Talk:3077: de Sitter

2025-04-23T01:14:47Z

172.71.151.156: Explain the joke part

the titletext still needs an explanation, but i'm not sure i get the connection to conformal field theory; i suspect it has to do with the explosive rate at which hyperolic space seems to "expand" when travelled through, as a pun on the club expanding at a similar rate? - [[User:Vaedez|Vaedez]] ([[User talk:Vaedez|talk]]) 07:01, 17 April 2025 (UTC)
[[Special:Contributions/162.158.90.137|162.158.90.137]] 07:21, 17 April 2025 (UTC) I think it's alluding to {{w|AdS/CFT correspondence}}, which I think is a string theory thing.

In hyperbolic space, parallel lines DON'T meet when extended, and in elliptic space they DO. Also, the rotation thing looks strange. In any of the basic geometries you have 360 degrees in a circle. The sum of angles in triangle will be different (smaller than 180 in hyperbolic space, larger in elliptic space). [[Special:Contributions/172.68.213.151|172.68.213.151]] 07:58, 17 April 2025 (UTC)
: Agreed. I went and changed it. Though technically, the stuff about parallel lines is still wrong. Parallel lines don't meet by definition, and spherical geometry doesn't have them. Maybe someone can add a better explanation? [[User:DanielLC|DanielLC]] ([[User talk:DanielLC|talk]]) 09:19, 17 April 2025 (UTC)

The yellow wood is a hyperbolic space.[[Special:Contributions/141.101.99.4|141.101.99.4]] 08:08, 17 April 2025 (UTC)

maybe a pun on "babysitters are not welcome here" [[User:Translated ORK|Translated ORK]] ([[User talk:Translated ORK|talk]]) 09:08, 17 April 2025 (UTC)

Fun Fact: the german version of Anti-de Sitter space in wikipedia refers to a [Randall–Sundrum model|https://en.wikipedia.org/wiki/Randall%E2%80%93Sundrum_model] {{unsigned ip|172.69.150.119|09:20, 17 April 2025 (UTC)}}

i think the joke is that his house is a Euclidian space. Because he wants all triangles to add up to 180 degrees and 2 parallel lines to never meet.

Basically he just wants his house to function normally, not fall down, and have regular corners

"...less than 180° in a full rotation" - Shouldn't this be either "...less than 360° in a full rotation" (or perhaps "...the angles of a triangle add up to less than 180°"). [[Special:Contributions/172.69.186.206|172.69.186.206]]

I've started to explain the title-text, but not well. I don't really understand either of these concepts. {{unsigned|Xnerkcd|17 April 2025 (UTC)}}

I don’t really know how to explain it well, but the wikipedia page on these spaces says it’s negative SCALAR curvature. That is a different concept from what is currently being explained here. The intuitive dimension of curvature applies only to 2-dimensional spaces. In higher dimensions you can look at 2D-slices, and the curvature of those is called the sectional curvature. Scalar curvature is then something of an average of those. Notably, if scalar curvature is negative, that does not mean sectional curvature necessarily always is (though perhaps the higher symmetry of these spaces enforces this? I’m really not sure). The main way you can measure scalar curvature is by calculating the volume of a sphere of radius r – if the scalar curvature is 0 it’ll be the usual formula from Euclidean space, but if it’s negative, then for sufficiently small radii the volume will be bigger than expected (intuitively, more space gets crammed around each point). Feel free to incorporate this into the article.

I thought it might be a play on "housesitter" and the fact that anti and de can denote negatives, but I'm not sure how [[User:BeeVee|BeeVee]] ([[User talk:BeeVee|talk]]) 14:37, 17 April 2025 (UTC)

This seems too well-timed to not reference Idaho's Everyone is Welcome Here controversy. {{unsigned ip|172.68.35.117|15:57, 17 April 2025 (UTC)}}

Is this the first strip where the title begins with a lower-case letter? Also, I just noticed that the site's strips use small-caps, while this site uses traditional case. Is that something worth examining? [[Special:Contributions/172.71.98.3|172.71.98.3]] 15:03, 17 April 2025 (UTC)
:1) Nope. 2) What? --[[User:FaviFake|FaviFake]] ([[User talk:FaviFake|talk]]) 17:55, 17 April 2025 (UTC)
::Then which one is the first? [[User:Translated ORK|Translated ORK]] ([[User talk:Translated ORK|talk]]) 09:04, 18 April 2025 (UTC)
:::The first I found was [[dPain over dt]], the (previous) latest was [[the Wrong Stuff]]. There were ''twenty-nine'' of them, in my quick scan (nine of them in the "xkcd Phone" series). Seven of them had no capital letters at all. (<s>Surprisingly, [[IPod]] doesn't start with "i", though two other direct Apple references do.</s> ''edit: Misread+misremembered it. It's [[IPoD]] and isn't even the direct Apple reference itself, at best an allusion to it. ;) '')
:::It happens frequently enough (around 1% of all comics, so far) to not be particularly noteworthy. [[Special:Contributions/172.71.26.106|172.71.26.106]] 10:15, 18 April 2025 (UTC)

Parallel lines by definition are lines that do not meet... So if they meet they are not parallel, though yes at close range they might appear parallel... --[[User:Trimutius|Trimutius]] ([[User talk:Trimutius|talk]]) 03:36, 18 April 2025 (UTC)
:Draw them on a sphere (i.e., a space with positive curvature, a.k.a. a de Sitter space) and they do. The canonical example of this is the lines of longitude on the Earth, which really are parallel at the equator and yet definitely meet at the poles. --[[Special:Contributions/172.68.205.150|172.68.205.150]] 07:50, 18 April 2025 (UTC)
::I think the point being that they aren't parallel lines if they do meet, they (just like on hyperbolic planes) have points where a line that crosses both does so at 90° to each. By the parallel postulate, there are no possible parallel lines (geodesics) in spherical geometry, though there are parallel-line surrogates (the parallel curves of lines of latitude, for example) that obey a looser interpretation. [[Special:Contributions/172.71.26.106|172.71.26.106]] 10:15, 18 April 2025 (UTC)
::Yes on a sphere you can have triangle made out of 3 right angles... Is it made out of three parallel lines? Of course not, at least that is not how mathematicians treat it... The proper replacement of parallel line postulate in de Sitter space is that all lines intersect, so there is no parallel lines... --[[User:Trimutius|Trimutius]] ([[User talk:Trimutius|talk]]) 14:07, 18 April 2025 (UTC)

I'm a chemist. Mr. Markovnikov shouldn't appear near my house! [[Special:Contributions/162.158.103.102|162.158.103.102]] 11:18, 18 April 2025 (UTC)

3049: Incoming Asteroid

2025-02-11T00:07:17Z

172.71.151.156: /* Explanation */

{{comic
| number = 3049
| date = February 10, 2025
| title = Incoming Asteroid
| image = incoming_asteroid_2x.png
| imagesize = 454x570px
| noexpand = true
| titletext = The bottom ones are also potentially bad news for any other planets in our solar system that have been counting on Earth having a stable orbit.
}}

==Explanation==
{{incomplete|Created by an incoming bearer of bad news - More accurate readings of the log scale, and provide detailed explanations of each point on the chart (should probably be a table, as well). Do NOT delete this tag too soon.}}

This comic may be inspired by the recent discovery of asteroid {{w|2024 YR4|2024 YR<sub>4</sub>}}, which is estimated to have about a 2% chance of striking Earth on December 22, 2032. Its size is estimated to be 40-90 meters.

This comic provides a log scale correlating the size of any incoming asteroid to whether its arrival is good or bad news. While asteroids on the smaller end of the scale are good news for sky watchers, as the upcoming objects get bigger, the potential for catastrophe grows. Many astronomy enthusiasts would be happy to see bigger meteors, as bigger generally means more exciting pictures. Of course, once the meteors grow past a certain size even the most enthusiast astronomer might grow concerned about their imminent extinction.{{cn}}

===List of sizes and consequences===

* '''~1cm''': Good news! Meteors are pretty!
** At this size, such a meteor is nothing more than a streak in the sky.

* '''~15cm''': Great news! You might see a fireball!
** At this size, a meteor might descend far enough for the flames of its entry to be visible with the naked eye.

* '''~5m''': Okay news, unless you have expensive windows or are very unlucky
** At this side, a meteor can expect to descend far enough for the shockwave of its passing to shatter windows. The comic mockingly claims this is only a problem if your windows are expensive.

* '''~100m''': Bad news, especially if you live near the city it's aimed at
* '''~1km''': Bad news, especially if you live on the continent it's aimed at
** Meteors of either size can easily cause localized extinction, and can be expected to have effects on the rest of the world as well.

* '''~10km''': Bad news for your species
* '''~90km''': Bad news for your phylum
* '''~500km''': Bad news for your biosphere
** For meteors of this size, a global extinction event is pretty much guaranteed.

* '''~5,000km''': Good news for any life that might some day evolve on Earth's new moon
** Earth's moon is believed to have been formed when Earth, in its infancy, was hit by an object of roughly this size. The comic assumes that another moon would form from another such impact, hypothesizes that life might evolve on that moon, {{tvtropes|BadNewsInAGoodWay|and pretends that it's good news}}.

* '''~50,000km''': Bad news for whatever planet is about to get hit by Earth.
** If Earth were hit by a meteor of this size, it would become a meteor in its own right, and might end up on a trajectory towards ''another'' planet.

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

:[Header:]
:An asteroid is headed straight for Earth! That's...

:[A log scale of lengths is shown.]
:[Length label:] Asteroid size
:1 cm: ...Good news! Meteors are pretty!
:10 cm
::...Great news! You might see a fireball!
:1 meter
::...Ok news, unless you have expensive windows or are very unlucky.
:10 meters
::...Bad news, especially if you live near the city it's aimed at.
:100 meters
::...Bad news, especially if you live on the continent it's aimed at.
:1 km
::...Bad news for your species.
:10 km
::...Bad news for your phylum.
:100 km
::...Bad news for your biosphere.
:1,000 km
::...Good news for any life that might someday evolve on Earth's new moon.
:10,000 km
::...Bad news for whatever planet is about to get hit by Earth.

{{comic discussion}}

[[Category:Charts]]
[[Category:Astronomy]]
[[Category:Space]]

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Talk:3077: de Sitter

3049: Incoming Asteroid