Wikipedia:Reference desk/Science

Welcome to the science section
of the Wikipedia reference desk.

skip to bottom

Select a section:

• Computing
• Entertainment
• Humanities
• Language
• Mathematics
• Science
• Miscellaneous
• Archives

Want a faster answer?

Main page: Help searching Wikipedia

   

How can I get my question answered?

• Select the section of the desk that best fits the general topic of your question (see the navigation column to the right).
• Post your question to only one section, providing a short header that gives the topic of your question.
• Type '~~~~' (that is, four tilde characters) at the end – this signs and dates your contribution so we know who wrote what and when.
• Don't post personal contact information – it will be removed. Any answers will be provided here.
• Please be as specific as possible, and include all relevant context – the usefulness of answers may depend on the context.
• Note:
  • We don't answer (and may remove) questions that require medical diagnosis or legal advice.
  • We don't answer requests for opinions, predictions or debate.
  • We don't do your homework for you, though we'll help you past the stuck point.
  • We don't conduct original research or provide a free source of ideas, but we'll help you find information you need.

Ready? Ask a new question!

How do I answer a question?

Main page: Wikipedia:Reference desk/Guidelines

• The best answers address the question directly, and back up facts with wikilinks and links to sources. Do not edit others' comments and do not give any medical or legal advice.

See also:

• Teahouse
• Help desk
• Village pump
• Help manual

December 6

Geodesics for Massive and Massless Particles

In general relativity, do massive and massless particles follow the same geodesic? Why or why not? Malypaet (talk) 23:19, 6 December 2024 (UTC)

According to the Einstein field equations, the worldline traced by a particle not subject to external, non-gravitational forces is a geodesic. Each particle follows its own worldline. Two particles that share their worldline are at all times at the same location and so have identical velocities.  --Lambiam 08:46, 7 December 2024 (UTC)

A massless particle must follow a null geodesic and massive particle must follow a time-like geodesic (in my limited understanding). catslash (talk) 22:20, 7 December 2024 (UTC)

So a massive particle with a velocity infinitely close to that of a photon (under the influence of a massive object) will have a geodesic infinitely close to that of the photon, right? Or is there another explanation and which one? Malypaet (talk) 22:11, 9 December 2024 (UTC)

I believe that is correct (perhaps there is an expert to hand who could confirm this?). catslash (talk) 23:42, 9 December 2024 (UTC)

In some frame of reference, the massive particle is at rest and so its spacetime interval along its geodesic is as spacelike time-like as can be (and thereby as non-null-like as can be for a non-tachyonic particle). So it depends on the point of view of the observer. Simplifying the case to special relativity and considering a particle traveling with speed $v$ in the x-direction, the spacetime interval $\Delta {s}$ between two events separated by a time $\Delta t$ is given by:

$(\Delta s)^{2}=(\Delta ct)^{2}-(\Delta x)^{2}=(\Delta ct)^{2}-(\Delta vt)^{2}=(c^{2}-v^{2})(\Delta t)^{2}.$

In frames of reference in which $v$ approaches $c,$ the interval can become arbitrarily small, making it experimentally indistinguishable from that of a massless particle.  --Lambiam 07:40, 12 December 2024 (UTC)

@User:Lambian, could you re-read the spacetime interval section? I reckon that if there exists a frame of reference in which an interval is purely a time difference, then it is time-like, and if there exists a frame of reference in which the interval is purely a difference in location, then it is space-like. catslash (talk) 10:14, 12 December 2024 (UTC)

Yes, I used the wrong term, now corrected.  --Lambiam 07:30, 13 December 2024 (UTC)

December 7

Source

The articles Radium dial and Radium Girls blithely speak of the element as though infinitesimal quantities of pure metal were employed, whereas the iron law of economics dictate that some partially processed yellowcake with a minuscule (and difficult to extract) percentage of some radium salt would be the raw material. Does someone have this information? Doug butler (talk) 22:02, 7 December 2024 (UTC)

The paint, marketed as Undark, was a powdery mixture of radium sulfate, zinc sulfide and phosphor.^[1] The young women had to mix this powder with water and glue before it could be applied. The radium-226 percentage had to be high enough to produce sufficient luminosity. For its pernicious effect, its chemical form is immaterial.  --Lambiam 23:19, 7 December 2024 (UTC)

the chemical form is mostly immaterial. Radium sulfate is insoluble enough that it's unable to get a hold in the physiology and so has only minimum effects. 176.0.131.138 (talk) 09:45, 8 December 2024 (UTC)

Because radium is not an actinide it can be easily separated from the other elements. So the economic pressure is not to give away something to a customer what you can sell to another customer. 176.0.131.138 (talk) 09:52, 8 December 2024 (UTC)

December 8

Unit questions

1. How widely is the metric system used in the Philippines? Do people there use metric for both short and long distances? Is centimeter a widely used unit in the Philippines? Does Philippines use metric mass and volume units almost exclusively?
2. How widely is the metric system in former British colonies in Africa (Gambia, Sierra Leone, Ghana, Nigeria, Rwanda, Uganda, Kenya, Tanzania, Malawi, Zambia, Zimbabwe, Botswana, Namibia, South Africa, Eswatini, Lesotho)? Are there still some applications for which some people might use imperial units?
3. How widely is the metric system used in Caribbean island countries? Do these countries use imperial system widely?
4. Is there any application that commonly uses fractions with metric units?
5. Can exact one-third of a meter be measured in most devices, as its decimal representation contains just repeating threes? --40bus (talk) 20:56, 8 December 2024 (UTC)

It's worth pointing out that item 5 is one reason the English System is preferable, because feet, yards and miles, as well as acres, are easily divided by 3. ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:19, 8 December 2024 (UTC)

This Australian, having now worked with the metric system for two thirds of his longish life, has never screamed "I wish this unit was divisible by three!" HiLo48 (talk) 06:58, 9 December 2024 (UTC)

Is there any metric unit, other than units of time, which is easily divisible by 3? --40bus (talk) 06:14, 9 December 2024 (UTC)

1 metre is easily divided by 3. A third of a metre is 1/3 meter. Do you mean 1/3 meter cannot be precisely written in decimal form? Just use fractions. problem solved. 2001:8003:429D:4100:186E:C147:C792:1055 (talk) 09:25, 9 December 2024 (UTC)

The Metric system article lists the basic units. For several of them, division by 3 doesn't seem like it would be all that useful. Temperature, for example. ←Baseball Bugs ^{What's up, Doc?} carrots→ 08:28, 9 December 2024 (UTC)

1. Have you read Metrication? The article says The Philippines first adopted the metric system in 1860 because of the Spanish Colonial government; imperial units were introduced by the American Colonial government; however, the metric system was made the official system of measurement in 1906 through Act No. 1519, s. 1906. US customary units still in use for body measurements and small products while the metric system is used for larger measurements; e.g. floor area, highway length, tonnage. Shantavira|^{feed me} 09:30, 9 December 2024 (UTC)

December 9

I'm collecting examples of a purely "physical property of a physical property" (of a body).

By (purely) physical property, I mean any measured property whose measurement depends on (purely) physical [dimensions usually measured by physical] units. A few examples of physical properties include: momentum, energy, electric charge, magnetic charge, velocity, and the like (actually the elementary particles carry plenty of purely physical properties).

However, by purely (physical property), I mean that it's not also a mathematical or geometric property, i.e. excluding: numeric value (size) of a physical property, density of energy ("density" is also a mathematical concept - e.g. in density of primes), center of mass ("center" is also a geometric concept), and the like. But I do consider velocity to be a purely physical property, because its description invloves (e.g.) the temporal dimension (which actually "flows" - whereas the way time "flows" can't be described by any mathematical equation. Anyway this "flow" is another issue I don't want to discuss in this thread).

So, for finding a purely "physical property of a physical property" (of a body), I've thought about one example so far: the physical units dimensions of any physical property.

I'll be glad for any additional examples. 2A06:C701:746D:AE00:ACFC:490:74C3:660 (talk) 11:22, 9 December 2024 (UTC)

The physical units in which physical quantities are expressed (such as erg, eV, foe, joule, therm) are somewhat arbitrary social constructions. The dimension of a physical quantity is a much more purely physical property. It is a point in an abstract vector space. One may argue that there is some arbitrariness in the choice of the basis of this space. The SI standard uses time (${\mathsf {T}}$), length (${\mathsf {L}}$), mass (${\mathsf {M}}$), electric current (${\mathsf {I}}$), absolute temperature (${\mathsf {\Theta }}$), amount of substance (${\mathsf {N}}$) and luminous intensity (${\mathsf {J}}$) as the basis, but other choices for the base physical dimensions span the same vector space.  --Lambiam 12:42, 9 December 2024 (UTC)

Yes, I really meant "dimensions" of a physical property, thank you. 2A06:C701:746D:AE00:ACFC:490:74C3:660 (talk) 14:24, 9 December 2024 (UTC)

December 10

Proton decay and cosmic expansion

A friend's physicist father opined that the phantom energy causing more and more rapid cosmic expansion will never be as strong as the attraction of the strong force, so protons will not be ripped apart in the big rip. Be that as it may, if the phantom energy is counter to the strong force, however weakly, wouldn't protons, consisting of quarks held together by the strong force, have an increased rate of decay in the far future? I have heard that the theories that protons do undergo decay at all have not yet been supported by experiments, though. Rich (talk) 13:41, 10 December 2024 (UTC)

We have to suppose quite a few things to get to the question: suppose there is some form of proton decay, suppose there is phantom energy, and suppose that the phantom energy reaches some plateau before getting to an energy scale high enough to create a quark-gluon plasma. Would protons then decay at a faster rate? I don't think that's necessarily the case. Proton decay is not the same kind of process as making a quark-gluon plasma. I believe the answer depends on what kinds of operators lead to the hypothetical proton decay. --Amble (talk) 22:49, 10 December 2024 (UTC)

Thanks, nice clarification of the issues. You've thought through the issues more clearly and knowledgeably than I did. That's a valuable answer. But having said that, is there more information available about current speculations and theoretical work by physicists concerning proton decay interacts with cosmic expansion? I can't be the only one wondering about it and many of the people wondering about it would be physicists.Rich (talk) 07:30, 13 December 2024 (UTC)

The nearest paper I came across is [2], but there "proton decay" actually means p⁺ → n + e⁺ + ν and not p⁺ → e⁺ + 2γ. --Amble (talk) 20:22, 13 December 2024 (UTC)

December 13

What is the most iconic tornado photo

Request for opinions
The following discussion has been closed. Please do not modify it.
What photo of a tornado would you say is the most iconic? I'm researching the history of tornado photography for an eventual article on it and I've seen several specific tornadoes pop up over and over again, particularly the Elie, Manitoba F5 and the "dead man walking" shot of the Jarrel, Texas F5. Which would be considered more iconic? ApteryxRainWing🐉 | Roar with me!!! | My contributions 17:21, 13 December 2024 (UTC) At the top of this page is a bullet point stating "We don't answer requests for opinions, predictions or debate": this reads to me like a request for subjective opinions. Perhaps you would like to consider what quantifiable and referenceable metric would answer what you want to know? Presumably you also want only real tornadoes considered? Otherwise some might nominate the the twister from The Wizard of Oz, or from more recent tornado-related movies – Sharknado, anyone? :-). {The poster formerly known as 87.81.230.195} 94.1.223.204 (talk) 18:07, 13 December 2024 (UTC) "Swegle Studios" has a couple of YouTube videos dedicated to the backstories of famous tornado photos and video; you might find them useful in your research. Photos, Videos. Matt Deres (talk) 18:40, 13 December 2024 (UTC) I googled "most iconic tornado photo" and a bunch of different possibilities popped up. I don't see how you could say that any given photo is the "most iconic". ←Baseball Bugs What's up, Doc? carrots→ 18:57, 13 December 2024 (UTC)

December 15

help to identify File:Possible Polygala myrtifolia in New South Wales Australia.jpg

possible w:Polygala myrtifolia in New South Wales Australia

Did I get species right? Thanks. Gryllida (talk, e-mail) 06:56, 15 December 2024 (UTC)

related: https://species.wikimedia.org/wiki/Wikispecies:Village_Pump#help_to_identify_species Gryllida (talk, e-mail) 06:57, 15 December 2024 (UTC)

FWIW, I can't detect any visible differences between the plant in this photo and the ones illustrated in the species and the genus articles. However, the latter makes it clear that Polygala is a large genus, and is cultivated, with hybrids, so it's possible that this one could be a close relative that differs in ways not visible here, such as in the bark or roots. That may or may not matter for your purposes. {The poster formerly known as 87.81.230.195} 94.1.223.204 (talk) 10:11, 15 December 2024 (UTC)

How to address changes to taxonomy

Hi all, I am a biology student brand new to wiki editing who is interested in cleaning up small articles/stubs for less known taxa. One that I've encountered is a mushroom that occurs in the pacific northwest (Fomitopsis ochracea). The article mentions that this fungus is occasionally mistaken for another fungus, Fomitopsis pinicola.

However, the issue I've run into is that F. pinicola used to be considered a single species found around the world, but relatively recently was split into a few different species. The original name was given to the one that occurs in Europe, and the one in the pacific northwest (and thus could be mistaken for F. ochracea) was given the name Fomitopsis mounceae.

The wiki page says

Historically, this fungus has been misidentified as F. pinicola. When both species are immature, they can look very similar, but can be distinguished by lighting a match next to the surface of the fungus.[1] F. pinicola will boil and melt in heat, while F. ochracea will not.[1]

Since the source says pinicola (as likely do most/all other sources of this info given the change was so recent), and since technically it's true that they used to be mistaken for it... what would be the most appropriate way to modernize that section?

My questions are: Should I replace F. pinicola with F. mounceae? Or is that wrong because the source doesn't refer to it by that name? Would it be better to write something like (now known as/considered F. mounceae) next to the first mention of the species? Or is that a poor choice because it implies all the members of F. pinicola were renamed F. mounceae?

Any advice on how to go about updating this section is incredibly appreciated
TheCoccomycesGang (talk) 10:21, 15 December 2024 (UTC)

First, take these sorts of questions to the relevant Wikiproject, in this case Wikipedia talk:WikiProject Fungi. I am not as familiar with the consensus at WP:FUNGI, but it seems like they defer to Species Fungorium/Index Fungorium and Mycobank to decide. Those sources presently seem to consider Fomitopsis pinicola a good species. Also, be careful about "replacing", there are rules to ensure the continuity of the article history. By the way, there is a hilarious but unencyclopedic/copyvio recipe appended to the Fomitopsis mounceae article. Abductive (reasoning) 11:09, 15 December 2024 (UTC)

Thanks for the tips, I didn't know about projects so I'll go read up on that. And thanks for the warnings about replacing things. I've been reading a lot of help pages, but I'm still in the process of learning the all conventions and what mechanics break if you do things the wrong way.

I actually saw the recipe ages ago before I made my account and completely forgot about it... it was one of many things that prompted me to get into wiki editing. TheCoccomycesGang (talk) 23:12, 15 December 2024 (UTC)

Does stopping masturbation lead to sperm DNA damage?

I'm looking for information on the potential link between the frequency of ejaculation (specifically through masturbation) and sperm DNA damage. I've come across some conflicting information and would appreciate it if someone could point me towards reliable scientific studies or reviews that address this topic.

Specifically, I'm interested in whether prolonged periods of abstinence from ejaculation might have any negative effects on sperm DNA integrity. Any insights or links to relevant research would be greatly appreciated. HarryOrange (talk) 17:08, 15 December 2024 (UTC)

Only males may abstain from sperm-releasing Masturbation that serves to flush the genital tract of old sperm that in any case will eventually dissipate. No causal relationship between masturbation and any form of mental or physical disorder has been found but abstinence may be thought or taught^{1 2 3} to increase the chance of wanted conception during subsequent intercourse. Philvoids (talk) 00:51, 16 December 2024 (UTC)

There's many rumors about that topic. One is that not ejaculating frequently increases the risk of developing prostate cancer. Abductive (reasoning) 01:02, 16 December 2024 (UTC)

Nothing really conclusive but there's some evidence that short periods are associated with lower DNA fragmentation, see

• Du, Chengchao; Li, Yi; Yin, Chongyang; Luo, Xuefeng; Pan, Xiangcheng (10 January 2024). "Association of abstinence time with semen quality and fertility outcomes: a systematic review and dose–response meta‐analysis". Andrology. 12 (6): 1224–1235. doi:10.1111/andr.13583. ISSN 2047-2919.
• Hanson, Brent M.; Aston, Kenneth I.; Jenkins, Tim G.; Carrell, Douglas T.; Hotaling, James M. (16 November 2017). "The impact of ejaculatory abstinence on semen analysis parameters: a systematic review". Journal of Assisted Reproduction and Genetics. 35 (2): 213. doi:10.1007/s10815-017-1086-0. ISSN 2047-2919. PMC 5845044. PMID 29143943.
• Ayad, Bashir M.; Horst, Gerhard Van der; Plessis, Stefan S. Du; Carrell, Douglas T.; Hotaling, James M. (14 October 2017). "Revisiting The Relationship between The Ejaculatory Abstinence Period and Semen Characteristics". International Journal of Fertility & Sterility. 11 (4): 238. doi:10.22074/ijfs.2018.5192. ISSN 2047-2919. PMC 5641453. PMID 29043697.

for example. Alpha3031 (t • c) 02:12, 16 December 2024 (UTC)

Mature sperm cells do not have DNA repair capability.^[3] Inevitably, as sperm cells get older, they will naturally and unavoidably be subject to more and more DNA damage. Obviously, freshly produced spermatozoa will, on average, have less DNA damage. It is reasonable to assume that the expected amount of damage is proportional to the age of the cells, which is consistent with what studies appear to find. Also, obviously, the more the damage is to a spermatozoon fertilizing an oocyte, the larger the likelihood that the DNA repair in the resulting zygote, which does have DNA repair capability, will be incomplete. The studies I've looked at did not allow me to assess how much this is of practical significance.  --Lambiam 09:40, 16 December 2024 (UTC)

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."^[4] 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.^[5]  --Lambiam 11:45, 19 December 2024 (UTC)}}

Old French plus Latin.[6] ←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 [7], 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)

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)