explain xkcd - User contributions [en]

2902: Ice Core

2024-03-05T09:21:24Z

DeeJaye6:

{{comic
| number = 2902
| date = March 4, 2024
| title = Ice Core
| image = ice_core_2x.png
| imagesize = 318x333px
| noexpand = true
| titletext = If you find an ash deposition layer from a year in which an eruption destroyed an island that had Camellia sinensis growing on it, you can make a Gone Island Ice_τ.
}}

==Explanation==
{{incomplete|Created by a PALEOCLIMATOLOGIST CELEBRATING HIS 21st BIRTHDAY - Please change this comment when editing this page. Do NOT delete this tag too soon.}}
Some people may like to taste a wine dated to the year they were born, or perhaps are subject to it as a family tradition, This would more typically be for a special occasion such as a milestone birthday than because it happens to be a 'good year' for the wine(s) they favor (unless they were particularly fortunate). Reaching the legal drinking age would be an appropriate opportunity to partake in a wine that is the same age as themselves. This comic extends this practice into a joke that paleoclimatologists, who study the climate, use dated ice instead of dated wine, drilling into the ground to find the layer of ice matching the birth year of the recipient, either to drink 'neat' (once sufficiently melted) or as the '{{w|Bartending terminology#On the rocks|on the rocks}}' part of another drink, perhaps a cocktail.

[[Megan]], a {{w|paleoclimatologist}}, decides to make a cocktail with the ice from the icesheets (present in the Arctic and Antarctic, for example). Normally, scientists would try to date the ice and then use it to describe the state of the climate when these icesheets formed. Here, Megan tries to find the ice layer corresponding to [[Knit Cap]]'s birth year with the intent of using the ice for the chosen drink. The caption asserts that this method of creating drinks is “traditional” for paleoclimatologists. She then asks if Knit Cap has the cocktail shaker that they presumably brought to the site ready. Cocktail shakers are used in the preparation of many mixed drinks, which often contain ice (usually sourced locally).{{Citation needed}}

The title text says that if they manage to find some ice with ash coming from an eruption which destroyed an island with {{w|Camellia sinensis}} (common name, "tea plant") growing on it, they'll be able to get a cocktail with tea infused in it. Camellia sinensis is generally used for making tea. Gone Island Ice_τ is a punning reference to the cocktail known in the United States as a {{w|Long Island iced tea}}. The use of tau for "tea" may be a reference to the [https://icecube.wisc.edu/news/research/2023/01/icecube-reports-first-detection-of-candidate-astrophysical-tau-neutrinos/ IceCube Collaboration's] "reported two candidate events for the final unobserved Standard Model cosmic messenger: astrophysical tau neutrinos". Who knew that the rapper and actor was also an astrophysics stud?

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

:[Knit Cap and Megan both wearing knit caps and scarves in a snowy environment taking a look at an ice drill. There is a helicopter on the ground in the background, with their footprints between them and the helicopter. Knit Cap is holding a small container between her hands while Megan is holding the middle of the drill.]
:Megan: Next, we'll identify the ice core layer matching your birth year. Do you have the shaker ready?

:[Caption below the panel:]
:Making the traditional paleoclimatologist cocktail

{{comic discussion}}

[[Category:Comics featuring Knit Cap]]
[[Category:Comics featuring Megan]]
[[Category:Characters with hats]]
[[Category:Geology]]
[[Category:Food]]

2892: Banana Prices

2024-02-11T10:36:07Z

DeeJaye6: /* Explanation */ Setting the incomplete comment correct again.

{{comic
| number = 2892
| date = February 9, 2024
| title = Banana Prices
| image = banana_prices_2x.png
| imagesize = 564x378px
| noexpand = true
| titletext = It's a linear extrapolation, Michael. How big could the error be? 10%?
}}

==Explanation==
{{incomplete|Created by a MANDALORIAN BANANA ARMORER - Please change this comment when editing this page.}}

[https://www.youtube.com/watch?v=Nl_Qyk9DSUw ‘It’s one banana, Michael. What could it cost, $10?'] is a line from an {{w|Arrested Development}} episode (Season 1, Episode 6, "Charity Drive", 2003) that became well known as a meme used to mock out-of-touch elites. The character who spoke this line—Lucille Bluth, a rich socialite—didn't know the cost of a banana and made a wildly incorrect estimate because she had never bought her own groceries. According to the graph, the banana price at the time of that episode was actually just under 25 cents, and the price "now" (2024) is around 30 cents.

This comic illustrates a number of ways to violate statistical best practices and to "lie with data." The additional use of an "unreliable narrator" device gives this comic several layers of meaning. The caption writer, in this case, is an unreliable narrator who is ''also'' humorously out-of-touch like Lucille Bluth, but in a different way. The comic speculates that the error in their conclusion is less than 10%, even when their own three predictions (from 120 years to 220 years) differ by over 80%.

To initially mislead the reader and to ultimately demonstrate how easy it is to be fooled by various methods of "lying with data," Randall ably combines several statistical "sins" in one graph, such as:
* false [[Precision vs Accuracy|precision]]
* [[Extrapolating|extrapolating]] an order of magnitude deeper into the future than is advisable
* referring to a logarithmic extrapolation as linear
* ignoring historical norms and high variability in making future predictions
* articulating multiple potential scenarios that are actually highly correlated with each other

At first, the comic looks like a wry observation that the irony of this sitcom line will "probably" be obsolete in a century or two. This comic shows a graph of three, predicted prices for bananas over the next 250 years, extrapolating from the current price. One uses the general inflation rate, a value dominated by the cost of housing. Another uses the more specific inflation rate for fresh fruit. The final line is an extrapolation from 50 years of historic banana prices. The comic seems to say that it will take a century or two before the irony of the sitcom quote becomes anachronistically meaningless.

(While these extrapolations look linear, they are, in fact, exponential, since a linear extrapolation on a graph with a logarithmic scale is actually an exponential extrapolation. The graph is log-linear, with price as a logarithmic scale on the vertical (left) axis, which makes it possible to visualize exponential growth as a straight line.)

The accuracy of this prediction depends on these particular extrapolations being valid. The "general inflation rate" line assumes an average rate of around 3%, matching the historic average in the USA. However, assuming a constant inflation rate for the next 200 years is extremely simplistic. Inflation fluctuates quite a lot in response to economic factors and government policies. It was as high as 6% during recent rounds of economic stimulus and caused fears of hyper-inflation. And pre-Covid, it was around 1% for a decade.

Besides getting the inflation rate wrong, another way the extrapolation could be wrong was if—in the next 100 years—there were a {{w|Banana#Pests, diseases, and natural disasters|massive banana crash or extinction}}, as has {{w|Gros Michel banana|happened before}}, due to the banana's lack of genetic diversity. In which case, the sharply reduced supply of bananas could send the price past $10 very quickly.

(Two elements of finance that grow exponentially—but are traditionally plotted on linear graphs—are compound interest and investment growth in stock markets.)

Another, more subtle, illustration of false precision is the graph's use of three different models for the extrapolation of banana prices. At first glance, using three different trend lines seems to show a "range" of potential scenarios and acknowledge the prediction's uncertainty. (Scenario Thinking is the practice of articulating divergent, uncorrelated scenarios to explore various "potential futures.") However, the three underlying trends of the prediction models are correlated: general inflation is highly correlated to fruit price inflation and banana price inflation. Using three different trends that are all highly correlated is scant better than using just one.

Finally, the reference to "BLS/St. Louis Fred"—a widely respected source of economic data—appears to lend credibility to the graph, but the only data that is truly credible is the historic price data. It's one more example—citing respected sources—of a way to show how to fool unsuspecting readers into lending a prediction more credibility than it deserves.

The title text is a wink from Randall about this unreliable narrator by using the ignorant tone of Lucille Bluth to wryly acknowledge, in fact, that error of the extrapolations greatly exceeds 10%. Just as Lucille was very wrong about a $10 banana (a price threshold), so, too, is the speaker of the title text very wrong about the 10% error (a proportional change). It does so in the form of a meta-joke about the false precision of extrapolations, while continuing the theme of the speaker's extreme ignorance. Assuming that the error couldn't be more than 10% shows that the Lucille speaker continues to be hilariously off-base, presuming far more accuracy from a multi-century prediction than is warranted.

Overall, the comic is a clever commentary about the false precision of extrapolation and how easy it is to make absurdly precise predictions seem credible, illustrating its point by initially misleading the reader with its own false precision, and wrapping it all in a pop-culture reference.

In truth, any economic extrapolation into the distant future (based on past data points) is just an educated guess, likely to be quite wrong, with an expected error far in excess of 10%. (A rare example of a field in which 75-year predictions are highly accurate is demographic age charts, since the number of babies born this year is causal of the number of 75-year-olds alive in 75 years.)

This comic uses several common xkcd themes:
* '''Log scales''' and their peculiarities are a recurring xkcd theme, and this is the second comic in a row to play with logarithms (the prior one being [[2891: Log Cabin]]).
* It's also the second comic in the last four to involve '''predictions across centuries''' (i.e. [[2889: Greenhouse Effect]]).
* Another '''extrapolation''' comic include [[605: Extrapolating]]. This comic looks a lot like [[1007: Sustainable]].

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

:[A graph with the x-axis showing time, from the years 1950 to around 2275. The y-axis is a log scale showing the price of a banana from $0.10 to over $10.00. A label called "Price of a banana (BLS/St. Louis ''Fred''[https://fred.stlouisfed.org/])" show a rising trend in the price of a banana. There are two dots on that trend. One is labeled "Episode airs" and the other one "Now". 3 extrapolations shown as dashed lines labeled "General inflation rate", "Fresh fruit price trend" and "Banana price trend" extend until reaching the $10 mark, indicated by 3 dots.]

:[Caption above the graph:] "It's one banana, Michael. What could it cost? $10?"

:[Caption below the panel:] That line probably has another century or so left.

{{comic discussion}}

[[Category:Line graphs]]
[[Category:Timelines]]
[[Category:Fiction]]
[[Category:Extrapolation]]

2892: Banana Prices

2024-02-11T10:33:55Z

DeeJaye6: /* Explanation */ Minor grammar and punctuation edits (again).

{{comic
| number = 2892
| date = February 9, 2024
| title = Banana Prices
| image = banana_prices_2x.png
| imagesize = 564x378px
| noexpand = true
| titletext = It's a linear extrapolation, Michael. How big could the error be? 10%?
}}

==Explanation==
{{incomplete|Created by an IMPERIAL BANANA THERMAL DETONATOR - Is this explanation even correct? Do NOT delete this tag too soon.}}

[https://www.youtube.com/watch?v=Nl_Qyk9DSUw ‘It’s one banana, Michael. What could it cost, $10?'] is a line from an {{w|Arrested Development}} episode (Season 1, Episode 6, "Charity Drive", 2003) that became well known as a meme used to mock out-of-touch elites. The character who spoke this line—Lucille Bluth, a rich socialite—didn't know the cost of a banana and made a wildly incorrect estimate because she had never bought her own groceries. According to the graph, the banana price at the time of that episode was actually just under 25 cents, and the price "now" (2024) is around 30 cents.

This comic illustrates a number of ways to violate statistical best practices and to "lie with data." The additional use of an "unreliable narrator" device gives this comic several layers of meaning. The caption writer, in this case, is an unreliable narrator who is ''also'' humorously out-of-touch like Lucille Bluth, but in a different way. The comic speculates that the error in their conclusion is less than 10%, even when their own three predictions (from 120 years to 220 years) differ by over 80%.

To initially mislead the reader and to ultimately demonstrate how easy it is to be fooled by various methods of "lying with data," Randall ably combines several statistical "sins" in one graph, such as:
* false [[Precision vs Accuracy|precision]]
* [[Extrapolating|extrapolating]] an order of magnitude deeper into the future than is advisable
* referring to a logarithmic extrapolation as linear
* ignoring historical norms and high variability in making future predictions
* articulating multiple potential scenarios that are actually highly correlated with each other

At first, the comic looks like a wry observation that the irony of this sitcom line will "probably" be obsolete in a century or two. This comic shows a graph of three, predicted prices for bananas over the next 250 years, extrapolating from the current price. One uses the general inflation rate, a value dominated by the cost of housing. Another uses the more specific inflation rate for fresh fruit. The final line is an extrapolation from 50 years of historic banana prices. The comic seems to say that it will take a century or two before the irony of the sitcom quote becomes anachronistically meaningless.

(While these extrapolations look linear, they are, in fact, exponential, since a linear extrapolation on a graph with a logarithmic scale is actually an exponential extrapolation. The graph is log-linear, with price as a logarithmic scale on the vertical (left) axis, which makes it possible to visualize exponential growth as a straight line.)

The accuracy of this prediction depends on these particular extrapolations being valid. The "general inflation rate" line assumes an average rate of around 3%, matching the historic average in the USA. However, assuming a constant inflation rate for the next 200 years is extremely simplistic. Inflation fluctuates quite a lot in response to economic factors and government policies. It was as high as 6% during recent rounds of economic stimulus and caused fears of hyper-inflation. And pre-Covid, it was around 1% for a decade.

Besides getting the inflation rate wrong, another way the extrapolation could be wrong was if—in the next 100 years—there were a {{w|Banana#Pests, diseases, and natural disasters|massive banana crash or extinction}}, as has {{w|Gros Michel banana|happened before}}, due to the banana's lack of genetic diversity. In which case, the sharply reduced supply of bananas could send the price past $10 very quickly.

(Two elements of finance that grow exponentially—but are traditionally plotted on linear graphs—are compound interest and investment growth in stock markets.)

Another, more subtle, illustration of false precision is the graph's use of three different models for the extrapolation of banana prices. At first glance, using three different trend lines seems to show a "range" of potential scenarios and acknowledge the prediction's uncertainty. (Scenario Thinking is the practice of articulating divergent, uncorrelated scenarios to explore various "potential futures.") However, the three underlying trends of the prediction models are correlated: general inflation is highly correlated to fruit price inflation and banana price inflation. Using three different trends that are all highly correlated is scant better than using just one.

Finally, the reference to "BLS/St. Louis Fred"—a widely respected source of economic data—appears to lend credibility to the graph, but the only data that is truly credible is the historic price data. It's one more example—citing respected sources—of a way to show how to fool unsuspecting readers into lending a prediction more credibility than it deserves.

The title text is a wink from Randall about this unreliable narrator by using the ignorant tone of Lucille Bluth to wryly acknowledge, in fact, that error of the extrapolations greatly exceeds 10%. Just as Lucille was very wrong about a $10 banana (a price threshold), so, too, is the speaker of the title text very wrong about the 10% error (a proportional change). It does so in the form of a meta-joke about the false precision of extrapolations, while continuing the theme of the speaker's extreme ignorance. Assuming that the error couldn't be more than 10% shows that the Lucille speaker continues to be hilariously off-base, presuming far more accuracy from a multi-century prediction than is warranted.

Overall, the comic is a clever commentary about the false precision of extrapolation and how easy it is to make absurdly precise predictions seem credible, illustrating its point by initially misleading the reader with its own false precision, and wrapping it all in a pop-culture reference.

In truth, any economic extrapolation into the distant future (based on past data points) is just an educated guess, likely to be quite wrong, with an expected error far in excess of 10%. (A rare example of a field in which 75-year predictions are highly accurate is demographic age charts, since the number of babies born this year is causal of the number of 75-year-olds alive in 75 years.)

This comic uses several common xkcd themes:
* '''Log scales''' and their peculiarities are a recurring xkcd theme, and this is the second comic in a row to play with logarithms (the prior one being [[2891: Log Cabin]]).
* It's also the second comic in the last four to involve '''predictions across centuries''' (i.e. [[2889: Greenhouse Effect]]).
* Another '''extrapolation''' comic include [[605: Extrapolating]]. This comic looks a lot like [[1007: Sustainable]].

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

:[A graph with the x-axis showing time, from the years 1950 to around 2275. The y-axis is a log scale showing the price of a banana from $0.10 to over $10.00. A label called "Price of a banana (BLS/St. Louis ''Fred''[https://fred.stlouisfed.org/])" show a rising trend in the price of a banana. There are two dots on that trend. One is labeled "Episode airs" and the other one "Now". 3 extrapolations shown as dashed lines labeled "General inflation rate", "Fresh fruit price trend" and "Banana price trend" extend until reaching the $10 mark, indicated by 3 dots.]

:[Caption above the graph:] "It's one banana, Michael. What could it cost? $10?"

:[Caption below the panel:] That line probably has another century or so left.

{{comic discussion}}

[[Category:Line graphs]]
[[Category:Timelines]]
[[Category:Fiction]]
[[Category:Extrapolation]]

Talk:555: Two Mirrors

2024-02-10T08:23:03Z

DeeJaye6: Thanking another for their comment.

Am i the only one who think of the ne555?
[[Special:Contributions/87.179.191.141|87.179.191.141]] 21:46, 11 December 2012 (UTC)
:No idea. What I was thinking was who reads books like that?

(There again who responds to sites like this?)
And: Shouldn't the mirrors be at a slight angle to one another?
[[User:Weatherlawyer| I used Google News BEFORE it was clickbait]] ([[User talk:Weatherlawyer|talk]]) 18:06, 30 January 2015 (UTC)
:He refers to the NE555, the most famous IC, used mainly to create timers and oscillators. Its use matches perfectly the comic's theme. In fact, I came to this Discussion section expecting a reference to the NE555. [[User:Ajgelado|Ajgelado]] ([[User talk:Ajgelado|talk]]) 05:33, 1 September 2016 (UTC)

:A slight angle would amplify with each reflection breaking the chain. It would make more sense for them to be parallel but off-center from one another. [[User:Flewk|flewk]] ([[User talk:Flewk|talk]]) 07:38, 5 January 2016 (UTC)

::What difference does it make where the centre of the mirror is? I don't get it. [[User:Jkshapiro|Jkshapiro]] ([[User talk:Jkshapiro|talk]]) 01:50, 26 September 2021 (UTC)

In the last frame, you can see her reflection still standing in the right-most mirror.{{unsigned ip|162.158.123.119}}
: Thank you for mentioning that! I had missed it until I read your comment. [[User:DeeJaye6|DeeJaye6]] ([[User talk:DeeJaye6|talk]]) 08:23, 10 February 2024 (UTC)

2892: Banana Prices

2024-02-09T22:00:42Z

DeeJaye6: /* Explanation */ General grammar and punctuation edits. These are not the edits we're looking for. You're free to go about your business. Move along. Move along...

{{comic
| number = 2892
| date = February 9, 2024
| title = Banana Prices
| image = banana_prices_2x.png
| imagesize = 564x378px
| noexpand = true
| titletext = It's a linear extrapolation, Michael. How big could the error be? 10%?
}}

==Explanation==
{{incomplete|Created by an IMPERIAL BANANA THERMAL DETONATOR - Please change this comment when editing this page. Do NOT delete this tag too soon.}}

[https://www.youtube.com/watch?v=Nl_Qyk9DSUw ‘It’s one banana, Michael. What could it cost, $10?'] is a line from an {{w|Arrested Development}} episode (Season 1, Episode 6, "Charity Drive", 2003) that became well known as a meme used to mock out-of-touch elites. The character who spoke this line -- Lucille Bluth, a rich socialite -- didn't know whether a banana cost $10 in 2003 because she never did any grocery shopping "because we have people for that." According to the graph, the banana price at the time of that episode was actually just under 25 cents.

'''This comic illustrates a whole suite of ways to violate statistical best practices and to 'lie with data.' And the additional use of an "unreliable narrator" device gives this comic several layers of meaning.'''

To initially mislead the reader and to ultimately demonstrate how easy it is to be fooled by various methods of 'lying with data,' Randall impressively combines several statistical 'sins' in one graph, such as:
* false precision
* extrapolating an order of magnitude deeper into the future than is advisable
* referring to a logarithmic extrapolation as linear
* ignoring historical norms and high variability in making future predictions
* logarithmic scales when they're inappropriate and misleading
* articulating multiple potential scenarios that are actually highly correlated with each other.

At first, the comic looks like a wry observation that the irony of this sitcom line will be obsolete in a century or two. This comic shows a graph of three, different, projected, future prices for bananas over the next 250 years. One extrapolates from the current inflation rate in general. Another uses the more specific inflation rate for fresh fruit, which is made from less data but is more relevant than a general rate dominated by the cost of housing. The final line is a "linear" extrapolation from 50 years of historic banana prices. The comic seems to say that it will take a century or two before the irony of the sitcom quote becomes anachronistically meaningless. This prediction depends on these particular extrapolations being accurate.

(While these extrapolations look linear, they are in fact logarithmic, since a linear extrapolation on a graph with a logarithmic scale is actually a logarithmic extrapolation. The graph is drawn to a logarithmic vertical scale on the vertical (left) axis, which makes it possible to visualize exponential price-rise as the dotted line.)

Upon closer inspection though, it's apparent that the graph-maker-cum-caption-writer is making some absurd assumptions about inflation continuing at its current level of about 3.5%. The caption writer, in this case, is an unreliable narrator who is ''also'' humorously out-of-touch like Lucille Bluth, but in a different way. If inflation returns to its recent historic norm of 1%, then it will actually take 300 years for the price of a banana to rise past $10. But as recently as 2022 the rate of inflation was as high as 6% in the US, a rate at which the banana would reach $10 in a mere 60 years (if it were sustained for 60 years). Even a short period of high inflation would be equivalent to a long period of low inflation. Simply assuming a constant 3% inflation rate for the next 100 years -- despite historical evidence -- is extremely simplistic.

Another, more subtle, illustration of false precision is the graph's use of three different assumptions for the extrapolation of banana prices. At first glance, using three different trend lines seems to show a "range" of potential scenarios and acknowledge the prediction's uncertainty. However, all three underlying trends are correlated: general inflation is highly correlated to fruit price inflation and banana price inflation. Using three different trends that are all highly correlated is scant better than using just one.

An additional example of "lying with data" is the use of a logarithmic graph for economic data. It's highly unusual to graph economic data logarithmically, as economic variables rarely show exponential change over time -- and even when they do, it's easier to show that change on a normal linear graph. If this same set of extrapolations were shown on a linear graph, the absurdly accelerating slope of the extrapolations would give away how ridiculous these extrapolations are.

(The main exception is financial market analysis, in which some traders like to use logarithmic graphs as one of many tools to perceive and predict hidden price trends that don’t show up in normally scaled charts.)

Finally, the reference to "BLS/St. Louis Fred" -- a widely respected source of economic data -- appears to lend credibility to the graph, but the only data that is truly credible is the historic price data. It's one more example -- citing respected sources -- of a way to fool unsuspecting readers into giving a prediction more credibility than it deserves.

The title text is a wink from Randall about this unreliable narrator by using the ignorant tone of Lucille Bluth to wryly acknowledge that, in fact, that error of the extrapolations greatly exceeds 10%. Just as Lucille was very wrong about a $10 banana (a price threshold), so too is the Lucille of the title text very wrong about the 10% error (a proportional change). It does so in the form of a meta-joke about the false precision of extrapolations, while continuing the theme of the speaker's extreme ignorance. Assuming that the error couldn't be more than 10% shows that the Lucille speaker continues to be hilariously off-base, presuming far more accuracy from a multi-century prediction than is warranted.

Besides the inflation example, another way the extrapolation could be wrong was if -- in the next 100 years -- there were a massive banana crash or extinction {{w|Banana#Pests, diseases, and natural disasters|as has happened}} {{w|Gros Michel banana|before}} due to the banana's lack of genetic diversity, in which case the sharply reduced supply of bananas could send the price past $10 very quickly.

Overall, the comic is a clever commentary about the false precision of extrapolation and how easy it is to be fooled by it, illustrating its point by initially misleading the reader with its own false precision, and wrapping it all in a pop-culture reference. Any economic extrapolation into the distant future based on past data points is just an educated guess likely to be quite wrong, with an expected error far in excess of 10%. (A rare example of a field in which 75-year predictions are highly accurate is demographic age charts, since the number of babies born this year is causal of the # of 75-year-olds alive in 75 years.)

Log scales and their peculiarities are a recurring xkcd theme, and this is the second comic in a row to play with logarithms (the prior one being [[2891: Log Cabin]]). It's also the second comic in the last four to involve predictions across centuries (i.e. [[2889: Greenhouse Effect]]).

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

:[A graph with the x-axis showing time, from the years 1950 to around 2275. The y-axis is a log scale showing the price of a banana from $0.10 to over $10.00. A label called "Price of a banana (BLS/St. Louis ''Fred''[https://fred.stlouisfed.org/])" show a rising trend in the price of a banana. There are two dots on that trend. One is labeled "Episode airs" and the other one "Now". 3 extrapolations shown as dashed lines labeled "General inflation rate", "Fresh fruit price trend" and "Banana price trend" extend until reaching the $10 mark, indicated by 3 dots.]

:[Caption above the graph:] "It's one banana, Michael. What could it cost? $10?"

:[Caption below the panel:] That line probably has another century or so left.

{{comic discussion}}

[[Category:Line graphs]]
[[Category:Timelines]]
[[Category:Fiction]]
[[Category:Extrapolation]]

2888: US Survey Foot

2024-02-07T23:52:31Z

DeeJaye6: /* Explanation of the comic's underlying assumptions and implications */ Claification

{{comic
| number = 2888
| date = January 31, 2024
| title = US Survey Foot
| image = us_survey_foot_2x.png
| imagesize = 740x606px
| noexpand = true
| titletext = Subway refuses to answer my questions about whether it's an International Footlong or a US Survey Footlong. A milligram of sandwich is at stake!
}}

==Explanation==
{{incomplete|Created by a VERY SHORT 84 FEET - Please change this comment when editing this page. Do NOT delete this tag too soon.}}

This comic pokes fun at the difference in length between the {{w|Foot_(unit)#U.S._survey_foot|US Survey Foot}} and the {{w|Foot_(unit)|International Foot}}. After Carl Edvard Johansson's {{w|Carl_Edvard_Johansson#Johansson_and_the_inch|gauge blocks}} in 1912 led to {{w|International_yard_and_pound|an international agreement}} in 1959, the foot has been defined to be exactly 0.3048 metres, whilst the US survey foot continued to use the {{w|Mendenhall Order|definition of 1893}}, making it a bit longer than the international foot at 1200/3937 meters. However, the difference between the two is proportionately too small to be meaningful for most purposes, as they only differ by 2 parts per million. At foot-length scales, the difference is a fraction of a micron, with longer measures (where the error grows to a notable degree) requiring an already excessive implied precision likely to mismatch its true accuracy. Some engineering or scientific applications ''may'' involve such tolerances, but would be expected to consistently use some more modern standard of measurement to {{w|Mars Climate Orbiter|avoid such confusion}}.

In the third panel, Cueball says that someone is using the survey foot again: it turns out to be [[Black Hat]], an action that sounds very typical for him. Cueball claims that he is drawing the world 610nm closer to madness, which is about the difference between the two measures (per foot). Cueball, outraged, then says that the {{w|National Institute of Standards and Technology}} (usually abbreviated as NIST) will capture Black Hat to stop him from using the US survey foot. The joke here is that his coordinates show that he is 8,000 miles away, but since he is using the US survey foot, he is 0.016 miles away from the search team, making them unable to find him at that exact spot. (A good strike team would likely keep looking, but perhaps being strictly NIST-trained to adhere to particularly exacting standards has ironically made them vulnerable to the same inaccuracies that they are supposed to be preventing.)

Note – 0.016 miles is about 28.16 yards (84.48 feet), or 84.4798 US Survey Feet, or 25.749 metres; they are shown as probably being at the same lake in the last two frames, with maybe little more than a frame border between them.

Part of the joke is the imaginative idea that NIST employs and dispatches strike teams to apprehend persons that use incorrect measurements. This may be a play on words about the {{w|Nuclear Emergency Support Team}}, or "NEST", a {{w|United States Department of Energy}} group who respond to nuclear and radiological emergencies such as reactor accidents or nuclear terrorism, and who might reasonably have access to resources such as the helicopters depicted during a crisis.

The title text references a {{w|Subway (restaurant)#Sandwich_size|2013 lawsuit}} over the length of a "Footlong" sandwich sold by Subway fast food chain. However – in contrast to the issue at stake in that lawsuit – the difference in length between an 'international footlong' sandwich and a 'US survey footlong' sandwich is way below the precision ''or'' accuracy by which sandwiches are usually produced – making it understandable that Subway would not think it necessary to clarify which definition of 'foot' they use for their products.

===Explanation of the comic's underlying assumptions and implications===
Randall appears to be playing a bit fast-and-loose here. To make this joke work implies a rather absurd situation: that both Black Hat and the searchers have set their devices to measure and report location ''in reference to'' the same location (the place where Cueball is and that is at one end of the 8,000 mile measurement) and not just use GPS and lat/long like every other smartphone on the planet.

There is nothing in the comic to imply that Cueball is at NIST headquarters in Gaithersburg, Maryland. That frees up the joke about 8,000 miles away and therefore, Black Hat can easily be in U.S. territory.

In the unlikely event that the searchers' phones measure and report location in reference to Cueball's location, evidently Black Hat has also overridden his device's in-built GPS to report its location in reference to Cueball's location as a way to toy with him and the NIST teams, and then traveled EXACTLY 8,000 miles away, knowing NIST would be sent in pursuit. After all, Black Hat is known for his preternatural powers of mischief.

==Transcript==

:[Closeup on Cueball.]
:Cueball: We thought it was over. After 60 years of struggle, the US survey foot was dead, deprecated by NIST in 2023.

:[Cueball is shown to be talking to Ponytail, Hairy, and Megan. He has a presentation behind him.]
:Cueball: We thought architects and engineers could rest easy, free of the headaches of having two conflicting definitions of the foot that differ by 610 nanometers.
:International foot: 0.304 800 000 m
:US survey foot [crossed over in gray] R.I.P.: 0.304 800 609... m

:[Cueball points at an image of Black Hat with unreadable writing above it.]
:Cueball: But I bring dire news:
:Cueball: ''Someone has started using the US survey foot again.''

:[Closeup on Cueball again.]
:Off-panel voice: Why!?
:Cueball: We don't know.
:Cueball: Some people just want to drag the world 610nm closer to madness.

:[Farther view of Cueball only. He clenches a fist.]
:Off-panel voice: What can we do!?
:Cueball: A NIST team is already in the air. We will capture the scofflaw and end this nightmare.

:[Two helicopters flying, with mountains in the background.]

:Caption: 8,000 miles away
:[Two operatives in a forest by a pond with NIST helmets. One talks on a walkie-talkie.]
:Operative: We've reached the coordinates of the target's device. There's no one here.
:Voice from walkie-talkie: How!?

:Caption: 8,000.016 miles away
:[Black Hat walking elsewhere (by the same pond) in the forest, very close by. He appears to be holding a device of some sort.]
:Black Hat: ♫ ♪

==Trivia==

The number of miles in the last panel was [https://www.explainxkcd.com/wiki/images/archive/5/5f/20240131173446%21us_survey_foot_2x.png originally] 8,000.014, but was changed to 8,000.016. The latter matches the 2 ppm difference between the international foot and the US survey foot.

{{comic discussion}}

[[Category:Comics featuring Cueball]]
[[Category:Comics featuring Ponytail]]
[[Category:Comics featuring Hairy]]
[[Category:Comics featuring Megan]]
[[Category:Comics featuring Black Hat]]
[[Category:Characters with hats]]
[[Category:Geography]]
[[Category:Food]]

2888: US Survey Foot

2024-02-07T23:49:20Z

DeeJaye6: /* Explanation */ It is not even hinted that Cueball is at NIST HQ, nor that he is even associated with NIST. He does say "We," but that's similar to sports fans referring to the team they support using the collective personal pronoun.

{{comic
| number = 2888
| date = January 31, 2024
| title = US Survey Foot
| image = us_survey_foot_2x.png
| imagesize = 740x606px
| noexpand = true
| titletext = Subway refuses to answer my questions about whether it's an International Footlong or a US Survey Footlong. A milligram of sandwich is at stake!
}}

==Explanation==
{{incomplete|Created by a VERY SHORT 84 FEET - Please change this comment when editing this page. Do NOT delete this tag too soon.}}

This comic pokes fun at the difference in length between the {{w|Foot_(unit)#U.S._survey_foot|US Survey Foot}} and the {{w|Foot_(unit)|International Foot}}. After Carl Edvard Johansson's {{w|Carl_Edvard_Johansson#Johansson_and_the_inch|gauge blocks}} in 1912 led to {{w|International_yard_and_pound|an international agreement}} in 1959, the foot has been defined to be exactly 0.3048 metres, whilst the US survey foot continued to use the {{w|Mendenhall Order|definition of 1893}}, making it a bit longer than the international foot at 1200/3937 meters. However, the difference between the two is proportionately too small to be meaningful for most purposes, as they only differ by 2 parts per million. At foot-length scales, the difference is a fraction of a micron, with longer measures (where the error grows to a notable degree) requiring an already excessive implied precision likely to mismatch its true accuracy. Some engineering or scientific applications ''may'' involve such tolerances, but would be expected to consistently use some more modern standard of measurement to {{w|Mars Climate Orbiter|avoid such confusion}}.

In the third panel, Cueball says that someone is using the survey foot again: it turns out to be [[Black Hat]], an action that sounds very typical for him. Cueball claims that he is drawing the world 610nm closer to madness, which is about the difference between the two measures (per foot). Cueball, outraged, then says that the {{w|National Institute of Standards and Technology}} (usually abbreviated as NIST) will capture Black Hat to stop him from using the US survey foot. The joke here is that his coordinates show that he is 8,000 miles away, but since he is using the US survey foot, he is 0.016 miles away from the search team, making them unable to find him at that exact spot. (A good strike team would likely keep looking, but perhaps being strictly NIST-trained to adhere to particularly exacting standards has ironically made them vulnerable to the same inaccuracies that they are supposed to be preventing.)

Note – 0.016 miles is about 28.16 yards (84.48 feet), or 84.4798 US Survey Feet, or 25.749 metres; they are shown as probably being at the same lake in the last two frames, with maybe little more than a frame border between them.

Part of the joke is the imaginative idea that NIST employs and dispatches strike teams to apprehend persons that use incorrect measurements. This may be a play on words about the {{w|Nuclear Emergency Support Team}}, or "NEST", a {{w|United States Department of Energy}} group who respond to nuclear and radiological emergencies such as reactor accidents or nuclear terrorism, and who might reasonably have access to resources such as the helicopters depicted during a crisis.

The title text references a {{w|Subway (restaurant)#Sandwich_size|2013 lawsuit}} over the length of a "Footlong" sandwich sold by Subway fast food chain. However – in contrast to the issue at stake in that lawsuit – the difference in length between an 'international footlong' sandwich and a 'US survey footlong' sandwich is way below the precision ''or'' accuracy by which sandwiches are usually produced – making it understandable that Subway would not think it necessary to clarify which definition of 'foot' they use for their products.

===Explanation of the comic's underlying assumptions and implications===
Randall appears to be playing a bit fast-and-loose here. To make this joke work implies a rather absurd situation: that both Black Hat and the searchers have set their devices to measure and report location ''in reference to'' the same location (the place where Cueball is and that is at one end of the 8,000 mile measurement) and not just use GPS and lat/long like every other smartphone on the planet.

There is nothing in the comic to imply that Cueball is at NIST headquarters in Gaithersburg, Maryland. That frees up the joke about 8,000 miles away and therefore, Black Hat can easily be in U.S. territory.

In the unlikely event that the searchers' phones measure and report location in reference to NIST HQ, evidently Black Hat has also overridden his device's in-built GPS to report its location in reference to NIST headquarters as a way to toy with them and then traveled EXACTLY 8,000 miles away, knowing NIST would be in hot pursuit. After all, Black Hat is known for his preternatural powers of mischief.

==Transcript==

:[Closeup on Cueball.]
:Cueball: We thought it was over. After 60 years of struggle, the US survey foot was dead, deprecated by NIST in 2023.

:[Cueball is shown to be talking to Ponytail, Hairy, and Megan. He has a presentation behind him.]
:Cueball: We thought architects and engineers could rest easy, free of the headaches of having two conflicting definitions of the foot that differ by 610 nanometers.
:International foot: 0.304 800 000 m
:US survey foot [crossed over in gray] R.I.P.: 0.304 800 609... m

:[Cueball points at an image of Black Hat with unreadable writing above it.]
:Cueball: But I bring dire news:
:Cueball: ''Someone has started using the US survey foot again.''

:[Closeup on Cueball again.]
:Off-panel voice: Why!?
:Cueball: We don't know.
:Cueball: Some people just want to drag the world 610nm closer to madness.

:[Farther view of Cueball only. He clenches a fist.]
:Off-panel voice: What can we do!?
:Cueball: A NIST team is already in the air. We will capture the scofflaw and end this nightmare.

:[Two helicopters flying, with mountains in the background.]

:Caption: 8,000 miles away
:[Two operatives in a forest by a pond with NIST helmets. One talks on a walkie-talkie.]
:Operative: We've reached the coordinates of the target's device. There's no one here.
:Voice from walkie-talkie: How!?

:Caption: 8,000.016 miles away
:[Black Hat walking elsewhere (by the same pond) in the forest, very close by. He appears to be holding a device of some sort.]
:Black Hat: ♫ ♪

==Trivia==

The number of miles in the last panel was [https://www.explainxkcd.com/wiki/images/archive/5/5f/20240131173446%21us_survey_foot_2x.png originally] 8,000.014, but was changed to 8,000.016. The latter matches the 2 ppm difference between the international foot and the US survey foot.

{{comic discussion}}

[[Category:Comics featuring Cueball]]
[[Category:Comics featuring Ponytail]]
[[Category:Comics featuring Hairy]]
[[Category:Comics featuring Megan]]
[[Category:Comics featuring Black Hat]]
[[Category:Characters with hats]]
[[Category:Geography]]
[[Category:Food]]

2888: US Survey Foot

2024-02-01T02:24:56Z

DeeJaye6: Added detail to correct assumption about the "8,000 miles away" line.

{{comic
| number = 2888
| date = January 31, 2024
| title = US Survey Foot
| image = us_survey_foot_2x.png
| imagesize = 740x606px
| noexpand = true
| titletext = Subway refuses to answer my questions about whether it's an International Footlong or a US Survey Footlong. A milligram of sandwich is at stake!
}}

==Explanation==
{{incomplete|Created by a 610 US-SURVEY-NANOMETER MONKEY - Please change this comment when editing this page. Do NOT delete this tag too soon.}}

This comic pokes fun at a difference in length of the {{w|Foot_(unit)#U.S._survey_foot|US Survey Foot}} and the {{w|Foot_(unit)|International Foot}}. After {{w|International_yard_and_pound|an international agreement}} in 1959, the foot has been defined to be exactly 0.3048 metres, whilst the US survey foot is defined as 1200/3937 meters and is a bit longer than the international foot. However, the difference between the two is proportionately too small for most purposes, as they only differ by 2 parts per million. At foot-length scales, the difference is a fraction of a millimetre, with longer measures (where the error grows to a notable degree) requiring an already excessive implied precision likely to mismatch its true accuracy. Some engineering or scientific applications ''may'' involve such tolerances, but would be expected to consistently use some more modern standard of measurement to {{w|Mars Climate Orbiter|avoid such confusion}}.

In the fourth panel, Cueball says that [[Black Hat]] is drawing the world 610nm closer to madness, which is about the difference between the two measures (per foot). Cueball, outraged, then tells that the {{w|National Institute of Standards and Technology}} has been authorized to capture Black Hat to stop him from using the US survey foot. The joke here is that his coordinates show that he is 8,000 miles away, but since he is using the US survey foot, he is 0.016 miles away from the search team, making the search team unable to find him.

Note – 0.016 miles is about 28.16 yards (84.48 feet), or 25.749 metres.

Randall is playing a bit fast-and-loose here. To make this joke work implies a rather absurd situation: that both Black Hat and the searchers would need to have set their devices to measure location ''in reference to'' NIST headquarters and not just use GPS and lat/long. That's where we get the 8,000 miles from to make the joke. So even in the unlikely event that the searchers' phones measure location like this because they're from NIST, it's very unlikely that Black Hat would override his device's in-built GPS to report its location in reference to NIST headquarters – unless he knew that NIST searchers also did this and knew they wouldn't find it suspicious for him to do it too.

The title text references a {{w|Subway (restaurant)#Sandwich_size|2013 lawsuit}} over the length of a "Footlong" sandwich sold by Subway fast food chain. However – in contrast to the issue at stake in that lawsuit – the difference in length between an 'international footlong' sandwich and a 'US survey footlong' sandwich is way below the precision ''or'' accuracy by which sandwiches are usually produced – making it understandable that Subway would not think it necessary to clarify which definition of 'foot' they use for their products.

There is no U.S. territory which is [https://www.mapdevelopers.com/draw-circle-tool.php?circles=%5B%5B12874687.81%2C39.1450494%2C-77.2161307%2C%22%23AAAAAA%22%2C%22%23000000%22%2C0%5D%5D exactly 8,000 miles from NIST headquarters in Gaithersburg, Maryland] (regardless of which foot is used), so it's not clear how the NIST strike team would have jurisdiction over Black Hat. The closest U.S. territory would probably be Cocos Island, Guam, 7923.92 miles away from Gaithersburg; the closest U.S. jurisdiction is probably the U.S. Embassy in Dhaka, Bangladesh, at 8015.14 miles. However, there is nothing in the comic saying that Cueball et. al. are at NIST HQ, nor that the measurement is from there. The "8,000 miles away" is likely referring to the distance from wherever Cueball is.

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

:[Closeup on Cueball.]
:Cueball: We thought it was over. After 60 years of struggle, the US survey foot was dead, deprecated by NIST in 2023.

:[Cueball is shown to be talking to Ponytail, Hairy, and Megan. He has a presentation behind him.]
:Cueball: We thought architects and engineers could rest east, free of the headaches of having two conflicting definitions of the foot that differ by 610 nanometers.
:International foot: 0.304 800 000 m
:US survey foot [crossed over in gray] R.I.P.: 0.304 800 609... m

:[Cueball points at an image of Black Hat]
:Cueball: But I bring dire news:
:Cueball: ''Someone has started using the US survey foot again.''

:[Closeup on Cueball again.]
:Off-panel voice: Why!?
:Cueball: We don't know.
:Cueball: Some people just want to drag the world 610nm closer to madness.

:[Farther view of Cueball only. He clenches a fist.]
:Off-panel voice: What can we do!?
:Cueball: A NIST team is already in the air. We will capture the scofflaw and end this nightmare.

:[Two helicopters flying, with mountains in the background.]

:Caption: 8,000 miles away
:[Two operatives in a forest with "NIST" helmets. One talks on a walkie-talkie.]
:Operative: We've reached the coordinates of the target's device. There's no one here.
:Voice from walkie-talkie: How!?

:Caption: 8,000.016 miles away
:[Black Hat walking elsewhere in the forest, very close by.]
:Black Hat: ♫ ♪

==Trivia==

The number of miles in the last panel was [https://www.explainxkcd.com/wiki/images/archive/5/5f/20240131173446%21us_survey_foot_2x.png originally] 8,000.014, but was changed to 8,000.016. The latter matches the 2 ppm difference between the international foot and the US survey foot.

{{comic discussion}}

[[Category:Comics featuring Cueball]]
[[Category:Comics featuring Hairy]]
[[Category:Comics featuring Megan]]
[[Category:Comics featuring Black Hat]]
[[Category:Characters with hats]]
[[Category:Geography]]
[[Category:Food]]

2364: Parity Conservation

2020-09-28T04:43:18Z

DeeJaye6: /* Explanation */

{{comic
| number = 2364
| date = September 25, 2020
| title = Parity Conservation
| image = parity_conservation.png
| titletext = Bloody Mary is made of antimatter. It explains so much.
}}

==Explanation==

{{w|Bloody Mary (folklore)|Bloody Mary}} is a legend of a ghost, phantom, or spirit conjured to reveal the future. She is said to appear in a mirror when her name is chanted repeatedly. This is why Cueball says he said her name three times. This is her second apperance in xkcd, the first being [[555: Two Mirrors]].

The remark on parity conservation and cobalt-60 is almost surely a reference to the {{w|Wu experiment}}. In 1956, physicist {{w|Chien-Shiung Wu}} and her team at the National Bureau of Standards found that the {{w|weak interaction}} breaks parity: beta rays leave the decaying nucleus in the direction opposite to nuclear spin.

One of the results of this is that it becomes possible to differentiate between the concepts of left and right on a purely technical level, even if the person (or distant alien) you're talking to can't see you. When we say that "parity is not conserved," we mean that the concepts of left and right are not purely symmetrical across all areas of physics. As Richard Feynman put it, this means that "nature's laws are different for the right hand and the left hand, that there's a way to define the right hand by physical phenomena."

It seems as if Cueball is trying to "hand" Bloody Mary his experimental apparatus either physically (as he is asking her to take the cobalt-60 "before she comes out of the mirror"), or perhaps by reflecting it onto her side. Because Bloody Mary exists in mirrors, her world is implicitly a mirror of ours. This would allow her to conduct mirror physics experiments, such as whether or not the beta rays leave the cobalt-60 in the same direction as they do in our universe.

The title text references {{w|antimatter}}. In physics, antimatter is like a mirrored version of matter —mirrored in in charge, parity and time— composed of antiparticles rather than particles. Antimatter and matter spontaneously {{w|Annihilation|annihilate}} each other when they meet, releasing extremely high-energy radiation. Therefore, Bloody Mary being made of antimatter explains why she kills people when she comes out of the mirror. (Bloody Mary would also be annihilated in such an interaction, so the fact that she keeps coming back may be attributable to her being a ghost.)

There have been a lot of science fiction-y stories featuring antimatter people; often, these are duplicates of "regular"-matter people. The stories often show unrealistic ideas of what would happen if matter and antimatter versions of people met. Sometimes, the duplicates simply disappear; sometimes, if the plot requires it only ''one'' may disappear. Or sometimes the entire universe is destroyed. In reality, what would happen is that the matter and antimatter would mutually annihilate, as pairs of subatomic particles, creating enormous radiation and heat. It's likely that only a small fraction of the matter and antimatter would actually come into contact, rather than being propelled apart by the explosion. Indeed, if the duplicates are in their versions of air, the air and anti-air particles would interact first! In these stories, it's often presumed that the corresponding duplicates of people can annihilate only each other, but can safely touch anything else. In reality, the matching is at the subatomic level: any proton with any antiproton, any electron with any antielectron (or "positron"), etc.

==Transcript==

:[Cueball is standing in front of an oval wall mirror hanging over a small table. He's holding a tube connected to an electronic device. A face is dimly reflected in the mirror.]

:Cueball: Listen, I know I said your name three times.

:Cueball: But before you come out of the mirror and murder me, can you hold this cobalt-60 and take some measurements?

:Cueball: See, I'm researching parity conservation...

:[Caption below the comic]:
:It took some negotiating, but I've finally become the first person to coauthor a paper with Bloody Mary.

{{comic discussion}}
[[Category:Comics featuring Cueball]]
[[Category:Physics]]

2364: Parity Conservation

2020-09-28T04:41:48Z

DeeJaye6: /* Explanation */ Added detail showing that Wu was not alone in her experiment, but leaving clear that the team was hers.

{{comic
| number = 2364
| date = September 25, 2020
| title = Parity Conservation
| image = parity_conservation.png
| titletext = Bloody Mary is made of antimatter. It explains so much.
}}

==Explanation==

{{w|Bloody Mary (folklore)|Bloody Mary}} is a legend of a ghost, phantom, or spirit conjured to reveal the future. She is said to appear in a mirror when her name is chanted repeatedly. This is why Cueball says he said her name three times. This is her second apperance in xkcd, the first being [[555: Two Mirrors]].

The remark on parity conservation and cobalt-60 is almost surely a reference to the {{w|Wu experiment}}. In 1956, physicist {{w|Chien-Shiung Wu}} and her team at the National Bureau of Standards found that the {{w|weak interaction}} breaks parity: beta rays leave the decaying nucleus in the direction opposite to nuclear spin.

One of the results of this is that it becomes possible to differentiate between the concepts of left and right on a purely technical level, even if the person (or distant alien) you're talking to can't see you. When we say that "parity is not conserved," we mean that the concepts of left and right are not purely symmetrical across all areas of physics. As Richard Feynman put it, this means that "nature's laws are different for the right hand and the left hand, that there's a way to define the right hand by physical phenomena."

It seems as if Cueball is trying to "hand" Bloody Mary his experimental apparatus by reflecting it onto her side (as he is asking her to take the cobalt-60 "before she comes out of the mirror"). Because Bloody Mary exists in mirrors, her world is implicitly a mirror of ours. This would allow her to conduct mirror physics experiments, such as whether or not the beta rays leave the cobalt-60 in the same direction as they do in our universe.

The title text references {{w|antimatter}}. In physics, antimatter is like a mirrored version of matter —mirrored in in charge, parity and time— composed of antiparticles rather than particles. Antimatter and matter spontaneously {{w|Annihilation|annihilate}} each other when they meet, releasing extremely high-energy radiation. Therefore, Bloody Mary being made of antimatter explains why she kills people when she comes out of the mirror. (Bloody Mary would also be annihilated in such an interaction, so the fact that she keeps coming back may be attributable to her being a ghost.)

There have been a lot of science fiction-y stories featuring antimatter people; often, these are duplicates of "regular"-matter people. The stories often show unrealistic ideas of what would happen if matter and antimatter versions of people met. Sometimes, the duplicates simply disappear; sometimes, if the plot requires it only ''one'' may disappear. Or sometimes the entire universe is destroyed. In reality, what would happen is that the matter and antimatter would mutually annihilate, as pairs of subatomic particles, creating enormous radiation and heat. It's likely that only a small fraction of the matter and antimatter would actually come into contact, rather than being propelled apart by the explosion. Indeed, if the duplicates are in their versions of air, the air and anti-air particles would interact first! In these stories, it's often presumed that the corresponding duplicates of people can annihilate only each other, but can safely touch anything else. In reality, the matching is at the subatomic level: any proton with any antiproton, any electron with any antielectron (or "positron"), etc.

==Transcript==

:[Cueball is standing in front of an oval wall mirror hanging over a small table. He's holding a tube connected to an electronic device. A face is dimly reflected in the mirror.]

:Cueball: Listen, I know I said your name three times.

:Cueball: But before you come out of the mirror and murder me, can you hold this cobalt-60 and take some measurements?

:Cueball: See, I'm researching parity conservation...

:[Caption below the comic]:
:It took some negotiating, but I've finally become the first person to coauthor a paper with Bloody Mary.

{{comic discussion}}
[[Category:Comics featuring Cueball]]
[[Category:Physics]]

2364: Parity Conservation

2020-09-28T04:38:56Z

DeeJaye6: /* Explanation */ Removed explanation that does not fit with the wording of the comic, and added that wording as an reason for the actual one.

{{comic
| number = 2364
| date = September 25, 2020
| title = Parity Conservation
| image = parity_conservation.png
| titletext = Bloody Mary is made of antimatter. It explains so much.
}}

==Explanation==

{{w|Bloody Mary (folklore)|Bloody Mary}} is a legend of a ghost, phantom, or spirit conjured to reveal the future. She is said to appear in a mirror when her name is chanted repeatedly. This is why Cueball says he said her name three times. This is her second apperance in xkcd, the first being [[555: Two Mirrors]].

The remark on parity conservation and cobalt-60 is almost surely a reference to the {{w|Wu experiment}}. In 1956, physicist {{w|Chien-Shiung Wu}} found that the {{w|weak interaction}} breaks parity: beta rays leave the decaying nucleus in the direction opposite to nuclear spin.

One of the results of this is that it becomes possible to differentiate between the concepts of left and right on a purely technical level, even if the person (or distant alien) you're talking to can't see you. When we say that "parity is not conserved," we mean that the concepts of left and right are not purely symmetrical across all areas of physics. As Richard Feynman put it, this means that "nature's laws are different for the right hand and the left hand, that there's a way to define the right hand by physical phenomena."

It seems as if Cueball is trying to "hand" Bloody Mary his experimental apparatus by reflecting it onto her side (as he is asking her to take the cobalt-60 "before she comes out of the mirror"). Because Bloody Mary exists in mirrors, her world is implicitly a mirror of ours. This would allow her to conduct mirror physics experiments, such as whether or not the beta rays leave the cobalt-60 in the same direction as they do in our universe.

The title text references {{w|antimatter}}. In physics, antimatter is like a mirrored version of matter —mirrored in in charge, parity and time— composed of antiparticles rather than particles. Antimatter and matter spontaneously {{w|Annihilation|annihilate}} each other when they meet, releasing extremely high-energy radiation. Therefore, Bloody Mary being made of antimatter explains why she kills people when she comes out of the mirror. (Bloody Mary would also be annihilated in such an interaction, so the fact that she keeps coming back may be attributable to her being a ghost.)

There have been a lot of science fiction-y stories featuring antimatter people; often, these are duplicates of "regular"-matter people. The stories often show unrealistic ideas of what would happen if matter and antimatter versions of people met. Sometimes, the duplicates simply disappear; sometimes, if the plot requires it only ''one'' may disappear. Or sometimes the entire universe is destroyed. In reality, what would happen is that the matter and antimatter would mutually annihilate, as pairs of subatomic particles, creating enormous radiation and heat. It's likely that only a small fraction of the matter and antimatter would actually come into contact, rather than being propelled apart by the explosion. Indeed, if the duplicates are in their versions of air, the air and anti-air particles would interact first! In these stories, it's often presumed that the corresponding duplicates of people can annihilate only each other, but can safely touch anything else. In reality, the matching is at the subatomic level: any proton with any antiproton, any electron with any antielectron (or "positron"), etc.

==Transcript==

:[Cueball is standing in front of an oval wall mirror hanging over a small table. He's holding a tube connected to an electronic device. A face is dimly reflected in the mirror.]

:Cueball: Listen, I know I said your name three times.

:Cueball: But before you come out of the mirror and murder me, can you hold this cobalt-60 and take some measurements?

:Cueball: See, I'm researching parity conservation...

:[Caption below the comic]:
:It took some negotiating, but I've finally become the first person to coauthor a paper with Bloody Mary.

{{comic discussion}}
[[Category:Comics featuring Cueball]]
[[Category:Physics]]