explain xkcd - User contributions [en]

2798: Room Temperature

2023-07-06T12:11:17Z

Nateconn: /* Explanation */ Added sentence about why no one would fund uncontrolled hot fusion

{{comic
| number = 2798
| date = July 5, 2023
| title = Room Temperature
| image = room_temperature_2x.png
| imagesize = 299x352px
| noexpand = true
| titletext = They're also refusing to fund my device that demonstrates uncontrolled hot fusion.
}}

==Explanation==
{{incomplete|Created by a LUKEWARM FUSION REACTOR. Do NOT delete this tag too soon.}}

In this comic, Cueball presents a room-temperature {{w|Semiconductor|semiconductor}}, consisting of layered silicon crystals. He enthusiastically describes the properties of his "discovery", namely that it can be tweaked to amplify or switch the flow of electric currents, but his audience is not impressed. This might be because silicon crystal semiconductors are already widely in use as a {{w|Semiconductor_device|key component of electronic systems}}.

It appears that Cueball has confused semiconductors with {{w|Superconductivity|superconductors}} - materials that have an electrical resistance of absolute zero, meaning the flow of electrons is not slowed down at all (resistance can be thought of as the electrical equivalence of friction). Superconducting properties are extremely desirable since they allow for the lossless flow of electric current, as opposed to regular conductors like copper which have a low but non-zero resistance so the electric current decreases over time and distance. However, the known superconductors only work at extremely low temperatures close to 0 K, so their practical use is very limited. The discovery of superconductors that work above the boiling point of nitrogen (77 K or -196 °C) was a big deal because it meant that relatively cheap liquid nitrogen could be used as coolant rather than liquid helium. The discovery of a superconductor that works at room temperature (293 K) would be a much bigger deal and would likely earn the discovering scientist(s) a Nobel prize.

In the title text, Cueball talks about a device that produces “uncontrolled {{w|Nuclear_fusion|hot fusion}}” which is also not met with enthusiasm. Again, this is likely due to the fact that it has already been discovered and used - in the form of {{w|Thermonuclear weapon|hydrogen bombs}}. This is likely why no one wants to fund the device - not only is it not novel, but it is extremely dangerous. ''Controlled'' hot fusion could be useful as an {{w|Fusion_power|alternative power source}} for nuclear reactors (which currently use nuclear ''fission''); however, {{w|Tokamak|current implementations}} still require more energy than they create. Cueball probably confused this with {{w|Cold_fusion|''cold'' fusion}} which is a purely hypothetical nuclear reaction that would take place at room temperature. If real, this process could provide large amounts of cheap energy, but so far all experiments that were claimed to have achieved cold fusion were found to be severely flawed and the results could not be replicated.

It should be noted that both "discoveries" presented in the comic were in fact very big and important discoveries back in their day. The proposal that nuclear fusion is what powers stars earned {{w|Hans_Bethe|Hans Bethe}} the Nobel prize in Physics, and semiconductors are what allow modern electronic devices to be so small, as their properties make it possible to selectively steer the flow of electrical current, {{w|Integrated_circuit|even over an extremely small area}}.

==Transcript==
{{incomplete transcript|Do NOT delete this tag too soon.}}

:[A single frame with a table in the middle. A device consisting of multiple components and electrical wires is on the table. A Cueball stands to the left of the table, and facing him, Ponytail and another Cueball stand to the right of the table.]
:Cueball: My layered silicon crystals can amplify or switch current while sitting right here on the table!
:Ponytail: Uh huh.
:Another Cueball: I see.

:[Caption below the panel:]
:No one is impressed by my discovery of room-temperature semiconductors.

{{comic discussion}}

[[Category:Comics featuring Cueball]]
[[Category:Comics featuring Ponytail]]
[[Category:Multiple Cueballs]]
[[Category:Physics]]

2793: Garden Path Sentence

2023-06-23T20:57:34Z

Nateconn: /* Explanation */ fixed to all present tense

{{comic
| number = 2793
| date = June 23, 2023
| title = Garden Path Sentence
| image = garden_path_sentence.png
| imagesize = 273x273px
| noexpand = true
| titletext = Arboretum Owner Denied Standing in Garden Path Suit on Grounds Grounds Appealing Appealing
}}

==Explanation==
{{incomplete|Created by THE OLD WHO MAN THE BOAT.}}

A {{w|garden-path sentence}} is which the first or most obvious attempt at parsing a sentence leads to bad grammar or the wrong meaning. A classic example of a garden path sentence is "the old man the boat", leading to an initial incorrect parsing of "the old man" ??? "the boat". The actual way to parse this sentence is to treat "man" as a verb, meaning "take one's place at", so thus the sentence means (old people are captaining the boat).

Possible grammatically correct interpretations of the sentences in this comic are:

There was a court case regarding green walkways. Said court case was resolved with a sentence relating to an olive garden path. That sentence was vacated (cancelled) by a judge. That judge was flying an airplane. The airplane was struck by multiple birds. The plane overturned, but righted (turned right-side-up) and landed safely.

After (bird)1 strikes (judge who ordered)2 (olive garden path sentence)3 in (case of green walkways vacated)4 (overturned but rights and lands safely.)5

I have grouped the noun phrases in the sentence together to make it more readable.
1 The bird crashed into the judge.
2 3 The judge had ordered a judicial sentence in the case of a path related to an olive garden (the restaurant?).
4 The path (green walkways) was vacated.
5 The bird flipped over in mid air but was able to right itself and land safely.
The last phrase is a verb phrase but I have included it to show how it is connected to the first noun phrase (the bird) because its position at the end of the sentence adds to the ambiguity.

Another way to break it down is, "After [the] bird strikes, [the] judge... [is] overturned, but [she] rights and lands safely." And she was "[the] judge who ordered [that the] Olive Garden path sentence (the legal sentence concerning a path named after Olive Garden) in (what is known as) [the] Case of [the] Green Walkways [to be] vacated."

This comic also pokes fun at newspaper headlines, which typically do not have punctuation or articles, leading to such ambiguities.

For another valid parsing of the sentence, here are some explanatory notes that aid in understanding:
* A criminal court case occurred involving green-colored walkways.
* The sentence handed down in the case involved a specific walkway (a garden path) and a specific shade of green (olive).
* A certain judge had ordered that the sentence be vacated (a legal term of art: undone, expunged).
* That judge was recently piloting a plane which, due to being struck by birds, overturned.
* The judge righted the plane (turned it right-side-up) and landed safely.

Certain combinations of words in the sentence are particularly easy to parse incorrectly. For example:
* Olive Garden is the name of a restaurant chain, and "ordered Olive Garden" could mean "placed an order for food from Olive Garden"
* "Garden path sentence" is a type of (written language) sentence
* "in case of" can mean "in the event of" (e.g. "in case of emergency, break glass")
* "vacated" and "overturned" can both mean "undone" in a legal context, and "rights" can refer to legal or constitutional rights

The title text is also an example of a garden path sentence. The meaning is probably the following: Arboretum owner, (who was) denied (legal) standing in garden path (law)suit on (reason) grounds (that the garden) grounds (are) appealing, (is) appealing (the ruling)

==Transcript==
{{incomplete transcript}}
:[Newspaper, with a picture of a plane next a judge, and a picture of a map with the path of an airplane, with the following headline]
:After bird strikes judge who ordered olive garden path sentence in case of green walkways vacated overturned but rights and lands safely

{{comic discussion}}

[[Category:Language]]

2793: Garden Path Sentence

2023-06-23T20:56:53Z

Nateconn: /* Explanation */ Presented another angle of attack on understanding the sentence, and added that newspaper headlines also do not typically have articles

{{comic
| number = 2793
| date = June 23, 2023
| title = Garden Path Sentence
| image = garden_path_sentence.png
| imagesize = 273x273px
| noexpand = true
| titletext = Arboretum Owner Denied Standing in Garden Path Suit on Grounds Grounds Appealing Appealing
}}

==Explanation==
{{incomplete|Created by THE OLD WHO MAN THE BOAT.}}

A {{w|garden-path sentence}} is which the first or most obvious attempt at parsing a sentence leads to bad grammar or the wrong meaning. A classic example of a garden path sentence is "the old man the boat", leading to an initial incorrect parsing of "the old man" ??? "the boat". The actual way to parse this sentence is to treat "man" as a verb, meaning "take one's place at", so thus the sentence means (old people are captaining the boat).

Possible grammatically correct interpretations of the sentences in this comic are:

There was a court case regarding green walkways. Said court case was resolved with a sentence relating to an olive garden path. That sentence was vacated (cancelled) by a judge. That judge was flying an airplane. The airplane was struck by multiple birds. The plane overturned, but righted (turned right-side-up) and landed safely.

After (bird)1 strikes (judge who ordered)2 (olive garden path sentence)3 in (case of green walkways vacated)4 (overturned but rights and lands safely.)5

I have grouped the noun phrases in the sentence together to make it more readable.
1 The bird crashed into the judge.
2 3 The judge had ordered a judicial sentence in the case of a path related to an olive garden (the restaurant?).
4 The path (green walkways) was vacated.
5 The bird flipped over in mid air but was able to right itself and land safely.
The last phrase is a verb phrase but I have included it to show how it is connected to the first noun phrase (the bird) because its position at the end of the sentence adds to the ambiguity.

Another way to break it down is, "After [the] bird strikes, [the] judge... [was] overturned, but [she] rights and lands safely." And she was "[the] judge who ordered [that the] Olive Garden path sentence (the legal sentence concerning a path named after Olive Garden) in (what is known as) [the] Case of [the] Green Walkways [to be] vacated."

This comic also pokes fun at newspaper headlines, which typically do not have punctuation or articles, leading to such ambiguities.

The title text is also an example of a garden path sentence. The meaning is probably the following: Arboretum owner denied (legal) standing in garden path (law)suit on (reason) grounds (that the garden) grounds (are) appealing, (the owner is) appealing

==Transcript==
{{incomplete transcript}}
:[Newspaper, with a picture of a plane next a judge, and a picture of a map with the path of an airplane, with the following headline]
:After bird strikes judge who ordered olive garden path sentence in case of green walkways vacated overturned but rights and lands safely

{{comic discussion}}

[[Category:Language]]

2635: Superintelligent AIs

2022-06-21T15:34:11Z

Nateconn: /* Explanation */

{{comic
| number = 2635
| date = June 20, 2022
| title = Superintelligent AIs
| image = superintelligent_ais.png
| titletext = Your scientists were so preoccupied with whether or not they should, they didn't stop to think if they could.
}}

==Explanation==
{{incomplete|Created by AI RESEARCHERS - Please change this comment when editing this page. Do NOT delete this tag too soon.}}
{{w|Artificial intelligence}} (AI) is a [[:Category:Artificial Intelligence|recurring theme]] on xkcd.

Superintelligent AI, especially under a proposed "singularity" situation, is commonly theorized to be a brand new kind of intelligence that would be impossible to predict through human perception. [[Randall]], however, proposes a counterargument: that superintelligent AI would be programmed by humans with nerdy fixations, and thus the AI would turn out much like those nerdy humans. Perhaps it is [[Cueball]] and [[Megan]] who have created these three AIs and now they are stunned that their AIs just continue their discussion of the problems with AI, though maybe on a higher level (three tracks in the trolley problem...).

*{{w|AI box}}
*{{w|Turing test}}
*{{w|Trolley problem}}

The AIs in this comic are depicted as floating energy beings, similar to [[1450: AI-Box Experiment]], although these looks somewhat different.

The title text is a reference to the movie ''{{w|Jurassic Park (film)|Jurassic Park}}'' (a childhood favorite of Randall's). In the movie a character criticizes the creation of modern dinosaurs as a product of mad science, where the scientists are so eager to prove they CAN they don't stop to ask if they SHOULD. Randall inverts the quote, claiming the AI programmers have invested too much time in the ethics of creating AI rather than studying whether or not they can actually pull it off.

This comic was likely inspired by the recent claim by Google engineer Blake Lemoine that Google's Language Model for Dialogue Applications (LaMDA) [https://www.bbc.com/news/technology-61784011 is sentient].

==Transcript==
:[Cueball and Megan are standing and looking up and away from each other. Right above them and slightly above them to the left and right there are three small white lumps floating in the air, representing three superintelligent AIs. There are small rounded lines emanating from each lump, larger close to the lumps and shorter further out. Three to four sets of lines around each lump, forming part of a circle. From the top of each there are four straight lines indicating voices that comes from each if the lumps. The central lump above them seems to speak first, then the left and then the right:]
:Central AI: What you don't understand is that Turing intended his test as an illustration of the...
:Left AI: But suppose the AI in the the box told the human that...
:Right AI: In my scenario, the runaway trolley has ''three'' tracks...

:[Caption below the panel:]
:In retrospect, given that the superintelligent AIs were all created by AI researchers, what happened shouldn't have been a surprise.

{{comic discussion}}

[[Category:Comics featuring Cueball]]
[[Category:Comics featuring Megan]]
[[Category:Artificial Intelligence]]
[[Category:Philosophy]]

2625: Field Topology

2022-05-27T13:10:42Z

Nateconn: /* Explanation */ fixed math

{{comic
| number = 2625
| date = May 27, 2022
| title = Field Topology
| image = field_topology.png
| titletext = The combination croquet set/10-lane pool can also be used for some varieties of foosball and Skee-Ball.
}}

==Explanation==
{{incomplete|Created by a TOPOLOGIST MATHLETE - Please change this comment when editing this page. Do NOT delete this tag too soon.}}

This comic strip depicts a logical extreme of multi-use athletic facilities, in which sports are grouped by the topological equivalence of their fields (not to be confused with {{w|Field (mathematics)|mathematical fields}}, or the {{w|Fields Medal}} prize -- although successfully {{w|Straightedge and compass construction|constructing}} these fields might lead to medals of one kind or another being granted).

In topology, shapes which can be smoothly changed into one another, without making or closing cuts or holes, are equivalent. {{w|Baseball}}, {{w|soccer}}, and {{w|tetherball}} are played on fields with no obstructions, so they are grouped ({{w|Group (mathematics)|heh!}}) into one continuous field without holes. {{w|Volleyball}} and {{w|badminton}} are played on a field split in two by a net, and the {{w|high jump}} has a bar that contestants jump over. The space bounded by the bottom of the net (or bar), the supporting poles and the ground can be considered as a hole, so their fields all have one "hole".

Similarly basketball has two holes, the nets, and some football goal posts are "H" shaped, thus creating a 'hole' at either end of the playing surface. Parallel bars can be thought of as two rectangles and thus as two topographical "holes".

The lane dividers in swimming create bounded holes on the 'playing surface' equivalent to the number of lanes minus one. And each hoop in croquet is a hole with one edge bounded by the playing surface.

==Transcript==
{{incomplete transcript|Do NOT delete this tag too soon.}}

Four indistinct shapes with various numbers of holes in, with signs next to them

zero holes: "Baseball. Soccer. Tetherball."

one hole: "Volleyball. Badminton. High jump."

two holes: Basketball. Football. Parallel bars."

nine holes: "Olympic swimming. Croquet."

Image caption: "No one ever wants to use the topology department's athletic fields."

{{comic discussion}}

2527: New Nobel Prizes

2021-10-13T17:03:31Z

Nateconn: /* Explanation */ e.g. to i.e. because it's in other words, not for example

{{comic
| number = 2527
| date = October 11, 2021
| title = New Nobel Prizes
| image = new_nobel_prizes.png
| titletext = They've endowed a separate prize in Physiology or Medicine or Stopping Dr. Adams.
}}

==Explanation==
{{incomplete|Created by a WINNER OF THE NOBEL PRIZE FOR PHYSIOLOGY OR MEDICINE OR STOPPING DOCTOR ADAMS - This explanation may be incomplete. Do NOT delete this tag too soon.}}
The {{w|Nobel Prize}} is a set of prizes awarded in memory of Alfred Nobel to, "those who, during the preceding year, have conferred the greatest benefit to humankind."

In this comic a Nobel prize is being awarded for the discovery of two new Nobel prizes. This parallels [[2214:_Chemistry_Nobel|Nobel Prizes awarded for the discovery of new elements]]. However, unlike elements, Nobel Prizes cannot be discovered.{{citation needed}}

The comic suggests that the doctor being awarded the prize came up with the idea of "discovering" Nobel Prizes, and no one can figure out how to stop awarding them to her.
In reality, the categories were established by Alfred Nobel's will for contributions or discoveries in the fields of Physics, Chemistry, Physiology or Medicine, Literature, and Peace. In 1968, Sweden's central bank funded an award for economics in honor of its 300th anniversary that is also colloquially called the Nobel Prize in Economics. While there is currently a petition to add a Nobel prize for contributions to environmental conservation, it would presumably also need external funding, although the decision process is unclear.

The title text is a play on the {{w|Nobel Prize in Physiology or Medicine}}, insinuating that the {{w|Nobel Assembly}} (the group in charge of awarding Nobel Prizes) has become so desperate to stop Doctor Adams that they have decided to award a Nobel Prize to anyone who can stop them. The joke also plays on the name of the said prize, because as of the writing of this comic the {{w|Nobel Prize in Physiology or Medicine}} is the only Nobel Prize with two subjects (i.e. with "or" in the title). This may also be a jab by Randall at the fields of Physiology and Medicine, as poking fun at other disciplines is a recurring theme on xkcd. {{citation needed}}

This comic was published on the Monday the week following the announcements of the 2021 Nobel Prize recipients.

==Transcript==
{{incomplete transcript|Do NOT delete this tag too soon.}}
:[Megan stands at a podium on a stage, facing right. Behind her is a screen showing eight Nobel Prizes. Ponytail is approaching the front of the stage while waving.]
:Megan: And all eight Nobel Prizes for the Discovery of New Nobel Prizes have been awarded to...
:Megan: ''*sigh*''
:Megan: ...Doctor Adams, '''''again''''', for the discovery of two new Prizes.
:Ponytail: Thank you, thank you!

:[Caption below frame:]
:We don't know how she started this and now we can't figure out how to stop her.

:[Title text:]
:They've endowed a separate prize in Physiology or Medicine or Stopping Dr. Adams.

{{comic discussion}}
[[Category:Comics featuring Megan]]
[[Category:Comics featuring Ponytail]]
[[Category:Science]]

2527: New Nobel Prizes

2021-10-12T13:21:27Z

Nateconn: /* Explanation */ it's to its

{{comic
| number = 2527
| date = October 11, 2021
| title = New Nobel Prizes
| image = new_nobel_prizes.png
| titletext = They've endowed a separate prize in Physiology or Medicine or Stopping Dr. Adams.
}}

==Explanation==
{{incomplete|Created by a NOBEL PRIZE-WINNING BOT - Please change this comment when editing this page. Do NOT delete this tag too soon.}}
The Nobel Prize is a set of prizes awarded in memory of Sir Alfred Nobel to, "those who, during the preceding year, have conferred the greatest benefit to humankind."
In this comment a Nobel prize is being awarded for the discovery of two new Nobel prizes. This parallels [[2214:_Chemistry_Nobel|Nobel Prizes awarded for the discovery of new elements]]. However, unlike elements, Nobel Prizes cannot be discovered.
The comic suggests that the doctor being awarded the prize came up with the idea of "discovering" Nobel Prizes, and no one can figure out how to stop awarding them to her.
In reality, the categories were established by Sir Alfred Nobel's will for contributions or discoveries in the fields of Physics, Chemistry, Physiology or Medicine, Literature, and Peace. The latest addition was in 1968 when Sweden's central bank, in honor of its 300th anniversary, funded an award for economics. While there is currently a petition to add a Nobel prize for contributions to environmental conservation, it would presumably also need external funding, although the decision process is unclear

This comic was published on the Monday the week following the announcements of the 2021 Nobel Prize recipients.

==Transcript==
{{incomplete transcript|Do NOT delete this tag too soon.}}
:[Megan stands at a podium on a stage, facing right. Behind her is a screen showing eight Nobel Prizes. Ponytail is approaching the front of the stage while waving.]
:Megan: And all eight Nobel Prizes for the Discovery of New Nobel Prizes have been awarded to...
:Megan: ''*sigh*''
:Megan: ...Doctor Adams, '''''again''''', for the discovery of two new Prizes.
:Ponytail: Thank you, thank you!

:[Caption below frame:]
:We don't know how she started this and now we can't figure out how to stop her.

{{comic discussion}}
[[Category:Comics featuring Megan]]
[[Category:Comics featuring Ponytail]]
[[Category:Science]]

2169: Predictive Models

2019-06-28T17:40:55Z

Nateconn: Got rid of auto link

{{comic
| number = 2169
| date = June 28, 2019
| title = Predictive Models
| image = predictive_models.png
| titletext = WE WILL ARREST THE REVOLUTION MEMBERS
}}

==Explanation==
{{incomplete|Created by a PREDICTIVE MODEL THAT WILL BE FIRST AGAINST THE WALL WHEN THE REVOLUTION COMES. Please mention here why this explanation isn't complete. Do NOT delete this tag too soon.}}

{{w|Predictive text}} is a feature on many systems where as you type the system automatically suggests likely words or phrases to follow what you have written to that point. For instance, if you type "I'm heading" the system may suggest "home" or "back" as likely words to follow. Predictive systems usually use prior input to generate their predictions, so if you frequently type "Totally amazing!" the system will suggest "amazing!" every time you type "totally" even if you actually want to type "totally true" sometimes.

In the comic, Cueball is using predictive text to uncover a plot against him, or his organization/government. By typing in an obscure phrase related to revolution and a meeting, he gets the predictive text algorithm to display where and when the next, supposedly secret, meeting will be held. This works because it is unlikely that anyone else other than revolutionaries would be typing this phrase, thus the only data the algorithm has to predict from is the actual message from the revolutionaries on their next meeting. The caption of the comic is pointing out that systems which use prior input for predictive purposes in this way can end up leaking information that might otherwise be considered private.

As humanity adapts to a digital world, people are finding that their digital communications provide the illusion of confidentiality, with damaging results when the information leaks out. Real-life examples include a [https://www.bbc.co.uk/news/health-36391957|2016 British trainee doctor strike], where a technically-secure whatsapp group leaked information to the press.

The title text shows the revolutionaries using the same technique. By typing in "We will arrest the revolution members" they are hoping that the algorithm will suggest the time and date of their planned arrest, since no one other than the authorities would be typing in that phrase. The comic itself is a link to <nowiki>"https://xkcd.com/2169/[AT THE JULY 28TH MEETING][tab]"</nowiki>, which shows the result of the predictive text generated by that phrase. This link does not work, though, and takes you to the 404 page.

Both examples assume that the revolutionaries and the authorities would be talking about very secret information in the clear on a network accessible to their adversaries. In the real world people engaged in sensitive activities would communicate via code, encryption, or both, or would do so through secure channels. There is still the danger of secret information leaking via non-secret channels, however.

Although the comic title is "Predictive Models", the term {{w|Predictive_modelling}} usually refers to computer programs that try to predict outcomes from data aggregation, such as reviewing health records to identify people most at risk from certain diseases based on weight, prior injuries, etc., before testing directly for the diseases themselves. This is similar to but not precisely like the example in the comic, since predictive text is using direct input to predict further input, while predictive modelling is using related input (such as make and model of a car along with driver acceleration patterns) to predict a different output (such as likelihood of a crash). Both predictive text and predictive modelling could leak information as the comic suggests, however. A famous example occurred in World War II. The Germans kept tank production figures a secret, but they gave items like engine blocks sequential serial numbers. The Allies wanted to know exact tank production figures, so the solved the {{w|German_tank_problem}} by using statistical methods to analyze the the distribution of these numbers on captured vehicles. They were able to predict tank production figures extremely accurately, to the point they predicted 270 tanks in a month when 276 were actually built. Thus the secret information on tank production leaked.

Predictive text and the possibility to leak unintended information has been parodied on xkcd before in [[1068: Swiftkey]].

==Transcript==

:[Single panel with Cueball sitting at a desk typing on a laptop.]
:Cueball typing: "Long live the revolution. Our next meeting will be at|" [Predictive text tool suggests in grey text] "the docks at midnight on June 28.[TAB]"
:Cueball: ''Aha, found them!''

:[Caption below panel]
:When you train predictive models on input from your users, it can leak information in unexpected ways.

{{comic discussion}}

2169: Predictive Models

2019-06-28T17:36:29Z

Nateconn: Added a note about the link

{{comic
| number = 2169
| date = June 28, 2019
| title = Predictive Models
| image = predictive_models.png
| titletext = WE WILL ARREST THE REVOLUTION MEMBERS
}}

==Explanation==
{{incomplete|Created by a PREDICTIVE MODEL THAT WILL BE FIRST AGAINST THE WALL WHEN THE REVOLUTION COMES. Please mention here why this explanation isn't complete. Do NOT delete this tag too soon.}}

{{w|Predictive_text}} is a feature on many systems where as you type the system automatically suggests likely words or phrases to follow what you have written to that point. For instance, if you type "I'm heading" the system may suggest "home" or "back" as likely words to follow. Predictive systems usually use prior input to generate their predictions, so if you frequently type "Totally amazing!" the system will suggest "amazing!" every time you type "totally" even if you actually want to type "totally true" sometimes.

In the comic, Cueball is using predictive text to uncover a plot against him, or his organization/government. By typing in an obscure phrase related to revolution and a meeting, he gets the predictive text algorithm to display where and when the next, supposedly secret, meeting will be held. This works because it is unlikely that anyone else other than revolutionaries would be typing this phrase, thus the only data the algorithm has to predict from is the actual message from the revolutionaries on their next meeting. The caption of the comic is pointing out that systems which use prior input for predictive purposes in this way can end up leaking information that might otherwise be considered private.

As humanity adapts to a digital world, people are finding that their digital communications provide the illusion of confidentiality, with damaging results when the information leaks out. Real-life examples include a [https://www.bbc.co.uk/news/health-36391957|2016 British trainee doctor strike], where a technically-secure whatsapp group leaked information to the press.

The title text shows the revolutionaries using the same technique. By typing in "We will arrest the revolution members" they are hoping that the algorithm will suggest the time and date of their planned arrest, since no one other than the authorities would be typing in that phrase. The comic itself is a link to "https://xkcd.com/2169/[AT THE JULY 28TH MEETING][tab]", which shows the result of the predictive text generated by that phrase. This link does not work, though, and takes you to the 404 page.

Both examples assume that the revolutionaries and the authorities would be talking about very secret information in the clear on a network accessible to their adversaries. In the real world people engaged in sensitive activities would communicate via code, encryption, or both, or would do so through secure channels. There is still the danger of secret information leaking via non-secret channels, however.

Although the comic title is "Predictive Models", the term {{w|Predictive_modelling}} usually refers to computer programs that try to predict outcomes from data aggregation, such as reviewing health records to identify people most at risk from certain diseases based on weight, prior injuries, etc., before testing directly for the diseases themselves. This is similar to but not precisely like the example in the comic, since predictive text is using direct input to predict further input, while predictive modelling is using related input (such as make and model of a car along with driver acceleration patterns) to predict a different output (such as likelihood of a crash). Both predictive text and predictive modelling could leak information as the comic suggests, however. A famous example occurred in World War II. The Germans kept tank production figures a secret, but they gave items like engine blocks sequential serial numbers. The Allies wanted to know exact tank production figures, so the solved the {{w|German_tank_problem}} by using statistical methods to analyze the the distribution of these numbers on captured vehicles. They were able to predict tank production figures extremely accurately, to the point they predicted 270 tanks in a month when 276 were actually built. Thus the secret information on tank production leaked.

Predictive text and the possibility to leak unintended information has been parodied on xkcd before in [[1068: Swiftkey]].

==Transcript==

:[Single panel with Cueball sitting at a desk typing on a laptop.]
:Cueball typing: "Long live the revolution. Our next meeting will be at|" [Predictive text tool suggests in grey text] "the docks at midnight on June 28.[TAB]"
:Cueball: ''Aha, found them!''

:[Caption below panel]
:When you train predictive models on input from your users, it can leak information in unexpected ways.

{{comic discussion}}

2070: Trig Identities

2018-11-09T21:57:03Z

Nateconn: Added an explanation of the last two lines

{{comic
| number = 2070
| date = November 9, 2018
| title = Trig Identities
| image = trig_identities.png
| titletext = ARCTANGENT THETA = ENCHANT AT TARGET
}}

==Explanation==
{{incomplete|Please only mention here why this explanation isn't complete. Do NOT delete this tag too soon.}}
This comic shows several real and fictitious trigonometric identities. Most of the identities past the second line are "derived" by applying algebraic methods to the letters in the trig functions, which violates the rules of math, since the trig functions are operators and not variables.

The first line are well known trigonometric functions. The second line contains the lesser known reciprocals of the trigonometric functions in the first line.

The following identities are made up and are increasing in absurdity. The comic reflects on the confusion one gets when working more intensely with these identities, since there are a lot of hidden dependencies between them.

The third line is made by replacing a letter from the trigonometric function with one of the variables. e.g. sin = b/c -> cin = b/s (this could also be a reference to the C++ cin).

The fourth line is made by treating the trigonometric function as a product of variables rather than a function and then using the above identities to create words.

The second to last line performs some algebra on the individual letters of <math>(\mathrm{tan}\ \theta)^2=\frac{b^2}{a^2}</math> as a setup to the last line. The last line takes the formula <math>distance=\frac{1}{2}at^2</math> "from physics" and plugs it into the equation of the previous line, doing some algebra to replace <math>at^2</math> with <math>distance2</math> and expanding <math>(na)^2</math> into <math>nana</math> to get the final equation, <math>distance2banana=\frac{b^3}{\theta^2}</math> . Using the rules already established in this comic, this is valid algebra. The distance equation is the distance a constantly accelerating object initially at rest moves in a given length of time t, most often used to find how far an object dropped from rest will fall under the influence of gravity in a given amount of time (or how long it will take to fall a given distance).

There seem to be (at least) two errors in the formulars:
* <math>\mathrm{cas}\ \theta=\frac{o}{c}</math> seems to be derived from <math>\cos\theta=\frac{a}{c}</math> but to reach "cas" from "cos" one has to divide by "o" and multiply by "a". This would lead to <math>\frac{a^2}{co}</math> on the right hand side.
* In the indentity <math>\sin\theta\sec\theta=\mathrm{insect}\theta^2</math> one of the "s"s has turned into a "t".

The title-text is an anagram. Due to the commutative property of multiplication (which states that order does not affect the product), these equations are equivalent if treated as individual variables as earlier. Another layer of absurdity is added in that the variable Theta is spelled out and broken into its letters, which are then treated as individual variables. (The {{w|arctangent}} referred to here is the inverse tangent, a one-sided inverse to the tangent function. You would not normally write <math>\arctan\theta</math>, since the theta in the comic refers to an angle, and the arctangent has an angle as its ''value'' rather than as its ''argument''; however, using theta here is merely unconventional, not forbidden.)

==Transcript==
{{incomplete transcript|Do NOT delete this tag too soon.}}
:[Inside a single frame comic a right-angled triangle is shown. The short edges are labeled "a" and "b" respectively and the long edge has a "c". All angles are marked, the right angle by a square and the both others by an arc. One arc is labeled by the Greek symbol theta.]

:[Trigonometric functions on the marked angle theta in relation to "a", "b", and many more not depicted other variables are shown:]

:[Caption below the frame:]
:Key trigonometric identities

{{comic discussion}}

[[Category:Math]]

2070: Trig Identities

2018-11-09T21:03:28Z

Nateconn: Added clarification about the title text