explain xkcd - User contributions [en]

Talk:2608: Family Reunion

2022-04-18T22:22:50Z

162.158.62.234: Negative cousins

How are relatives related by asexual reproduction defined and named?

[[User:While False|While False]] ([[User talk:While False|talk]]) 21:01, 18 April 2022 (UTC)
: Any particular organisms in mind? It seems like you'd still have a generational parent, but there are a number of forms of asexual reproduction, blurring the line of what is a new lifeform and what is part of the old. Many plants, for example, can spread via colonies of their roots, whether severed from each other or not. I'm curious if there are organisms with more than two parents, and how many generations out of sync those parents can be. I think some plants might do this as well. [[Special:Contributions/172.70.114.147|172.70.114.147]] 22:06, 18 April 2022 (UTC)

This is an important comic in xkcd lore

If the chair is made of wood, doesn't it mean that it's made of the dead remains of another relative? Isn't that rather gloomy?

[[User:Eje211|Eje211]] ([[User talk:Eje211|talk]]) 21:30, 18 April 2022 (UTC)
:"Good old Umpteen-billionth-cousin oaktree has practically become part of the furniture!" [[Special:Contributions/172.69.79.209|172.69.79.209]] 22:00, 18 April 2022 (UTC)

Siblings would also technically be zeroth cousins, and the self would be a negative first cousin. No idea what higher order negative cousins would imply. Incidentally, the this structure fixes the lack of a gender neutral term for uncle/aunt/nephew/niece, who could be referred to as zeroth cousins, once removed. This does remove the directionality of the terms, though. [[Special:Contributions/172.70.130.5|172.70.130.5]] 22:09, 18 April 2022 (UTC)
: Higher order negative cousins would require that you are both descended from one of your own descendants. This either requires time travel, as in "All You Zombies", or counting step-parents, as in "I Am My Own Grandpa".--[[Special:Contributions/162.158.62.234|162.158.62.234]] 22:22, 18 April 2022 (UTC)

2599: Spacecraft Debris Odds Ratio

2022-03-28T23:20:32Z

162.158.62.234:

{{comic
| number = 2599
| date = March 28, 2022
| title = Spacecraft Debris Odds Ratio
| image = spacecraft_debris_odds_ratio.png
| titletext = You say this daily walk will reduce my risk of death from cardiovascular disease by 30%, but also increase my risk of death by bear attack by 300%? That's a 280% increased! I'm not a sucker; I'm staying inside.
}}

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

This comic is a misunderstanding of statistics very similar to [https://www.explainxkcd.com/wiki/index.php/1252:_Increased_Risk 1252: Increased Risk]. It explains that going outside for more than 5 hours a day significantly increases your risk of head injury from falling spacecraft, and advises to limit outside activity to avoid this risk. However, since the odds of being hit in the head by (part of) a falling spacecraft are astronomically low to begin with, so quadrupling it is still a negligible probability.

The specific reference to falling spacecraft is likely inspired by current events. Around a month before this was posted, the head of the Russian space agency, Roscosmos, warned that sanctions against Russia (mostly those over the Russia-Ukraine war) could result in the ISS crashing. Since the Russian section of the space station is the one that provides propulsion (although it is built to rely on the power generated by the other sections), this was taken seriously and as of when this was posting, NASA was trying to come up with alternative stabilization strategies in case the situation worsened.

The title text makes a similar joke: while the increase in chances of death by bear are greater than the decrease in chances of death by cardiovascular disease, it is incorrect to add them together, since cardiovascular disease has a much higher starting chance of death, and reducing it by 30% has a much more significant effect on overall life expectancy than quadrupling the very very small chance of death by bear.

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

{{comic discussion}}
[[Category:Charts]]
[[Category:Statistics]]

1935: 2018

2022-01-23T00:13:40Z

162.158.62.234: Link to relevant earlier comic?

<noinclude>:''This page refers to the comic named "2018". For comic #2018, see [[2018: Wall Art]].''</noinclude>
{{comic
| number = 1935
| date = December 29, 2017
| title = 2018
| image = 2018.png
| titletext = We should really start calculating it earlier, but until the end of December we're always too busy trying to figure out which day Christmas will fall on.
}}

==Explanation==
In this, the first of two [[:Category:New Year|New Year comics]] in a row, [[Megan]] wonders whether 2018 will be a {{w|Leap year|leap year}}. [[Cueball]] thinks 2018 will not be a leap year, and Megan responds that she "doubts anyone knows at this point." This appears to be a jab at people who suggest that anything they don't know is generally unknown. As Cueball says, leap years occur every four years (though there are a few exceptions - a year divisible by 100 is not a leap year, unless it is also divisible by 400), adding an extra day to account for the fact that Earth takes a bit longer than 365 days to orbit the Sun. Therefore, most years that are a multiple of four are leap years. As Megan says, this is easy for odd-numbered years, since no odd numbers are divisible by four. However, for even-numbered years, it isn't quite as simple. (Though, since the number 2,000 is evenly divisible by 4, the problem can be reduced to the much simpler question of whether the number 18 is divisible by 4.)

The last panel expresses a misunderstanding of modern public-key {{w|Cryptography|cryptography}}, which relies on the fact that it is difficult to factorize large numbers. Megan is applying this concept to the year, claiming that it is hard to determine whether or not 2,018 is a multiple of four and hence is a leap year. In reality, factorization is not needed here, since we already know the factor in question, which is four. Megan states that, if it were possible to factor large numbers with a calculator, modern cryptography would collapse. While true, it is true only for truly large numbers (hundreds of digits), and no factorization is needed in this case.

At the end of the strip, Megan hopes the answer can be {{w|Brute-force attack|brute-forced}} by February. Brute force is a method of breaking cryptography by trying every possible option until one works. This is misdirection upon misdirection, in that, even if we needed to factorize 2,018 (which we don't), the simplest brute-forcing algorithm would need to try only 14 numbers -- each prime from 2 to 43 (the square root of 2,018 is closest to 44). In cryptography, the algorithms use numbers much, much bigger than 2,018 -- on the order of hundreds or even thousands of digits.

The title text refers to calculating which day {{w|Christmas}} will fall on. As Christmas always lands on December 25 by definition, the day of the week varies from year to year, though it's always the 359th or, in leap years, the 360th day of the year. Still, determining which day of the week December 25 lands on is not a difficult problem to solve, requiring only a few mathematical operations to compute. Alternatively, this might be an oblique reference to Easter, the date of which jumps from year to year according to a {{w|Computus|multi-layered algorithm}} that most people don't know. The changing date of Easter was recently included in [[1930: Calendar Facts]]. Additionally, uncertainty with the regard to the date of Christmas has also been referenced in [[679: Christmas Plans]].

==Transcript==

:[Megan is walking.]
:Megan: I wonder if 2018 will be a leap year.

:[Now it turns out that Cueball walks behind Megan.]
:Cueball: ...it won't be, right?
:Megan: I doubt anyone knows at this point.

:[Same scene in a frame-less panel.]
:Cueball: No, it's definitely not. Leap years are divisible by 4.
:Megan: Right, and for odd numbers, that's easy.
:Megan: But 2018 is even.
:Megan: 50/50 chance.

:[Zoomed-out view with both walking in silhouette on a dark slightly curved ground.]
:Cueball: I can settle this with a calculator.
:Megan: No way. If it were easy to factor large numbers like that, modern cryptography would collapse.
:Cueball: I see.
:Megan: I just hope we manage to brute-force it by February.

==Trivia==
*Released on Friday, December 29, this was the last comic of 2017. The next comic, [[1936: Desert Golfing]], was released soon after midnight (in Randall's time zone) on New Year's Day 2018.

*Every year that is exactly divisible by four is a leap year, except for years that are exactly divisible by 100, but these centurial years are leap years if they are exactly divisible by 400. For example, the years 1700, 1800, and 1900 were not leap years, but the years 1600 and 2000 were.

*Since 100 is divisible by 4, only the last two digits of a number are needed to determine if that number is divisible by 4. So to determine if 2018 is divisible by 4, we only need to check whether 18 is divisible by 4, which is easy.

*2018 is not divisible by 4, so the year was not a leap year. 2016 and 2020 are leap years. This is true for both the Gregorian and the Julian calendar. A year is roughly 365.2422 days long.

*{{w|Eastern Christian Churches}} celebrate Christmas also on December 25 but on the older Julian calendar, which currently corresponds to January 7 on the Gregorian calendar.

*This is the third year in a row with New Year's comics with only the year used as the title; before that there were two more comics with such titles, but those two (and thus the first three) were only released in the even years: [[998: 2012]] in 2012, [[1311: 2014]] in 2014, [[1624: 2016]] in 2016 and [[1779: 2017]] in 2017.

{{comic discussion}}

[[Category:New Year]]
[[Category:Comics featuring Megan]]
[[Category:Comics featuring Cueball]]
[[Category:Comics sharing name|2017]]
[[Category:Number theory]]
[[Category:Calendar]]
[[Category:Cryptography]]

2447: Hammer Incident

2021-04-08T04:55:41Z

162.158.62.234: /* Explanation */

{{comic
| number = 2447
| date = April 7, 2021
| title = Hammer Incident
| image = hammer incident normal.png
| titletext = I still think the Cold Stone Creamery partnership was a good idea, but I should have asked before doing the first market trials during the cryogenic mirror tests.
}}

==Explanation==
{{incomplete|Created by AAAHHH THE IMAGE WAS TOO BIG! Please mention here why this explanation isn't complete. Do NOT delete this tag too soon.}}

The {{w|James Webb Space Telescope}} (JWST) is a {{w|space telescope}} created to be the successor of the {{w|Hubble Space Telescope}} under construction at time of publishing and expected to launch in October 2021.

It's implied that Cueball dropped a hammer on the mirror of the JWST, and breaking mirrors in superstition causes seven years of bad luck. But since the mirror panel are not glass it is likely that a dropped hammer would dent and distort the panel rather than shatter it.

The title text refers to the ice cream chain {{w|Cold Stone Creamery}}. Since the cryocooler of the JWST cools things down to 7 degrees Kelvin it would a bit of an overkill.

The JWST has previously been mentioned in [[2014: JWST Delays]], [[1730: Starshade]], and [[1461: Payloads]]

For some reason, the image for this comic is very large. It is unclear if this is a mistake.

==Transcript==
{{incomplete transcript|Do NOT delete this tag too soon.}}
:[Cueball stands before a seated panel of four people (Ponytail, Hairy, a second Cueball and Hairbun).]
:Cueball: Yes, I know you're mad that I dropped that hammer.
:Cueball: But think about me—
:Cueball: '''''Seven years of bad luck!'''''
:[Caption below the panel]:
:Man, NASA is really on my case about the James Webb Space Telescope.

{{comic discussion}}
[[Category:Comics featuring Cueball]]
[[Category:Comics featuring Ponytail]]
[[Category:Comics featuring Hairy]]
[[Category:Comics featuring Hairbun]]
[[Category:Multiple Cueballs]]
[[Category:Telescopes]]