explain xkcd - User contributions [en]

3095: Archaea

2025-05-29T11:16:54Z

172.69.224.200: /* Explanation */ Principle of priority doesn't apply at the level of domain

{{comic
| number = 3095
| date = May 28, 2025
| title = Archaea
| image = archaea_2x.png
| imagesize = 404x412px
| noexpand = true
| titletext = Under the two-domain system, anyone who punches you is technically an Archaean pathogen.
}}

==Explanation==
{{incomplete|This page was created by an Archean pathogen. Don't remove this notice too soon.}}
{{w|Archaea}} is one of the three main lineages (domains) of free-living lifeforms. The other two are {{w|Bacteria}} and {{w|Eukaryote|Eukaryota}}. Organisms within Archaea and Bacteria are {{w|Prokaryote|prokaryotes}}, and were treated as a single domain until the Archaea were split off in the 1970s.

The bacterial and eukaryotic domains each contain numerous species that cause human disease (are pathogens). However, to date, no species of Archaea has been unequivocally shown to be a human pathogen. Whether such pathogens exist, and why, even if they do, they are rare and have low impact, are [https://microbiologysociety.org/blog/why-dont-archaea-cause-disease.html matters of debate].

The joke in this comic is that one or more strains of Archaea, being cultivated in a laboratory, have overheard a conversation among three human scientists (represented by Cueball, Megan, and White Hat), have taken offense at Megan's disparaging comments, and have resolved to become human pathogens. The caption reports this as "bad news" for humanity. Presumably, it turns out that they always had the ''potential'' to harm humans, but had chosen not to, because they're just nice like that.

Most of the species of Archaea that were known at the time that the domain was recognized, and for some time thereafter, were {{w|Methanogen|methanogens}}, cells that require anaerobic conditions for life and emit methane as a byproduct, or {{w|Methanotroph|methanotrophs}}, cells that use methane (also anaerobically) as a carbon source ("food"). Methanogens and methanotrophs are common in the guts of humans and other animals, therefore have proximity to human cells and opportunity to infect them - hence (the inappropriate anthropomorphism aside) their indignance at Megan's comment, especially since neither group contains methane "breathers". Archaea are now known from many different environments, including aerobic ones, so do not have the limited metabolic options that one might assume that they do from Megan's statement.

"Archaea has" in the caption is unfortunate, as it denotes that a lineage (a branch of a phylogenetic tree) has become pathogenic. Pathogens are living cells, not lines on a page. "Archaeans have" would have been better.

The title text alludes to the hypothesis that the domain Eukaryota arose from within the domain Archaea, allowing for a {{w|two-domain system}} which classifies everything into Bacteria and Archaea, with Eukaryota being included as a sub-division of Archaea. Since humans belong within Eukaryota, by extension they would also belong within Archaea. A human attacker of another human could therefore be considered both a pathogen and an archaeon. The same would be true of an attack by any other animal.

==Transcript==
{{incomplete transcript|Don't remove this notice too soon.}}
:[Cueball, Megan, and White Hat are standing in a lab in front of a root-like phylogeny diagram. Behind them is a desk with a microscope on it.]
:Cueball: It's weird how, despite being one of the main branches of the tree of life, no Archaea species are known to cause disease in humans.
:Megan: Personally, I think it's because those gross methane breathers are too weird and incompetent to figure out how to hurt us even if they wanted to.
:Archaea sample: ''Hey!''

:[Caption below the panel:]
:Bad news: After overhearing a conversation in our lab, Archaea has finally started harming humans.
{{comic discussion}}<noinclude>
[[Category:Comics featuring Cueball]]
[[Category:Comics featuring Megan]]
[[Category:Comics featuring White Hat]]
[[Category:Biology]]

3094: Mass Spec

2025-05-28T11:03:52Z

172.69.224.200: /* Explanation */

{{comic
| number = 3094
| date = May 26, 2025
| title = Mass Spec
| image = mass_spec_2x.png
| imagesize = 407x253px
| noexpand = true
| titletext = Patients at least found it to be an improvement over Millikan's incredibly messy and unpleasant oil drop suspension procedure.
}}

==Explanation==
{{incomplete|This page was created by HARVEY FLETCHER (UNCREDITED). Don't remove this notice too soon.}}
In the early 1920s, the domestic bathroom scale (initially a form of {{w|Spring_scale|spring scale}}) was introduced to customers in the United States of America. The device soon became popular, and has remained so to the present. Although means to ascertain the weight of the human body existed before the 1920s, they were not in common use, and were not thought necessary in routine physical / medical examinations.

The joke in this comic arises from the claim that, before the invention of the "modern" bathroom scale, human body weights needed to be obtained, not by earlier, less convenient, forms of scale technology, but by Rube Goldberg-esque implementations of {{w|Mass_spectrometry|mass spectrometry}}.

Mass spectrometry, a late 19th-century invention (thus, available only a few decades earlier than the bathroom scale), was developed to obtain the masses of atomic particles by ascertaining their mass-to-charge ratios. The basic steps, as represented in the comic, are ionization of the mass (rubbing the scalp with the balloon), separating the resulting particles on the basis of their mass-to-charge ratio (the magnet), and observing the result on a detector (the target). Since the ionization procedure for ''bona fide'' mass-spectrometry assays involves turning the mass to be analyzed into a gas, the method would quickly be recognized as unsuited for obtaining human body weights, especially over the course of a dieting program, and become unpopular{{cn}}. There are other ionization techniques to transfer larger compounds intact into the gas phase, but a human body would be way too heavy to be analyzable by this technique.

The title text compares the mass-spectrometry-based method for obtaining human body weights with the method based on the {{w|Oil_drop_experiment|Milliken-Fletcher procedure}}, also available only a few years prior to bathroom scales, in which the mass to be analyzed takes the form of atomized oil droplets that are ionized by X-rays. Neither is suited for weight measurements over time scales of any length, but the cleanup procedures for a human body converted into ionized gas are certainly less onerous than those for a similar mass converted into an oil spray. The original procedure was intended to determine the mass of an electron, based on the known mass/density of the oil droplets. The title text seems to imply the converse, determining the mass/density of a person based on the (now) known mass of an electron.

Note: Randall uses the correct term "mass spectrometry". The term "mass spectroscopy" was used in the beginnings of the technique but is not used anymore. Today, a spectroscopy method entails the interaction of matter with electromagnetic radiation (e.g. IR light - as in IR spectroscopy or radio waves - as in NMR spectroscopy, nuclear magnetic resonance spectroscopy). In the case of mass spectrometry, this is not the case. Here, ions are manipulated or interacting with static electric and/or magnetic fields and thereby the mass-to-charge ratio is determined. Both "spectrometry" and "spectroscopy" allude to a "spectrum" of possible results that can be used to quantify and qualify any inputs being measured, and a distribution of molecular weights ''can'' be usefully represented in a rainbow-like visual, but doesn't bear any direct relation with the electromagnetic spectrum, hence the technical name difference.

==Transcript==
{{incomplete transcript|Don't remove this notice too soon.}}
:[Ponytail, wearing a lab coat, is giving a balloon to Cueball. Behind Cueball, there is a ramp on the ground, a magnet hanging from the ceiling, and a target on a poster on the wall.]
:Ponytail: Rub this balloon against your head, then go jump past that magnet toward the target on the wall.

:[Caption below the panel:]
:Before the bathroom scale was invented, the only way to weigh people was mass spectrometry.

{{comic discussion}}<noinclude>
[[Category:Comics featuring Ponytail]]
[[Category:Comics featuring Cueball]]
[[Category:Physics]]

Talk:3091: Renormalization

2025-05-20T15:51:11Z

172.69.224.200:

It's been an hour. Does nobody know what this is about? Are we all dumb? [[User:Pgn674|Pgn674]] ([[User talk:Pgn674|talk]]) 22:43, 19 May 2025 (UTC)

I'm not certain. Renormalisation is a concept from quantum field theory in which coupling constants take different values at different scales. I believe the intuition for this is that at longer scales, particles are shielded by a cloud of virtual particles which spring into 'existence' around them and take some of the apparent strength out of the interaction. The best I've got is that somehow this is like an electron hitting off of other imaginary electrons? Maybe the old, since a photon ''(another editor here: of course you meant to say "positron"... [[Special:Contributions/162.158.74.68|162.158.74.68]] - thank you, good catch [[Special:Contributions/172.69.79.164|172.69.79.164]])'' can be interpreted as an electron going backwards in time, there might only be one electron in the universe, it's just bouncing back and forth a lot? But in this case any electron interacting in any way with another electron would be 'hitting itself', so I don't see how that would be a renormalisation specific thing. [[Special:Contributions/172.70.58.112|172.70.58.112]] 22:52, 19 May 2025 (UTC)

Wait, I was dumb. Renormalisation is a self interaction, the interpretation in terms of virtual particles is irrelevant. I was over thinking it. Interacting with itself => hitting itself, simple. [[Special:Contributions/172.70.58.150|172.70.58.150]] 22:59, 19 May 2025 (UTC)

Can someone who understands renormalisation better than I add the bit about self-interaction to the explanation? I did not get that at ALL from the linked Wikipedia page (although I did get the Endless Mike reduction joke from it. [[Special:Contributions/162.158.62.106|162.158.62.106]] 03:52, 20 May 2025 (UTC)
:I feel you. It seems like the ''site itself'' feels you, the topic is so heavy (maybe it will let me in this time). FWIW, my digging around led me [https://tvtropes.org/pmwiki/pmwiki.php/Main/StopHittingYourself here] and, especially, [https://www.smbc-comics.com/comic/2011-01-07 here]. [[Special:Contributions/162.158.42.88|162.158.42.88]] 04:50, 20 May 2025 (UTC)

I'm confused about how the joke works with bullying. My best guess: he's hitting the electron whilst telling it to stop hitting itself, so the incongruity becomes cruelty. Is this a common tactic for bullies? [[Special:Contributions/172.69.68.121|172.69.68.121]] 07:59, 20 May 2025 (UTC)
:Not sure how common, but it's a trope, pretty much a staple "jocks vs. nerd" establishing scene in any 'high school' setting in film or TV, at times.
:The idea is that the strong and imposing bully grabs the weak and meek bullied's wrist(s) (perhaps even to prevent blows, albeit mostly just annoying and ineffectual, from the victim) and then uses their superior strength to wrest the target's arms so as to strike themselves, accompanied by taunts such as "why are you hitting yourself..? You shouldn't be hitting yourself...", punctuated by the enforced 'self hits'. More towards the "play-tap" range of actual strength, either for practical reasons (they're more like "one-inch punches" than what they'd inflict, directly in a 'proper fight', and the recipient isn't going to try to help any hit from their own hand) or because its intended more as humiliation than actual intent to physically cause great pain (though lesser pain would be part of the 'game').
:It's a performative thing, probably done more to impress the bully's hanger-ons (and/or further embarass the target in front of any other onlookers, especially the girl that the bully thinks it'll impress/dissuade from associating with the target). They may even be some troll logic involved, in that they can ''try'' to claim "they never hit 'em", should authority figures get involved (even be witness to it), though with variable chances of how well that denial is accepted.
:Not that I've ever seen (or experienced or, of course, enacted) it IRL, but I'm sure I've seen the likes in many on-screen situations, at least 'of an era'. If there isn't a TVTropes page, for otz then I'd be surprised, but I'm not going down ''that'' rabbit hole just now, so here's just my own understanding. [[Special:Contributions/172.69.224.200|172.69.224.200]] 15:51, 20 May 2025 (UTC)