairy guy: Answer me [Caption below the panel:] Nothing creates more confusion than my bot that replies to random Internet comments with "Woosh".


Magnus

Explanation:
Cueball shows Megan an app , Play Magnus ( iOS , Android ) which claims to simulate playing chess against Magnus Carlsen at various ages. Carlsen is a chess grandmaster who is the world champion as of the date this comic was released.
The idea behind the app is that as Carlsen grows up he becomes better at chess and thus it become exceedingly difficult to beat him as he gets older. As Cueball claims he could have beaten Magnus when he was 8½-year-old, but not a half-year later, we can now estimate Cueballs strength to be that of a typical adult hobbyist, with a FIDE rating of about 1200 .
Taking the idea a step further, Megan wants such an app for other sports tennis and swimming , where skill couldn't imaginably be simulated via an app at all. She wants to compare herself to an 8-year-old Serena Williams , a top-ranked professional tennis player. Or to a 6-year-old Michael Phelps , the most decorated Olympian competitor of all time.
Cueball expands beyond sport, wishing to determine if he could cook better than an 11-year-old Martha Stewart (author of several cookbooks). Megan wonders if she'd have won an election against a 12-year old JFK ( John F. Kennedy , the 35th American President). Obviously, cooking and politics were skills acquired later in life for both figures.  Also, the U.S. Constitution prohibits anyone from serving as President before the age of 35 , so it seems unlikely that any 12-year-old candidate could win, regardless of skill level, simply because voters would not want to elect someone ineligible to serve for another 23 years. Such a contest would likely be prohibited altogether, as ineligible candidates tend to have ballot access issues.
Cueball and Megan continue speculating about an app simulating the skills of random celebrities at various ages, even beyond the talents that made them famous. They finally end up comparing 8-year-old Magnus's swimming skill against 9-year-old Martha's (he wins). But they'd both lose a hot dog - eating contest against the championship race horse Secretariat . At this point even Megan realizes (with considerable understatement) their project "has gotten weird".
The title text extends the point to even greater absurdity, e.g. the ludicrous prospect of a young Martha Stewart knocking an adult Ronda Rousey (professional wrestler and actress) unconscious, or 9-year-old Muhammad Ali (professional boxer and activist) beating a 10-year-old JFK in air hockey . The former may be a reference to the fact that professional wrestling is more entertainment than competition, and the outcomes are often pre-staged, so the victor would not depend on which contestant was more skilled. This was also referenced in the title text of 2291: New Sports System . The horse also gets re-mentioned in the title text, losing in a hot dog eating contest against 12-year-old Ken Jennings (at time of comic writing record-holder of winning streak on television game show Jeopardy! ).
Chess was previously compared to basketball in 1392: Dominant Players , which also mentioned Magnus. This is the tenth comic about chess on xkcd .
[Cueball walks from the right towards Megan while holding up his smartphone.] Cueball: Magnus Carlsen has an app where you can play chess against a simulated version of him at different ages. Cueball: I can beat the 8½-year-old, but lose to him at 9.
[While Megan talks to Cueball he lifts his hand to his chin, while holding the smartphone down.] Megan: I want that, but for other games. Can I beat 8-year-old Serena Williams at Tennis? Swim laps faster than a 6-year-old Michael Phelps? Cueball: We should make a simulator.
[Cueball walks out left and Megan follows him. He must have pocketed his phone as it is not in his hand.] Cueball: ...Why limit it to games? Can I cook a better chicken than 11-year-old Martha Stewart? Megan: Win an election against 12-year-old JFK?
[At the top frame of this panel there is a small frame with a caption. Below lies Megan on the floor to the left in front of her laptop, while Cueball sits on the floor to the right facing her in front of his own laptop. Between them are some heavy books.] Soon... [Cueball and Megan sitting at laptops in the bottom of the panel.] Megan: Looks like 8-year-old Magnus Carlsen can swim faster than 9-year-old Martha Stewart. Cueball: But they both lose a hot-dog-eating contest to 2-year-old Secretariat. Megan: This project has gotten weird.


Tools

Explanation:
Cueball asks Megan what she does, and she begins by answering "I make tools that make tools." So far, this is a common expression of the way a sophisticated technology is built on simple building blocks, with one set of tools used to build a more powerful set of tools, and so on.
However, the iterations are carried to comical lengths, with Megan spending twenty minutes reeling off various steps including development of software code and software code debugging and development tools. And she is not even finished when Cueball breaks into her endless list after she once again says tools for by asking what is it for? (See also: 1579: Tech Loops ).
Megan readily admits that she doesn't even know the goal of these tasks, and guesses that it is probably for porn, referencing the not-entirely-unfounded stereotype that the majority of internet traffic is pornographic websites . Knowing that many information technologies, from printing to computers, are quickly adopted by porn producers and distributors, this is not a bad guess on Megan's part. Further, many internet related advances have had their way paved by a porn industry that needed secure and secret payments options, and better bandwidth for downloading films, as well as making it more accessible, etc.
In the title text there is a recursion as someone (maybe Cueball) tells what they do. And in this case they make tools for managing job-hunting sites for people who make tools for managing job-hunting sites for people who make tools for ... (ad infinitum). See also other comics about Recursion .
Regarding porn in xkcd see also 305: Rule 34 .
[Cueball talks to Megan.] Cueball: What do you do? Megan: I make tools that make tools
[Megan continues talking to Cueball in this frameless image.] Megan: ...That monitor code that deploys tools that build tools for deploying monitors...
[Cueball finally stops Megan from talking. At the top there is a small frame with a caption overlaid on the top frame:] 20 minutes later... Megan: ...For monitoring deployment of tools for- Cueball: But what's it all for? Megan: Honestly, no idea. Porn, probably.


Quadcopter

Explanation:
There is large controversy over unmanned small-scale quadcopters , which are a type of radio-controlled helicopter . Some people have objections towards the usage of quadcopters as, if equipped with cameras, they can potentially interfere with personal privacy and may pose a physical aerial hazard.
For this reason the US Federal Aviation Administration is now requiring any "drone" (unmanned aerial vehicle) to be registered so that it can find out whose fault it might be that a quadcopter interfered with commercial aircraft-or carried off a citizen to be devoured.
This comic takes place during such a lesson where Cueball is a teacher of such a class. He is standing in front of his students ( Megan , Ponytail and another Cueball-like guy), presenting the class. He has a quadcopter ready, lying on the ground behind him, and has already handed the remote control to the other guy so he can try it once the introduction is over.
But then the teacher is attacked by three rogue quadcopters flying in from behind him. They grab him and lift him off the ground (a very complicated maneuver) and fly away with him. Meanwhile, his students just stand there watching and do nothing to help him. Afterwards Megan asks if they should actually have tried to help him, but then Ponytail takes the view that now that the drones are sentient, they have become a part of nature, and that you should not interfere but just "let nature take its course". This is a common comment in nature programs about wildlife, where the speaker tries to explain why the team that was there to film the animals dying did nothing to help them - because they will not interfere with nature. This would not be possible in real life assuming they weren't using secret military technology as Cueball outweighs the drones by several factors. [ citation needed ]
This comic shows how hypocritical that comment is, because if a lion decides to kill and eat humans, that would be natural, but we would do anything in our power to kill this lion, and not just let it run off with our children or the old and weak people. So in such a case with Cueball being taken by wild quadcopters we would not just let nature takes its course.
There is currently a drone called MQ-1 Predator which is used a lot by the CIA and USAF . Although it's not a quad-copter, the idea behind this comic could come from drone names just like this. Here the comic takes the name literally, giving drones predatory behavior. This comic thus takes people's worries to the extreme, suggesting that the drones become sentient and can cooperate together just like a pack of wolves and grab a human being and fly off with him like an eagle would do with a smaller animal.
The title text refers back to the above as Randall confesses that he has to turn off any nature documentaries which show scenes of animals killing their prey, while the speaker tells that this would be part of nature. This continues the theme of treating drones as an occasionally-ugly but accepted part of nature.
Sentient quadcopters were part of the game in 1608: Hoverboard , where one quadcopter is speaking to the other over the lava lake in the Mount Doom crater to the left. How to solve the problem of too many drones was mentioned in 1523: Microdrones . Just over a week before this comic was released another comic also had as subject a situation where our technological inventions begins to take control over us, see 1626: Judgment Day . Comparing drones to animals is also present in 1881: Drone Training , when Black Hat Guy asks for a spray bottle for his drone.
[Cueball to the left talks to Megan, Ponytail and a Cueball-like person, with a remote control. They are standing to the right. Behind Cueball, on the ground, there is a quadcopter.] Cueball: Welcome to Quadcopter-flying school.
[Cueball looks over his shoulder as three other quadcopters fly in towards him from above and left. The other three people are in the same position.] Cueball: Today we'll be learning the basics of- Cueball: ...Uhh...
[In this frameless image the three quadcopters all grabs hold of Cueball, two in each of his arms, one takes hold of his legs. And then they lift him up from the ground. He is thus hanging almost horizontally, with his head over Megan and his feet over the place where he stood before. The other three just stands there looking up at him.] Cueball: Um
[Cueball is carried off by quadcopters, his head has already exited the top right corner, only his legs and the last quadcopter still in the frame. The other three have turned around looking up and right after him.]
[Megan looks down again and the other two turns towards Megan. Cueball is gone and has only left his "tame" quadcopter behind on the ground.] Megan: Should we have helped? Ponytail: No. It's cruel, but we have to let nature take its course.


Longer Than Usual

Explanation:
The comic starts a small flow chart with "This seems to be taking longer than usual." It then presents two alternative continuations of the sentence, which radically alter the interpretation of the starting sentence, resulting in humor.
"This seems to be taking longer than usual" is an error message displayed by Gmail (see here ) and other software, for example Disqus , (see here ). We realize the allusion to Gmail by the first continuation, "Try reloading Gmail if the problem persists".
In the second continuation, "Maybe we should just go to bed", the opening instead refers to a person suffering from sexual performance anxiety , taking "longer than usual" to achieve either orgasm or erection , probably despite considerable efforts of their partner. Often such frustration then becomes a self-fulfilling prophecy that renders orgasm/erection virtually impossible by ruining the mood. In such situations it is likely that one or the other partner becomes frustrated and gives up, suggesting "let's go to bed" instead of 'pointlessly' continuing the sexual activity.
The title text ties both interpretations together by referencing an infamous error message given by the Firefox internet browser . As an error message, it fits nicely with the Gmail interpretation of the comic, though it is equally likely to be used as an apology or frustrated slight in the sexual interpretation. It would be a likely next line after "this is taking longer than usual". Alternatively, it would be embarrassing to get the two responses confused, thus necessitating a flowchart as a guide.
It could also simply be a jab to people who stay online late even when doing nothing, as when a lag occurs, and finally realising it might be better to switch off the computer and go to bed; or people who stay up late obsessed that " Someone is wrong on the internet ".
This is not the first time Randall juxtaposes sex and more abstract topics, such as sex and math in 487: Numerical Sex Positions or sex and engineering in 592: Drama
[A flowchart with one starting bubble at the top. Two arrows goes left and right below this bobble to two other bobbles.] Top: "This seems to be taking longer than usual-"
Left: "-Try reloading Gmail if the problem persists."
Right: "-Maybe we should just go to bed."


Palindrome

Explanation:
A palindrome is a word, phrase, or sentence that reads the same whether you read forwards or backwards, like race car .  Normally capitalization, spacing, and punctuation are ignored.
This comic is based on the famous palindrome: "A Man, A Plan, A Canal: Panama", devised by Leigh Mercer , which references the construction of the Panama Canal and is the first mentioned on the Wikipedia page for palindromes at the time this comic was released.
Megan recites a much longer palindrome for Cueball . This palindrome is based on the original, and was posted in this forum thread more than three years before the release of this comic. It is much less logical, and manages to include the word anal (which then refers to the title text and sex toys, see below).
'Nam is an apheresis of Vietnam. See more explanation of the words in the palindrome in the Trivia section. Note that in the original version from the link above there was a comma before tables so it is two items in the list: God's 'Nam, tables, etc.
Due to its list like structure, the Panama palindrome is easily extensible by adding additional noun phrases , and some of these extensions lay claim to being " The Longest Palindrome Ever ".
The title text references the maximum size of ships that can fit through the Panama Canal, which is Panamax . Randall would really enjoy if this was the last option (i.e. biggest size) on a drop-down menu on a sex toy site. For instance such a site could have a banner saying; "If you have a Panama Anus , then try our Panamax Butt plug ".
In the game 1608: Hoverboard there is also a reference to the palindrome and the Panama canal with the song that Cueball sings at the ruin to the right. The first four lines of the song is the same as in the original palindrome but with the "A " changed out with Spider- , and then also Spider in front of Panama:
Cueball singing: Spider-man Spider-plan Spider-canal Spider-Panama Gates let in Spider boats Flood the locks Spiders float Look out! Spiders in both oceans.
Although it is less logical it is indeed a palindrome:
Original : A man, a plan, a God's 'Nam tables, nitrate, tar, tinsel, Batman's dog: Anal Panama.
Palindrome , i.e. original sentence reversed: amanaP lanA :god s'namtaB ,lesnit ,rat ,etartin ,selbat maN' s'doG a ,nalp a ,nam A
With no spaces or other punctuation and in all lowercase: amanaplanagodsnamtablesnitratetartinselbatmansdoganalpanama
[Cueball and Megan are walking. She holds up her arm and hand while reciting a palindrome:] Megan: A man, a plan, a God's 'Nam tables, nitrate, tar, tinsel, Batman's dog: Anal Panama.


Possible Undiscovered Planets

Explanation:
This comic is about Planet Nine , a possible Neptune -sized planet far beyond the farthest planet, Neptune . Astronomers Mike Brown and Konstantin Batygin published a paper on 2016-01-20, only two days before the release of this comic. The paper is called Evidence for a Distant Giant Planet in the Solar System and shows indirect evidence that such a planet may exist, inferred from an otherwise unlikely correlation between the unusual orbits of several dwarf planets . See for instance also explanations, for the layman, of the results here: Astronomers say a Neptune-sized planet lurks beyond Pluto and Planet X Discovered??
As this paper came out on the day of the previous comic's release ( 1632: Palindrome ), this comic's release day was the first release day after the news came out. This explains why this comic was released in the late afternoon rather than just past midnight as is often the case with normal releases.
Once Randall heard this news, he had to decide to do this comic instead of the scheduled comic, and then invent and draw a completely new and actually very complicated comic (resulting in several position errors ) about " Planet X " before he could release this comic.
Now this planet could be called Planet IX (and is labeled Planet nine? on the chart), as Pluto , the previously "planet 9" has been degraded to a dwarf planet. The "X" did, however, not only refer to the roman numeral! Note that Mike Brown is the astronomer that killed Pluto , or at least reduced Pluto to a dwarf planet, something that has been a subject in xkcd before; see for instance 473: Still Raw .
This was the first of two times within a month where a new astronomical announcement (of something discovered months before the actual announcement) resulted in a related comic. The second being 1642: Gravitational Waves . But in that case Randall seemed to know about it in advance, as he even changed the normal release schedule to post the comic on the day of the announcement, unlike here, where he seems to have been forced to make a new comic up on the fly.
Stating the obvious, this log–log plot shows that for an object to be an unknown planet it has to be very far away, since planets are big, to explain why we haven't seen it yet. With the log scale it is possible to go from a diameter of less than 1 mm to an astronomical unit (AU) on the Y-axis and from a distance of just 1 cm up to thousands of AU on the X-axis.
Randall's chart is somewhat humorously parochial (if not downright egocentric ) in that it purports to measure distance not "from Earth" or from an arbitrary observer, but specifically from himself ("from me"). There is also more detail (e.g. a differentiation between bird, bugs, and skin flora) in the zone closest to the observer, somewhat reminiscent of the classic New Yorker cover illustration View of the World from 9th Avenue .
The distance calculations are somewhat problematic (see more on this below). Close distances seem to be measured from the surface of Randall's body (skin/eyes) rather than from his center of mass. All the planets (and moon) that are marked on the chart are so far away that it will not matter if the distance is measured from Randall's surface, his center of mass, or by the way anywhere on Earth . Also, the planets' diameters are so much smaller than the distance from Earth that their real size would hardly take up any space in the chart due to the log-scale . The dots marking these 7 planets are thus not drawn to scale that should represent their actual size compared with the other planets. But their distance from Earth (and Randall) is not constant even on the log-scale, especially not for the nearest planets, as they can be on either side of the Sun compared to Earth.
The chart correctly states that if there was a planet that was at a distance from him smaller than its diameter, he would be inside it (although at the bottom of that region, it's more like the planet that would be inside him, as this line goes down to a diameter of 1 cm). If the distance is to the planets center, this would also fit if he was only a radius away from the planet. As Randall is not inside the Earth but really close to it, Earth is correctly positioned on this line. However, for Earth, which is marked with the largest of the dots, he seems to have put himself a full Earth diameter away from Earth. Even using the center of mass of Earth as it's position he should only have been 6,350 km away from it, but now he places the measuring point of his distance to Earth on the opposite side of the Earth so his distance to it is equal to its diameter (which would make a choosing a distance of 0 km just as correct). Earth is just left of the 10,000 km line on both axis, and Earth has a diameter of 12,700 km, which will fit fine with the center of the dot, but not with the distance which should have been the maximum distance Randall could be from it (0 or 6350 km depending on the definition of distance from Randall).
The IAU definition of planet requires a solar orbit, gravitational rounding, and "clearing the neighborhood", a controversial (at the time of its introduction) calculation of relative size that excludes Kuiper Belt Objects such as Pluto. The calculation regarding Planet Nine would make it large enough to meet the IAU definition. Using this definition the chart quickly rules out birds and bugs, although at a glance they could be mistaken for planets, something that is especially the case for planes (at night) which are even called fool’s planets’ in the chart, a reference to fool's Gold . Note that anything that is actually on Earth is positioned within 60 km from Randall. This is because if it is further away he cannot see them due to the curvature of the Earth. This does not mean that he intends to indicate that they cannot be further away from him than that.
The already known planets are prominently marked on the chart. They are the solid black dots. Besides Earth and Planet Nine? , the bottom row of three small dots are Mercury , Venus and Mars . The top row of four larger dots (but smaller than the dot that marks Earth) are (from left to right) Jupiter and Saturn (visible to the naked eye) and Uranus and Neptune (visible through a telescope).
It is unclear how Randall is calculating these distances, especially to the three terrestrial planets , since neither of these options work: closest approach, average, mean, current or maximum distance. In the comic 482: Height Randall shows (among other) the distance from the Earths surface to all the planets. For especially Venus and Mars he shows that their distance changes a lot based on theirs and Earth's orbital positions. But he has neither used these loops to base the dot size or position, as these loops clearly go closer than 1 AU and only one of the planets are drawn closer than that. It is thus unclear which of the three represents which planet, but in the table below it has been reasoned that the dot situated at the largest diameter of the three inner planets planets should represent Venus (12,000 km) as it is almost twice as big as Mars (6,700 km), which on the other hand is more similar to Mercury (5,000 km) and given that the two dots furthest out are almost the same size, it would make most sense if they represent Mercury and Mars. Since the outer dot never comes closer than 2.5 AU and Mercury never gets further away than 1.5 AU it makes most sense to place Mercury as the middle of the three and Mars as the outer of the three dots.
Below some objects are mentioned that are not on the chart, and also other errors in position (probably due the hasty creation of such a complex comic.) Many of these objects as well as the planets with the errors mentioned clearly revealed can be see in this modified image , which is also inserted and explained in the trivia section below.
Pluto, no longer considered a planet (it was the ninth until 2006), is not marked on the chart, but it would be below Neptune just outside the pink region (2,300 km diameter and 30-50 AU away). This makes sense since that region is for dwarf planets not yet discovered and any one as big and close as Pluto would have been discovered by now. There are thus also other dwarf planets that would not belong in the pink region, one of them is even much much closer and is easily visible with a telescope: Ceres , which would appear roughly below Mars and Jupiter. (950 km diameter and 1.5-4 AU away from Earth). But this pink region is there to show where there could (and most likely will) still be undiscovered dwarf planets.
The Moon is also marked on the chart, with a gray dot (almost as large as the gas giants dots). The name is written in brackets since it's not a planet (because Earth is clogging up its neighborhood). Randall has messed up the positioning and the diameter of the Moon as it is clearly positioned past a million km, and it is only up to 400,000 km away from the Earth.
The Sun is not marked at all, even though it is extremely prominent, but as it is clearly not a planet it is left out. It would per definition have been at a distance of 1 AU, and with a diameter of 1.4x10 6 km it would be well inside the region of things that we can see during the day. Note that objects this big will always be shining, already a large planet such as Jupiter is brighter than if it could reflect 100% of Sun's light. In general, planets ruled out because we would see them during the day refers to objects big enough to be stars or brown dwarfs , but the only star system , other than Sun, that would fit on the chart is Alpha Centauri , which at 4.37 light-years (ly) is well within the right boundary that falls at 5.68 ly, just before the distance to the next nearest star Barnard's Star at 5.96 ly from the Sun. A light year is 63,241 AU, and with the 10,000 AU mark far from the right edge of this log-log plot, it is clear that also 100,000 AU and thus a light year is within the chart. And this also goes for 5 ly.
"Planets ruled out by the WISE survey" refers to the Wide-field Infrared Survey Explorer (WISE), a space telescope designed to look for warm objects such as brown dwarfs, which generate heat at their centers. It was capable of detecting Saturn-sized or larger planets in the outer reaches of our solar system, but did not find any. WISE would not have detected "Planet Nine" (even if it exists) because it is too small and thus too cold to be detected. There is a chance that it can be seen in some more temperature sensitive measurements. But these have not been checked for such a planet yet, (see here ).
The word satellites is written on the border of two regions indicating that these can be in both regions. Some are small enough (10 cm) to be comparable to the space junk below, (see cubesats ), others are much bigger and would fit in the region above: Stuff we can see through telescopes . Although it may not be called a satellite in daily talk, the International Space Station is in fact a satellite, which is over 100 m in the longest direction. It would thus be on the border to the Planets ruled out because I would have noticed them above my house region just above the "A" in satellites (400 km above the surface). Some satellites can be seen without a telescope, like the space station.
The title text explains why some people confuse Superman for a bird or a plane , since Superman often flies at the limit between the two categories in the diagram. This is though not really true as can be seen in the bottom of the table below. (This was later referenced in Bird/Plane/Superman .)
[Caption above the chart.] Possible Undiscovered Planets in our Solar System By size and distance (from me)
[A chart of possible undiscovered planets with a log-log plot, with the objects diameter on the y-axis and the distance from “me” (Randall) on the X-axis. Both axes are labeled and have several ticks most of which also have labels. A region to the right, with possible new planets including Planet 9 with a “?”, is shaded light red, and a small rectangle at the top left with the same color tells what this color means. The region, of undiscovered dwarf planets, is shaded pink, also to indicate that here may be more of these, but the lighter color indicate that these will not be new “planets”. The eight known planets are marked with a black dot, and also this is explained with a dot under the colored rectangle. The Moon is indicated with a similar dot, but in gray, and the name is in brackets. The chart itself is divided into several labeled regions, the smallest with the label outside and an arrow pointing in. In one case a label breaks a border, and in two regions there are more labels, although these clearly belong to different regions within these regions, with different sizes and/or distances.]
[Y-axis, with a label written to the left, from bottom and up, with an arrow pointing up, and 15 ticks with a label each:] Diameter 1 mm 1 cm 10 cm 1 m 10 m 100 m 1 km 10 km 100 km 1,000 km 10,000 km 100,000 km 10 6 km 10 7 km 1 AU
[X-axis, with a label written below, with an arrow pointing right, and 17 ticks but only 11 labels as the ticks at 100 km, between 1000 and 10 6 km, 10 7 km as well as 10 and 1000 AU is not labeled:] Distance from me 10 cm 1 m 10 m 100 m 1 km 10 km 1000 km 10 6 km 1 AU 100 AU 10,000 AU
[At the top left of the chart is the light-red rectangle and the black dot labeled:] Possible undiscovered planets Known planets
[Going down and anti-clockwise from these two labels, the rest of the chart is transcribed:] Planets ruled out because I would be inside them Earth Planets ruled out because I would have noticed them above my house Planets ruled out because they wouldn’t fit through my door Birds that got into my house Skin flora Bugs (Not planets) Giant bugs Planets which are actually birds Airplanes (Fool’s planets’) Space junk Comets and asteroids Oort cloud Satellites Stuff we can see through telescopes Planets we can see at night (Moon) Dwarf planets Planet Nine? ? Planets ruled out by the WISE survey Planets ruled out because we would see them during the day


In Case of Emergency

Explanation:
Sometimes in order to deter vandalism or avoid accidentally moving/setting off something of importance, an important item like a fire extinguisher will be covered behind a wall of glass. "In case of emergency, break glass" - and retrieve the tool.
However the depicted situation is funny, because the thing behind the breakable glass is a glass repair kit. This is ironic, considering that the only way to reach it is by breaking the glass. One might even use it to fix the glass broken to get it... This joke is similar in nature to a Useless machine . However, the broken glass that needs to be repaired is an emergency situation, so it is important to have some less important glass to break, to be able to get to the important emergency glass repair kit . In this way it is not necessarily useless, just ironic.
In the title text Randall notes that he keeps his first aid kit in just such a type of emergency locker as shown in the comic. He complains that it is expensive to have them installed in the wall. But then the title text takes a gruesome turn when he continues by saying that at least for those lockers with first aid in them there is no need to pay extra for using safety glass for the cover. Safety glass doesn't break into sharp shards, so would be used for the cover of such an above-mentioned fire extinguisher cabinet, for instance, ensuring that the user will not cut themselves when breaking the glass to retrieve it. But Randall indirectly says that since the person breaking the glass will soon have access to a first aid kit then, if wounded in the process of breaking the normal window glass, they can as well be treated on the spot - so it will be OK to let them get injured.
First aid kits and for instance defibrillators can be found at frequent places such as bus stations and shopping malls, but never behind a glass that needs to be broken.
[On a box behind a panel of glass, with a hammer hung below, is written:] Glass repair kit


Birdsong

Explanation:
The comic shows Cueball walking and singing along with the songbird singing above him; Cueball is apparently enjoying the perfect weather and the birdsong as he comments on both. In the next panel, the bird continues to sing but now it sings actual words (to the song " Smooth " ( official video ) by Santana featuring Rob Thomas ). This gives the word songbird a completely new meaning. The bird's singing begins to annoy Cueball, so he chases the bird with a butterfly net in an attempt to catch it. Meanwhile, the bird just continues with the song. (Interestingly, the two lines from the last two panels follow each other in the song, but Cueball manages to get hold of the net in between).
The lines the bird sings are (most) of the last three lines from the chorus (see the lyrics ):
The comic is a play on the words bird and song .  Songbirds, of course, don't actually sing: the sounds they make are territorial challenges, mating cries, etc. But in Western cultural traditions, particularly the pastoral one, imagining these sounds as 'song' is part of seeing nature as beautiful and harmonious. Ironically, the fact that this bird is really singing pop music is perceived by Cueball to be an intrusion.
In the title text Cueball suggest playing pastoral music to 'reprogram' the bird, which is of course an even more unnatural intervention - all with the purpose of restoring the pastoral naturalness of the bird. Of course, some birds can actually emulate human words , and in this way also sing real words, like with the common hill myna . Other birds can mimic any odd and unusual sounds, particularly the lyrebird of Australia is known to reproduce all types of sounds from chainsaws to barking dogs and certainly also music.
The title text of "reprogramming" the bird by placing it in a box also refers to B.F. Skinner and his development of programmed learning through his theories of operant conditioning and behaviorism in psychology. By famously using birds in so-called Skinner boxes , he conditioned birds to respond to certain stimuli and expect rewards for particular behaviors, leading to an understanding of many impulsive behaviors in humans like addiction. Cueball apparently hopes to "correct" the bird and its song through this method.
Animal conditioning was also referred to in 1156: Conditioning .
Lately Randall has had his characters catch several things (but never butterflies ) with a butterfly net; most recently in 1622: Henge , where it was the Sun that was caught in the net.
[Cueball is walking and talking, while a bird, flying above him is singing, with four notes floating around it to indicate this. The notes are clearly above and removed from Cueball's text.] Cueball (singing): The sun is shining, the birds are singing—
[Cueball stops and looks up when the bird above him starts to sing using human language; four notes are floating around the text. The text of the bird's song is in italic text to indicate this.] Bird (singing): Got the kind of lovin' that can be so smooth, yeah
[Cueball looks down and black smoke emanates from the top of his head. The bird now flies above the panel but still sings in human language, four notes are floating below the text.] Bird (singing - off-panel): Give me your heart, make it real
[Cueball is chasing the bird with a butterfly net, the bird is flying away from Cueball, continuing to sing, four notes are floating around the text.] Bird (singing): Or else forget about it


XKCD Stack

Explanation:
In software engineering, a tech stack is the set of technology platforms and tools that a company or app uses. A common tech stack is LAMP , composed of a Linux operating system , an Apache Web server , a MySQL Database , and the PHP programming language. In this comic, the XKCD stack is introduced. The technologies it comprises are either non-existent, unreliable, outdated, or entirely irrelevant.
Another example of a tech stack is featured in 2166: Stack .
EBNF/CSS BNF or Backus–Naur Form is a syntax used for describing context-free grammars . EBNF is "Extended BNF", it is the same thing as BNF with a few more syntactic constructs intended to ease its use in the most common cases. 1343: Manuals mentioned EBNF. CSS or Cascading Style Sheets is a language used to describe what a web page should look like. Web pages are usually written in HTML , which describes the structure of the page (i.e. divides the document into paragraphs, lists, etc.) complemented with CSS which describes the look and feel of the page (colors, fonts, margins, etc.). EBNF/CSS would suggest CSS with strange syntax. Broken Java Applet In recent years it has become more difficult to run Java applets in several browsers. Chrome 45 stopped supporting NPAPI , Firefox dropped support in version 52, and Edge does not support NPAPI plugins at all. Furthermore, two days before this comic was published Oracle (the developer of Java) announced plans to officially end support of Java applets in an upcoming version. Archive.org Mirror Archive.org is a website which archives websites, and created the Wayback Machine . It's ambiguous whether the "Archive.org mirror" would be a copy of the xkcd server or of Archive.org itself. Hypercard.js HyperCard can be considered as a kind of predecessor for powerpoint developed at Apple . The file extension .js indicates that is was rewritten in JavaScript . A similar reference to JavaScript is found in 1508: Operating Systems . QBasic on Rails A mix between QBasic and Ruby on Rails . BASIC is a programming language that was very widespread during the 80s. QBasic is an implementation of BASIC created by Microsoft in early 90s, that, among other things, added support for structured programming . QBasic, lacking several of the features present on modern computer languages, is known for its spaghetti code. Ruby is a rather modern language, often used with Ruby on Rails web application framework . QBasic on Rails would likely mean a port of Ruby on Rails, replacing Ruby with QBasic. QBasic no longer runs on modern computers, but there are a couple of free open source implementation of QBasic, one being QB64 and the other FreeBASIC , which are available for Windows, Linux, Mac, and Android. There also exists a webserver on BASIC called RunBasic . [Blocked by AdBlocker] Ad blocking software are extensions to browsers that try to remove ads from web pages, so the user is not distracted by them. 624: Branding shows what "browsing without adblock" looks like. The joke is that AdBlocker is preventing us from seeing what makes up this portion of the stack. This could be because: Someone inserted an ad in the stack description. Some sites do insert ads in the middle of tables and lists, a typical case being between posts in forums. An ad is actually an integral part of the stack. Some sites make ads an integral part of the site content, so that users with ad blocking software will be forced to disable ad blocking to be able to properly interact with the site. Usually, in real life, this is not really a case of ads being part of the site, only that the site artificially refuses to work until it has some confirmation that ads have been properly loaded in the client side (by means of some script within the ads which sends the confirmation to the server). Ad blocking software has misidentified that portion of the stack as an ad, when in fact it is not (i.e. a false positive). This happens in real life, and it is a common source of great pains for the owner of the site which is being misidentified as an ad.
MongoDB/Excel MongoDB is a modern NoSQL database system, Microsoft Excel is a spreadsheet program from Microsoft, which is sometimes used as a database system (rarely a good choice). Some piece that works so nobody asks any questions Writing any non-trivial piece of software always require a phase of debugging , which consists in finding and fixing bugs . With complex software, this is a long and tiring process, so when the product is finally finished no one dares to modify it any further for fear that it will fail in unexpected ways. After some time passes, it is even worse because nobody really remembers how the software was supposed to work, so the product becomes some kind of godlike treasure which must be treated with the utmost respect and reverence because, you know, if it stops working we're all doomed ( 1421: Future Self ). After completion, Refactoring is the process of rewriting code for greater efficiency or reliability. However, if the performance is not 'too bad' (i.e. not unusably terrible in normal use) there is a great temptation to avoid this, in favour of the 'if it ain't broke, don't fix it' methodology. This could lead, for example, to a trained monkey and an abacus being used to crunch numbers. It works, but could be done far better. However, nobody wishes to change it, for fear of breaking a presently functional, if inefficient, system. Triply-Nested Docker Docker is a software container , which is a way that allows a complete operating system to run under different operating system (OS) (as long they share the same kernel, among other things). Triply-nested docker would mean OS A running under OS B running under OS C running under OS D (running under OS E?). That would likely be a performance and management nightmare Paravirtual Boy® This is a reference to the Virtual Boy , a failed portable console created by Nintendo . It was promoted as being a highly immersive, incredible experience , but the poor technology that it used caused it to be very criticized for not meeting the high expectations. Paravirtualization is a way of virtualization, that requires cooperation of the guest operating system, contrary to full virtualization , on which the guest operating system is not required to do anything special and the host handles everything. A dev typing real fast A dev is a software developer . This is possibly a reference to 341: 1337: Part 1 , where Mrs. Roberts edits the TCP stream live while wearing oven mitts and baking cookies. It looks like the xkcd Webserver is not a computer after all -- we have a person manually replying to HTTP protocol queries. Such a  feat would indeed require real fast typing. If this is the case, then it's possible that almost none of the other layers of the stack actually do anything. Older version of our software People are often reluctant to switch to newer versions of software because, even though newer versions are supposed to have more features and fewer bugs, they end up confusing users. Users of older versions are used to doing everything with less features and circumventing old bugs. They don't know how to use the new features, which of course come with new bugs they haven't learned how to circumvent yet. It is also often the case that newer versions remove weird unused old features, breaking the workflow of users who actually did use such features and are left without a suitable replacement ( 1172: Workflow ). Alternately, since higher parts of a stack are dependent on lower parts, this could also be a reference to how the consumer versions of Microsoft Windows (3.x, 95, 98, and ME) ran on the "older version" software Microsoft DOS until Windows NT. Paired with the previous layer, it could instead mean that the human is merely retyping the output of the older version. Mystery Networking Horror Randall suggests here that the whole networking stuff behind the XKCD service is both mysterious (no one actually knows the details) and horrific (technically questionable architecture and implementation, or somehow tentacled and eldritch in nature). Microsoft Bob Server® Microsoft Bob was a short-lived, failed attempt by Microsoft, around 1995, to provide a user-friendly interface for the Windows 3.1x, Windows 95 and Windows NT operating systems. It consisted of a virtual "house" and "rooms", and clicking on objects in the room would open applications, for instance clicking on a pen would open the word processor. It was heavily criticized and was soon discontinued. Randall seems to be making the suggestion that Bob has continued to be developed and now there's a Bob Server, similarly to Windows server. A giant CPU someone built in Minecraft Minecraft is a popular sandbox game where you place blocks to build things. Since the introduction of Redstone objects (materials used to create basic electric circuits within the game) people have made many machines within Minecraft, including calculators and clocks. The most complex of these machines simulate simple computers, capable of storing several lines of code and performing basic mathematical operations such as division, which requires thousands of blocks and extremely complex designs. A Minecraft CPU capable of hosting a website would be ridiculously huge and nearly impossible to work with: the input/output would be needlessly unwieldy, and by the time the data is parsed any other computer could have finished the job already; and Redstone circuits in Minecraft work much slower than in real life, quite literally trillions of times slower.
The title text contains several jokes about the Java programming language:
[A simple table with only one column and fifteen rows is shown. Text above:] Introducing The XKCD Stack
[The list of cells:] EBNF/CSS Broken Java Applet Archive.org Mirror Hypercard.js QBasic on Rails [Blocked by AdBlocker] MongoDB/Excel Some piece that works so nobody asks any questions Triply-Nested Docker Paravirtual Boy® A dev typing real fast Older version of our software Mystery Networking Horror Microsoft Bob Server® A giant CPU someone built in Minecraft


Salt Mine

Explanation:
Ponytail has built a particle detector (an expensive device used in experimental particle physics ) in a salt mine . Hairbun assumes that this is to block out cosmic rays , as is the case with the real life Irvine-Michigan-Brookhaven (IMB) detector, started in Lake Erie in 1979, or the Enriched Xenon Observatory (EXO), placed in the Waste Isolation Pilot Plant (WIPP) salt mine in 2007.
The IMB detector was initially used to search for proton decay in very pure water kept in the mine, and it was thus important to keep out cosmic rays that would create the same type of signal as a decaying proton. Although the IMB became famous for detecting neutrinos from supernova 1987a (which pass through virtually all materials, salt or lead etc. with only the smallest fraction of them interacting), it never observed a single proton decay out of the 10 31 protons present in the water of the detector. If it had detected even a single positive observation it would have contributed to the ratification of the Grand Unified Theory , which predicts that protons eventually decay. At the time of this comic the lower limit for proton half-life from experimental evidence is of the order 10 34 years.
Ponytail affirms Hairbun's assumption; however, based on the wording of her response, it is clear that Ponytail and her colleagues, Cueball and Megan , have an ulterior motive of using the mine to get access to an enormous supply of salt for eating. This is absurd, since salt is already plentifully available in grocery stores, the cost of the particle detector far exceeds the value of the salt and their intake appears to be far beyond any medically-advised healthy limit (and likely to be sickening in other regards).
In the comic, when Ponytail says "Yes. That is definitely why," it is obvious that when queried about the reason for building the detector, apparently to gain access to large quantities of salt, Ponytail is quick to leap on Hairbun's more scientific-sounding explanation, in an attempt to save face and appear professional.
The title text is intended to be absurd. Salt is normally used to add flavor to otherwise bland foods . However, the "bland" food that the speaker is eating is itself a chunk of salt, and they wish to season their salt with yet more salt. Additionally, the title text's wording is a bit ambiguous; "this one" could refer to the comic itself, and Randall is calling the comic bland. And, in keeping with the subject, is asking for salt to spruce it up, or it could refer to the detector planted inside the mine.
This was the first of two comics this week that concerns one of the basic condiments for food, and also regards one of the five basic tastes . The second, about sugar, was 1639: To Taste . Lately Randall has made several food related comics .
Ponytail's response is very similar to Luke's in 1397: Luke .
[Hairbun (with glasses), Ponytail, Megan and Cueball are in a salt mine. Hairbun and Ponytail talk in front of what appears to be a control console for a particle detector with a chair on each side. To the right Megan and Cueball are eating salt in large amounts straight of the rocks in the mine. They are eating so fast that salt spills from their hands and falls to the ground.] Hairbun: So you've built this particle detector in a salt mine to block out cosmic rays? Ponytail: Yes. Ponytail: That is definitely why. Cueball and Megan: Homf nomf nomf


Backslashes

Explanation:
Most programming languages use the concept of a string literal, which is just a text between some delimiters, usually quotes. For example, "Hello, world" is a string literal. The text being represented is Hello, world without the quotes. However, the quotes are also written to mark the beginning and end of the string. This is a problem when the text itself contains a quote, as in "This is a "quoted" string". The quotes around the word "quoted" are intended to be part of the text, but the language processor will likely confuse it for the end of the string, which would thus be two strings with quoted outside these strings (probably resulting in a syntax error).
To avoid this problem, an escape character (usually a backslash) is prepended to non-string-terminating quotes. So, the previous text would be written as "This is a \"quoted\" string". The language processor will substitute every occurrence of \" with only the quote character, and the string terminates at the quote character which does not immediately follow a backslash. In this case the resulting text string would be This is a "quoted" string as intended.
However, the problem now is that the intended text might contain a backslash itself. For example, the text "C:\" will now be interpreted as an unterminated string containing a quote character. To avoid this, literal backslashes also are escaped with a second backslash, i.e. instead of "C:\" we write "C:\\", where the language processor interprets \\ as one single backslash and the quote terminates the string to give C:\ as the output.
This doubling of backslashes happens in most programming and scripting languages, but also in other syntactic constructs such as regular expressions . So, when several of these languages are used in conjunction, backslashes pile up exponentially (each layer has to double the number of slashes). See example of a backslash explosion and alternatives to avoid this below .
This kind of backslash explosion is known as Leaning toothpick syndrome , and can happen in many situations . Below is an explanation of all the entries in the comic .
The backslash explosion in the title text is about a bash command (which uses the backslash to escape arguments) invoking the grep utility which searches for text following a pattern specified by means of a regular expression (which also uses the backslash to escape special characters). This leads to 3 backslashes in a row in the command, which could easily become 7 backslashes in a row if the text being searched for also contains a backslash.
Even advanced users who completely understand the concept often have a hard time figuring out exactly how many backslashes are required in a given situation. It is hopelessly frustrating to carefully calculate exactly the number of backslashes and then noticing that there's a mistake so the whole thing doesn't work. At a point, it becomes easier to just keep throwing backslashes in until things work than trying to reason what the correct number is.
It's unclear whether the regular expression in the title text is valid or not. A long discussion about the validity of the expression has occurred here on this explanation's talk page . The fact that many editors of the site, often themselves extremely technically qualified, [ citation needed ] [ citation needed ] can't determine whether the expression is valid or not, adds a meta layer to the joke of the comic. This is an example of nerd sniping (oh, the irony\!\!\!\).
A reasonable example of a backslash explosion would be a PHP script on a web server which writes JavaScript code with a Regular Expression to be run on the client. If the JavaScript code has to test a string to see if it has a double-backslash, the Regular Expression to do so would be:
where the first two backslashes represent a single backslash and the second two also represent a single backslash, so this searches for two consecutive back slashes.
And the JavaScript would be:
where every two backslashes means just one backslashes in the string, so the 8 backslashes in JavaScript become 4 backslashes in the Regular Expression.
However, since this JavaScript code is to be written through a PHP script, the PHP code would be:
where:
So, the presented scenario has escalated from a simple test for \\ to no less than seventeen backslashes in a row without stepping out of the most common operations.
If we go a bit further and try to write a Java program that outputs our PHP script, we'd have:
Here, we have 35 backslashes in a row: the first 34 produce the 17 we need in our PHP script, and the last one is for escaping the quote character. (This comes closer to The true name of Ba'al, the Soul-Eater ).
Some programming languages provide alternative matching string literal delimiters to limit situations where escaping of delimiters is needed. Often, one can begin and end a string with either a single quote or a double quote. This allows one to write 'This is a "quoted" string' if double quote marks are intended in the string literal or "This is a 'quoted' string" if single quote marks are intended. Both kinds of delimiters can't be used in the same string literal, but if one needs to construct a string containing both kinds of quote marks one can often concatenate two string literals, each of which uses a different delimiter.
Another feature that seems to be popular in modern programming languages is to provide an alternative syntax for string delimiters designed specifically to limit leaning toothpick syndrome. For example, in Python, a string literal starting with r" is a "raw string" [1] in which no escape processing is done, with similar semantics for a string starting with @" in C#. This allows one to write r"C:\Users" in Python or @"C:\Users" in C# without the need to escape the backslash. This does not allow one to embed the terminating delimiter in the middle of the string and prevents the use of the backslash to encode the newline character as \n , but comes in handy when writing a string encoding of a regular expression in which the backslash is escaping one or more other punctuation characters or a shorthand character class (e.g., \s for a whitespace character). For example, when looking for an anchor tag in HTML, developers may encode the regular expression as <[Aa]\s[^>]*> . If they express this regular expression as a raw string literal, the code looks like r"<[Aa]\s[^>]*>" instead of "<[Aa]\\s[^>]*>" . The point here is that "leaning toothpick syndrome" is such a real problem that it has influenced programming language implementations.
[A list of the names of different numbers of backslashes. After each "item" there is a gray line to the text describing each item. As the text is aligned above each other, the lines becomes shorter as the sequence of backslashes becomes longer until there is just a line with the length of a single hyphen for the last item. There are 1 to 8 backslashes and then 11 plus "..." in the last entry.] \ ------------ Backslash \\ ----------- Real backslash \\\ ---------- Real real backslash \\\\ ---------- Actual backslash, for real this time \\\\\ --------- Elder backslash \\\\\\ -------- Backslash which escapes the screen and enters your brain \\\\\\\ ------- Backslash so real it transcends time and space \\\\\\\\ ------ Backslash to end all other text \\\\\\\\\\\... - The true name of Ba'al, the Soul-Eater
The title text when first published was
It was changed within a few days to
The original title text seems to be more relevant to the comic, but the revised title text seems to make more sense as a legitimate command line due to the way backslashes are interpreted in regular expressions. See the Discussion below for much more on the topic.