explain xkcd - User contributions [en]

2783: Ruling Out

2023-06-01T21:59:31Z

Thecat: Note related comic

{{comic
| number = 2783
| date = May 31, 2023
| title = Ruling Out
| image = ruling_out_2x.png
| imagesize = 295x396px
| noexpand = true
| titletext = We were able to replicate and confirm prior authors' detection of a moon orbiting the Earth with high confidence.
}}

==Explanation==
{{incomplete|Created by a TECTONICALLY-ACTIVE BOT WITH SUBSURFACE OCEANS. Do NOT delete this tag too soon.}}

Most science studies are intended to discover new knowledge. In astronomy, the goal is often to find different types of objects in space, or learn how astronomical objects are formed and behave. But often from studying things that exist, we also learn about limits of the kinds of things that ''can'' exist; when this happens, we say that we've "ruled out" the excluded phenomena.

[[Cueball]] lists five obviously impossible objects.

* "Earthlike stars": A play on "Earth-like planets" which scientists are very interested in finding. The Earth is not a star, hence stars cannot be Earthlike.
: Searches for both {{w|List of potentially habitable exoplanets|Earth-like planets}} and {{w|Solar analog|Sun-like stars}} go unabated, with various near matches found.

* "Exoplanets in our solar system": {{w|Exoplanet}}s are by definition not in our solar system.
: Planets in our solar system (even {{w|Planets beyond Neptune|undiscovered ones}}) are unaffected, as is the {{w|List of exoplanet search projects|search for exoplanets}} around other stars, with conclusive evidence of both.

* "Habitable-zone quasars": {{w|Quasar}}s in the {{w|habitable zone}}s of stars are only theoretically feasible for small {{w|black hole}}s with active {{w|accretion disk}}s near the Earth and brighter than the Sun, because of the technical criteria for classifying them in terms of their {{w|apparent magnitude}} relative to that of their galaxy.[https://iopscience.iop.org/article/10.1088/0004-637X/728/1/26] None such have ever been observed.{{fact}} While typical galaxies usually have only one quasar in their center, merging galaxies often have two far apart.
:While not certain, habitable zones around some quasars have absolutely not been ruled out.[https://iopscience.iop.org/article/10.3847/1538-4357/ab1b2f/meta][https://iopscience.iop.org/article/10.1088/1742-6596/2364/1/012057/meta]

* "Stars with subsurface oceans": Because the temperatures inside stars are higher than that which can support the existence of liquids as we understand them, stars cannot have subsurface oceans. After many billions of years, a {{w|white dwarf}} will cool to the point where it no longer emits significant heat or light, becoming a {{w|black dwarf}}, eventually cooling to the point where it might develop subsurface liquids.{{acn}} However, the universe is not old enough for any black dwarfs to exist yet,[https://iopscience.iop.org/article/10.1086/375341/pdf] and sufficiently cool black dwarfs would probably not even be considered stars, but rather {{w|rogue planet}}s.
: The possibility of subsurface oceans within various planets and moons is an {{w|Extraterrestrial liquid water|active subject of study}}. and was previously mentioned 10 comics ago in [[2773: Planetary Scientist]]

* "Tectonically active black holes": Black holes do not have {{w|tectonic plate}}s, so they cannot be tectonically active.
: There are theories that neutron stars can exhibit {{w|Quake (natural phenomenon)#Starquake|tectonic-like movements}} (as some of the more typical rocky bodies certainly do), but the physics of the 'inside' of a black hole are thought to involve {{w|Black hole#Singularity|strange physics}} incompatible with any form of geology, and cannot be observed anyway – it is believed that the only externally-observable properties of black holes are mass, electric charge, and angular momentum, poetically called the '{{w|no-hair theorem}}'.

The joke is that you don't actually have to study anything to come to these almost patently obvious conclusions. The counter-proposals would need far more effort to even justify them as valid theories, by common understanding, and greater still to try to observe any supporting proof.

Some studies are also done to confirm the results of previous studies, to ensure that the conclusions were not mistaken or a fluke. The title text describes a study that was done to confirm the existence of a moon orbiting Earth, even though the existence of the Moon has been known for at least as long as humanity has existed, and the fact that it orbits the Earth has been assumed or known for upwards of 3000 years. The ancient Greeks and Babylonians, for example, thought that the Moon orbited the Earth, though they lacked a detailed physical understanding of the system (they also believed, erroneously,{{Citation needed}} that {{w|Geocentric model|everything else in the universe orbited the Earth too}}). {{w|Anaxagoras}} (c. 500–428 BC) is credited with the correct explanation of lunar eclipses, and reportedly was the first to explain that the Moon shines due to reflected light from the Sun. However, it was not until the work of {{w|Nicolaus Copernicus}} in the 16th century that a detailed and accurate model of the Moon's orbit around the Earth was developed. Regardless, at this stage, a study to confirm the validity of Copernican orbits would contribute nothing to the scientific process, much less a study confirming the mere existence of the Moon.

==Transcript==

:[Cueball is talking to Megan.]
:Cueball: So far our astronomy group has published studies ruling out the existence of Earthlike stars, exoplanets in our solar system, habitable-zone quasars, stars with subsurface oceans, and tectonically active black holes.

:[Caption below the panel:]
:Science got way easier when we realized you were allowed to do studies just to rule stuff out.

{{comic discussion}}

[[Category:Comics featuring Cueball]]
[[Category:Comics featuring Megan]]
[[Category:Astronomy]]
[[Category:Science]]

2753: Air Handler

2023-03-23T03:56:59Z

Thecat: Very start of a thing

{{comic
| number = 2753
| date = March 22, 2023
| title = Air Handler
| image = air_handler_2x.png
| imagesize = 591x228px
| noexpand = true
| titletext = It maintains odor levels in a normal familiar range, so if you open the windows and the air gets too fresh, it filters it through some dirty laundry samples to compensate.
}}

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

Black Hat is showing off a device that can maintain certain aspects of air quality. Dust, smoke and orders should usually be minimized, not kept within a reasonable range, while temperature is generally difficult and energy-intensive to maintain. Most household heating and cooling systems will be far larger than the box shown. As most homes aren't tightly sealed, pressure could only ever be the same as what it is outside, so a device couldn't regulate indoor pressure.
==Transcript==
{{incomplete transcript|Do NOT delete this tag too soon.}}

{{comic discussion}}

Talk:2648: Chemicals

2022-07-21T04:48:28Z

Thecat:

Does anyone know the significance of nitrobenzen, the compound indicated? Per Wikipedia " The production of nitrobenzene is one of the most dangerous processes conducted in the chemical industry because of the exothermicity of the reaction (ΔH = −117 kJ/mol)" but I wonder if there's something else too.
[[Special:Contributions/108.162.237.221|108.162.237.221]] 20:07, 20 July 2022 (UTC)
: It's almost certainly the exothermic (read: potentially explosive) reaction that he's going for. [[Special:Contributions/172.70.110.207|172.70.110.207]] 20:11, 20 July 2022 (UTC)

: It is also the formula of Niacin, one of the B vitamins (same atoms, different arrangement) Possibly this is the point: the molecular formula is ambiguous, there are several well-known chemicals with this formula, with very different properties [[User:Zeimusu|Zeimusu]] ([[User talk:Zeimusu|talk]]) 20:58, 20 July 2022 (UTC)

I wouldn't know which way to put this, but "make your own molecules" could be parodying the "build your own PC from bits", "compile your own OS distro", "actually cook food from raw ingredients, not packets" or various other supply/consumer things that some people (those who know enough about what they're doing) will actually do, many people (who don't care to know) won't even consider and some (with a little bit of knowledge, but not actually enough) might find the revelation that they ''could'' do some things themselves far more compelling than the valid question of whether they ''should'' just leap in and try to do it (making all kinds of mistakes/reinventing various wheels along the way) without further research. [[Special:Contributions/141.101.99.32|141.101.99.32]] 21:14, 20 July 2022 (UTC)
:There are also a lot of make-your-own-film-developer nerds, which is a little bit closer in that you're using household items to try to recreate the reactions created by otherwise expensive chemicals. [[Special:Contributions/172.70.130.217|172.70.130.217]] 22:37, 20 July 2022 (UTC)

It would appear we have a vandal on the loose again. [[Special:Contributions/172.70.110.135|172.70.110.135]] 22:42, 20 July 2022 (UTC)

: How exactly do we block these people? [[Special:Contributions/108.162.246.196|108.162.246.196]] 04:05, 21 July 2022 (UTC)

: Request for the wiki: require special permissions to post an image that isn't from xkcd.com, and auto-ban any IP that spams racial slurs. [[User:Thecat|Thecat]] ([[User talk:Thecat|talk]]) 04:48, 21 July 2022 (UTC)

<s>I wonder if we should mention the economic difference between small quantities of chemicals typically used in laboratory experiments compared to bulk quantities for industrial manufacturing. The latter often ''is'' cost-effective to do in-house, and the current version of the explanation doesn't make that clear at all. We have no idea if Megan and Cueball work in a lab or a factory! [[Special:Contributions/172.69.33.229|172.69.33.229]] 00:37, 21 July 2022 (UTC)</s> Resolved. [[Special:Contributions/172.70.210.233|172.70.210.233]] 00:44, 21 July 2022 (UTC)