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December 16

Abelian sandpile model

Thanks to those who answered my last question, I think it should be added to a disambiguation page. If anyone wants to help me write that, reach out.

A sandpile seems disorganized and inert, but these are critically self-organizing. Do the frequency and size of disturbances on sand dunes and snowy peaks follow power law distribution? Gongula Spring (talk) 01:18, 16 December 2024 (UTC)

Shouldn't this be at the Math Desk? Abductive (reasoning) 05:12, 16 December 2024 (UTC)

If the question is not about the model mentioned in the heading but about the physical properties of sand dunes and snowy peaks, this here is the right section of the Reference desk.  --Lambiam 08:51, 16 December 2024 (UTC)

I await a non-mathematical answer. Abductive (reasoning) 09:23, 16 December 2024 (UTC)

It depends is probably a fairly reasonable non-mathematical answer for these kinds of systems. For sand dunes anyway, sometimes avalanche frequency is irregular and the size distribution follows a power law, and sometimes it's close to periodic and the avalanches span the whole system. It seems there are multiple regimes, and these kinds of systems switch between them. Sean.hoyland (talk) 09:35, 16 December 2024 (UTC)

Thank you! I'm impressed this seems so casual, but surely you read this somewhere that might have a URL?

Gongula Spring (talk) 22:29, 19 December 2024 (UTC)

Hi, this is an interesting and somewhat open question! A lot of work is done on these models but much less on careful analyses of real dunes. I did find this dissertation that is freely accessible and describes some physical experiments and how well they fit various models. The general answer seems to be that the power law models are highly idealized, and determining the degree to which any real system's behavior is predicted by the model ahead of time is very difficult. Update: This is one of the earlier important works on the topic and it does include discussion of how well the model fits experiments.SemanticMantis (talk) 17:21, 16 December 2024 (UTC)

That dissertation is great!

Gongula Spring (talk) 22:30, 19 December 2024 (UTC)

Polar night

Are there any common or scientific names for types of polar night? The types that I use are:

• polar night - meaning a day when sun's altitude remains below horizon entire day (there is no daylight at solar noon, only civil twilight), occurring poleward from 67°24′ north or south
• civil polar night - meaning a day when sun's altitude remains below -6° entire day (there is no civil twilight at solar noon, only nautical twilight), occurring poleward from 72°34′ north or south
• nautical polar night - meaning a day when sun's altitude remains below -12° entire day (there is no nautical twilight at solar noon, only astronomical twilight), occurring poleward from 78°34′ north or south
• astronomical polar night - meaning a day when sun's altitude remains below -18° entire day (there is no astronomical twilight at solar noon, only night), occurring poleward from 84°34′ north or south

These names were changed on Polar night article, and I wnat to know whether these named I listed are in use in any scientific papers, or in common language. (And I posted that question here and not in language desk because I think that this is not related to language very tightly.) --40bus (talk) 18:56, 16 December 2024 (UTC)

Some definitions at The Polar Night (1996) from the Aurora Research Institute. Alansplodge (talk) 22:55, 16 December 2024 (UTC)

These seem to be generalizable as: X polar night is a period, lasting not less than 24 hours, during which the sun remains below the horizon and there is no X twilight. The specific definitions depend then on the specific definitions of civil/nautical/astronomical twilight. These can be defined with a subjective observational standard or with an (originally experimentally determined) objective standard.  --Lambiam 10:36, 17 December 2024 (UTC)

FWIW, I as a former amateur astronomer have never previously thought about the question of Polar twilight and night nomenclatures, but immediately and completely understood what the (previously unencountered) terms used in the query must mean without having to read the attached descriptions. {The poster formerly known as 87.81.230.195} 94.1.223.204 (talk) 16:34, 17 December 2024 (UTC)

December 17

differential equations with complex coefficients

In an intro ODE class one basically studies the equation ${\dot {x}}=Ax$ where x is a real vector and A is a real matrix. A typically has complex eigenvalues, giving a periodic or oscillating solution to the equation. That is very important in physics, which has various sorts of harmonic oscillators everywhere. If A and x are complex instead of real, mathematically the ODE theory works out about the same way. I don't know what happens with PDE's since I haven't really studied them.

My question is whether the complex case is important in physics the way the real case is. Can one arrive at it through straightforward coordinate transformations? Do the complex eigenvalues "output" from one equation find their way into the "input" of some other equation? Does the distance metric matter? I.e. in math and old-fashioned physics we use the Euclidean metric, but in realtivity one uses the Minkowski metric, so I'm wondering if that leads to complex numbers. This is all motivated partly by wondering where all the complex numbers in quantum mechanics come from. Thanks. 2601:644:8581:75B0:0:0:0:DA2D (talk) 22:54, 17 December 2024 (UTC)

Perhaps I don't understand what you are getting at but simple harmonic motion is xdot=j*w*x where w is angular frequency and j is i Greglocock (talk) 00:35, 18 December 2024 (UTC)

If PDEs count, the Schrödinger equation and the Dirac equation are examples of differential equations in the complex domain. A linear differential equation of the form ${\dot {x}}=Ax$ on the complex vector space $\mathbb {C} ^{n}$ can be turned into one on the real vector space $\mathbb {R} ^{2n}$. For a very simple example, using $n=1,$ the equation ${\begin{bmatrix}{\dot {z}}\end{bmatrix}}={\begin{bmatrix}i\end{bmatrix}}{\begin{bmatrix}z\end{bmatrix}}$ can be replaced by

${\begin{bmatrix}{\dot {x}}\\{\dot {y}}\end{bmatrix}}={\begin{bmatrix}0&-1\\1&0\end{bmatrix}}{\begin{bmatrix}x\\y\end{bmatrix}}.$

 --Lambiam 01:11, 18 December 2024 (UTC)

Shouldn't this be at the Math Desk? It almost seems like the IP could be trolling, given the same question just above. Abductive (reasoning) 14:49, 18 December 2024 (UTC)

The question whether the complex case is important in physics the way the real case is, is not a maths issue. IMO the Science section is the best choice. I do not see another post that asks the same or even a related question.  --Lambiam 21:51, 18 December 2024 (UTC)

Just as above, I await a non-mathematical answer to this question. Abductive (reasoning) 07:01, 19 December 2024 (UTC)

Thanks all. Greglocock, your SHO example is 1-dimensional but of course you can have a periodic oscillator (such as a planetary orbit) in any orientation in space, you can have damped or forced harmonic oscillators, etc. Those are all described by the same matrix equation. The periodic case means that the matrix eigenvalues are purely imaginary. The damped and forced cases are where there is a real part that is negative or positive respectively. Abductive, of course plenty of science questions (say about how to calculate an electron's trajectory using Maxwell's equations) will have mathematical answers, and the science desk is clearly still the right place for them, as they are things you would study in science class rather than math class. Lambiam, thanks, yes, PDE's are fine, and of course quantum mechanics uses complex PDE's. What I was hoping to see was a situation where you start out with real-valued DEs in some complicated system, and then through some coupling or something, you end up with complex-valued DEs due to real matrices having complex eigenvalues. Also I think the Minkowski metric can be treated like the Euclidean one where the time coordinate is imaginary. But I don't know how this really works, and Wikipedia's articles about such topics always make me first want to go learn more math (Lie algebras in this case). Maybe someday. 2601:644:8581:75B0:0:0:0:DA2D (talk) 07:25, 19 December 2024 (UTC)

December 18

Why don't all mast radiators have top hats?

Our mast radiator article describes a device called a "top hat" which increases the range for mast radiators that can't be built tall enough.

So, why would you bother building a mast radiator without a top hat? Couldn't you just build it shorter with the top hat, and save steel? Marnanel (talk) 15:00, 18 December 2024 (UTC)

The main source cited in our article states, "Top loading is less desirable than increased tower height but is useful where towers must be electrically short due to either extremely low carrier frequencies or to aeronautical limitations. Top loading increases the base resistance and lowers the capacitive base reactance, thus reducing the Q and improving the bandwidth of towers less than 90° high."^[1] If "reducing the Q" is an undesirable effect, this is a trade-off design issue in which height seems to be favoured if circumstances permit.  --Lambiam 21:41, 18 December 2024 (UTC)

Name of our solar system

Is our star system officially called "Sol", or is that just something that came from science fiction and then became ubiquitous? 146.90.140.99 (talk) 22:06, 18 December 2024 (UTC)

It's called the Solar System, and its star is called Sol, from Latin via French. Hence terms like "solstice", which means "sun stands still" in its apparent annual "sine wave" shaped path through the sky. ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:31, 18 December 2024 (UTC)

Via French? According to the OED, it came direct from Latin.^[2]  --Lambiam 11:45, 19 December 2024 (UTC)}}

Old French plus Latin.[3] ←Baseball Bugs ^{What's up, Doc?} carrots→ 14:25, 19 December 2024 (UTC)

Also in Old French, the word meaning "sun" was soleil.  --Lambiam 23:42, 19 December 2024 (UTC)

Let's say to that claim. The star is indeed called Sol if you're speaking Latin, but in English it's the Sun (or sun). Of course words like "solar" and "solstice" derive from the Latin name, but using "Sol" to mean "the Sun" does seem to be something from science fiction. --142.112.149.206 (talk) 06:04, 19 December 2024 (UTC)

"Sol" is occasionally used to mean the Sun by astronomers. I feel like it is used in contexts where it is necessary to distinguish our experience with the Sun here on Earth, such as sunsets, from more "sterile" aspects of the Sun one might experience off the Earth. Abductive (reasoning) 08:56, 19 December 2024 (UTC)

Being an astronomer myself, I don't think I've ever heard anyone use "Sol" outside of a science fiction context. --Wrongfilter (talk) 09:06, 19 December 2024 (UTC)

Scientific articles that use the term Sol; Development of the HeliosX mission analysis code for advanced ICF space propulsion and Swarming Proxima Centauri: Optical Communication Over Interstellar Distances. These are rather speculative but as I mentioned, the usage is for off-planet situations. Abductive (reasoning) 13:05, 19 December 2024 (UTC)

Using Sol, Terra and Luna to refer to the Sun, Earth and Moon only happens if you write your entire article in Latin and in science fiction, not in regular science articles. They are capitalised though. Just as people write about a galaxy (one of many) or the Galaxy (the Milky Way Galaxy, that's our galaxy). The Solar System is also capitalised. PiusImpavidus (talk) 10:38, 19 December 2024 (UTC)

The article says "Sol" is the "personification" of the sun. Google Image the term "old Sol" and you'll see plenty of images of the sun with a face, not just Sci-Fi stuff. And "Luna" is obviously the basis for a number of words not connected with Sci-Fi. Lunar orbit, lunar module, etc. And the term "terra firma" has often been used in everyday usage. ←Baseball Bugs ^{What's up, Doc?} carrots→ 11:34, 19 December 2024 (UTC)

And yet, if you ask 1,000 people "What's that big yellow thing up in the sky called?", you'll get 1,000 "the Sun"s and zero "Sol"s. Yes, in specialised contexts, Sol is used; but that doesn't justify saying our solar system's star "is called Sol" without any qualification, as if that were the normal, default term. It's not. -- Jack of Oz ^{[pleasantries]} 12:16, 19 December 2024 (UTC)

And after you've gotten that response, ask them why it isn't the "Sunner System". And why a sun room attached to a house isn't called a "sunarium". And why those energy-gathering plates on some roofs are not called "sunner panels". ←Baseball Bugs ^{What's up, Doc?} carrots→ 14:22, 19 December 2024 (UTC)

What does that have to do with anything? The question was 'Is our star system officially called "Sol"?' (my emphasis). The answer is it is not. And that does not preclude other terms being derived from Latin sol (or, often enough, from Greek helios), nobody denies that, it is irrelevant to the question. --Wrongfilter (talk) 14:52, 19 December 2024 (UTC)

The problem is that the OP's question contains false premises. One is the question of what the "official" name is. There is no "official" name. It's the "conventional" name. And the second part, claiming that "Sol" comes from Sci-fi, is demonstrably false. ←Baseball Bugs ^{What's up, Doc?} carrots→ 15:05, 19 December 2024 (UTC)

Then demonstrate (that the usage of "Sol" as a name for the Sun, in English, not its use to derive adjectives, originated outside of SF), with references. The original question does not even include any premises, with maybe the exception of "ubiquitous". --Wrongfilter (talk) 15:18, 19 December 2024 (UTC)

"Is our star system officially called "Sol" [answer: NO], or is that just something that came from science fiction [answer: NO] and then became ubiquitous? [whatever that means]". And the wording of your own question, just above, does not make sense. ←Baseball Bugs ^{What's up, Doc?} carrots→ 15:24, 19 December 2024 (UTC)

Looking at Newspapers.com (pay site), I'm seeing colloquial references to "old Sol" (meaning the sun) as far back as the 1820s. No hint of sci-fi derivation. ←Baseball Bugs ^{What's up, Doc?} carrots→ 15:32, 19 December 2024 (UTC)

Great! Well done. --Wrongfilter (talk) 15:41, 19 December 2024 (UTC)

Feel free to box up this section. ←Baseball Bugs ^{What's up, Doc?} carrots→ 15:52, 19 December 2024 (UTC)

The 1933 OED entry for Sol, linked to above, gives several pre-SF uses, the earliest from 1450.  --Lambiam 23:48, 19 December 2024 (UTC)

Yes, of course, but that's not surprising, is it? 15th century humanists, astrologers and pre-Victorian poets liked to sprinkle their texts with Latin words. But I don't think this is what the question is about. It's a matter of context, but it should be up to OP to clarify that. --Wrongfilter (talk) 08:48, 20 December 2024 (UTC)

It's not surprising, but the discussion was not whether the use of Sol in English texts is surprising, but whether it originated outside of SF.  --Lambiam 10:52, 20 December 2024 (UTC)

In my view, the question has a clear scifi bent, and that particular usage ("Where shall we go for our vacation? Alpha Centauri or Sol?") does not originate in the 15th century. The word is much older, of course it is, but the usage is not. In the 15th century people didn't even know that the Sun is just an ordinary star and could do with a particular name to distinguish it from the others. The connotations of sol were vastly different from what they are today and from what is implied in OP's question. Incidentally, the IAU doesn't even define a name [4], although they recommend using capitalised "Sun". Certainly no "Sol" anywhere. --Wrongfilter (talk) 12:04, 20 December 2024 (UTC)

Does that make it a Sol-ecism? Clarityfiend (talk) 12:19, 19 December 2024 (UTC)

More like a Sol-ips-ism. Meaning a factory where suns are made. From Sol = sun, and ipso = facto. Thus endeth the entymogology lesson for today. Go in peace to love and serve whomsoever. -- Jack of Oz ^{[pleasantries]} 19:37, 19 December 2024 (UTC)

Mountains

Why there are no mountains on Earth with a height above 10,000 m? As the death zone is about at 8,000 m, and above 19,000 m, there is an Armstrong limit, where water boils at normal human body temperature, it is good that there are no more mountains higher than 8,000 km than just 14, but if there were hundreds of mountains above 9,000 m, then these were bad to climb. If there were different limits for death zone and Armstrong limit, would then there be possible to have higher mountains? I have just thought that, it is not a homework? --40bus (talk) 22:29, 18 December 2024 (UTC)

There are mountains elsewhere in the solar system that are over 20km high. Given that some of those are on airless worlds, I don't think the air pressure has any bearing on it. 146.90.140.99 (talk) 22:57, 18 December 2024 (UTC)

Multiple sources from web searching suggest the theoretical maximum height for mountains on Earth is around 15,000 m – the limiting factor is Isostasy; the higher (therefore more voluminous) a mountain is, the more its weight causes the crust beneath it to sink. The actual heights of mountains are a trade-off between how fast tectonic movements can raise them versus isostatic sinking and how quickly they are eroded, and tectonic movements do not last for ever. See also Orogeny. {The poster formerly known as 87.81.230.195} 94.1.223.204 (talk) 00:25, 19 December 2024 (UTC)

And erosion goes faster as the mountain gets higher, in particular when it's high enough to support glaciers – one reason why mountains can get higher on an airless world. Now it gets interesting for a mountain high enough to reach into the stratosphere, as it would be too dry to have anything but bare rock. I suppose it would locally raise the tropopause, preventing that. PiusImpavidus (talk) 11:13, 19 December 2024 (UTC)

December 19

Does human DNA become weaker with each generation?

As with photocopying something over and over, the text becomes less clear each time.

Does human DNA become weaker with each generation? HarryOrange (talk) 21:22, 19 December 2024 (UTC)

Sure, DNA replication is not perfect, although proofreading reduces the error rate to about 1 mistake per 10⁹ nucleotides (see our article on DNA Replication). But that is per generation of cells, not of the whole organisms. Many mutations will be neutral in effect (because much of our DNA is redundant), some will be deleterious, and a few might be advantageous. It is the process of natural selection that hinders the spread of deleterious mutations: sometimes this aspect is called purifying selection. One thus usually expects a stable mutation–selection balance over time rather than that "DNA becomes weaker with each generation". Medical science is reducing the selection pressure against some mutations, which consequently may become more common. One of the problems for asexual organisms is referred to as Muller's ratchet; assuming that reverse mutations are rare, each generation has at least the mutational load of its predecessor. In contrast, in sexual organisms genetic recombination generates the variation that, combined with selection, can repair the situation. Sexual organisms consequently have a lighter genetic load. JMCHutchinson (talk) 22:42, 19 December 2024 (UTC)

So purifying selection won't work properly in case of Inbreeding ? HarryOrange (talk) 23:16, 19 December 2024 (UTC)

The larger the degree of inbreeding, the larger the chance that deleterious traits are expressed. But this very expression of traits leading to decreased biological fitness of their bearers is what actually enables purifying selection in the longer term.  --Lambiam 23:36, 19 December 2024 (UTC)

@Lambiam so DNA repair won't stop these deleterious traits to get expressed? HarryOrange (talk) 14:11, 20 December 2024 (UTC)

No, this is not an issue of damage to the DNA. The genes involved are faithfully reproduced and passed on from generation to generation.  --Lambiam 15:53, 20 December 2024 (UTC)

Or stronger e.g. "...we found that genes specifically duplicated in the Greenland shark form a functionally connected network enriched for DNA repair function", and those guys live for centuries and have much more DNA than us. Sean.hoyland (talk) 15:21, 20 December 2024 (UTC)

@Lambiam If not due to DNA damage, why do babies from inbreeding appear like DNA-damaged species? HarryOrange (talk) 17:29, 20 December 2024 (UTC)

Inbred offspring of species that normally outcross may show abnormalities because they are more likely than outcrossed offspring to be homozygous for recessive alleles that are deleterious. In individuals that are heterozygous at these loci, the recessive alleles will not be expressed (because the other wild-type dominant allele is sufficient to do their job adequately). See our article on inbreeding depression. JMCHutchinson (talk) 19:26, 20 December 2024 (UTC)

Larvae going south

In a novel I've just finished (The Chemistry of Death by Simon Beckett) he writes:

• [The larvae] leave the body in an orderly fashion, following each other in a neat procession that always heads south. South-east or south-west sometimes, but never north. No-one knows why.

The author has done considerable international research on the science of forensic identification of decayed bodies and I assume his details can be trusted.

I've looked online for any verification of this surprising statement, but found only this, which seems to debunk it.

Is there any truth to this? -- Jack of Oz ^{[pleasantries]} 23:38, 19 December 2024 (UTC)

Can't speak to its truth, but . . .

• Does Beckett state this in his own auctorial voice (i.e. as an omniscient narrator)? If so, he might be genuinely mistaken.
• The book was published nearly 20 years ago, what was the accepted wisdom then?
• What specific species (if any) is the book describing? – your linked Quora discussion refers only to "maggots" (which can be of numerous species and are a kind of larva, but there are many others, including for example Processionary caterpillars).
• Alternatively, if the statement is made by a character in the book, is that character meant to be infallible, or is he portrayed as less than omniscient, or an 'unreliable narrator'?

Regarding the statement, in the Northern hemisphere the arc of South-east to South-west is predominently where the Sun is found well above the horizon, the North never, so the larvae involved might simply be seeking maximum warmth or light. {The poster formerly known as 87.81.230.195} 94.1.223.204 (talk) 02:18, 20 December 2024 (UTC)

This appears in the very first paragraph of Chapter I, which starts out:

• A human body starts to decompose four minutes after death. Once the encapsulation of life, it now undergoes its final metamorphoses. It begins to digest itself. Cells dissolve from the inside out. Tissue turns to liquid, then to gas. No longer animate, the body becomes an immovable feast for other organisms. Bacteria first, then insects. Flies. Eggs are laid, then hatched. The larvae feed on the nutrient-rich broth, and then migrate. They leave the body in an orderly fashion ... (then the quote above completes the paragraph).

It's not until para 2 that he starts talking about any human characters, and not until para 4 that he invokes the first person.

That's as much as I know. But I find it hard to believe he'd just make up a detail and put it in such a prominent place if it could so easily be debunked if it were not true. -- Jack of Oz ^{[pleasantries]} 02:39, 20 December 2024 (UTC)

I wonder how they would measure the migratory path of maggots within a sealed coffin. ←Baseball Bugs ^{What's up, Doc?} carrots→ 02:51, 20 December 2024 (UTC)

The context of the novel is about finding decaying corpses that have been dumped in a forest. No coffins involved. -- Jack of Oz ^{[pleasantries]} 06:08, 20 December 2024 (UTC)

Baseball Bugs, see also body farm research facilities. Alansplodge (talk) 13:44, 20 December 2024 (UTC)

Could it be that the larvae are setting off in search of another corpse? The prevailing wind in the UK is from the south-west, so by heading into the wind they won't be distracted by the frangrance of the one they've just left. Shantavira|^{feed me} 09:30, 20 December 2024 (UTC)

If you can, have a look at 'Heinrich, Bernd. “Coordinated Mass Movements of Blow Fly Larvae (Diptera: Calliphoridae).” Northeastern Naturalist, vol. 20, no. 4, 2013, pp. N23–27. JSTOR, http://www.jstor.org/stable/43288173.' Here are some extracts

• On the fourth day, after a cooling night with dew on the grass, a stream of tens of thousands of larvae exited from beneath the carcass within 1 h after sunrise, and proceeded in a single 1-2-cm-wide column directly toward the rising sun...
• However, in this case, the larvae left at night, within 1 h after a cloudburst (at 21 :00 hours). But, unlike before, this nocturnal larval exodus in the rain was diffuse; thousands of larvae spread out in virtually all directions over an 8 m2area. Apparently, the sudden moisture had cued and facilitated the mass exodus, but the absence of sun had prevented a unidirectional, en masse movement.
• However, on the following morning as the sun was starting to illuminate the carcass on the dewy grass, masses of larvae gathered at the east end of the carcass at 07:00 hours. In one half hour later, they started streaming in a column directly (within one degree) toward the rising sun, and the carcass was then nearly vacated.

It goes on. Maggot migration appears to be a bit more complicated than the novel suggests. Sean.hoyland (talk) 09:39, 20 December 2024 (UTC) I suppose you could try to address it from the other direction and look at the technology your average maggot has access to in terms of light detection, heat detection, olfactory systems, orientation in magnetic fields (like many arthropods) etc. They presumably have quite a lot of tools. Sean.hoyland (talk) 10:13, 20 December 2024 (UTC)

If orderly migrating maggots tend to move towards the sun, they should display a northward tendency in Oztralia.  --Lambiam 10:31, 20 December 2024 (UTC)

Maybe, but the novel is set in England.

I must say, as soon as I read the quoted para for the first time, my immediate thought was that it might have something to do with the magnetic field of the earth. -- Jack of Oz ^{[pleasantries]} 10:42, 20 December 2024 (UTC)

Prime suspect might be the Bolwig organ, the photoreceptor cluster many fly larvae have. Sean.hoyland (talk) 10:49, 20 December 2024 (UTC)

Obviously, Jack, you need to create a corpse, place it in a nearby forest, and carefully observe which way the maggots go. For Science! And Literary Criticism! {The poster formerly known as 87.81.230.195} 94.1.223.204 (talk) 21:01, 20 December 2024 (UTC)

December 20

Winter solstice and time of sunrise?

How is it that despite December 21st supposedly being the shortest day of the year, sunrise here happens later and later until December 26 and only on January 05 starts to turn around to occur earlier and earlier. On December 25 it takes place at about 08:44, between December 26 and January 04 it takes place at about 08:45, and on January 05 it takes place again at about 08:44. (Google rounds out the seconds). Is it Google's fault? Is it everywhere the same? Confused in Brussels, Belgium. 178.51.16.158 (talk) 12:06, 20 December 2024 (UTC)

The pertinent article is Analemma, start with the section Earliest and latest sunrise and sunset. The details are not that simple to understand, but it's basically due to the ellipticity of Earth's orbit and its axial tilt. --Wrongfilter (talk) 12:22, 20 December 2024 (UTC)

Also note that sunset begins to be later on 22 December so that the time between sunrise and sunset is a few seconds longer than on 21 December (3 seconds longer on 22/12/24 in Brussels according to this). Alansplodge (talk) 13:33, 20 December 2024 (UTC)

Also see Equation of time#Major components. The obliquity of the ecliptic (that is, the Earth's axial tilt) is the main component and hardest to understand. But the idea is that the time when the Sun is exactly south (that is, the true noon) moves some minutes back and forth throughout the year and it moves quite rapidly to later times in late December. PiusImpavidus (talk) 19:05, 20 December 2024 (UTC)

By the way is there a chart somewhere of the date of earliest/latest sunrise/sunset by latitude? —Tamfang (talk) 21:45, 29 December 2024 (UTC)

Three unit questions

1. Why territorial waters are defined by nautical miles instead of kilometers?
2. Why GDP is usually measured in US dollars rather than euros? Euro would be better because it is not tied into any country.
3. Are there any laws in United States that are defined by metric units?

--40bus (talk) 23:30, 20 December 2024 (UTC)

1. There were nautical miles in use before there were kilometers.
2. There were US dollars in use before there were Euros.
3. Yes.

The questions all reduce to Why can't millions of people make a change of historically widely accepted units that continue to serve their purpose, and convert to different units that would have no substantive difference, because someone has an opinion. Philvoids (talk) 00:52, 21 December 2024 (UTC)

Do any people use metric units in marine and air navigation like "The ship is 10 kilometers from the port", "The plane is 10 kilometers from the destination? And is there any European country with metric flight levels? --40bus (talk) 07:22, 21 December 2024 (UTC)

Inland shipping (rivers, canals and lakes) in Europe (except the UK) is fully metric. Ships going for example Tilbury – Duisburg may have to switch units along the way. Gliders and ultralight aircraft in Europe often use metric instruments and airport dimensions are also metric (including runway length). Countries are free to define their territorial waters in whatever way they deem fit, so with nautical miles having no legal status in a fully metric country, they may define their territorial waters as extending 22224 metres. PiusImpavidus (talk) 11:23, 21 December 2024 (UTC)

Our nautical mile article says: "In 1929 the international nautical mile was defined by the First International Extraordinary Hydrographic Conference in Monaco as exactly 1,852 metres (which is 6,076.12 ft). The United States did not adopt the international nautical mile until 1954. Britain adopted it in 1970..."

As the US customary units are actually defined in terms that relate them to metric units, any US law based on measurements is technically defined by metric units.--User:Khajidha (talk) (contributions) 01:55, 21 December 2024 (UTC)

The US dollar has been the world's dominant reserve currency for about 75 years. As for the metric system in the US, it is standard in scientific, medical, electronics, auto manufacturing and other highly technical industries. By law, all packaged foods and beverages have metric quantities as well as customary quantities. See Metrication in the United States. Cullen328 (talk) 02:28, 21 December 2024 (UTC)

The Wikipaedia article on the Nautical Mile talks about how the term originated, it was originally defined in terms of latitude not as a number of meters 114.75.48.128 (talk) 10:03, 24 December 2024 (UTC)

The euro is tied to multiple specific countries is it not? If you use euros you're just changing from one "dependency" to a "dependency" on the eurozone countries. A statement of the problem or problems intended to be addressed would be useful. Currency values are interconvertible in any case. Economics does sometimes use the "international dollar" for certain things, which is intended to adjust for differences in purchasing power between countries and over time. But since it's not an actual "real" currency it's not something one can easily "visualize" in their heads, which is likely why it's not used more. --Slowking Man (talk) 05:41, 26 December 2024 (UTC)

December 24

Unknown species of insect

Am I correct in inferring that this guy is an oriental beetle? I was off-put by the green head at first, but the antennae seem to match. JayCubby 03:00, 24 December 2024 (UTC)

(reference: https://www.genesdigest.com/macro/image.php?imageid=168&apage=0&ipage=1)

It looks like one of the invasive Japanese beetles that happens to like my blackberries in the summer. Modocc (talk) 13:11, 24 December 2024 (UTC)

I would say not necessarily a Japanese beetle, but almost certainly one of the other Scarab beetles, though with 35,000 species that doesn't help a lot. Looking at the infobox illustration in that article, 16. & 17., "Anisoplia segetum" looks very similar, but evidently we either don't have an article or (if our Anisoplia article is a complete list) it's been renamed. {The poster formerly known as 87.81.230.195} 94.1.223.204 (talk) 14:18, 24 December 2024 (UTC)

Yes, it's not the Japanese beetle for this beetle appears to lack its white-dotted fringe although its condition is deteriorated. Its shape is also more or less more slender; and not as round. Modocc (talk) 15:02, 24 December 2024 (UTC)

Perhaps it is the shining leaf chafer Strigoderma pimalis. Shown here. Modocc (talk) 16:09, 24 December 2024 (UTC)

That looks like easily the best match I've seen so far, and likely correct. {The poster formerly known as 87.81.230.195} 94.1.223.204 (talk) 17:09, 24 December 2024 (UTC)

December 25

Mass of oscillating neutrino

From the conservation of energy and momentum it follows that a particle that is not subject to external forces must have constancy of mass.

If I am right, this means that the mass of the neutrino cannot change during the neutrino oscillation, although its flavoring may. Is this written down somewhere? Thank you. Hevesli (talk) 19:24, 25 December 2024 (UTC)

Any (flavored) neutrino that is really observed is a superposition of two or three mass eigenstates. This is actually the cause of neutrino oscillations. So, the answer to your question is complicated. Ruslik_Zero 19:40, 25 December 2024 (UTC)

Important note: particle physicists today generally only ever use "mass" to mean "invariant mass" and never anything else: [5]. Like the term says, invariant mass is well, invariant, it never changes ever, no matter what "external forces" may or may not be involved. Being proper particle-icans and following the standard practice in the field, then, the three neutrino masses are constant values. ..."Wait, three?" Yeah sure, turns out neutrinos come in three "flavors" but each flavor is a mixture of the three possible mass "states". As mentioned, due to Quantum Weirdness we aren't able to get these different states "alone by themselves" to measure each by itself, so we only know the differences of the squares of the masses. Yeah welcome to quantum mechanics.

Richard Feynman: "Quantum mechanics describes nature as absurd from the point of view of common sense. And yet it fully agrees with experiment. So I hope you can accept nature as She is  – absurd." --Slowking Man (talk) 06:06, 26 December 2024 (UTC)

The equation $E^{2}=(pc)^{2}+\left(m_{0}c^{2}\right)^{2}$ uses invariant mass m₀ which is constant if E and p are constant. The traveling neutrino has a varying mass mixture of different flavors with different masses. If a mixture of different masses changes, you would expect the resulting mass to change with it. But somehow this does not happen as the neutrino mass mixture changes. These mixture changes cannot be any changes. The changes must be such that the resulting mass of the traveling neutrino remains constant. My question is whether this is described somewhere. Hevesli (talk) 11:16, 26 December 2024 (UTC)

I freely confess I'm uncertain exactly what's being "asked for" or "gotten at" here. Have you looked at the neutrino oscillation article? From it: That is, the three neutrino states that interact with the charged leptons in weak interactions are each a different superposition of the three (propagating) neutrino states of definite mass. Neutrinos are emitted and absorbed in weak processes in flavor eigenstates[a] but travel as mass eigenstates.[18]

What is it that we're "doing" with the energy–momentum relation here? For the neutrino, we don't have a single value of "mass" to plug in for $m_{0}$, because we can't "see" the individual mass eigenstates, only some linear combination of them. What you want for describing neutrino interactions is quantum field theory, which is special relativity + QM. (Remember, relativity is a "classical" theory, which presumes everything always has single well-defined values of everything. Which isn't true in quantum-world.) --Slowking Man (talk) 18:41, 26 December 2024 (UTC)

Not all potential evolutions of a linear combination of unequal values produce constant results. Constancy can only be guaranteed by a constraint on the evolutions. Does the fact that this constraint is satisfied in the case of neutrino oscillation follow from the mathematical formulation of the Standard Model, or does this formulation allow evolutions of the mass mixture for which the combination is not constant? If the unequal values are unknown, I have no idea of how such a constraint might be formulated. I think the OP is asking whether this constraint is described somewhere.  --Lambiam 00:51, 27 December 2024 (UTC)

December 27

Low-intensity exercise

If you exercise at a low intensity for an extended period of time, does the runner's high still occur if you do it for long enough? Or does it only occur above a certain threshold intensity of exercise? 2601:646:8082:BA0:CDFF:17F5:371:402F (talk) 20:13, 27 December 2024 (UTC)

Hows about you try it and report back? :) ←Baseball Bugs ^{What's up, Doc?} carrots→ 21:31, 27 December 2024 (UTC)

I wanted to try it just today, but I had to exchange the under-desk elliptical trainer I got for Christmas for a different model with more inclined treadles because with the one I got, my knees would hit the desk at the top of every cycle. Anyway, I was hoping someone else tried it first (preferably as part of a formal scientific study) so I would know if I could control whether I got a runner's high from exercise or not? 2601:646:8082:BA0:9052:E6AF:23C7:7CAF (talk) 03:09, 28 December 2024 (UTC)

Also, sorry for adding to my own question, but here's a related one: is it known whether the length of a person's dopamine receptor D4 (which is inversely correlated with its sensitivity) influences whether said person gets a runner's high from exercise (and especially from low-intensity exercise)? 2601:646:8082:BA0:9052:E6AF:23C7:7CAF (talk) 03:14, 28 December 2024 (UTC)

fastidious organism vs auxotroph

Hi,

What is the difference between an auxotroph and a fastidious organism? It seems to me the second one would have more requirements than the first one, but the limit between the two definitions is rather unclear to me.

Thank you 212.195.231.13 (talk) 23:17, 27 December 2024 (UTC)

I'm not 100% sure, but it seems to me that an auxotroph is a specific type of a fastidious organism. 2601:646:8082:BA0:9052:E6AF:23C7:7CAF (talk) 03:02, 28 December 2024 (UTC)

Symbiosis aside, it would seem that most auxotrophs would be fastidious organisms, but there could be many more fastidious organisms that aren't auxotrophs. Auxotrophs specifically can't produce organic compounds on their own. There are a LOT of organisms that rely on the availability of non-organic nutrients, such as specific elements/minerals. For instance, vertebrates require access to calcium. Calcium is an element; our inability to produce it does not make us auxotrophs.

But perhaps symbiosis would allow an organism to be an auxotroph without being a fastidious organism? For instance, mammals tend to have bacteria in our guts that can digest nutrients that our bodies can't on their own. Perhaps some of those bacteria also assemble certain nutrients that our bodies can't? -- Avocado (talk) 14:27, 28 December 2024 (UTC)

December 28

Paper with wrong enantiomer in a figure

In the following reference:

Quack, Martin; Seyfang, Georg; Wichmann, Gunther (2022). "Perspectives on parity violation in chiral molecules: theory, spectroscopic experiment and biomolecular homochirality". Chemical Science. 13 (36): 10598–10643. doi:10.1039/d2sc01323a. PMID 36320700.

it is stated in the caption of Fig. 8 that S–bromochlorofluoromethane is predicted to be lower in energy due to parity violation, but in the figure the wrong enantiomer is shown on this side. Which enantiomer is more stable, according to the original sources for this data? –LaundryPizza03 (dc̄) 08:18, 28 December 2024 (UTC)

Where can I find data on the circulation and citation rates of these journals?

Hello everyone, To write an article about a scientist, you need to know, where can I find data on circulation and citation rates of journals from this list? Vyacheslav84 (talk) 09:58, 28 December 2024 (UTC)

So-called “Hydrogen water”

I saw an ad promoting a device which presumable splits water into hydrogen and oxygen and infuses water with extra hydrogen, to a claimed surplus of perhaps 5 ppm, which doesn’t seem like much. I found a review article which looked at several dozen related studies that found benefits:https://pmc.ncbi.nlm.nih.gov/articles/PMC10816294/ .

I’ve noticed that carbon dioxide or chlorine (chloramine?) dissolved in water work their way out pretty easily, so I wonder if dissolved hydrogen could similarly exit hydrogen enriched water and be burped or farted out, rather than entering the blood stream and having health benefits. is it more than the latest snake oil? Edison (talk) 23:01, 28 December 2024 (UTC)

Yes, the dissolved hydrogen will exit the water just as quickly (even faster, because of its low molecular mass and complete lack of polarity or capability for ionic dissociation), and even if it does enter the bloodstream, it will likewise get back out in short order before it can actually do anything (which, BTW, is why deep-sea divers use it in their breathing mixes -- because it gets out of the bloodstream so much faster and therefore doesn't build up and form bubbles like nitrogen does) -- so, I don't think it will do much! 2601:646:8082:BA0:209E:CE95:DB32:DD64 (talk) 01:50, 29 December 2024 (UTC)

It's conceivable it might take out the chloramine, I guess. I don't think there's very much of it, but it tastes awful, which is why I add a tiny bit of vitamin C when I drink tap water. It seems to take very little. Of course it's hard to tell whether it's just being masked by the taste of the vitamin C. --Trovatore (talk) 02:12, 29 December 2024 (UTC)

If you just want to split water into hydrogen and oxygen all you need is a battery and two bits of wire. You don't say where you saw this ad but if it was on a socia media site forget it. Shantavira|^{feed me} 11:47, 29 December 2024 (UTC)

December 29

Potential energy vs. kinetic energy. Why not also "potential velocity" vs. "kinetic velocity"? E.g. in the following case:

In a harmonic oscillator, reaching the highest point involves - both a minimal kinetic energy - along with a maximal potential energy, whereas reaching the lowest point involves - both a maximal kinetic energy - along with a minimal potential energy. Thus the mechanical energy becomes the sum of kinetic energy + potential energy, and is a conserved quantity.

So I wonder if it's reasonable to define also "potential velocity" vs. "kinetic velocity", and claim that in a harmonic oscillator, reaching the highest point involves - both a minimal "kinetic velocity" (i.e. involves what we usually call a rest) - along with a maximal "potential velocity", whereas reaching the lowest point involves - both a maximal "kinetic velocity" (i.e. involves what we usually call the actual velocity) - along with a minimal "potential velocity". Thus we can also define "mechanical velocity" as the sum of "kinetic velocity" + "potential velocity", and claim that the mechanical velocity is a conserved quantity - at least as far as a harmonic oscillator is concerned.

Reasonable?

Note that I could also ask an analogous question - as to the concept of "potential momentum", but this term is already used in the theory of hidden momentum for another meaning, so for the time being I'm focusing on velocity.

HOTmag (talk) 12:26, 29 December 2024 (UTC)

'kinetic velocity' is just 'velocity'. 'potential velocity' has no meaning. Andy Dingley (talk) 13:56, 29 December 2024 (UTC)

Per my suggestion, the ratio between distance and time is not called "velocity" but rather "kinetic velocity".

Further, per my suggestion, if you don't indicate whether the "velocity" you're talking about is a "kinetic velocity" or a "potential velocity" or a "mechanical velocity", the very concept of "velocity" alone has no meaning!

On the other hand, "potential velocity" is defined as the difference between the "mechanical velocity" and the "kinetic velocity"! Just as, this is the case if we replace "velocity" by "energy". For more details, see the example above, about the harmonic oscillator. HOTmag (talk) 15:14, 29 December 2024 (UTC)

You could define the potential velocity of a body at a particular height as the velocity it would hit the ground at if dropped from that height. But the sum of the potential and kinetic velocities would not be conserved; rather $v_{\mathrm {tot} }={\sqrt {v_{p}^{2}+v_{k}^{2}}}$ would be constant. catslash (talk) 18:54, 29 December 2024 (UTC)

Thank you. HOTmag (talk) 20:07, 29 December 2024 (UTC)

'Potential velocity' has no meaning. You seem to be arguing that in a system where energy is conserved, but is transforming between kinetic and potential energy, (You might also want to compare this to conservation of momentum.) then you can express that instead through a new conservation law based on velocity. But this doesn't work. There's no relation between velocity and potential energy.

In a harmonic oscillator, the potential energy is typically coming from some central restoring force with a relationship to position, nothing at all to do with velocity. Where some axiomatic external rule (such as Hooke's Law applying, because the system is a mass on a spring) happens to relate the position and velocity through a suitable relation, then the system will then (and only then) behave as a harmonic oscillator. But a different system (swap the spring for a dashpot) doesn't have this, thus won't oscillate. Andy Dingley (talk) 00:00, 30 December 2024 (UTC)

Let me quote a sentence from my original post: Thus we can also...claim that the mechanical velocity is a conserved quantity - at least as far as a harmonic oscillator is concerned.

What's wrong in this quotation? HOTmag (talk) 07:52, 30 December 2024 (UTC)