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September 21

Variables in chemistry?!

I've seen the symbols M and X in chemistry, what do they mean? HAt 04:07, 21 September 2024 (UTC)

Well M could represent a metal, and X could represent a halogen in a chemical formula, eg NaX could be a halide salt of sodium. X is probably F, Cl, Br or I. Theoretically it could be At, but not in any visible amount. If the symbols are in italic text they may represent a number. Graeme Bartlett (talk) 06:04, 21 September 2024 (UTC)

September 22

B-boson

Besides a link to our article electroweak interaction that mentions the B-boson without telling anything about it, we have no article about this boson. Why?

I'm eager to know some basic data about it, e.g. mass, electric charge, spin, isospin, stability, experiments trying to detect it, and likewise. But... nothing? HOTmag (talk) 16:27, 22 September 2024 (UTC)

You'll find it at B meson. Sorry, although the B meson is a boson, it is not the beast that's mentioned in electroweak interaction. --Wrongfilter (talk) 17:23, 22 September 2024 (UTC)

What a pity. HOTmag (talk) 08:57, 23 September 2024 (UTC)

The B-boson isn’t a well-known particle in the standard model of particle physics. Are you thinking of the Higgs boson that was discovered in 2012? Philvoids (talk) 08:47, 23 September 2024 (UTC)

No, I'm looking for basic data (e.g. mass charge spin isospin parity etc.) of the B-boson mentioned in our article electroweak interaction. HOTmag (talk) 08:57, 23 September 2024 (UTC)

The thing is that the B boson doesn't exist as an entity in our Universe. It "exists" before symmetry breaking, but since our world has a broken symmetry the observable bosons are the Z⁰ and the photon instead of the W₃ and B. As the B cannot be observed, many of your questions are moot. --Wrongfilter (talk) 09:07, 23 September 2024 (UTC)

Got it. HOTmag (talk) 09:31, 23 September 2024 (UTC)

September 24

Cloning the Carolina parakeet

In theory, would it be possible to clone the extinct Carolina parakeet by taking whatever existing DNA we have of the species and filling any gaps with DNA from the sun conure (closest living relative and very common pet) and then putting that into a sun conure egg? I have read that it's very difficult to clone birds though. 146.200.126.178 (talk) 23:12, 24 September 2024 (UTC)

Here's an Audubon Magazine write up on the topic. It foolishly says that the Carolina parakeet, ivory-billed woodpecker, and passenger pigeon could be invasive, which is nonsense; only the Carolina parakeet could conceivably be successful beyond its former range. See monk parakeet for why. Abductive (reasoning) 23:55, 24 September 2024 (UTC)

Yes, there's been a lot of talk about removing monk parakeets from areas where they are non-native. But the public tend to get extremely angry about the idea of culling parrots specifically, even to the point of taking direct action when nests are removed. I believe there was even a politician a few years ago who said something along the lines of "absolutely not" when it came to the idea of removing that species being raised by his advisors. 146.200.126.178 (talk) 00:19, 25 September 2024 (UTC)

Would you then get an actual Carolina parakeet, or merely a hybrid that kind of looks like it? ←Baseball Bugs ^{What's up, Doc?} carrots→ 01:30, 25 September 2024 (UTC)

Yes, I was thinking that myself. How much of the Carolina parakeet's DNA can be replaced by another (very closely related) species before it can no longer be considered a Carolina parakeet? 146.200.126.178 (talk) 01:42, 25 September 2024 (UTC)

Has the genome of any of these extinct species been mapped? I don't think the article says. But that would be a way to maybe get closer to a real clone. And I understand what they mean by invasive. If a species wasn't someplace, and then appears in that place, by definition it's invasive. That doesn't necessarily mean it will be harmful to other species in that place, but it could be. ←Baseball Bugs ^{What's up, Doc?} carrots→ 07:18, 25 September 2024 (UTC)

See Ship of Theseus. -- Jack of Oz ^{[pleasantries]} 17:41, 25 September 2024 (UTC)

"Reconstructed", bit by bit. In the case of an organism, some careful selective breeding could eventually render the species closer to the original. ←Baseball Bugs ^{What's up, Doc?} carrots→ 00:55, 26 September 2024 (UTC)

We have an article on the concept De-extinction. It mentions the passenger pigeon example discussed in Abductive's link. It also briefly mentions the Carolina parakeet and claims a "full genome of the carolina parakeet was sequenced" in 2019 although I'd suggest reading the sources as I suspect this isn't a complete genome. Revive & Restore seem to be the ones most involved in this for birds or at least the ones who seemed to have received the most publicity. (Colossal Biosciences is also popular but although they did make noises about the dodo they seem more concentrated on mammalian species. And while I personally think anyone involved in this is fairly PR oriented, Colossal Biosciences chosen projects seem to be more flash.) At the moment, in terms of actual "de-extincting" species they seem to be concentrating on the above mentioned passenger pigeon which is their flagship project with also some work on the heath hen. Interesting they've set a goal of the "first generation of new Passenger Pigeons before 2025" but considering their progress page [1] hasn't been updated since 2019, I have doubts we're going to see this first generation in the next 3 months. In fact, even their 2023 report [2] doesn't seem to mention the passenger pigeon. With the heath hen project they at least seem to have been less optimistic about promising stuff by certain dates [3]. However that too doesn't seem to have had an updated since 2020 [4]. Possibly COVID-19 related disruption to their work hasn't helped, still it's been a while since it should have been a barrier to any lab work etc. BTW, I'd say Revival of the woolly mammoth and Thylacine#Research are perhaps the projects which have generally received the most historic interest so might be a good place to look beyond general discussions about de-extinction about the feasibility of such proposals and whether the result if we did succeed should really be compared with the original species. Although the research related to the Maclear's rat mention in our article might be another recent place to look in to. Nil Einne (talk) 10:09, 27 September 2024 (UTC)

September 25

Etymology of wheldone

What is the etymology of wheldone? The references doi:10.1021/acs.orglett.0c00219 and doi:10.1021/acs.jnatprod.4c00649 only described the chemical as a fungal metabolite isolated from the coculture of Aspergillus fischeri and Xylaria flabelliformis. --Leiem (talk) 09:00, 25 September 2024 (UTC)

The clue is in the acknowledgments section of the first paper: "This Letter is dedicated to the late Daniel (Dan) Clive Wheldon". And since Wikipedia has everything: Dan Wheldon. --Wrongfilter (talk) 09:57, 25 September 2024 (UTC)

I understand. Thank you! --Leiem (talk) 15:38, 25 September 2024 (UTC)

One might even say...well done. :P SnowRise ^{let's rap} 22:39, 25 September 2024 (UTC)

Botanical nuts

I'm trying to split Nut (fruit) back into separate articles for food and fruit (because currently a lot of the article content is about things that aren't botanical nuts), but there's not much left after you strip out the food content. Are there any botanists in the house who can recommend sources on botanical nuts and/or weigh in on what should be covered and isn't? AlmostReadytoFly (talk) 10:10, 25 September 2024 (UTC)

Not a botanist, but I think there's a bit of a problem for having a botanical nut. It is an even fuzzier idea than that of tree. But there's an article on trees so I suppose the could be one like that on nuts. You'd have to decide whether it is a very resticted topic on the botanical idea of a nut which doesn't contain most of what people mean by a nut or a wider one like the article on trees. Would you include pine nuts, coconuts peanuts, and the stones of drupes like almonds or pecans or plums? NadVolum (talk) 14:33, 25 September 2024 (UTC)

The plan is for them to go back to Nut_(food) as part of the unmerge. The unmerge discussion is here. AlmostReadytoFly (talk) 08:51, 26 September 2024 (UTC)

Measure relative UVB / UVC intensity

For SODIS water disinfection I'm interested in testing how much UVB and UVC passes through various types of plastic and other materials. I don't care so much about absolute levels as relative intensity compared to unfiltered sunlight. I'd also like to check out whether my cheap sunglasses are letting any UV through. I see this device says peak spectral response 300-350mm which is describes as UVA (I thought that was the A-B range). Is that sufficient, i.e. is something that transits UVA unlikely to block UVB/UVC? Thanks. 2601:644:8581:75B0:0:0:0:C813 (talk) 22:21, 25 September 2024 (UTC)

I doubt that it's any indication one way or the other, different materials can have widely different transmission spectra both within and outside the visible band; one would have to test each one specifically (if references aren't available). {The poster formerly known as 87.81.230.195} 94.1.171.3 (talk) 02:20, 26 September 2024 (UTC)

September 26

Body Roundness Index formula

Body_roundness_index#Calculation gives the formula

364.2 − 365.5  × √(1 − [waist circumference in cm / 2π]2  /  [0.5 × height in cm]2)

which seems unnecessarily complicated. Why isn't it simply simplified to

$364.2-365.5{\sqrt {1-{\Big (}{\frac {\text{waist circumference in cm}}{\;\;\;\;\pi \;\;\;\;\;\times \;\;\;\;\;\,{\text{height in cm}}}}{\Big )}^{2}}}$ ?

Moreover, as both numerator and denominator have length units, the unit doesn't matter as long as they are the same e.g. cm, mm or inches.

Thanks, cmɢʟee⎆τaʟκ 04:31, 26 September 2024 (UTC)

Probaly because the editor who added that didn't know how to render mathematical formulae. You're welcome to change it. Shantavira|^{feed me} 09:16, 26 September 2024 (UTC)

Thanks. I don't mean the formatting but the division by 2π on top with multiplication by 0.5 below.

Presumably, they meant waist / (2π) instead of (waist / 2)π – BEMDAS is confusing! cmɢʟee⎆τaʟκ 10:17, 26 September 2024 (UTC)

Because it's left over from its derivation from the eccentricity formula for an ellipse, ${\sqrt {1-{\frac {b^{2}}{a^{2}}}}}$, where the semi-minor axis, b, is the "radius" of the waist and the semi-major axis, a, is half the body height. AlmostReadytoFly (talk) 11:05, 26 September 2024 (UTC)

Makes sense, thanks! cmɢʟee⎆τaʟκ 11:34, 26 September 2024 (UTC)

September 27

Demonstration of Planck's law in radiation power per unit area?

To demonstrate his law, Max Planck converted radiation power measurements per unit area into energy density ($\times 4\pi /c$).
Is there a demonstration directly with the radiation power from the experiment without conversion into energy density?
I can't find any, but maybe I'm not seeing the correct wording for search engines.
Malypaet (talk) 21:28, 27 September 2024 (UTC)

The Stefan-Boltzmann constant can be derived by integrating the spectral radiance of a blackbody. Spectral radiance is the power emitted by a surface per unit area per unit solid angle per unit frequency (or wavelength). The Stefan-Boltzmann law states that the power radiated per unit area of a black body is proportional to the fourth power of its absolute temperature. Answer generated with Bing CoPilot — Preceding unsigned comment added by 217.180.227.58 (talk) 20:38, 30 September 2024 (UTC)

Unsuitable tool! Malypaet (talk) 20:22, 2 October 2024 (UTC)

Unsuitable how? The Stefan–Boltzmann law derived from Planck's law by considering a small flat black body surface radiating out into a half-sphere has been used to find the temperature of the Sun, other stars and an Effective temperature of the Earth. Philvoids (talk) 14:56, 3 October 2024 (UTC)

My question was about the demonstration of Planck's law, which does not use the same SI units as the Stefan-Boltzmann law. So, is there a demonstration that stays in spectral radiance from the beginning to the end without converting into energy density and back to give the result in spectral radiance? Malypaet (talk) 20:07, 3 October 2024 (UTC)

September 28

Is the following argument sufficient, for logically proving that any material can become energy - without using Einstein's formula?

Here are three accepted assumptions:

1. There are black holes.

2. A given black hole can-theoretically absorb any given material.

3. A given black hole can-theoretically evaporate, by becoming Hawking radiation.

Hence, logically, any given material can-theoretically become energy: Just let this material be absorbed by a black hole, and then let the black hole evaporate and become Hawking radiation.

Apparently, all of this is done without using Einstein's formula $[E=mc^{2}]$. So, it seems that Einstein's formula is not needed for proving that any given material can-theoretically become energy, right? HOTmag (talk) 18:00, 28 September 2024 (UTC)

Hawking radiation is not all energy. It contains particles (and anti) too. To theorize about Hawking radiation you (or Hawking) need(ed) Einstein's equation. So you need it, but you need not write about it. 176.0.164.155 (talk) 19:55, 28 September 2024 (UTC)

1. Re. the particles contained in Hawking radiation: So why does the lead of our article Hawking radiation only describe it as "black body radiation", i.e. "electromagnetic radiation", without mentioning any "particles" contained in Hawking radiation?

2. Are you sure the formula $E=mc^{2}$ is needed for concluding that black holes emit Hawking radiation? HOTmag (talk) 22:09, 28 September 2024 (UTC)

1 See the first paragraph in Emission

2 See the first paragraph in black hole evaporation

In 1 you need to pay special attention to the word "particle". 176.0.164.155 (talk) 23:35, 28 September 2024 (UTC)

Re. 1: Yes I'd seen this paragraph, but it doesn't answer my previous question, so let me repeat it: Why does the lead of the article only describe Hawking radiation as "black body radiation", i.e. "electromagnetic radiation", without mentioning any "particles" contained in Hawking radiation? Are you claiming that black body radiation can contain particles (besides energy)?

Re. 2: Yes this paragraph really shows how Hawking uses Einstein's formula for concluding that the black hole, not only creates energy, but also becomes energy. However, this article indicates also that "some [authors] find Hawking's original calculation unconvincing" - because it uses an "infinite frequency" as well as "a wavelength much shorter than the Planck length", while these authors use techniques other than Hawking's one, so I still wonder whether Hawking's technique using Einstein's formula is necessary for concluding that the material in the black hole, not only creates energy, but also becomes energy. HOTmag (talk) 01:06, 29 September 2024 (UTC)

Particles are energy and electromagnetic waves are particles; they are two aspects of the same. It's just that at typical temperatures used for blackbody radiation, the only particles you can make are photons. (There's enough energy too to make neutrinos, but that requires some weak interactions, so it's unlikely to happen.) Once energies go to the MeV scale (temperatures of gigakelvins), your blackbody radiation will contain other particles.

Not sure what you mean by "creates energy" or "becomes energy". Energy cannot be created or destroyed; it's always there. It just changes shape. Mass is equivalent to energy, that's an intergal part of relativity. And "equivalent to" doesn't mean "can be turned into", it means "is an alternative view of". PiusImpavidus (talk) 09:34, 29 September 2024 (UTC)

The lede indeed says "black-body radiation" and I think that's misleading. It was introduced here. I've changed it to prevent misunderstandings. --Wrongfilter (talk) 11:44, 29 September 2024 (UTC)

Thank you for this important correction. HOTmag (talk) 17:29, 29 September 2024 (UTC)

the only particles you can make are photons. (There's enough energy too to make neutrinos, but that requires some weak interactions, so it's unlikely to happen.) Are you claiming, that the "particles" mentioned in the first paragraph of the chapter Emission only mean "photons" (or neutrinos but it's unlikely), for "regular" tempratures?

Not sure what you mean by "creates energy" or "becomes energy". When I wrote "this paragraph really shows how Hawking uses Einstein's formula for concluding that the black hole, not only creates energy, but also becomes energy", I meant that the first paragraph in black hole evaporation really showed how Hawking used Einstein's formula for concluding that the black hole, not only emitted energy, but also lost mass equivalent to the emitted energy.

Mass is equivalent to energy, that's an intergal part of relativity. Who said that that was not? I only said, that without Einstein's formula $E=mc^{2},$ [you'd have had no special relativity, so] you couldn't have concluded: "Mass is equivalent to energy".

Energy cannot be created or destroyed; it's always there. Correct, but without Einstein's formula $E=mc^{2},$ that paragraph couldn't have concluded that "When particles escape, the black hole loses a small amount of its energy and therefore [loses] some of its mass", because without Einstein's formula - one could imagine a body emitting energy - while the body's mass remains the same as before the emission - while the emitted energy does not disappear but is only released ousdise. HOTmag (talk) 17:29, 29 September 2024 (UTC)

You also need Einstein's equation to prove that black holes can exist (assumption 1). PiusImpavidus (talk) 20:28, 28 September 2024 (UTC)

I was referring to Einstein's formula, i.e. $E=mc^{2}.$ Are you sure this equation (=formula) is needed for concluding that black holes exist? HOTmag (talk) 22:09, 28 September 2024 (UTC)

You want to remove special relativity, but maintain General relativity? You can't. The latter relies upon the former. 2A0D:6FC0:767:D900:3439:2201:29C1:1A87 (talk) 08:31, 29 September 2024 (UTC)

Theoretically, one could consider General relativity without considering Special relativity: Combining both theories, gives us a Pseudo Riemannian manifold - and as a special case - a Lorentz 4D space. But Special relativity alone - would only give us a Pseudo Euclidean 4D space - and as a special case - Minkowsky space, while General relativity alone - would only give us a Riemannian 4D space. To sum up: Theoretically, one could imagine a Generally relativistic 4D space, that ignores Special relativity. The same is true for the issue of mass-energy equivalence you're talking about: Also without Special relativity, one could still consider the Einstein field equations of General relativity, so that the geometry of spacetime would be shaped by the density and flux of momentum and of energy according to these field equations, but without assuming anything about any relation between mass and energy.

But this is a side point. My main question to user:PiusImpavidus was about whether Einstein's formula $E=mc^{2}$ is really needed for concluding that black holes exist. So I'm still asking: Is it needed? HOTmag (talk) 17:29, 29 September 2024 (UTC)

No it's not needed. There was a theory of black holes before Einstein (by Gottfried Wilhelm Leibniz,I think), but they were way bigger than according to Einstein. 176.0.162.8 (talk) 12:47, 30 September 2024 (UTC)

Since Hawking radiation includes particles, no your asumptions don't logically lead to that any material can become energy. NadVolum (talk) 19:06, 29 September 2024 (UTC)

Yes.

Due to the current thread, the article Hawking radiation has just been corrected by user:Wrongfilter, so now it explicitly states (in the lede) that Hawking radiation includes also particles. But when I posted my original post, the lede of the article had only mentioned electromagnetic radiation. That's why I posted my original post. HOTmag (talk) 19:33, 29 September 2024 (UTC)

e-bike = 1000 miles per gallon gasoline?

1. 1 gallon gasoline = 127 megajoule (per the gasoline article) = 35KWH thermal energy
2. If you can convert that to electricity at 28% efficiency (portable generator), that's 10KWH electric
3. Ebikes can go around 50 miles on a 500 WH battery charge, so 100 miles per KWH
4. So that's 1000 miles per gallon if you power the bike from a generator.

Questions: 1) Amirite? I.e. does the math above look ok? 2) Why are motorized bikes/mopeds so much less efficient? They typically get 100 mpg or so.

Thanks. 2601:644:8581:75B0:0:0:0:C813 (talk) 22:20, 28 September 2024 (UTC)

28% is way high for a generator. Tires, mass, are significantly different. Does your genny meet the emissions regs for a moped? Moped's aren't optimised for economy, bicycles are. Greglocock (talk) 08:03, 29 September 2024 (UTC)

A Stirling engine with 1200 Kelvin input (and 300 Kelvin output) has an efficiency of 75% (theoretically). And 1200 Kelvin is not outrageously high. So an efficiency of 28% is not high, but rather low. 176.0.162.8 (talk) 12:37, 30 September 2024 (UTC)

Nonsense, Greglocock (talk) 07:52, 1 October 2024 (UTC)

Care to elaborate? 176.0.159.38 (talk) 10:00, 1 October 2024 (UTC)

Sure. The most efficient internal combustion engines are far short of 75% efficient, and the engines used in gennies are fairly basic. Yes I have been an engine design engineer. And as the article on stirlings says "Stirling engines cannot achieve total efficiencies typical of an internal combustion engine, the main constraint being thermal efficiency" Greglocock (talk) 10:35, 1 October 2024 (UTC)

Did you read the part about why that is too? In short it says that the internal combustion engine does not need to transfer the heat through the wall of the engine thereby losing temperature and therefore efficiency. But you said a "fairly basic" engine. And there you have it. You could get good efficiency from a basic Stirling engine where you need a fancy internal combustion engine for. The trend to direct fuel injections reduces the part of volume where the maximum temperature is achieved, which is good for nitrous gas emissions but bad for efficiency. On the other hand a Stirling engine heats the outer volume which is a larger part of the volume than in an internal combustion engine with a cooled wall. Which leads to another average.

But as you are an engine design engineer, I want to give you a design that is fairly basic of a Stirling engine that should have a good efficiency because there's relatively few steps in generating power. Imagine a torus with a cold half and a hot half. Every half is made from metal, both are connected by ceramic. In the torus two bent cylinders chase each other, keeping distance by means of magnetic repulsion. Now you may ask about eddy currents in the metallic halfs of the torus. So I have to tell you that the metal is not purely metal, but there are many small metallic cylinders in a ceramic matrix. If you want to ask about the Currie temperature I wanted to answer you that the magnetic core in the bent cylinders have to be thermally isolated and that isolation is lifted (by an external magnetic field, which is needed anyhow because the distance between the cylinders has to be modulated in response to the position in the torus) when the (bent) cylinder is in the cold part of the torus. One of the cylinders has the regenerator in it and therefore lets the fluid flow through the center, the other cylinder need to get the work out of the fluid. The result of the chase is a changing magnetic field around the torus and a coil at the ceramic part can get the AC of the device. It may be that more (bent) cylinders (alternating power and regenerator) makes the magnetic interaction easier (and makes it possible to make the cylinders (and therefore the engine) smaller, thereby reducing thermal inertia needed) but that would need more thermal sectors and that would need additionally thermal distribution devices. The trade-off would depend on the reachable efficiency. Part of that efficiency would be a blower to make a hotter flame that needs part of the generated electricity. 2A02:3032:308:A7D3:6020:6890:D467:113B (talk) 20:51, 2 October 2024 (UTC)

E-bikes (which are basically light electric mopeds; I don't see why the law makes a distinction between those) typically cruise at about 6 m/s (22 km/h). A regular moped cruises at 12.5 m/s (45 km/h), twice as fast. That quadruples drag and energy use. Combine that with the low efficiency of small (but still oversized), two-stroke petrol engines and the much lower rolling resistance of bicycle tyres, in particular when compared to the tyres of motorscooters. PiusImpavidus (talk) 09:08, 29 September 2024 (UTC)

Yes, aero and higher cruising speeds are the most likely cause. Greglocock (talk) 07:52, 1 October 2024 (UTC)

If it helps, I am using a gas generator right now because we have no power. It is producing between 4 and 5 KWH per gallon of gas. It is not a bad generator at all. It is a brand new one in the upper price range: Westinhouse WGEN2000C (all the cheaper ones were sold out). I assume that industrial level generators will do better, but I doubt a residential one will get to 10KWH. (I updted the numbers after checking the generator today. After a rough start, it is doing better now.) 12.116.29.106 (talk) 11:01, 1 October 2024 (UTC)

September 29

Must a given body, that has just been a black hole, always remain a black hole, as long as the body exists?

In other words, what rules out the following scenario?

1. A body, being right now a Schwarzschild black hole, starts emitting Hawking radiation.

2. However, the body's radius remains constant during the emission.

3. When the body has lost too much energy - along with its equivalent mass, the body's mass inside the constant body's radius becomes less dense, untill the body's current radius becomes bigger than the body's Schwarzschild radius - because of the stability (constancy) of the body's radius, so the body - which has just been a black hole - stops being a black hole and becomes a regular body.

What's wrong with this scenario? Is this really assumption #2 ? HOTmag (talk) 18:54, 29 September 2024 (UTC)

THe theory says #2 is wrong - black holes become smaller as their mass goes down. NadVolum (talk) 19:10, 29 September 2024 (UTC)

Yes, both our article black hole and our article Hawking radiation state that when the black holes emit radiation they "shrink", but how do you know that their shrinkage refers, not only to the body's mass, but also to the body's radius? This is the main question of this thread.

Is this because of the internal gravitation, which is the only "force" active inside the black hole? HOTmag (talk) 19:47, 29 September 2024 (UTC)

I think you're giving the word 'body' too much meaning. The radius is a gravitational result which depends on the mass.You wouldn't notice the surface as you fell through. NadVolum (talk) 20:33, 29 September 2024 (UTC)

I used the term "body" on purpose. A given body, whether a black hole or a billiard ball, has a radius, literally speaking. It's a fact you can't ignore. Nor can you ignore the influence of the body's radius on the density of the body's mass, hence on the question of whether this body is a black hole, because the body's radius is not necessarily identical to the body's Schwarzschild radius: Actually the former is not bigger than the latter if and only if the body is a black hole. This is the basis of my #3 assumption. If you don't agree to it, please explain what's wrong there, in your opinion. If you do agree to it, then I'm still asking the question in my previous response. HOTmag (talk) 09:10, 1 October 2024 (UTC)

Assumption #4: a hole is not a body. 176.0.159.38 (talk) 10:04, 1 October 2024 (UTC)

Our article black hole refers to "the nearest known body thought to be a black hole, Gaia BH1". It also refers to Cygnus X-1 as the first "object" identified as a black hole. Actually when I wrote "body" I meant a region, located in spacetime, and characterized by dense mass which doesn't let light escape when it's close enough. What's wrong in that view? HOTmag (talk) 11:41, 1 October 2024 (UTC)

Do you think an atom is a body? What use is the concept of density for an atom, where is that density? Density has even less real meaning for a black hole than it does for an atom, you can calculate a number by dividing one number by another but what then - what does it actually refer to? NadVolum (talk) 12:39, 1 October 2024 (UTC)

Is a stellar black hole a body? Let's check out: Does it have a mass? If it does, then does this mass have a location? If it does, then is this mass located in one geometric point? If it doesn't, then the mass must be located in some region. Does this region have an (average) radius? If it does, then we can sum up: a stellar black hole has a mass located in an (average) radius, so is it a body? HOTmag (talk) 13:55, 1 October 2024 (UTC)

The problem is that you are using concepts from classical physics: region; radius; density; location; space; time. The whole point (ha!) is that a black hole is thought to contain a Gravitational singularity, where classical geometries, physics and mathematics, and the relationships that govern them, break down because infinities are involved. We truly do not know what lies within the event horizon of a black hole, even whether space and time, or spacetime, have meanings there (if there even is a there, there). Until we achieve a successful theory of Quantum gravity, we cannot describe the situation even mathematically, let alone in words, and cannot visualise or conceptualise it. {The poster formerly known as 87.81.230.195} 94.6.86.81 (talk) 22:38, 1 October 2024 (UTC)

Since we can attribute some properties to a black hole, like a mass (and other properties), the situation is not that obscure, despite the infinities. Further, if it had been that obscure, we couldn't have claimed anything about a black hole, not even that it emits a Hawking radiation, or that a black hole "shrinks" when it emits that radiation. But our article black hole does claim a black hole shrinks, and my question was, how do we know the shrinkage also refers to the size and not only to the mass, i.e. what's wrong in a scenario where the black hole's mass decreases while the black hole's size remains constant. My main question (in my original post) only refers to this scenario, provided that it's really possible. Is it? HOTmag (talk) 11:25, 2 October 2024 (UTC)

The only black hole parameter we're aware of that could possibly be considered its size is its Schwartzschild radius, which is proportional to its mass. So if it loses mass, it shrinks, if we're willing to make any statements about its size.

There's in GR no hidden parameter for the size of a body inside the event horizon, even less a prediction of what might happen if such a hypothetical body gets outside the event horizon. GR is however quite clear that any matter present within the event horizon must move towards the centre (we've no way to check), so no extended body can remain just inside the event horizon for a long time. It's also clear that at the centre, the theory breaks down. When enough of the black hole has evaporated in Hawking radiation to make quantum gravity matter, who knows? PiusImpavidus (talk) 17:58, 2 October 2024 (UTC)

Well it is an astronomical body. But body there does not mean something just like a billard ball but larger. Like body also doesn't mean it must be like a cadaver or the collective members of church or the main flavour of wine or the main text of a book or lots of other things it is applied to. It is a general word for a concept and not all astronomical bodies are the same in detail. NadVolum (talk) 22:58, 1 October 2024 (UTC)

When I say "body", I mean something that has a mass located in some region characterized by an (average) radius. Something like a stellar black hole. That's why my question affords to use the term "body". HOTmag (talk) 11:25, 2 October 2024 (UTC)

We don't know that a black hole shrinks, because we have not yet been able to observe the phenomenon, or observe Hawking radiation itself. But – the theories that include these predicted phenomena seem to successfully accord with what measurements and phenomena we can observe directly or firmly deduce. Perhaps next year someone will come up with an even better theory, or next century we will be able to make direct observations that prove or disprove the current theory. At the moment, however, this is the best we can do.

Further to my earlier remarks, you are implying that by measuring a black hole's mass (fairly easy) and its radius (less easy) from external observations we can calculate its density: this assumes that it has the same volume internally as we observe externally, but we cannot assume this because it's not necessarily classical (or even relativistic) in there – maybe it's 'bigger' on the inside than on the outside; maybe it has two, or four, or five spacial dimensions; maybe it has two time dimensions. All bets are off because 'singularity'. {The poster formerly known as 87.81.230.195} 94.6.86.81 (talk) 14:22, 2 October 2024 (UTC)

Worth mentioning here that "radius" doesn't have exactly its usual meaning in this context. It's the circumference divided by 2π, not the "distance to the center" in any usual sense. "Circumference" itself also takes some explanation, which I'm not sure I could give correctly. --Trovatore (talk) 22:56, 2 October 2024 (UTC)

The black hole is a particularly nasty construct from a theoretical standpoint. Assume that flat space is constructed from cubes a Planck length in size. Now curvature is represented by making the sides of the cubes inequal. If you do that, the size of the cubes approaches zero as you go near the event horizon. So inside the event horizon literally no space exists and a black hole is really a hole in spacetime.

That viewpoint, that I have described in the last paragraph is indistinguishable from a viewpoint where spacetime inside a black hole exists but can not be observed. 2A02:3032:305:F2EF:616E:4B30:D3CA:B0AE (talk) 20:14, 3 October 2024 (UTC)

Gin a black hole kiss a black hole / need a black hole cry? --Trovatore (talk) 20:00, 2 October 2024 (UTC)

I think the straightforward answer to "Must a given body, that has just been a black hole, always remain a black hole, as long as the body exists?" is it is very likely that a black hole stays being a black hole as long as it exists. However we have never actually observed one yet going out of existence. And there's no theory I know of which entertains the idea of a big but nearly massless black hole. NadVolum (talk) 14:28, 4 October 2024 (UTC)

September 30

Electron capture cross-sections for hydrogen

Is there any publication out there that discusses what the cross-section for energetic electrons converting free protons into neutrons is? It's energetically unfavourable but with sufficient electron energy it should be possible. Jo-Jo Eumerus (talk) 09:18, 30 September 2024 (UTC)

I have no publications. It is probably so small that it does have any practical significance. Ruslik_Zero 20:17, 2 October 2024 (UTC)

Biotransformation of TFA

Reference 22 (Kirschner, E., Chemical and Engineering News 1994, 8) does not seem to be appropriate for the statement "Biotransformation by decarboxylation to fluoroform has been discussed." In https://pubs.acs.org/toc/cenear/72/32, there is only one article by Kirschner, but about an entirely different subject. Could somebody please advise what to do? 162.23.30.16 (talk) 17:51, 30 September 2024 (UTC)

The simplest is to slap a template {{failed verification}} on the citation. But the statement itself may be true. Quoting this secondary source:

Visscher et al. [44] showed that trifluoroacetic acid could be microbially metabolized to fluoroform and consecutively defluorinated to acetate under aerobic and anaerobic conditions, respectively.
...
[44] Visscher, P.T., Culbertson, C.W. and Oremland, R.S. (1994) "Degradation of trifluoroacetate in oxic anoxic sediments". Nature (Land.) 369, 729-731.

I have not inspected the primary source, though, which has many citations ([5]).  --Lambiam 04:44, 1 October 2024 (UTC)

Thanks I replaced the ref [6] 162.23.30.16 (talk) 14:44, 1 October 2024 (UTC)

Parasites

Do parasites that feed off other parasites exist? ―Panamitsu (talk) 23:13, 30 September 2024 (UTC)

Do you consider bacteriophages to be parasites? ←Baseball Bugs ^{What's up, Doc?} carrots→ 00:19, 1 October 2024 (UTC)

See Hyperparasite. {The poster formerly known as 87.81.230.195} 94.6.86.81 (talk) 02:14, 1 October 2024 (UTC)

Big fleas have little fleas... (about halfway down). The overall text doesn't specifically mention any cases of recursive parasitism that I could see, nor does it cite a source for the rhyme. -- Verbarson  ^talk_edits 16:41, 1 October 2024 (UTC)

From Jonathan Swift's poem On Poetry: a Rhapsody (1733).  --Lambiam 08:31, 2 October 2024 (UTC)

October 2

Aspartame

Is aspartame zero-calorie sweetener? CometVolcano (talk) 16:14, 2 October 2024 (UTC)

The first paragraph of Aspartame#Uses answers this. --Floquenbeam (talk) 16:24, 2 October 2024 (UTC)

When and how did people notice that trovants grow?

Articles about trovants like this (or, less reliably, this) and others note that they grow over time, and that pieces are pushed out or break off and grow independently, leading to local legends that they're alive and grow and reproduce. That makes it sound like their growth has historically been noticeable to locals, enough that they developed legends about it. But the SF article I linked and others also say it takes trovants thousands of years to grow a few centimeters, which seems like something people would not notice.
When did people notice that trovants grow, and how did they notice? Is "a handful of centimetres in over 1,000 years" an average, and some trovants under some conditions grow fast enough to be noticeable? Have any of them grown around something (like a tree growing around a post, or made noticeable in some other way the fact of their growing? Did scientists only figure out recently that models predict they grow, and the local legends are only a very recent tourism marketing thing? Or what? (Ezequiel F. Médici, Alejandro D. Otero, Album of Porous Media: Structure and Dynamics (2023), page 36, says the term 'trovant' was introduced in 1907 by Gheorghe Murgoci.) -sche (talk) 23:37, 2 October 2024 (UTC)

For interest. Sean.hoyland (talk) 08:15, 3 October 2024 (UTC)

I am fairly certain that the story that these concretions grow like living entities, budding and all,^[7] is a folk myth based on appearance. They were formed underground around some organic core, like a fossil. The growth only occurs while embedded in sand containing calcite that can cement the grains into a concretion. Eventually they became exposed by erosion.  --Lambiam 09:02, 3 October 2024 (UTC)

Thanks for your responses. (Sean, your link reminds me of Mother Shipton's Cave. I can see how even a single millimeter or less of stone growth could be noticeable if it was growing over something which was not previously stone! But I had not gotten the impression that that was how people [supposedly or actually] noticed these large boulders growing; can anyone find otherwise?)
I recall seeing the statement that they grew underground and around fossils presented in one of the websites I came across while initially trying to find the answer to my question, but I also recall coming across a site that said that at least some of them don't have fossils (or anything but more sandstone) in their cores. And many sites say they grow due to rainwater (and can grow more on one side than another if one side is more exposed), although that doesn't per se contradict the idea that they form under ground into which rainwater seeps. But apart from SF, it's hard to find much of anything about them in reliable sources. I will try searching in Romanian later; ro.WP says a few things about them but with no inline sources and not much of a bibliography. -sche (talk) 20:23, 3 October 2024 (UTC)

I posted that mainly because it shows that even a couple of thousand years ago, there was the realization that the materials from which rocks are composed can change through interactions with water. And that is especially true for carbonate minerals. Not sure whether you have seen this. Sean.hoyland (talk) 13:40, 4 October 2024 (UTC) (ah..I now see that you have seen the Album of Porous Media).

I had looked this up too, and in 2008 "the International Geological Congress in Oslo claimed trovants were incorrectly classified as concretions because there was no mineral difference between the stones and the sandstone beds on which they sat. There was also no distinct nucleus inside them." howstuffworks 2024-02-27 and scienceabc 2023-02-07 (with good illustration). It appears that they legitimately do grow and bud, although I agree that it is likely folklore in the notion that humans would have observed this as a change rather than deduced it from static appearance. SamuelRiv (talk) 13:49, 4 October 2024 (UTC)

I guess the absence of a nucleus doesn't tell you whether there was a nucleus before diagenesis reorganized the system. Some of them certainly have a nucleus. Porosity and chemical gradients are presumably involved somehow in the cementation process. This is a nice picture of similar structures in situ where you can see that the depositional structures are preserved regardless of the variation in cementation. Here's another one. Sean.hoyland (talk) 15:34, 4 October 2024 (UTC)

October 4

Lens

Suppose a camera had lenses and one of them was a lens that was flat on one side and convex on the other, and you reversed it so the flat side was in the other direction. What would happen to the focal length? RJFJR (talk) 02:58, 4 October 2024 (UTC)

It would be like a minute change of a zoom objective. The direction of the change depends on the original orientation of the lens. That is because in this case the optical position of the lens is slightly beside the mechanical position. And the shift occurs because the direction of the difference goes to the opposite. 2A02:3032:305:F2EF:616E:4B30:D3CA:B0AE (talk) 09:55, 4 October 2024 (UTC)

Reversing the lens also affects the optical aberrations, which is why we sometimes want an asymmetrical lens. PiusImpavidus (talk) 15:08, 4 October 2024 (UTC)

Physical Conditions where childhood development is essential to diagnosis

As I understand it, when someone is assessed for autism they are asked questions about their childhood behaviour and development as well as their behaviour now, even if they are well into adult life. This means that two middle-aged men with identical behaviours could receive different diagnoses if one displayed signs of autism as a child and the other didn't.

If that is right, and sorry if it isn't, then are there any examples of physical conditions which are diagnosed the same way? Where displaying symptoms as a child is an essential part of the diagnosis, and two patients displaying identical symptoms in adult life may be diagnosed differently?

81.106.106.219 (talk) 12:43, 4 October 2024 (UTC)