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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)

Notice that under current conditions of the universe, stellar mass (and larger) black holes do not shrink due to Hawking radiation. They do emit it, but at a black body temperature that is lower than that of the cosmic microwave background. In other words, they gain more mass from the CMB than they lose due to Hawking radiation. This will reverse as the universe expands and the CMB cools down, but it will be a couple billion years under most current models. If there ever were very small primordial black holess, or if a Romulan warbird lost control of its quantum singularity, those might have radiated away. --Stephan Schulz (talk) 14:48, 8 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)

Why must a nearly massless black hole be big? 176.0.164.84 (talk) 14:21, 6 October 2024 (UTC)

Because of assumption #2 in the question, which is an invalid assumption according to current theories which state that nearly massless black holes cannot be big. Sean.hoyland (talk) 14:27, 6 October 2024 (UTC)

Not true! Assumption #2 only calls for constant size, not for constant big size. What if the size of the body (whatever that means) is small from the start? 176.0.164.84 (talk) 02:44, 7 October 2024 (UTC)

You are right. I assumed your question was in response to the statement "And there's no theory I know of which entertains the idea of a big but nearly massless black hole." because it quotes from it and I treated 'big' as a proxy for initial radius in the context of mass loss in the OP's question. Either way, the size of the boundary that separates the not-black-hole from the black-hole space-time regions is a function of the mass. Sean.hoyland (talk) 05:09, 7 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 ([1]).  --Lambiam 04:44, 1 October 2024 (UTC)

Thanks I replaced the ref [2] 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,^[3] 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)

The OP describes a plano-convex lens. The Focal length of the lens is the distance at which a beam of collimated light will be focused to a single spot and is given exactly by the lensmaker's equation. For most purposes this thin lens approximation can be used: ${\frac {1}{f}}\approx \left(n-1\right)\left[{\frac {1}{R_{1}}}-{\frac {1}{R_{2}}}\right].$. Philvoids (talk) 19:00, 4 October 2024 (UTC)

I have read the article about lenses. The thin approximation is mentioned three times or so. But the real formula is not at all. 176.0.164.84 (talk) 11:28, 7 October 2024 (UTC)

nevermind. Found it. Don't know how I could overlook it. 176.0.164.84 (talk) 11:32, 7 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)

Not an expert by any means, but our autism article says it is a neurodevelopmental disorder that is manifest in early childhood, and therefore a history of the condition is highly pertinent. Alansplodge (talk) 20:16, 6 October 2024 (UTC)

Correct. When even fairly young children are being evaluated, their earlier childhood gets questioned. When I inquired about this, I was told that the reason is to see what the behaviour of the person was like before they starting autistic masking. So, presumably, any other situations where masking (personality) can come into play would also form part of the OP's answer. Matt Deres (talk) 18:37, 10 October 2024 (UTC)

October 5

Polygenism

I can't remember who wrote that Homo sapiens derived from three different apes i.e. Europeans from chimpanzee, Africans from gorilla, and East Asians from orangutan. Thanks in advance.-- Carnby (talk) 07:23, 5 October 2024 (UTC)

Illustration from Winchell's Preadamites, 1888.

The biological racist Alexander Winchell 1824 - 1891 who vaguely states "The doctrine of evolution does not teach that any existing ape is in the direct line of man's ancestry, but that the simian line and the human line are united in remote generalized ancestors common to both groups".[4] is worth further searching in Preadamites Or, a Demonstration of the Existence of Men Before Adam (1888) . Philvoids (talk) 14:02, 5 October 2024 (UTC)

In the US, Samuel George Morton and Louis Agassiz were early exponents of the idea, at least in regard to black Africans. In Europe, Carl Vogt promoted the concept, and the influential Ernst Haeckel also espoused it. Both were German, and evidently the idea persisted well into the 20th century in Germany, because around 1980-ish I bought a UK paperback newly published (by Sphere Books?), translated from a German original, that gave a 'popular' modern account of it (and was of course utter tosh, though amusing): unfortunately I no longer seem to have it (though I collect wacky pseudoscience books) and can't remember the author or title.

[Edited to add] Strike that last, I've recalled (the name is, err, memorable) – it's The Beginning Was the End by Oscar Kiss Maerth, published in Germany in 1971 and in the UK 1973 (Sphere pb 1974, I suspect I bought a reprint). {The poster formerly known as 87.81.230.195} 94.6.86.81 (talk) 16:49, 5 October 2024 (UTC)

Are any of these three types of apes able to cross-breed? ←Baseball Bugs ^{What's up, Doc?} carrots→ 17:30, 5 October 2024 (UTC)

It seems unlikely because of how long ago their lineages diverged: For comparison: chimps and bonobos about 2 million years ago, and can; humans and chimps/bonobos about 5–7 mya, and can't (different chromosome count, other primates 48, humans 46 owing to a post-divergence merger of two chromosomes); gorillas and h/c/b about 8 mya; orangutans and g/h/c/b about 17±2 mya. As far as I'm aware, humans, bonobos, chimps, gorillas or orangutans have never been observed to attempt a mutual intraspecies mating (orangs would never encounter the others in the wild), and it would obviously be unethical to attempt to "assist" such a thing except in vitro (good luck with getting funding). {The poster formerly known as 87.81.230.195} 94.6.86.81 (talk) 19:36, 5 October 2024 (UTC)

Oh, it was tried by the Soviets, see Humanzee. Abductive (reasoning) 10:51, 6 October 2024 (UTC)

Well, the 46 vs 48 chrmosomes may not completely prohibit chimp-human interbreeding. A similar situation exists with horses and asses, but mules are still a thing. If human-chimp crosses are possible, the resulting "humanzee" would likely be sterile. But if you think chimp-gorilla breeding experiments would be unethical... hooo boy, those ain't got nuthin' on this. --User:Khajidha (talk) (contributions) 21:48, 5 October 2024 (UTC)

Hence, it seems highly unlikely that human descendants of these three species would somehow magically be able to interbreed, yet they can. Humans are a single species. ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:43, 5 October 2024 (UTC)

Although somewhat hybridised with Homo neanderthalis, Denisovans, and at least one other as-yet-unidentified archaic human (from genetic evidence).

There is some disagreement within anthropology as to whether these are or are not different species, or varieties of the same species (Professor Clive Finlayson, Director of the Gibralter National Museum thinks so, for one) and indeed which of the 30-odd differing definitions of 'species' is applicable. 94.6.86.81 (talk) 18:31, 6 October 2024 (UTC)

Very true. The concept of "species" is highly questionable. For example are Przewalski's horse and domestic horse the same species, despite the fact they have a different number of chromosomes? In the Plant kingdom it is even worse. I suspect that many different species in the well-known genera Quercus and Sorbus are variation of the same species.-- Carnby (talk) 21:01, 6 October 2024 (UTC)

There is only the one human species. ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:41, 6 October 2024 (UTC)

There is, now, of course: it even has a lower genetic diversity than all other primate species, and most other mammal species. The question is how many there were 50,000, or 200,000, or 500,000, or 1,500,000 years ago. {The poster formerly known as 87.81.230.195} 94.6.86.81 (talk) 00:50, 7 October 2024 (UTC)

No one doubts it. Except perhaps for some isolated African populations (i.e Khoisan and Pygmies) that could be considered perhaps subspecies, from a merely zoological standpoint. But no matter: a Senegalese, a Korean, and a Norwegian belong to the same species and subspecies.-- Carnby (talk) 09:24, 7 October 2024 (UTC)

October 6

Undissected in Geological Terms

I was looking at the article for Mount Kaimon and noticed the term "undissected" being used as a descriptive for the volcano. I'm unfamiliar with this usage of the term and am having trouble finding a clear explanation elsewhere. What's more, there's already a comment on Talk:Mount_Kaimon asking this same question, so there's surely more than just me who doesn't understand. Is there a clearer way to describe what "undissected" means as a descriptor in this article and the other articles that use the same terminology? Amstrad00 (talk) 00:48, 6 October 2024 (UTC)

It's one that's not dissected. Dissection in this sense means a volcanic cone that's built up by repeated eruptions, but has since been eroded or otherwise affected by processes other than its own eruption (folding, or being cut through by intrusive igneous features). So an undissected volcano is typically a younger one, either still or relatively recently active.

Here's one description of an old, dissected, volcano: Iddings, Joseph P. “The Dissected Volcano of Crandall Basin, Wyoming.” The Journal of Geology 1, no. 6 (1893): 606–11. http://www.jstor.org/stable/30054881. Andy Dingley (talk) 01:12, 6 October 2024 (UTC)

I see you've added a footnote to the article which resolves my issues as far as keeping things understandable for those unfamiliar with the term. Thanks for your explanation and edit to the article, I'll go ahead and add similar footnotes to the other volcano articles I've found with that term in the lead. Amstrad00 (talk) 03:20, 6 October 2024 (UTC)

I have created redirects for Dissected volcano and Undissected volcano (and a redirect target: Volcano#Dissection).  --Lambiam 16:17, 6 October 2024 (UTC)

Watching the gulls eat

I was wondering. Considering that a seagull can swallow a pound of food in about 10 seconds flat and seagulls will fight until bloody over scraps of food - what environment did they evolve into that necessitated this behaviour? Before humans got involved and the gulls came inland and scavenged rubbish and begged for food from people, just how harsh and brutal was their original biome? 146.90.140.43 (talk) 20:30, 6 October 2024 (UTC)

As noted at Gull#Diet_and_feeding, they'll eat just about anything. ←Baseball Bugs ^{What's up, Doc?} carrots→ 20:37, 6 October 2024 (UTC)

Indeed. A gull will eat just about anything. But I was thinking about how aggressive gulls are with each other when feeding and how fast they eat when food is available. Did they evolve somewhere that necessitated this behaviour? Out at sea? Because there's lots of available food on the sea shore. Cockles, mussels, limpets, crabs, etc. Or maybe the seagulls can't open the shells. 146.90.140.43 (talk) 20:55, 6 October 2024 (UTC)

The environment could well be our garbage dumps. Evolution can be rapid and in fact usually is. Here are two articles, Metabolic Adaptation of Certain Seagulls to Our Changing World, and Changing gull diet in a changing world: A 150-year stable isotope (δ13C, δ15N) record from feathers collected in the Pacific Northwest of North America. Abductive (reasoning) 22:46, 6 October 2024 (UTC)

In their natural environment, I think gulls mostly catch fish and scavenge carcasses floating in the sea. There is one species that does more than that, but it is quite rare when compared to the others. Iloveparrots (talk) 00:19, 7 October 2024 (UTC)

It's an error to think that Gulls are predominantly sea/ocean dwellers that have "come inland" recently. To quote from that article's lede:

"Gulls are typically coastal or inland species, rarely venturing far out to sea, except for . . .".

And from the Diet and feeding section:

"The food taken by gulls includes fish and marine and freshwater invertebrates, both alive and already dead; terrestrial arthropods and invertebrates such as insects and earthworms; rodents, eggs, carrion, offal, reptiles, amphibians, seeds, fruit, human refuse, and even other birds. No gull species is a single-prey specialist, and no gull species forages using only a single method. The type of food depends on circumstances, and terrestrial prey such as seeds, fruit, and earthworms are more common during the breeding season while marine prey is more common in the nonbreeding season when birds spend more time on large bodies of water."

{The poster formerly known as 87.81.230.195} 94.6.86.81 (talk) 01:01, 7 October 2024 (UTC)

October 7

Naming of gorgonin

I'm trying to write a history section on Gorgonin, a protein found in some corals. Searches for the discoverer turned up a 1939 paper and 2019 book (WP Library link), both of which agree that a specific 1855 paper by Valenciennes was the first to name it "gorgonin". But in the paper itself it appears to name the substance "cornéine". Am I'm missing something? It seems like they can't both have just not read the paper, especially considering the book has a different page range listed than the 1939 paper does.

Basically, I have three questions:

• (The book is unclear on this, and it's hard to understand through the bad English) Is gorgonin a substance (not just made of one protein and no other constituents), a single protein, or does it vary?
• Does anyone know what "iadogorgic acid" is? The book describes its discovery as the beginning of the study of "gorgonin as a substance"
• Am I missing something with regards to the naming situation? It seems confusing.

Mrfoogles (talk) 23:09, 7 October 2024 (UTC)

https://archive.org/details/zeitschriftfrbi23unkngoog/page/92/mode/1up had some discussion of the name. Apparently gorgonin and cornein are different? Personally I think both authors you linked must have made a mistake, since gorgonin isn't mentioned in the French paper. HansVonStuttgart (talk) 09:44, 9 October 2024 (UTC)

It seems that gorgonin is collagen-like. There are many collagens, in humans there are now 28 (last I read about this there were 21). In the case of gorgonin (and, like collagen, there has to be more than one, as it is found in 500 species that have had a long time to diverge), it seems that the collagen-like material is secreted (and possibly altered later) to be more resistant to dissolving in water than our collagen. Abductive (reasoning) 20:53, 9 October 2024 (UTC)

Oh, and it's named after the coral, Gorgonia, so named by Linnaeus in 1758, presumably after the Greek mythological Gorgons. Abductive (reasoning) 20:57, 9 October 2024 (UTC)

October 8

What percentage of a ship is under water?

I was wondering how much of a ship is actually under water. Of course we know that weight equals displacement, but what is the relationship between the volumes of the underwater parts to the overall volume of the main hull, and the overall volume of the cubic contents (including superstructure)? For a submerged sub, it's 100% under water - that's easy. But how a about the Japanese battleship Yamato? Or a modern ultra-large crude carrier like the TI-class supertankers? For those we at least get the difference between unloaded and loaded displacement (67,591 tonnes empty - which is still up there with the largest battleships ever built, and 509,484 tonnes fully loaded - which is stupendous). --Stephan Schulz (talk) 11:56, 8 October 2024 (UTC)

The fraction of volume under water is equal to the density of the ship divided by the density of the water. Problem is, how do you define the volume of the above water parts? Volume of the fully enclosed space, volume of the smallest convex surrounding (sorry, forgot the proper maths term), volume of the bounding box? PiusImpavidus (talk) 16:38, 8 October 2024 (UTC)

The mathematical term is "convex hull", but for a ship with a tall mast this is not a reasonable approach. A typical ship design has a relatively small number of relatively small openings, such as hatches and ports, that will be closed under severe storm conditions in order to keep the ship from taking water. This creates a closed surface enclosing the ship; it seems reasonable to me to use the enclosed volume for the total volume, also when the hatches and ports are open. This does not work for an open boat, such as a rowboat, but imagine a custom-made cover of fabric for the boat to keep rainwater out and we have again a closed surface that determines a specific volume.  --Lambiam 20:38, 8 October 2024 (UTC)

Indeed. The background (though not quite scientific) is that I'm currently looking for physics gaffes in ancient German pulp SF novels. One of the problems is that the authors don't quite get the square-cube law, and thus their giant spaceships with (so they think) giant masses turn out to have the density of a puff pastry. I would like to get some comparison data for real ships. So for volume think e.g. Space Battleship Yamato. --Stephan Schulz (talk) 21:06, 8 October 2024 (UTC)

I did calculate an airship. 2500 m high and 1:8:64 aspect ratio. With 10 cm average hull thickness it can lift a whole village into an earthquake area. With 15 cm it doesn't even fly. (There were other assumptions that may modify the numbers slightly) 176.0.162.62 (talk) 21:18, 8 October 2024 (UTC)

Surely it will depend entirely on the architecture and materials of each individual ship design? I don't see how there could be a simple formula or whatever relating to all ships. For example, the same design could be constructed using any one of many woods of different densities, or of various metals, and the percentage would be different for each variant.

Consider also vessels using hydrofoils. {The poster formerly known as 87.81.230.195} 94.6.86.81 (talk) 17:15, 8 October 2024 (UTC)

That's why I listed two concrete examples. --Stephan Schulz (talk) 20:21, 8 October 2024 (UTC)

Titanic = 100%, submarines = 100%, Enterprise = 0%. --217.149.171.88 (talk) 17:18, 8 October 2024 (UTC)

If you exclude your parenthetical (including superstructure) there is a term for this ratio which is reserve buoyancy. That is a redirect and probably a more explanatory article would be freeboard. I've looked for a value for Yamato but just WP's Yamato-class battleship#Armor "...designed with a very large amount of reserve buoyancy..." I don't know what would help for the volume of a superstructure but maybe you could put some limit on it by assuming a cuboidal cow (see block coefficient for different types of ships) and noting that metacentric height must be > 0. fiveby(zero) 00:56, 9 October 2024 (UTC)

Archimedes Principle: buoyant force (upwards) = volume displaced. For a watertight hull with gunwales (outer walls) above the waterline, you draw an imaginary line across the waterline: the volume of non-water-continuous-with-the-sea that's under that line, times weight-density of water (i.e. times density times g), equals the buoyant force. (To set this as an equation, for simple shapes and approximations you can use areas of triangles/prisms, while for more complex shapes you probably want to use integral calculus.)

With no other forces (such as lift from hydrofoils or flat-bottom planing), the boat's waterline is determined where buoyant force = its total weight -- that is, its total mass times g. (This is mass that you would measure by weighing on drydock, for example -- it's independent of how you would think about floating on water.) If your ship's total mass is unknown, but you generally know about stuff like the enclosed volume and what kind of materials are involved, then you would consider the wall thicknesses, enclosed space, etc.

Note that the air inside the enclosed space is often ignored in calculations because there is air outside too -- the air outside provides buoyancy as well, but since an enclosed seagoing ship is mostly filled with air, that cancels out. However, for an airship, the buoyancy of air is the critical consideration. SamuelRiv (talk) 19:16, 9 October 2024 (UTC)

October 9

A spacewalk odyssey

When Alexei Leonov couldn't get back into the airlock at the end of his space walk and had to let the air out of his space suit to get back in, for how long was he without air? Also, was this the inspiration for the decompression scene in Space Odyssey 2001? 2601:646:8082:BA0:2424:470:A683:D4AF (talk) 00:13, 9 October 2024 (UTC)

The article says, "He opened a valve to allow some of the suit's pressure to bleed off..." As to whether that influenced the 2001 scene, I couldn't say. ←Baseball Bugs ^{What's up, Doc?} carrots→ 03:10, 9 October 2024 (UTC)

The Voskhod 2 spacewalk was in March 1965; Stanley Kubrick and Arthur C. Clarke drafted the screenplay for 2001: A Space Odyssey in 1964–5, finishing in December, and filming was in 1966–7, during which both screenplay and novel were further amended. (Note that the screenplay was not based on the novel 2001: A Space Odyssey (novel) by Clarke and Kubrick [sic]; instead the two were written in parallel, with many variant scenes proposed and dropped, and the two works ended up with some differences.)

Leonov's difficulties and the necessity of depressurising his spacesuit were not immediately revealed by the Soviet authorities, and only emerged "later" (though I haven't discovered exactly when), so it's unlikely that Kubrick & Clarke knew about them when writing. Clarke doesn't mention the event in The Lost Worlds of 2001.

Yes, the Soviets were not terribly good at admitting their space programme cock-ups; both the 1960 Nedelin catastrophe and the 1980 Plesetsk launch pad disaster weren't publicly acknowledged until 1989. Alansplodge (talk) 11:54, 10 October 2024 (UTC)

An answer might be found in Michael Benson's 2018 book Space Odyssey: Stanley Kubrick, Arthur C. Clarke, and the Making of a Masterpiece, which unfortunately I don't have. Anyone? {The poster formerly known as 87.81.230.195} 94.6.86.81 (talk) 18:52, 9 October 2024 (UTC)

Thanks! So, the answer to the second question is that Clarke didn't know -- right? So that leaves the first question: for how long was Leonov without air? 2601:646:8082:BA0:98A8:D148:F8F4:4270 (talk) 02:25, 12 October 2024 (UTC)

Leonov was never without air because the decompression was partial. And what Clarke did know or not is pure speculation because Clarke was able to look into the future. Clarke did know about satellite tv before it was invented, to use a well known example. 176.0.154.204 (talk) 04:54, 12 October 2024 (UTC)

Your second question was, Was Leonov's having to let some air out of his space suit the inspiration for the decompression scene in 2001: A Space Odyssey? If Clarke, who co-wrote the screenplay, didn't know of the Leonov incident, the answer can only be "no". Leonov takes about the incident in an episode of the PBS special "The Russian Right Stuff", which aired in 1991. However, even if Clarke somehow already knew all about this when the screenplay was written, I see no reason to think that it might have been a source of inspiration for which in the film is a completely different scene.  --Lambiam 08:11, 12 October 2024 (UTC)

October 12

Space iceberg?

On average, what's more massive: an iceberg or a comet? 2601:646:8082:BA0:98A8:D148:F8F4:4270 (talk) 02:26, 12 October 2024 (UTC)

Google is your friend. "Density of a comet" gives 0.5-1.0 g/cm³[5] or a mean value of 0.52 ± .01 according to this 2022 paper, while "density of an iceberg" spits out 0.92. Clarityfiend (talk) 07:15, 12 October 2024 (UTC)

You answer on density, not on mass. To convert this info, we would also need the volume distributions of icebergs and comets. I don't think we even have good definitions of how small an iceberg can be and still be a berg ;-). The largest iceberg we have reliable data on is Iceberg B-15, with a surface area of 11007km². I could not find the height, but Ross estimated the depth of the ice shelf as a bit under 300m on the edge (where the berg would have broken off), so that would make it a volume of about 3700km³ corresponding, at the density given above, to 3400 million tons. NASA says comets are "from a few miles to a few tens of miles wide". Let's call it 30km for a biggish one, which makes it about 13500km³. That makes it significantly heavier than B-15, mo matter which density of the given range we use. And, of course, Pluto, at 1.3025e16t, would be a comet if it ever came to the inner solar system. So I would think that on average comets are bigger, but it depends on what you define as iceberg and comet. --Stephan Schulz (talk) 07:51, 12 October 2024 (UTC)

Unless you're asking about the average mass, in which case (ballpark numbers) 10¹⁴ kg vs 10¹⁰, respectively. Clarityfiend (talk) 07:28, 12 October 2024 (UTC)