explain xkcd - User contributions [en]

Talk:2731: K-Means Clustering

2023-01-30T17:45:10Z

172.70.206.150:

{{w|K-means_clustering|The wikipedia article}} does not clear anything up [[Special:Contributions/162.158.78.228|162.158.78.228]] 13:53, 30 January 2023 (UTC)Bumpf

The "Convergence of ''k''-means" animation is reasonably distinctive for a two-dimensional case, showing at least the motivation for the problem . Could it be attached here? [[User:Mia yun Ruse|Mia yun Ruse]] ([[User talk:Mia yun Ruse|talk]]) 14:08, 30 January 2023 (UTC)

Yeah, this is probably the least explanatory Explain xkcd I've read in the past 3 years. Still a lot of heavy math. [[Special:Contributions/162.158.186.95|162.158.186.95]] 16:50, 30 January 2023 (UTC)

This feels very similar to the joke "There are 10 types of people: those who know binary and those who don't." Except that the real joke here is that Ponytail doesn't have anything meaningful to justify her version. [[Special:Contributions/172.70.206.150|172.70.206.150]] 17:45, 30 January 2023 (UTC)

Talk:2730: Code Lifespan

2023-01-27T18:19:26Z

172.70.206.150:

I'm not sure if the thesis in this comic is accurate. But if it is, my explanation would be that a person with a more spontaneous live-in-the-moment attitude might program stuff that is more interesting, than the stuff made by the person who is (maybe neurotically) obsessed with making clean code.
 My own experience is that one loses the fun of programming something if the perfectionism plays to big of a role.{{unsigned ip|162.158.203.40|14:53, 27 January 2023}}‎
:The advice always given to me is "never let the perfect be the enemy of the good enough". Though I tend to bounce between being so obsessive, that I don't realise that I'm now gilding the lilly, or hastily kludging it because of the need for an immediate workaround, knowing that if it needs looking at again then I'll be doing it later anyway and that's when I'll get my gilding gear ready. (Hence why I'm 'always' being told that phrase. But I suspect that there really ''is'' no sweet spot between too little and too much, or at least no single keystroke at which I would earn universal praise for my finely balanced tenacity and moderation upon the handling of the issue. Always critics!) [[Special:Contributions/172.70.86.28|172.70.86.28]] 17:19, 27 January 2023 (UTC)

At least at a corporate level, I suspect this phenomenon has an extremely simple explanation. When your code is high-quality, people often won't even realize they are using and interacting with it, because it just does what it's supposed to. When your code is hackish, you and your coworkers will constantly find it breaking seemingly unrelated stuff, forcing them to go back to it over and over, trying to make it work, only to discover it breaks even more things when they try to fix it.
 Your high-quality code is still interacting with those seemingly unrelated things, it's simply not breaking the unrelated things, so you don't notice it's interacting with the seemingly unrelated things.[[Special:Contributions/172.69.68.97|172.69.68.97]] 16:32, 27 January 2023 (UTC)

This also reminds me of [[2347: Dependency]] where a single project made in 1990 has become the backbone of so many other applications. [[Special:Contributions/172.71.151.100|172.71.151.100]] 17:47, 27 January 2023 (UTC)

I won't do the edit myself (because I'm shy), but here is how the comic rings to me (from my own current experience):
- Often in dev, there are many daily repetitive tasks that are annoying (i.e., build-test-lint-commit-push). These get automated out of spite by someone in a quick'n'dirty way, just to make life easier.
It has a limited audience (the development team), but lives on forever, since it is used daily (and therefore maintained accordingly).
- On the other hand, the stuff the team codes and sells is subject to changing requirements (cf. next release, marketing, ...). So it gets overhauled often, all the more easily because developers are not familiar with it (because they don't use it, and they worked on some other part of the project).
There is also the fact that there is no budget for making changes on the tools, as opposed to the product, so no one really has time to refactor the former - that's how it lives so long!
~~Aveheuzed~~

The never ending war between "I don't have the time to do this right", and "this is way too complex for our simple needs" is exactly where this comic lives. The reality of programming is that general solutions are great for saving time writing, but are often bloated (with unneeded options), miss edge cases, or introduce extra dependencies and slow downs. plus the whole "not invented here" thing coupled with licensing headaches means this will probably still be a thing in a hundred years. PS I think the person explaining missed the point of the order in which the title text options are presented >.> [[Special:Contributions/172.70.206.150|172.70.206.150]] 18:19, 27 January 2023 (UTC)

2530: Clinical Trials

2023-01-19T19:50:01Z

172.70.206.150: /* Transcript */ research

{{comic
| number = 2530
| date = October 18, 2021
| title = Clinical Trials
| image = clinical_trials.png
| titletext = We don't need to do a clinical trial of this change because the standard of care is to adopt new ideas without doing clinical trials.
}}

==Explanation==
The comic begins with a simple process for adopting a new idea just by convincing people that it is a good idea. The joke is that this skips the important step of checking whether it actually ''is'' a good idea. That correction presumably comes about after ideas are adopted which sounded good but turn out to be harmful. The comic captions the addition of this checking step as "the invention of clinical trials".

The purpose of clinical trials in medicine is to make sure that a new medicine works and doesn't have serious side-effects. One example of the dangers of failing to make sure that it doesn't have serious side effects is {{w|thalidomide}}, which caused a lot of birth defects. In a clinical trial, the effect of a treatment is compared to the effect of a placebo, or an existing treatment, to make sure it actually has a beneficial effect. (Earlier trials establish that it is even a viable candidate for testing and establishing possible dosages/regimens that can then be carried forward to a treatment (Phase III) trial.)

Before the invention of clinical trials, people generally didn't know, or at least had no way of confirming, whether medicines actually worked. Although many herbs and medicines were effective, others were no better than a placebo, and some medical treatments such as {{w|trepanation}} and {{w|bloodletting}} not only had no benefit (except for a very few rare conditions) but were very likely to be harmful. Those treatments that did work at all were mostly those that had been tried (for {{w|doctrine of signatures|whatever reason}}) and just happened to be useful, but others had neutral or even adverse effects, but still managed to not be so dangerous that subsequent recoveries from the original ailment—regardless of (or despite!) dangers inherent in such treatments—were taken as proof of their efficacy.

Similar to more recent examples, some earlier treatments may have been gradually discovered to help a particular condition only by noticing beneficial side-effects when consumed for sustenance or for unrelated medical 'guesses'. However, they also remained without the full scientific rigour so long as it remained a 'traditional remedy' with at best an oral tradition across many disparate practitioners, and no consistent effort to formalise or test the falsifiability of any findings.

At the time that this comic was published, the world was in the middle of the {{w|COVID-19 pandemic}}, which made the existence of clinical trials more relevant to the public, who waited eagerly for what sounded like good ideas to get through clinical trials and available to the general public… or fail clinical trials and not do that. During this frustrating wait, many unscientific claims have been made that various drugs or non-drug treatments are cures for COVID-19, making it difficult to convince believers to get real treatments. On the other hand, many people were skeptical about COVID-19 vaccines which were made available to the public for emergency use before the clinical trials were finished, or had concerns about whether the clinical trials were rushed or otherwise flawed due how quickly they were conducted compared to the traditional speed for vaccine development and approval.

In the title text, "Standard of care" refers to the previously accepted practice which a new medicine needs to be compared against. Because the original 3-step "standard of care" in this comic didn't include clinical trials before their adoption, we didn't need to do any testing in order to decide to start using them. If we ''had'' had them as the standard of care, then we would have had to perform tests before we added a step and it would have taken longer. This assumes that the process itself is subject to the same scientific rigor as medical treatment; in practice that would be more of a political change that is still not tested.

This comic can be viewed to criticize several extreme political proposals that are obviously bad ideas to most people, such as abolishing the nuclear family, making gay marriage illegal, blocking the development of renewable energy sources and defunding the police. People tested the latter in Seattle, and {{w|Capitol Hill Occupied Protest#During the zone|the test didn't go well}}.

==Transcript==
:1. Come up with new idea
:2. Convince people it's good

:[Scrawled in red as an afterthought, an arrow inserting it between item 2 and the original item 3]
:3. Check whether it works

:3. [Now scribbled over and amended to "4."]
:New idea is adopted

:[Caption below the panel]
:The invention of clinical trials
{{comic discussion}}
[[Category: Science]]
[[Category: Comics with color]]
[[Category: Comics with lowercase text]]
[[Category: Scientific research]]

2400: Statistics

2023-01-19T19:48:14Z

172.70.206.150: /* Transcript */ research

{{comic
| number = 2400
| date = December 18, 2020
| title = Statistics
| image = statistics.png
| titletext = We reject the null hypothesis based on the 'hot damn, check out this chart' test.
}}

==Explanation==
This comic is another in a [[:Category:COVID-19|series of comics]] related to the {{w|COVID-19 pandemic}}, specifically regarding the [[:Category:COVID-19 vaccine|COVID-19 vaccine]]. It is also another one of [[Randall|Randall's]] [[:Category:Tips|Tips]], this time a statistics tip.

===Graph===
The main focus of the comic is a graph showing cases of COVID-19 versus time for two groups: one group was vaccinated and the other group was not. Graphs are ways to visualize data, and for real data indicate specific values. This graph seems to be based on [https://www.nejm.org/doi/full/10.1056/nejmoa2034577 the Pfizer vaccine's results]. The higher line ("placebo group") rises in a steep curve. The lower line ("vaccine group") follows the first for a bit but then levels out to a much slower rate of climb. Officially, a scientific assessment of the effectiveness of anything requires rigorous statistical analysis. This is particularly true in medical studies, where impacts of biology can be highly complex and subject to many factors, meaning that careful review of the data is necessary to confirm that an intervention was effective. The joke of this comic is that the intervention presented here is so ''obviously'' effective that it's obvious even to a layman with little understanding of the math. A few days after the vaccine was administered, cases in the vaccinated group essentially flatline, while cases in the placebo group continue to rise as a significant rate. The data is so "good", meaning that numbers for the treatment and control groups diverge so dramatically, that actual analysis becomes almost a formality: a glance at the chart would convince most people that the treatment is effective.

This comic was released one week after the FDA granted an emergency use authorization for the {{w|BNT162b2|Pfizer COVID-19 vaccine}} was released, and 8 days after results of its Phase 3 clinical trial were published in [https://www.nejm.org/doi/full/10.1056/nejmoa2034577 the ''New England Journal of Medicine'']. The document includes the following [https://www.nejm.org/doi/full/10.1056/nejmoa2034577 chart]. The charts draw the integral of the incidence data rather than the data itself ("cumulative" rather than "rate"): this results in changes in disease rate towards the left side of the chart, being added into the data on the right side, amplifying their difference. This technique for emphasizing the data is valid: the spread between the lines only continues to increase if the effect continues happening, such that the total spread at the right is proportional to the total effect the vaccine had. The charts do not show any information on other possible variables. Randall has described previously in his webcomics how very clear charts can be made to hide misleading data. The linked graph does not leave the numbers out, and the numbers indicate the vaccine is 91% effective at preventing the disease (and a 95% chance of being between 85 and 95% efficient).

The advice here could be seen as the inverse of the "science tip" in [[2311: Confidence Interval]], in which the data was so ''bad'' that its error bars fell outside of the graph and were not shown. Also there's some association with [[1725: Linear Regression]] where the data is not so good that you don't need to perform linear analysis.

===Null hypothesis===

The null hypothesis, mentioned in the title text, is the hypothesis in a statistical analysis that indicates that the effect investigated by the analysis does not occur, i.e. 'null' as in zero effect. For example, the null hypothesis for this study might be "The vaccine has no effect on whether subjects catch COVID." The null hypothesis was previously the subject of [[892: Null Hypothesis]]. The null hypothesis is rejected when the probability of something like the observed data would be very low were the null hypothesis true.

For a simplified example, imagine there are 10 000 people in the vaccinated group, and each has a 5% chance of catching COVID under the null hypothesis; we expect 500 people to catch COVID. If only 490 catch COVID, the null hypothesis remains plausible, but if just 10 do, the odds are (in Python; see {{w|binomial distribution}}) <code>sum([math.comb(10000, i) * 0.05**i * 0.95**(10000-i) for i in range(0,10)])</code> = 1.5 × 10-204. In other words, it is wildly improbably that an ineffective vaccine would have produced such excellent results. We therefore conclude that the vaccine is not ineffective, and have rejected the null hypothesis.

Most people however, on seeing the raw results, would have concluded that the vaccine worked and statistics were just a formality. As the title text says, they would have "reject[ed] the null hypothesis based on the 'hot damn, check out this chart' test."

==Transcript==
:[Shown is a graph with the x-axis labeled "time" and the y-axis labeled "COVID cases." There is a black line on the graph labeled "placebo group", which has a roughly linear slope moving toward the top right corner. There is a red line labeled "vaccine group", which follows the black line for about an eighth of the width of the graph before leveling off at a much slower increase.]

:Caption beneath the graph: Statistics tip: Always try to get data that's good enough that you don't need to do statistics on it

{{comic discussion}}

[[Category:COVID-19]]
[[Category:COVID-19 vaccine]]
[[Category:Comics with color]]
[[Category:Statistics]]
[[Category:Tips]]
[[Category:Scientific research]]

2661: Age Milestone Privileges

2023-01-09T18:39:44Z

172.70.206.150: /* Explanation */

{{comic
| number = 2661
| date = August 19, 2022
| title = Age Milestone Privileges
| image = age_milestone_privileges.png
| titletext = If you reach 122, you get complete unrevertible editorial control over Jeanne Calment's Wikipedia article.
}}

==Explanation==
This is a list of "age milestones" in the United States. As usual for Randall, he has added many fictional entries to supplement some real life ones. The real milestones are the ages at which Americans are generally allowed to do certain things for the first time. These are a mix of legal restrictions (such as the age for driving and voting), rules from private companies (such as movie theaters and car rental companies) and medical guidance (like the shingles vaccine).

{| class="wikitable"
! Age || Privilege || Real? || Description
|-
| 16 || Drive || Yes || Legal driving age in the US is set by the individual states, but the general rule is that Americans are allowed to begin driving on public roads at age 16. There are various levels of restrictions on this privilege, however. In Randall's state of {{w|Driver's licenses in the United States#Licenses for adults and minors; GDL laws|Massachusetts, and in 8 other states}}, 16 is the minimum age to apply for a learner's permit. {{w|Driver's licenses in the United States#/media/File:Restricted license age requirements by US state.svg|In most of the country, 16 years is the minimum age for a restricted driver's license.}}
|-
| 17 || Attend R-Rated movies alone || Yes || In the US, the Motion Picture Association assigns {{w|Motion_Picture_Association_film_rating_system|ratings}} to movies based on whether they consider the film's content to be suitable for children. In this classification, "R" stands for "restricted", and the guidance from the MPAA is that no one under the age of 17 should be allowed to see it if not accompanied by a parent or legal guardian. It should be noted that this guidance does not have force of law, but is sufficiently accepted that nearly all US theaters adopt it as a policy.
|-
| 18 || Vote || Yes || The Twenty-sixth Amendment to the United States Constitution prevents a minimum age of voting from being set above eighteen, meaning that eighteen-year-olds are old enough to legally vote anywhere in the country. Some states allow 17-year-olds to vote in primaries if they will turn 18 before the general election, but Randall's state of Massachusetts is not one of them.
|-
| 21 || Buy alcohol || Yes || While individual states have official power over the drinking age, the {{w|National Minimum Drinking Age Act}} restricts federal funding from states that do not enforce a drinking age of 21 years. This has resulted in a ''de facto'' national drinking age of 21 in the US, which is higher than most countries. It should be noted that some states allow minors to drink alcohol under certain circumstances, but no state allows anyone under 21 to buy alcohol.
|-
| 25 || Rent a car || Generally || Car rental companies set their own age restrictions on renting cars. The industry standard in the US is to charge a higher rate for drivers under the age of 25. Thus, there was not a "prohibition" per se, but 25 is a milestone for "regular" rates and fees on car rentals.
|-
| 30 || Run for Senate || Almost || This entry is slightly incorrect: According to {{w|Article_One_of_the_United_States_Constitution#Clause 3: Qualifications of senators|Article 1, Section 3, Clause 3 of the U.S. Constitution}}, one must be at least 30 years old in order to ''become'' Senator, not ''run'' for Senate. For example, Joe Biden was 29 years old when he was first elected to Senate but turned 30 before being sworn in.
|-
| 32 || Rent a Senator's car || No || This is the first joke entry in the table. For one thing, most Senators do not rent out their cars, which they probably need to use regularly themselves because they have jobs{{Citation needed}} to commute to, and it would be a security hazard to allow random strangers access to their vehicle.

This could also be a reference to the Ambassador, a now defunct car brand.
|-
| 35 || Run for president || Almost || In the United States, according to {{w|Article Two of the United States Constitution#Clause 5: Qualifications for office|Article 2, Section 1, Clause 5 of the U.S. Constitution}}, a person must be at least 35 years old to be eligible to hold the Office of President. Similar to the age 30 entry, this is slightly incorrect. However, unlike the Senate case, this technicality has not been relevant for anyone elected as United States president—at least not yet (as of 2022).
|-
| 40 || Rent a flying car || No || A 25-year-old might be able to rent a non-flying car today, but not a flying car, because the technology is not mature enough to the point where they're available to rent. The joke is that by the time a 25-year-old reader becomes 40, the technology will exist and they'll be able to rent a flying car. Unlike the earlier lines, the limitation has nothing to do with their age, just technological development.
Alternatively, even once flying cars are developed, their usage will be more restricted. For example, young people are perceived to be more reckless and/or otherwise dangerous.

This whole issue may be virtually negated if the newly developed flying cars are introduced only as ''self-''flying cars (an off-shoot of self-driving technology but devoid of many of the dangers of navigating roads, i.e. person-controlled vehicles, pedestrians and other ground-based hazards), in which case the age (or even presence) of the renter may be very much more irrelevant than the nature of any route/destination the guidance computer is tasked to fulfill. The question would then be how much a potential passenger would trust pure electronics to avoid all the actual dangers for what is essentially a flying taxi, compared to a human controller who may be fallible but presumably at least has their own fully developed common sense and a degree of self-preservation as well as any requisite training.
|-
| 45 || Learn about the God-Empress || No || Obviously, the restriction of knowledge of the "God-Empress" does not actually exist because this comic is visible to people under 45 years old.{{Citation needed}} According to [[1413]], she will be public knowledge by 2040 anyway.
|-
| 50 || Join AARP || Yes || Full {{w|AARP}} (formerly called the American Association of Retired Persons) membership is available to anyone age 50 and over. Officially, there are no age restrictions to membership, but members under the age of 50 do not have access to full benefits.
|-
| 50 || Get a shingles vaccine || Recommendation || At the time of the comic, the [https://www.cdc.gov/vaccines/vpd/shingles/public/shingrix/index.html CDC recommended] that adults 50 years and older get the shingles vaccine called Shingrix (this line was not in the original version of the comic, corrected later)
|-
| 52 || Click to skip captchas || No || Older people might have more difficulty understanding [[:Category:CAPTCHA|captchas]]. Also, they could be more inconvenienced because some older people move more slowly, so it would take them longer to move the mouse, and people would care more about older people anyway. However, this would be impractical to implement because if the computer knew the person's age, it would know that the user is a person, not a bot, so there would be no point in a captcha anyway.
|-
| 55 || Vote for God-Empress || No || It appears that a person must have knowledge of the existence of the God-Empress for ten years before they are sufficiently qualified to elect a new one. Since the God-Empress is (presumably) in power for life, it is likely that most people would have to wait much longer than ten years.
|-
| 62 || $80 national parks lifetime pass || Yes || The US National Parks Service has a [https://www.nps.gov/planyourvisit/passes.htm lifetime membership pass] for Americans ages 62 and over, which allows access to national parks and other areas managed by the NPS.
|-
| 65 || Eligible for Medicare || Yes || {{w|Medicare (United States)|Medicare}} is a US government-run health insurance for older people, and indeed begins eligibility at age 65 for the general public.
|-
| 67 || Collect Social Security || Yes || {{w|Social Security (United States)|Social Security}} is a system of benefits for retired individuals, disabled persons and widows/widowers. U.S. individuals may collect reduced Social Security benefits starting at age 62, and they can collect increased Social Security benefits if they wait until age 70. 67 is considered "Full Retirement Age." There is some debate about whether one would be better off waiting or taking it right away, but for most people Full Retirement Age (67) is at least close to optimal.
|-
| 68 || See "Skip ads" button on live TV|| No || Some DVRs and streaming applications have a feature to skip over commercial breaks in recorded programs, but this could not be available in live TV, since it would require jumping forward in time. Time travel is currently impossible.{{citation needed}}
|-
| 70 || Run for God-Empress || No || The name suggests that this would also only be available to women.
|-
| 75 || Ride any animal in a national park || No || The National Parks Service probably could institute this relatively safely because most people over 75 would not be able to run fast enough to outrun/catch up to an animal and mount it{{Citation needed}} and would not have the rebellious/risk-taking/adventurous streak that would incline them to try.{{Citation needed}}
|-
| 80 || Eligible for Megacare || No || This is based on becoming eligible for Medicare at age 65.
|-
| 85 || Click to toggle whether an ad is positive or negative about the product || No || In line with previous milestones regarding advertisements, this implies the ability to control reality and change the mood of the ad one is watching as it is running. Obviously, this is impossible, but could potentially be pulled off by adding an option to change the ad to another ad about the same product, but with the opposite viewpoint of the product. Ignoring the issue that ads that are just negative about a specific target don't tend to be commissioned. Except perhaps in certain areas of political campaigning. Furthermore, the wording appears to imply the new ad is the same as the one you were watching previously, ie. same actors, rather than a different ad about the same product.
|-
| 90 || Click to make any movie R-rated || No || It is unclear whether this would actually make the movie less appropriate or change the Motion Picture Association's rating to be erroneous. Also, what if the rating was previously NC-17?
|-
| 100 || Get a letter from the president || No || In the US (which other milestones, such as running for president starting at age 35, indicate is the country being referred to), you can instead get [https://www.today.com/series/today-celebrates/celebrate-today-ask-al-roker-wish-your-loved-ones-happy-t69606 congratulated] by the weatherman ({{w|Al Roker}}) on the {{w|Today (American TV program)|Today Show}}. However, the United Kingdom is much closer. People there can [https://www.royal.uk/anniversary-messages-0 apply to receive a card] (formerly a telegram, later a TeleMessage) from the Queen on their 100th birthday.
|-
| 102 || (35+67) Collect a {{w|Former_Presidents_Act#Pension|presidential pension}} || No || The idea behind this joke is that it is the minimum age of presidency plus the minimal age to collect Social Security. There are several reasons why this must be a joke. Two are that Social Security begins 67 years after the person was born, not 67 years after the person's job started, and that the United States government would not bother to set up such a system because the vast majority of people, including former presidents, do not live to 102 years old. In fact, as of 2022, no former United States president has ever lived to 102 years old. The current oldest former U.S. President is Jimmy Carter at 97. Good luck Jimmy, only 5 more years!
|-
| 105 || Get a birthday card from the God-Empress || No || Being a God-Empress would be more important than being the leader of a single country. This would make the God-Empress's time more valuable, so she only has to send a birthday card to the few people who reach the age of 105. Contrariwise, the God-Empress is presumptively all-powerful and furthermore capable of delegation of ministerial tasks such as card transmission, so the utilitarian fact that the scarcity of 105-year-old people reduces workload is not a plausible justification.
|-
| 111 || Leave your own birthday party early by putting on a magic ring || No || This is a reference to the {{w|Lord of the Rings}} where Bilbo leaves his eleventy-first birthday party (the Bilbo Baggins Farewell Birthday Party) invisibly by using {{w|the One Ring}}.
|-
| 118 || Vote 100 times || No || Presumably a joke meaning the person can now cast 100 votes, for each election issue that a younger person can only vote for once, giving their opinion a vastly increased personal weight (or subtlety, if they vote more across the board than merely grant 100 votes to the same outcome), although it may not greatly change the result unless sufficient voters exist (of a like mind) to disproportionately swing the result towards the result desired more by these elder voters than their one-vote juniors.
It is the 100th anniversary of their having (potentially) first voted, and as such is a century milestone. But if there were exactly one election at the same time each year, the first vote on or after their birthday would actually be the 101st vote the person has been eligible to cast in their lifetime. If the sole election of each year were held at a different time of each year, someone who voted in every election might vote for the 100th time at either age 116, 117, or 118. However this milestone would happen earlier because there are often multiple elections per year, e.g., primaries, general elections and possibly runoffs. There may also be several reasons why the person may not have been given the opportunity to vote every year since they were 18, e.g. prior to the {{w|Nineteenth Amendment to the United States Constitution|women's suffrage}} being officially ratified barely 100 years ago, but most importantly that the mandated minimum voting age was 21 until {{w|Twenty-sixth Amendment to the United States Constitution|much more recently}}.
|-
| 120 || Collect the pensions of all elected officials || No || It is very unlikely that any government would award the pensions of all elected officials to anyone because they have reached the age of 120 years.{{cn}}
|-
| 125 || Drink alcohol in an R-rated movie while getting a shingles vaccine from the president || No || This entry references four earlier milestones (attending an R-rated movie, drinking alcohol, becoming President, and getting the shingles vaccine) whose corresponding ages (17, 21, 35, and 50) sum to 123. While not exactly 125, this may have contributed to the inspiration or age selection of this milestone.
|-
| 128 || Age rolls over, become a baby again || No{{Citation needed}} || {{w|Integer overflow}} happens in computers when there are not enough bits (binary digits) to store the result of a calculation, and typically happens in computers at a given power of two, such as 128. An unsigned 7-bit number can hold the values 0 to 127 (127 being 27 - 1) and an attempt to go beyond 127 will overflow, also called rollover, back to zero. 7-bit numbers are not common native values in today's computers. For the more usual integers of one byte (8 bits), while a signed byte would roll over after 127, it would typically rollover to -128 rather than to zero, whereas an unsigned byte would rollover to zero but not until after 255. 

|}

The title text mentions {{w|Jeanne Calment}}, who holds the record for the oldest person ever (there are biblical references to older people, such as {{w|Methuselah}}, who supposedly lived to 969, but their ages haven't been verified). She reportedly was age 122 when she died in 1997. There's some controversy whether Calment actually claimed her mother's records, including birth certificate, as her own. "Editing wars" have been fought over her Wikipedia page. Randall claims that if you match her age you get sole editorial control over that article. However, if anyone managed to exceed her achieved age, presumably they would get their own page (albeit that they should not be encouraged to {{w|Wikipedia:Editing Your Own Page|edit it}} themselves) and hers would cease to be as interesting - although that might depend on what use is made of the unparalleled editorial control now granted.

==Transcript==

<big>Age Milestones</big> 
and associated privileges

16  Drive 
17  Attend R-rated movies alone 
18  Vote 
21  Buy alcohol 
25  Rent a car 
32  Run for senate 
35  Run for president 
40  Rent a flying car 
45  Learn about the God-Empress 
50  Join AARP 
50  Get a shingles vaccine 
52  Click to skip captchas 
55  Vote for God-Empress 
62  $80 National parks lifetime pass 
65  Eligible for Medicare 
67  Collect Social Security 
68  See "Skip Ads" button on live TV 
70  Run for God-Empress 
75  Ride any animal in a national park 
80  Eligible for MegaCare 
85  Click to toggle whether any ad is positive or negative about the product 
90  Click to make any movie R-rated 
100  Get a letter from the president 
102  (35+67) Collect a presidential pension 
105  Get a birthday card from the God-Empress 
111  Leave your own birthday party early by putting on a magic ring 
118  Vote 100 times 
120  Collect the pensions of all elected officials 
125  Drink alcohol in an R-rated movie while getting a shingles vaccine from the president 
128  Age rolls over, become a baby again

{{comic discussion}}
[[Category:CAPTCHA]]
[[Category:Politics]]
[[Category:Comics featuring real people]] 
[[Category:Wikipedia]]

Talk:2719: Hydrogen Isotopes

2023-01-04T12:21:31Z

172.70.206.150: Replies

This shows as a 404 on xkcd.com but in my RSS feed i can see the comic
: Works for me. [[Special:Contributions/172.69.34.9|172.69.34.9]] 02:25, 3 January 2023 (UTC)
::works for me now too but it didnt before
::: It works on m.xkcd.com and on the homepage of xckd, but the direct link gives me a 404. Various services such as the Wayback Machine show it as loading though. Could be a bad cache on some service. [[Special:Contributions/162.158.63.86|162.158.63.86]] 02:37, 3 January 2023 (UTC)

Could someone add an explanation of Nydnonen? I don't get it and it's google proof [[Special:Contributions/172.71.210.209|172.71.210.209]] 05:04, 3 January 2023 (UTC)Benzodiakanine
: Nothing. Was hopeful about {{w|List of Greek and Latin roots in English/N}} but nope. Tried stemming on all the Wiktionaries too. [[Special:Contributions/172.71.158.91|172.71.158.91]] 05:28, 3 January 2023 (UTC)
::Kudos to whomever figured it out, lol! [[Special:Contributions/172.71.158.231|172.71.158.231]] 08:02, 3 January 2023 (UTC)
:::Seems someone already did. There are four N's in that word replacing three of the consonant in Hydrogen so there are now four Ns one for each of the four neutrons in Nydnonen. ;-) --[[User:Kynde|Kynde]] ([[User talk:Kynde|talk]]) 08:10, 3 January 2023 (UTC)

Are these to scale? I recently read that the Helium is smaller in terms of measured atomic radius than the Hydrogen. Possibly this is true of Deuterium as well? [[Special:Contributions/172.70.85.45|172.70.85.45]] 06:50, 3 January 2023 (UTC)
:They are almost the same size but it depends on temperature: https://onlinelibrary.wiley.com/doi/abs/10.1002/anie.200800063 [[Special:Contributions/162.158.90.153|162.158.90.153]] 08:00, 3 January 2023 (UTC)
::Is the reason Helium is smaller not that there are double the positive charge which the electrons thus orbit in a lower orbit (I know this is not the correct in reality with the orbit). But if true then Deuterium would not have this effect as it is not the weight but the charge that changes the orbit. And Deuterium has the same charge as Hydrogen as does Tritium. --[[User:Kynde|Kynde]] ([[User talk:Kynde|talk]]) 08:10, 3 January 2023 (UTC)

Is "oops all neutrons" distinct from Neutronium, which is also all neutrons? [[Special:Contributions/172.70.100.131|172.70.100.131]] 07:38, 3 January 2023 (UTC)
:Neutronium is ultra-dense and bound by gravity, with a minimum of about 1.2x1058 neutrons in a 40 kilometer diameter sphere. [[Special:Contributions/162.158.90.153|162.158.90.153]] 08:00, 3 January 2023 (UTC)
::Well actually a {{w|neutron star}} is only 10 km in radius (20 km in diameter) according to Wikipedia. And it is 1057 neutrons acording to this [https://www.astronomy.ohio-state.edu/ryden.1/ast162_5/notes21.html lecture on Neutron Stars]. {{w|Neutronium}} was actually used as a name for neutrons without protons and suggested to be placed as number 0 on the periodical table. But is has also been used as a name for the matter in the center of neutron stars, but usually not in scientific papers! There it is called degenerate matter. The wiki article mentions how a single neutron decays to proton/electron/neutrino in 15 minutes. It also mentions that two neutrons could form for very short periods in nuclear decay. An then mentions that more than two neutrons together is not likely to exist. Specifically mentioning the three from Randall's Oops particle as not being stable for even the shortest of times. Of course a neutron would also not be able to orbit a group of neutrons. But even the three at the center is impossible. More neutrons together would be isotopes of number 0 element... --[[User:Kynde|Kynde]] ([[User talk:Kynde|talk]]) 08:22, 3 January 2023 (UTC)
::: My bad memory; thanks. [[Special:Contributions/172.71.154.38|172.71.154.38]] 05:08, 4 January 2023 (UTC)

I think "Maximum Strength" is a reference to medicines marketed as such - in particular brands of Ibuprofen "Maximum Strength Tablets". --[[Special:Contributions/172.69.79.132|172.69.79.132]] 14:59, 3 January 2023 (UTC)
: Yes - typically meaning that it contains far more of whatever its active ingredient is than is necessary to be efficacious.[[Special:Contributions/172.70.91.128|172.70.91.128]] 15:54, 3 January 2023 (UTC)

Considering that Deuterium is derived from Greek and Tritium works in both Greek and Latin, wouldn't the correct name for ⁴H be Tetartium?
:Tetrium maybe? Tetraium? [[Special:Contributions/172.71.154.38|172.71.154.38]] 05:08, 4 January 2023 (UTC)

Is it just me or have the recaptchas gotten much more difficult over the past week, to the point of ambiguous or indiscernibly blurred images and frequently rejecting correct responses (i.e. "please try again" in red)? Granted, I'm not saying this behavior makes it any less valid as a captcha, but it's a little surprising to always get several-step challenges lately. [[Special:Contributions/172.71.154.38|172.71.154.38]] 05:08, 4 January 2023 (UTC)
: Captchas are in a continual arms race with bot writers, and wax and wane in difficulty as new attacks and counter-measures are deployed. ReCAPTCHA occasionally becomes more lengthy when they refresh their image library; we may be experiencing that. It sure doesn't seem to be slowing down the creation of new phantom usernames -- does registration even have the captcha? [[Special:Contributions/172.71.154.159|172.71.154.159]] 07:43, 4 January 2023 (UTC)
:: Firstly yes, and that might be the problem, because ReCAPCHA is still quite mild on other sites. Whomever is automating username registration here (which has been going on at least five years) may have fallen prey to a new countermeasure increasing their failure rate and making our site's angry. [[Special:Contributions/172.70.206.150|172.70.206.150]] 12:21, 4 January 2023 (UTC)

Re "ium": Shouldn't we try to keep the explanation short and to the point? This comic is about "isotopes", i.e. about different options of how to construct a single atom (or atom-like entity). IMO, there is no need to include many-body effects in a set of multiple electrons ([https://www.explainxkcd.com/wiki/index.php?title=2719%3A_Hydrogen_Isotopes&type=revision&diff=303973&oldid=303971 "Fermi velocity"] or [https://www.explainxkcd.com/wiki/index.php?title=2719:_Hydrogen_Isotopes&oldid=304060 "electron degeneracy pressure"]); just as there is no need to discuss, say, the kinetic theory of gases made up of these isotopes, or how they would be able to form fluids or solids. It is good to see that people who contribute here know about these effects, but I think that the explanation does not benefit from extending the discussion too far beyond the subject of a given comic. If anything, it might be worthwhile to include a reference to {{w|ion trap|ion traps}} - especially since in a Penning trap electrons actually go in circulating orbits (although not exactly circular). --[[Special:Contributions/172.70.246.210|172.70.246.210]] 11:56, 4 January 2023 (UTC)
: Go for it. We all agree to have our "writing to be edited mercilessly" in the fine print just below the Summary. Editing on whims is good because if someone else liked something earlier they will just merge it back in somehow. [[Special:Contributions/172.70.206.150|172.70.206.150]] 12:21, 4 January 2023 (UTC)

Talk:2716: Game Night Ordering

2022-12-27T02:13:51Z

172.70.206.150: Quotes!

Should we create a category for comics about game night? It can contain at least this and https://xkcd.com/2486/. [[User:Barmar|Barmar]] ([[User talk:Barmar|talk]]) 22:32, 26 December 2022 (UTC)
:I'm not going to oppose it, but keep in mind that it would overlap with [[:Category:Board games]]. --[[Special:Contributions/172.70.178.48|172.70.178.48]] 22:50, 26 December 2022 (UTC)
::We absolutely need a general [[:Category:Games]] because we have e.g. roleplaying games under Board games. Does anyone know how to edit in a superclass category? The last time I ever did anything sophisticated with Mediawiki categories was like 2008. [[Special:Contributions/172.71.154.38|172.71.154.38]] 23:39, 26 December 2022 (UTC)

The rules would seem to be similar to the card game Cheat (or, at least, the version we used to play). Using an ordinary wholly-dealt pack of cards (for any number of players), it was a "blind bid and discard" game whereby each player has to state "<one to four> <card value>s" (or more than four, with merged packs, each of which might be whole or partial) was going on the discard pile, such that the card value was within one (-1, =, +1, with standard wrapping ...>10>J>Q>K>A>2>...) of the prior stated discard. And ''something'' had to be discarded, whether or not the player could technically do so. The forfeit for not continuing play ''or'' challenging, within a generally acceptable thinking time, was the same for either being successfully challenged (you stated you put down two threes, but on checking the dump pile you discarded two sevens) or for the person who wrongly challenged... to pick up the discard pile and be so much further from the ultimate goal of ending up with zero cards (the first the winner, optionally the second, third, etc to do so to earn further ranks just for the sake of continuing/last-ranking the one who ended up as the only one still with cards). - I presume this game just applies the same penalty (buying the food) to anyone who dithers over whether to challenge anything or 'play their own hand'. There doesn't need to be anything more complicated to it. Unless there's also an 'empty hand' winning state, that I can't discern from the brief discourse given in the comic. But it seems more geared to finding the eventual 'loser' (the one who pays up) than any single beneficiary. [[Special:Contributions/162.158.34.230|162.158.34.230]] 23:17, 26 December 2022 (UTC)
:If there is a link for Cheat you should add it. [[Special:Contributions/172.70.206.150|172.70.206.150]] 23:20, 26 December 2022 (UTC)
::Well, I think there's far too many variations... Though, surprisingly, it does look like {{w|Cheat (game)}} actually describes ''my'' learnt version quite well. But I don't think I see any 'time out' penalties mentioned there, and that was the key part of the "play or challenge, don't dither, or you lose" bit to my (sorry, rather long) description above... [[Special:Contributions/162.158.34.230|162.158.34.230]] 23:27, 26 December 2022 (UTC)
::: Never apologize for verbosity on talk; devote that energy to brevity on main. [[Special:Contributions/172.71.154.156|172.71.154.156]] 23:41, 26 December 2022 (UTC)
::::We need a quotes page. [[Special:Contributions/172.70.206.150|172.70.206.150]] 02:13, 27 December 2022 (UTC)
::(Plus there's the inverted "loser finder" rather than "winner finder" primary nature of the gameplay. It makes the methodology of play a bit too different.) [[Special:Contributions/162.158.34.231|162.158.34.231]] 23:30, 26 December 2022 (UTC)

We should make a payment service for providing crowdfunded rewards to the best contributors to explanations. [[Special:Contributions/172.69.134.16|172.69.134.16]] 01:16, 27 December 2022 (UTC)
:I love this idea but it would conflict with the ethos of completely anonymized contributions here. Unless someone can propose how it might not? I mean, if there was some way to include an SHA-256 identity-confirming hash in edit summaries? Would keeping track of them in terms of surviving text after, say, a month be a decent leaderboard scoring? [[Special:Contributions/172.69.33.84|172.69.33.84]] 01:42, 27 December 2022 (UTC)
::My meager anonymous IP contributions to explanations have been completely dwarfed by my attempts to revert vandalism on the official main page leaderboard, but is that a good or a bad thing? The idea needs to be carefully considered. I would absolutely kick in $25 to support other explainers, but I would need some assurance that the system couldn't be gamed by, e.g. paraphrasers, which I'm not sure is even possible. [[User:Liv2splain|Liv2splain]] ([[User talk:Liv2splain|talk]]) 01:54, 27 December 2022 (UTC)
::: It's easy to hijack someone else's contributions with paraphrasing and refactoring. It's a dead end. [[Special:Contributions/162.158.166.230|162.158.166.230]] 02:05, 27 December 2022 (UTC)

Talk:2716: Game Night Ordering

2022-12-26T23:20:11Z

172.70.206.150: reply

Talk:2712: Gravity

2022-12-16T23:51:18Z

172.70.206.150:

Whatever image is supposed to be in the center isn't showing up for me! D: Tried on both Safari and Chrome but it gives me the little broken picture icon. Hopefully it's fixed soon! (The comic's been up for about 10 minutes going by when the bot updated this page.) [[Special:Contributions/172.70.126.117|172.70.126.117]] 22:28, 16 December 2022 (UTC)

: The center image is trying to load this link, but there's nothing there: https://xkcd.com/tile/ship1/ship_gliding_2x.png. I hope that gets fixed soon. The "ship" seems to rotate a bit unpredictably over time. At first I thought it was responding to my mouse movements, but I don't think so anymore. [[User:Orion205|Orion205]] ([[User talk:Orion205|talk]]) 22:34, 16 December 2022 (UTC)

: Ah, the center image is controlled by the javascript, of course: https://xkcd.com/2712/comic.js. So this is some sort of interactive comic? [[User:Orion205|Orion205]] ([[User talk:Orion205|talk]]) 22:36, 16 December 2022 (UTC)

: Okay, left/right arrow keys seem to control the rotation. I'll check back in later in hopes of seeing the ship so I have some idea what the point of it all is. [[User:Orion205|Orion205]] ([[User talk:Orion205|talk]]) 22:39, 16 December 2022 (UTC)

: And now it's working. You fly a little spaceship around the little planet. Luckily you have shields if you slam into the ground too hard. [[User:Orion205|Orion205]] ([[User talk:Orion205|talk]]) 22:43, 16 December 2022 (UTC)

: Catch the cannonball for a spaceship upgrade. Also, not so easy to find a stable orbit around this little planet. [[User:Orion205|Orion205]] ([[User talk:Orion205|talk]]) 22:49, 16 December 2022 (UTC)

You can transform the ship into a different (seems faster to me) one by running into the last cannon ball.
[[Special:Contributions/108.162.241.249|108.162.241.249]]

Rough summary: The comic is an interactive space flight game, starting landed on an origin planet. The planet is static, and the player starts in a ship controlled by WASD or Directional keys. The ship can go up and down, and rotate left and right. Game simulates orbits and gravity, making navigation tricky. Around the player ship there are dots which indicate nearby planets - there are numurous planets, each with what seem to be drawings related to the What If book. Within the browser, planets are loaded in PNG format by chunk, names formatted as "planet_0_0" with numbers incrementing as grid co-ordinates. Planets and objects found: "origin" "europa", "road", "b612". NOTE: Several hazards exist, such as a field of black holes - if flown into, the ship can become stuck if let to be pulled close to the surface, locking in place. [[Special:Contributions/172.70.110.230|172.70.110.230]] 23:13, 16 December 2022 (UTC)

: Within browser dev console exists the objects "Ship" and "Comic", the latter containing a list of all objects and coordinates, as well as various setting for the game physics and settings. Comic contains the sub-object "Voyager", which contains the details and settings for the player ship, including location, speed, etc. [[Special:Contributions/172.70.110.230|172.70.110.230]] 23:13, 16 December 2022 (UTC)

:: There are 5 ship types in the game code, each with their own consumable transformative found in the world. The ship alternatives are (ship1, ship2, ship-tintin, ship-figure, ship-soccerball). These can be changed with console command [Comic.ship = "ship1"]. Note: At current, "ship-soccerball" returns an error and does not load correctly. [[Special:Contributions/172.70.110.230|172.70.110.230]] 23:13, 16 December 2022 (UTC)

:: The "ship.shields" is a boolean value that defaults to true, and when set to false, makes the game behave in a lunar lander mode (bad landing black screens the whole page). The "ship.engine" types I see in the code are "warp" (very fast speeds) and "infinite improbability drive" (teleports to 'improbable' places). Default engine is "standard", but it seems any value that is not the former two has the same effect. --[[Special:Contributions/172.70.254.165|172.70.254.165]] 23:32, 16 December 2022 (UTC)

: In addition to Europa, the space road, and B-612, there is the "Edge of the Universe" (complete with Milliways restaurant nearby), a... tree (which is extremely hard to land on), a planet populated by the characters from Dinosaur Comics (and the main cast of Jurassic Park), the USS Enterprice (NCC 1701-C), and likely quite a bit more. Orbital mechanics make it tough to land on the smaller targets. [[Special:Contributions/172.71.254.46|172.71.254.46]] 23:07, 16 December 2022 (UTC)

:: Plus what appears to be Earth, complete with the LHC. There's a 2nd "cannonball" there for an additional ship upgrade, but at the time I found it, that graphic was unavailable. [[Special:Contributions/172.70.126.232|172.70.126.232]] 23:15, 16 December 2022 (UTC)

: I went out a long ways away, and eventually found The Great Attractor. It attracts really hard. I couldn't leave the surface. (I wasn't able to leave the center of Europa either, though, so, not saying much.) There are also some terrifying black holes (a binary system?), though something's weird about their gravity; you kinda bounce off of them a quarter screen away or so? [[Special:Contributions/108.162.216.77|108.162.216.77]] 23:10, 16 December 2022 (UTC)
:: I *think* thats a wormhole, you go in one and then out the other. I got stuck right between them. Speaking of getting stuck, there is a bug where if you hit a planet with enough gravity fast enough, the ship is inside the planet. Holding W makes you go backwards (or at least towards the center maybe?) and you can get all the way to the other end of the planet where you slow down a lot, but can eventually leave. [[Special:Contributions/172.70.82.166|172.70.82.166]] 23:19, 16 December 2022 (UTC)Bumpf

::There's one planet that's supposed to be the "remnant of the sun", is that what you mean with The Great Attractor? (It has a bridge on it with a coin(?) blocking part of the way, and a space ship actively crashing into its surface, drawn as several frames.) You can leave that by skidding over the surface like a skipping stone to gather momentum - it's tricky, due to various obstacles, but possible! (It's possible you need two ship power-ups?! If they're indeed power-ups and not just aesthetic changes, I didn't pay attention.)
::Screenshot of [https://imgur.com/a/NZulBlb the Enterprise] and [https://imgur.com/2VSZYp7 Dinosaur Comics planet]. Sorry for the broken image in the middle, I picked up two powerups and [https://xkcd.com/2712/tile/ship-soccerball/ship_landing_down_2x.png my current ship image is broken]. -(pinkgothic) [[Special:Contributions/172.68.110.143|172.68.110.143]] 23:22, 16 December 2022 (UTC)
:::[https://i.imgur.com/fLU1cWy.png Dog Park planet] [[Special:Contributions/172.71.254.114|172.71.254.114]] 23:28, 16 December 2022 (UTC)

Using a tablet (no keyboard, but seems to respond to touch), controls are confusing. Presuming that touching bottom left activates left-rotate and touching bottom right does right-rotate (can't see the presumably white-lije controls over the white planet) but I can't get ''thrust'' anything but 'reverse' into the planet centre. No obvious top-edge hotspots, either. Maybe I need to do a "You will not go to space today" and then reverse ''upward''... BRB, after a bit more testing, though... [[Special:Contributions/172.69.79.185|172.69.79.185]] 23:39, 16 December 2022 (UTC)
On the

Using the developer console, the ship can be teleported to different coordinates via console command [Comic.voyager.pos.x = 0, Comic.voyager.pos.y = -1461], provided here with start location coordinates. This can be used for manual navigation to known coordinates. List of locations per game code added below, append landing X,Y to each as determined. [[Special:Contributions/172.70.110.230|172.70.110.230]] 23:42, 16 December 2022 (UTC)

b612: [x,y] dogplanet: [x,y] earth: [x,y] enterprise: [x,y] europa: [x,y] goodhart: [x,y] greatattractor: [x,y] japanmoon: [x,y] maw1: [x,y] maw2: [x,y] maw3: [x,y] maw4: [x,y] maw5: [x,y] maw6: [x,y] maw7: [x,y] maw8: [x,y] maw9: [x,y] maw10: [x,y] maw11: [x,y] maw13: [x,y] maw14: [x,y] nojapan: [x,y] origin: [0, -1461] peeler: [x,y] pigeons: [x,y] present: [x,y] remnant: [x,y] roads: [x,y] soupiter: [x,y] steerswoman: [x,y] sun: [x,y]

In your developer console, enter <code>window.ship.engines = 'infinite improbability drive'</code> and pressing up will randomly teleport you to interesting places.
<code>window.ship.engines = 'warp'</code> will let you escape normally inescapable objects.

2694: Königsberg

2022-11-09T19:45:13Z

172.70.206.150: /* Explanation */

{{comic
| number = 2694
| date = November 4, 2022
| title = Königsberg
| image = konigsberg_2x.png
| imagesize = 448x343px
| noexpand = true
| titletext = At first I thought I would need some gold or something to pay him, but then I realized that it was the 18th century and I could just bring a roll of aluminum foil.
}}

==Explanation==
{{incomplete|Created by A TIME-TRAVELLING BRIDGE COMPANY HIRED BY EULER. Do NOT delete this tag too soon.}}

[[File:Konigsberg_bridges.png|frame|right|{{w|Königsberg}}, Prussia in Euler's time, showing the Pregel river and its seven bridges. Two of the original seven bridges no longer exist,[https://goo.gl/maps/ChdBoeQMr3AQPi446] although there are three new bridges. The Baltic port city is now Kaliningrad, a Russian exclave.]]

This comic is about the {{w|Seven Bridges of Königsberg}}, a seminal {{w|graph theory}} problem solved by the famous mathematician {{w|Leonhard Euler}}.[https://www.maa.org/press/periodicals/convergence/leonard-eulers-solution-to-the-konigsberg-bridge-problem] The problem was whether a path through the city crossing each of the seven bridges just once exists, without crossing the river forks any other way. In 1736, Euler proved that no such path exists. This result is considered to be the first theorem of graph theory and the first proof in the theory of networks[http://www-personal.umich.edu/~mejn/courses/2004/cscs535/review.pdf] — a subject now generally regarded as a branch of {{w|combinatorics}} — and presaged the development of {{w|topology}}. Combinatorial problems of other types had been considered since antiquity. {{w|Graph (discrete mathematics)|Graphs}} are a data structure common in many algorithmic problems in computer science.

[[Cueball]] attempts to cheat on the final exam in his algorithms class by traveling back in time to commission the construction of an eighth bridge before Euler could learn of the problem, allowing a trivial solution that would remove the rationale for further analysis. He hopes that this would alter his present-day timeline in such a way that the test becomes easier because graph theory might never have been developed. The use of the word "tried" implies failure, which is probably a good thing since his success would create a {{w|Temporal_paradox#Grandfather_paradox|paradox}}. [[:Category:Time travel|Time travel]] is a recurring topic on xkcd and examples where attempts to change the past fails has also been used before like in [[1063: Kill Hitler]].

With the addition of the eighth bridge, it becomes possible to cross each bridge exactly once, starting at the north bank and ending on the larger eastern island, or vice-versa. However, there is still no way to traverse each bridge exactly once and return to the starting point, because the altered graph would have an {{w|Eulerian trail|Euler trail}} but not an Euler cycle. Thus the problem might still have been interesting to Euler.{{Citation needed}} (Adding a ninth bridge connecting the north bank to the east island would render the problem completely trivial.) We can't say whether Euler or others would have developed graph theory anyway, or whether Cueball's exam would have been any easier or more difficult.

An alternative modification allowing an easy solution is to remove bridges. During World War II, two bridges to the central island connecting it to the north and south banks were destroyed by bombing, so today there is an Eulerian trail across the five remaining bridges.

The title text alludes to the fact that ordinary {{w|aluminum foil}}, which was not commercially available until 1911, would have been a tremendously valuable curiosity in the 18th century, which didn't even have {{w|tin foil}}. Aluminum was a highly priced metal before the 1880s when inexpensive methods were developed to refine it. The {{w|Washington Monument#Aluminum_apex|Washington Monument}} was constructed with a tip made of pure aluminum due to its value and conductive capacity. Aluminum had not been extracted in its pure form at the time of Euler, and was known only in compounds such as {{w|alum}}, so the metal would have been unique and exotic. The value of aluminum and the use of it as the tip of the Washington Monument was also mentioned in [[1608: Hoverboard]] where a heist to steal the tip is [https://www.explainxkcd.com/wiki/images/6/6f/1608_0995x1083y_Tip_of_Washington_monument.png depicted].

==Transcript==
:[Cueball, standing next to two men wearing wigs, pointing with a pointer at a map showing the seven bridges problem, with an extra bridge added in dashed lines]
:Cueball: Lord Mayor of Königsberg, I will reward you handsomely if you construct this bridge before my friend Leonhard arrives.

:[Caption below the panel:]
:I tried to use a time machine to cheat on my algorithms final by preventing graph theory from being invented.

{{comic discussion}}

[[Category:Comics featuring Cueball]]
[[Category:Comics featuring real people]]
[[Category:Time travel]]
[[Category:Math]]
[[Category:Programming]]

2694: Königsberg

2022-11-05T20:34:39Z

172.70.206.150: /* Explanation */ cleanup, copyedit

{{comic
| number = 2694
| date = November 4, 2022
| title = Königsberg
| image = konigsberg_2x.png
| imagesize = 448x343px
| noexpand = true
| titletext = At first I thought I would need some gold or something to pay him, but then I realized that it was the 18th century and I could just bring a roll of aluminum foil.
}}

==Explanation==
{{incomplete|Created by a WOLF, TWO GOATS, AND THREE BAGS OF GRAPH NODES. Do NOT delete this tag too soon.}}

[[File:Konigsberg bridges.png|frame|right|{{w|Königsberg}}, Prussia in Euler's time, showing the Pregel river and its seven bridges. The Baltic port city is now Kaliningrad, a Russian exclave. Two of the original seven bridges no longer exist,[https://goo.gl/maps/ChdBoeQMr3AQPi446] although there are three new bridges.]]

This comic is about the {{w|Seven Bridges of Königsberg}}, a seminal {{w|graph theory}} problem solved by the famous mathematician {{w|Leonhard Euler}}.[https://www.maa.org/press/periodicals/convergence/leonard-eulers-solution-to-the-konigsberg-bridge-problem] {{w|Graph (discrete mathematics)|Graphs}} are a data structure common in many algorithmic problems in computer science. The problem was whether a path through the city crossing each of the seven bridges just once exists, without crossing the river forks any other way. In 1736, Euler proved that there is no such path. This result is considered to be the first theorem of graph theory and the first proof in the theory of networks[http://www-personal.umich.edu/~mejn/courses/2004/cscs535/review.pdf] — a subject now generally regarded as a branch of {{w|combinatorics}} — and presaged the development of {{w|topology}}. Combinatorial problems of other types had been considered since antiquity.

[[Cueball]] attempts to cheat on the final exam in his algorithms class by traveling back in time to commission the construction of an eighth bridge before Euler could learn of the problem, allowing a trivial solution that would remove the rationale for further analysis. He hopes that this would alter his present-day timeline in such a way that the test becomes easier because graph theory might never have been developed.

With the addition of the eighth bridge, it becomes possible to cross each bridge exactly once, starting at the north bank and ending on the larger eastern island, or vice-versa. However, there is still no way to traverse each bridge exactly once and return to the starting point, because the altered graph would have an {{w|Eulerian trail|Euler trail}} but not an Euler cycle. Thus the problem might still have been sufficiently interesting to spark Euler's curiosity and develop a nearly identical general principle on the way to demonstrating that locals could indeed find no route that ended at its initial starting point. Adding a ninth bridge connecting the north bank to the east island would render the problem completely trivial and the locals may then have developed entirely different obsessions, never drawing Euler into the issue and leaving him to focus upon different problems entirely. This could backfire on Cueball, and result in an even harder topic arising in his examination, one which was never even taught to him in his original timeline experience.

The title text alludes to the fact that ordinary {{w|aluminum foil}}, which was not commercially available until 1911, would have been a tremendously valuable curiosity in the 18th century, which didn't even have {{w|tin foil}}. Aluminum was a highly priced metal before the 1880s when inexpensive methods were developed to refine it. The {{w|Washington Monument}} was constructed with a tip made of pure aluminum due to its value and conductive capacity. Aluminum had not been extracted in its pure form at the time of Euler, and was known only in compounds such as {{w|alum}}, so the metal would have been unique and exotic.

==Transcript==

:[Cueball, standing next to two men wearing wigs, pointing with a pointer at a map showing the seven bridges problem, with an extra bridge added in dashed lines]
:Cueball: Lord Mayor of Königsberg, I will reward you handsomely if you construct this bridge before my friend Leonhard arrives.

:[Caption below the panel:]
:I tried to use a time machine to cheat on my algorithms final by preventing graph theory from being invented.

{{comic discussion}}
[[Category:Comics featuring Cueball]]
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[[Category:Math]]
[[Category:Programming]]