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December 4

Mothball smell

I recently purchased some insect specimens: they're mounted in wooden shadow boxes with clear plastic windows for viewing. There's a seal around the window as well. Inside each case is a tiny box containing some form of mothball to deter other critters from munching on them. The thing is, the smell is pretty overpowering. What can I do to reduce it from being a nuisance while still hopefully retaining the preservative effect? The boxes appear pretty well sealed already, but mothballs are pretty intense, so even the tiniest crack would leave me in the same boat. Right now I have them sitting out in my garage to gas out for a bit; are there any other suggestions? Matt Deres (talk) 00:25, 4 December 2023 (UTC)[reply]

NatSCA advises investigating methods other than PDB, Naphthalene, and Camphor, mentions cedar and lavender oils, but doesn't go as far as to recommend them.[1] fiveby(zero) 04:10, 4 December 2023 (UTC)[reply]

It may be that most of the smell is coming from residual traces on the outside of the boxes. Try leaving them, sitting so as to expose the undersides as well, exposed to a continual draught for a week, and see if it lessens. {The poster formerly known as 87.81.230.195} 51.194.245.32 (talk) 13:14, 4 December 2023 (UTC)[reply]

Colors: What's unique in our planet, that lets us see this photon as yellow, rather than redshifted or blueshifted as seen by another galaxy's inhabitants?

Let there be a photon in our universe, outside our planet.

The photon is independent, i.e. it's not emitted by any system.

Let's assume our planet's inhabitants see this photon as yellow (i.e. with the respective frequency), while another galaxy's inhabitants see this photon have another color - whether redshifted or blueshifted.

I wonder what unique physical attributes our planet has (e.g. velocity and likewise), that let us predict that we will see this photon as yellow (i.e. with the respective frequency), as opposed to the other galaxy which doesn't have these physical attributes.

Note our planet's physical attributes I'm looking for cannot rely on what the other galaxy's inhabitants see, because we only know they see the photon have another color without us knowing - what this different color is - and whether it's redshifted or blueshifted. HOTmag (talk) 10:52, 4 December 2023 (UTC)[reply]

What do you mean by "predict that we will see this photon yellow"? We cannot predict that. Also, if we see the photon then the other galaxy's inhabitants don't. Detecting a photon destroys it, or at least changes its properties (ignoring the question of the identity of photons). It is not at all clear what you're asking and what the ideas behind the question are. --Wrongfilter (talk) 11:50, 4 December 2023 (UTC)[reply]

Now you are using Quantum considerations: Measuring it destroys it. But I'm asking from a statistical point of view. Note that under your Quantum considerations, but without statistics, the Doppler effect would have no meaning, because it discusses a photon's frequency (i.e. a photon's color) measured by two different frames of reference. HOTmag (talk) 12:14, 4 December 2023 (UTC)[reply]

Didn't you just answer your own question? --OuroborosCobra (talk) 13:42, 4 December 2023 (UTC)[reply]

Where? HOTmag (talk) 13:51, 4 December 2023 (UTC)[reply]

Reference frames. --OuroborosCobra (talk) 15:46, 4 December 2023 (UTC)[reply]

Yes, by "our planet" I meant "our planet's reference frame". I asked, if you can point at any quantified attributes our planet's reference frame has, which let us predict we will see this photon have the yellow color - rather than the other color (whether redshifted or bluseshifted) as seen by the other galaxy's inhabitants who have another reference frame. HOTmag (talk) 16:37, 4 December 2023 (UTC)[reply]

The fact that the observed wavelength in our reference frame is that of yellow, and the observed wavelength in another reference frame is a different wavelength. I don't really understand what type of quantifiable thing you are asking, not if you understand the color/wavelength relationship and what a reference frame is. --OuroborosCobra (talk) 17:10, 4 December 2023 (UTC)[reply]

Of course I understand well, the color/wavelength relationship, and what a reference frame is.

Actually, instead of asking about colors, I could ask the same question about wavelengths, so wherever I mentioned "yellow", you are allowed to replace it by its respective wavelength, and then you will see that my question still remains.

I will do the job for you: So, I'm only asking, if you can point at any quantified attributes our planet's reference frame has, which let us predict we will see this photon have the wavelength of yellow - rather than the wavelength of the other color (whether redshifted or bluseshifted) as seen by the other galaxy's inhabitants who have another reference frame. HOTmag (talk) 17:40, 4 December 2023 (UTC)[reply]

A reference frame is a definition, it isn't anything that can have quantifiable attributes. It isn't a thing that physically exists. --OuroborosCobra (talk) 18:50, 4 December 2023 (UTC)[reply]

But the very relation between two different reference frames is defined, by the relative velocity between them. Do you see my point? On the one hand, the difference between reference frames is relative: if I see you approach me - then you see me approach you, and if I see you move away from me - then you see me move away from you; On the other hand, colors (as well as their respective wavelength) are objective: If you see it "redder" than how I see it (e.g. when I'm on the other galaxy), then I see it "bluer" than how you see it.

Let me present my question from another viewpoint, because I don't want you to misinterpret me by "objective": so my question is, what makes you see the photon as yellow, rather than the other color (whether redshifted ot bluehsifted) - as seen by me when I'm on the other galaxy? Why don't our colors interchange, so that I will see the photon as yellow, and you will see it have the other color (whether redshifted ot bluehsifted)? HOTmag (talk) 19:28, 4 December 2023 (UTC)[reply]

We are in the same reference frame, at least as far as it is relevant to light coming from a common source towards both of us. The difference in location and velocity between you and me, no matter where you are on the planet, is incredibly minute in the scale we are discussing. Outside of that, you’ve answered your own question in how you have phrased it. That, or you are still not understanding what a reference frame is. —OuroborosCobra (talk) 19:59, 4 December 2023 (UTC)[reply]

What makes you suspect I don't understand what a reference frame is?

Contrary to what you ascribe to me (as your suspicion), I don't ascribe to you misunderstanding, but only (maybe) misinterpretation. Maybe you misinterpreted the words "other galaxy" I'd used from the very beginning. Actually, I'd written "other galaxy", just because the relative velocity between planets and stars in the same galaxy is usually very low with respect to the speed of light, while my question is about two totally different frames of reference - the relative velocity between each other being pretty close to the speed of light. This is what I've been asking about. I was sure you correctly interpreted my question - from the very beginning, but now I suspect you didn't.

Actually, when I posted my question, I didn't feel I had to indicate that the relative velocity between the frames of reference was close to the speed of light, because I was sure this was what everyone should have inferred, reading that my question was about - our planet's inhabitants seeing the photon as yellow - while the other galaxy's inhabitants see it have another color whether redshifted or blueshifted. I'd written "other galaxy", and "redshifted or blueshifted", just for this purpose: For my readers to realize that the relative velocity between both frames of reference was close to the speed of light. Naturally (i.e. disregarding electrons being the "observers" in a particle accelerator and the like), such a high relative velocity is only possible (naturally) if the question involves two different galaxies. I hope my question is clear to you now. HOTmag (talk) 20:58, 4 December 2023 (UTC)[reply]

Measured from what place and time on Earth? The yellow photon will be slightly redder/bluer due to relativistic velocity addition regardless of whether it's been recently emitted. Note that we are certainly using local instruments (and perhaps different models of these) to measure each. Modocc (talk) 13:03, 4 December 2023 (UTC)[reply]

As to your question in your first sentence: When we measure a galaxy we usually say we see it (e.g.) redder than what it really is. We don't ask "measured from what place and time on Earth", because the color is pretty similar from every place on earth and at any time on earth. So the same is true for the photon I'm asking about. My question is: Can you point at any quantified attributes our planet has, which let us predict we will see this photon have the yellow color - rather than the other color (whether redshifted or bluseshifted) as seen by the other galaxy's inhabitants? HOTmag (talk) 13:50, 4 December 2023 (UTC)[reply]

All the observable galaxies are in the same boat, so to speak, with respect to their inhabitants' measurements. We, as in our galaxy, are not special in that regard. Modocc (talk) 14:05, 4 December 2023 (UTC)[reply]

Of course. By "our planet" I meant "our galaxy". Can you point at any quantified attributes our galaxy has, which let us predict we will see this photon have the yellow color - rather than the other color (whether redshifted or bluseshifted) as seen by the other galaxy's inhabitants? HOTmag (talk) 14:11, 4 December 2023 (UTC)[reply]

Your question is premised on the assumption that the photon is not correlated with anything. Yes? Not with matter or even other photons. Then this question is like asking us to predict what the weather will be like tomorrow without sufficient data. Modocc (talk) 14:33, 4 December 2023 (UTC)[reply]

If I know, that your velocity is 2 units (of velocity), and that your mass is 3 units (of mass), I can "predict" your momentum is 6 units (of momentum).

Please fill in the blanks: If I know, that our galaxy's ________ is _ units (and so forth), then I can "predict" our galaxy's inhabitants will see the photon as yellow (with the respective frequency).

The question is, if you can fill in the blanks in the second sentence, just as I could fill in the blanks in the first sentence. If you think you can't fill in the blanks in the second sentence, then how can you explain that our galaxy's inhabitants see the photon have the yellow color (i.e. with the respective frequency) - rather than the other color (whether redshifted or blueshifted) as seen by the other galaxy's inhabitants? HOTmag (talk) 16:06, 4 December 2023 (UTC)[reply]

Now you seem to be asking me to try to kick this ball/sphere/galaxy within the usual paradigm of removing it from consideration with respect to the ground/graviton sea/field. Hmm. I'm not Charlie Brown. Modocc (talk) 16:58, 4 December 2023 (UTC)[reply]

Actually, my question was about whether we can point at any factors that make our galaxy's inhabitants see this photon as yellow, just as we can point at the meteorological factors (e.g. humidity and barometric pressure) that made the day of 1.1.1743 so rainy in LA, just as we can point at the physical factors (e.g. velocity and mass) that make this Chinese man's momentum so and so. I can't see how my question is related to kicking the ball you've mentioned. In my opinion, my question is more similar to the question about the rainy day and about the man's momentum. HOTmag (talk) 17:24, 4 December 2023 (UTC)[reply]

Classically, both the KE of mass and the color of light are always reference frame dependent. With both, the energy of an interaction between the photon and any galaxy is in fact relative. What other factors would you have in mind that would be sufficient?? Of course, classical Doppler is asymmetric (and not symmetric which is why it was mothballed), a paradox that my unpublished work resolves. Modocc (talk) 17:43, 4 December 2023 (UTC)[reply]

Your question: "What other factors would you have in mind that would be sufficient??", is pretty similar to mine: Is there any eqaution in your mind, that may let us predict, that our galaxy's reference frame will make us see this photon have a yellow color - rather than the other color seen by the other galaxy's inhabitants. Of course, you are allowed to replace the word "yellow" by its respective propery: whether frequency or wavelength or momentum or energy.

As for your comment about the classical Doppler effect: The same is true for the relativistic one. HOTmag (talk) 17:58, 4 December 2023 (UTC)[reply]

None. Modocc (talk) 18:26, 4 December 2023 (UTC)[reply]

I'm sad. HOTmag (talk) 18:33, 4 December 2023 (UTC)[reply]

I'm patient. Thanks. Modocc (talk) 19:00, 4 December 2023 (UTC)[reply]

We have the right reference frame to make the photon yellow.

In every reference frame, the photon has a direction and a wavelength (let's ignore polarisation and phase). No reference frame is any better than any other reference frame. Redshift and blueshift of this photon are only relative to a different reference frame. This yellow photon is blueshifted relative to the frame where it appears red and redshifted relative to the frame where it appears blue.

Multiple observers can't measure the same photon, but there's nothing stopping us from making multiple identical photons. Lasers do it all the time. PiusImpavidus (talk) 13:06, 4 December 2023 (UTC)[reply]

I agree to all of what you've written. Obvious, and yes: by "this photon" I mean one of those multiple identical photons. But still the fact is, that our planet's inhabitants see this photon have the yellow color - rather than the other color (whether redshifted or bluseshifted) as seen by the other galaxy's inhabitants, so can you point at any quantified attributes our planet has, which let us predict we will this see this photon have the yellow color - rather than the other color (whether redshifted or bluseshifted) as seen by the other galaxy's inhabitants? HOTmag (talk) 13:50, 4 December 2023 (UTC)[reply]

How would a photon (or a collection of them) not be emitted by something? ←Baseball Bugs ^{What's up, Doc?} carrots→ 14:14, 4 December 2023 (UTC)[reply]

Do you have any sources for your alluded claim, that every photon can't be idependent but rather must be emitted by a system? HOTmag (talk) 16:12, 4 December 2023 (UTC)[reply]

I'm not claiming anything. I'd just like to know what the basis of your premise is. ←Baseball Bugs ^{What's up, Doc?} carrots→ 18:25, 4 December 2023 (UTC)[reply]

See my response to NadVolum, below. HOTmag (talk) 18:30, 4 December 2023 (UTC)[reply]

If there is a monochromatic source of light somewhere in the cosmos that can be seen from the Earth and is found to have a wavelength of about 589 nm, it will appear yellow to us. There is no reason to think observers in other galaxies will find a different wavelength, unless they move with a very high velocity with respect to us. --Lambiam 15:28, 4 December 2023 (UTC)[reply]

Exactly. The other galaxy I'm talking about moves with a very high velocity with respect to us. Still, I'm looking for the attributes our glaxy has, that let us predict that we we will see this photon have the yellow color - rather than the other color (whether redshifted or bluseshifted) as seen by the other galaxy's inhabitants. HOTmag (talk) 16:10, 4 December 2023 (UTC)[reply]

Here's a direct answer to your question: There are no attributes our galaxy has that let us predict that we will see this photon have the yellow colour. Put differently: Your question makes no sense. --Wrongfilter (talk) 16:47, 4 December 2023 (UTC)[reply]

If so, then how can you explain the fact, that our galaxy's inhabitants see the photon have the yellow color (i.e. with the respective frequency) - rather than the other color (whether redshifted or blueshifted) as seen by the other galaxy's inhabitants? By the way, note that I have already responded to your previous comment: See above. HOTmag (talk) 16:55, 4 December 2023 (UTC)[reply]

Because they are in different reference frames, which I still don't think you fundamentally understand if you are asking this question. --OuroborosCobra (talk) 02:12, 5 December 2023 (UTC)[reply]

What's the issue/concept you think I don't fully understand? You and me are supposed to fully understand, that the relation between two different reference frames is defined by the relative velocity between them, and this relation has an impact on the color measured. But this has nothing to do with my question, because I've never asked about why the colors seen in two different frames of reference are different. The anwser to this other question I haven't asked is clear: the two obsevers see different colors because the two observers belong to two different frames of reference. However, my question is another one (as I have already explained in a previous response to you): Since you see the photon as yellow, rather than the other color (whether redshifted ot bluehsifted) - as seen by me when I'm on another frame of reference, why don't our colors interchange, so that I will see the photon as yellow, and you will see it have the other color (whether redshifted ot bluehsifted)? Note that the difference between the frames of reference we belong to, only explains why we see different colors, but does not explain why the colors don't interchange.

Let me present my question from another viewpoint (as I have already presented in a previous response to you): On the one hand, the difference between reference frames is relative: if I see you approach me - then you see me approach you, and if I see you move away from me - then you see me move away from you; On the other hand, colors (as well as their respective wavelength) are objective: When we are in different frames of reference then, if you see the photon "redder" than how I see it, then I see it "bluer" than how you see it. This fact proves that the answer to my question which discusses an objective fact, has nothing to do with the relative difference between the frames of reference. HOTmag (talk) 16:23, 7 December 2023 (UTC)[reply]

The premise is flawed: "The photon is independent, i.e. it's not emitted by any system." Photons do not have any existence independent of their emitters and absorbers. As pointed out by Gilbert Newton Lewis when he invented the term "photon", the emitting and absorbing events are separated from each other by a spacetime interval of zero. From the photon's point of view, traveling at the speed of light, no time elapses from when it is emitted until when it is absorbed, and its wavelength is infinite. From the point of view of the emitter and absorber, the energy, momentum, and wavelength are related, but identical only if the two have no velocity between them in a reference frame. No photon can be "seen" by two different observers, but photons of the same energy from the emitter will have different energies by different aborbers moving at different velocities. The idea of a photon as a "particle" confuses this picture, suggesting that a photon might have an independent existence. It's better to think of the photon as a "process", exchanging a quantum of energy between the emitter and the absorber, though here the "quantum" concept again confuses the picture, since the emitter and absorber don't see the same size quantum in the exchange if they have a relative velocity. There are lots of other ways to look at this, too, but it's nothing special about our place in the universe, just about relative velocities. Dicklyon (talk) 16:15, 4 December 2023 (UTC)[reply]

If so, then could you please answer my question in my previous thread? You can answer it on my own talk page if you want to. HOTmag (talk) 16:30, 4 December 2023 (UTC)[reply]

Both this question and your last presupposes something that doesn't fit with ay current physical theory I know of. Pleas try reading Dicklyon's response above with a view to accepting your current beliefs make no sense in physics.The reference desk is not going to provide some fairytale to bolster your worldview. NadVolum (talk) 18:00, 4 December 2023 (UTC)[reply]

I had already read Dicklyon's answer thoroughly. His answer, which was totally different from the other answers given here (except for Baseball Bugs's hint alluded in his question), was actually the answer I had had in my mind before I posted this thread, but I was not sure if this was the correct answer, so I wanted to know if other users thought what I had thought, and that's why I posted this thread, emphasizing the assumption that the photon was independent. Eventually, DickLyon noticed this assumption (as Baseball Bugs did in his question). But if his answer (identical to what I'd had in my mind before I posted this thread) is really correct, then my previous thread becomes more actual. That's why I wanted him to respond to it, and I'm still waiting. (As I responded to him, he can respond back on my talk page, if he doesn't want to respond here to my previous thread). HOTmag (talk) 18:23, 4 December 2023 (UTC)[reply]

You got lots of reasonable answers, there is no cathecism of approved answers and you got ones appropriate to the level of understanding you showed. NadVolum (talk) 21:05, 4 December 2023 (UTC)[reply]

Some of the answers were wrong, while several answers referred to other questions I didn't ask. Other answers were reasonable but still inappropriate to me, because they were imperfect, i.e. the users who gave those imperfect answers ignored my request for further clarifications - me explaining exactly what was still missing in those imperfect answers. Anyway, I didn't want "reasonable" answers, but rather "the best answer". Meanwhile, the best answer I've received was the one I had had in my mind before I posted this thread, and this answer was actually the one you thought I hadn't read. HOTmag (talk) 21:38, 4 December 2023 (UTC)[reply]

How have you decided that they were wrong? How have you decided that they were imperfect? Why do you refuse to consider the idea that your premises and understanding of physics are, well, wrong? --OuroborosCobra (talk) 02:13, 5 December 2023 (UTC)[reply]

Because my analysis is logically inferred from my premises.

On the other hand, I'm sure you can never quote any wrong premise I've relied on. If you think you can quote any such a wrong premise, please quote it, and then I will prove that you haven't read my first response (rather than the second one) to Nadvolum. For the time being you've quoted nothing. HOTmag (talk) 16:24, 7 December 2023 (UTC)[reply]

A slight digression here: A single photon cannot be "seen as yellow", because it can activate only a single photorecptor, and our cone cells correspond roughly to red, green, and blue. --Trovatore (talk) 19:01, 4 December 2023 (UTC) [reply]

Agreed. HOTmag (talk) 19:32, 4 December 2023 (UTC)[reply]

The rods can respond to single photons okay, but no signal is sent to the brain unless about ten or more nearby rods register something within a short time - so normally about a hundred photons are required. And the cones are far less sensistive. NadVolum (talk) 20:57, 4 December 2023 (UTC)[reply]

There is so much light pollution where I am the sky is a dull red and one can walk around at night even without street lights. NadVolum (talk) 21:12, 4 December 2023 (UTC)[reply]

It's a good point. I assumed he just meant the detected photon had a wavelength that we'd consider yellow. But you can't really measure the wavelength of a photon, can you? You can make detectors with different spectral sensitivities, so if you get a hit you know something about the wavelength, but not precise. And there's an uncertainly relationship between energy and time, so the more precisely you know the wavelength, the less precisely you know the time of detection. Ain't physics fun? Dicklyon (talk) 03:01, 5 December 2023 (UTC)[reply]

You can do it reasonably well with a prism and some detectors behind it. NadVolum (talk) 12:36, 5 December 2023 (UTC)[reply]

Stone ~~walls~~ balls do not a prism break ... -- Jack of Oz ^{[pleasantries]} 20:14, 5 December 2023 (UTC) [reply]

For a rather different approach, consider that photon to be one of many from a distant coherent source (a laser in another galaxy). Ignoring quantum effects, that looks locally like a uniform plane EM wave with a definite wavelength that to us is what we'd call yellow. But Maxwell's equations respect special relativity, and that plane wave will be seen blue or red shifted by observers with a velocity relative to us (component in the direction of the wave vector, that is). So, to answer the original question, what's special to us as observers is our velocity component in the direction of the wavevector; if that were different we'd see a different wavelength. Perhaps the confusion in the original question was that OP didn't realize a photon has a wavevector, or momentum vector, that is, a direction as well as a wavelength. Dicklyon (talk) 03:58, 6 December 2023 (UTC)[reply]

Without any data we cannot predict a color as was asked by the OP, but we can certainly better explain why different observers may observe different colors... "...what's special to us as observers is our velocity component in the direction of the wavevector;" Bingo. Our velocity component in the direction of the wave vector is paramount to generalizing what is measured when we approach or recede from a particle-wave with its wave vector aligned with the axis of our motion. It's music to my ears.

Modocc (talk) 09:41, 6 December 2023 (UTC)[reply]

Of course a photon has a wavevector, or momentum vector. I didn't ignore that. But if your new answer is really given from "a rather different approach" (as you claim), then you must assume that the photon is not emitted from any source, but rather is "independent". Otherwise, your new answer will still be the same answer as before. That said, you have to expalin the following fact: On the one hand, you see the photon as yellow, rather than the other color (whether redshifted ot bluehsifted) - as seen by me when I'm on another galaxy (belonging to another frame of reference). My question actually is, why don't our colors interchange, so that I will see the photon as yellow, and you will see it have the other color (whether redshifted ot bluehsifted)? Can you point at anything in the equations that lets us predict that the color you will see must be yellow and the color I will see must be the other color (whether redshifted ot bluehsifted)?

Let me present my question from another viewpoint: On the one hand, the difference between wavevectors is relative, like every vector and ;like every velocity: if I see you approach me - then you see me approach you, and if I see you move away from me - then you see me move away from you; On the other hand, colors are objective: If you see the photon "redder" than how I see it (because I am in a different frame of reference), then I see the photon "bluer" than how you see it. This fact proves that the answer to my question which discusses an objective fact, has nothing to do with the relative wavevector. HOTmag (talk) 16:42, 7 December 2023 (UTC)[reply]

Within the non-relativistic limit v/c≪1, all sorts of wave phenomena, like sound waves, are asymmetric. Consider two observations: one of the sound of a train approaching one and the other of the train receding. The different pitches heard are inherently different and cannot be swapped. Modocc (talk) 19:14, 7 December 2023 (UTC)[reply]

See my comment below, referring both to your response and to DickLyon's response. HOTmag (talk) 19:36, 10 December 2023 (UTC)[reply]

Yes, what Modocc says. Nothing special to photons, light, or relativity, just simple Doppler shift (but in the relativistic case, you get varying wavelength, not just varying frequency). It's not the relative motion between the two observers that matters, so much as the components of their motion in the direction of the wavevector. The difference of those is signed (positive for one, negative for the other), not symmetric. In either the classical or relativistic case, you can pick any non-accelerating reference frame to measure all those things in. I agree that in the wave case you can consider the wave to be "independent" if you acknowledge that it comes from a direction; that's part of what makes it a different approach, but doesn't lead to a different answer. That is, given a wavevector in a reference frame of your choice, we can "predict" the wavelength in any other reference frame. Dicklyon (talk) 00:02, 8 December 2023 (UTC)[reply]

Yes, the rule is as follows: We can predict that: any observers seen by us as moving in the direction identical to the photon's direction, will report they see the photon redder than how we see it, whereas any observers seen by us as moving in a direction opposite to the photon's direction, will report they see the photon bluer than how we see it. That's a well known fact.

This proves that the photon's color has a relative component, i.e. one dependent on the reference frame. However, the photon's color has also an absolute component, not depentent on any reference frame, because we see this photon's color is not the same as that photon's color - even though both photons are watched in the same reference frame.

The question arising now is, whether there is a general rule, involving both components (as opposed to the first rule above involving the relative component only). In this old thread, I tried to present such a general rule, but it refers to a photon emitted by a given system, so that the photon's color seen in its emitting system defines the absolute component of the color, while any other reference frame defines the relative component. However, I can't think of any general rule referring to an "independent" photon. This leads me to DickLyon's initial comment about the impossibility of any "independent" photon. HOTmag (talk) 19:36, 10 December 2023 (UTC)[reply]

It sounds to me like you believe the corpuscular theory of light and James Bradley's ideas about how it should behave. That was back in the 1700's, The luminiferous aether theory then supplanted it till the Michelson–Morley experiment in 1887 showed it didn't work either. The special theory of relativity replaced that in 1905 - and in that there is no need for any innate absolute color of a light photon. NadVolum (talk) 21:10, 10 December 2023 (UTC)[reply]

By "It sounds to me like you [=HOTmag] believe the...", are you referring to my ideas presented in my last response, or to my ideas presented in my old thread mentioned in my last response?

If you are referring to the ideas mentioned in my last repsonse, so please notice I've only claimed that a given photon's color involves two components, being: the absolute component (which makes the difference between a given photon's color and another photon's color when both photons are watched in the same reference frame), and the relative component (which depends on the reference frame and on the Doppler effect). I can't see how these components - which I guess you agree to, have anything to do - with the old fashioned corpuscular theory of light - or with James Bradley's old ideas.

However, if you are referring to my old thread mentioned in my last response, so please notice this old thread only asked whether there existed a justifiable analogy between - a photon's energy whether absoloute or relative (as described above) - and an electron's energy whether absoloute or relative respectively (the electron's absolute energy being its rest mass and the electron's relative energy being its relativistic mass), and again I can't see the relation between - that analogy suggested in that old thread - and the corpuscular theory of light or James Bradley's ideas. HOTmag (talk) 00:39, 11 December 2023 (UTC)[reply]

You assert "...the photon's color has also an absolute component, not depentent on any reference frame, because we see this photon's color is not the same as that photon's color - even though both photons are watched in the same reference frame." It's unclear as to why you are talking about two photons being watched instead of one. In addition, you seem to be inquiring about the existance/nonexistence of a classical picture, like: do ocean waves (of absolute sizes and frequencies) coexist with its dolphins' measurements (either absolute and/or relative in nature with respect to classical simultaneity, distance invariants and velocity-addition (and not rapidity, disjoint time-like and space-like worldlines, etc))? I counter that SR and GR have been our best model to date, but does its utility thus far mean it will remain the best model? Of course not. Modocc (talk) 22:28, 10 December 2023 (UTC)[reply]

As to your question about why I was talking about two photons being watched instead of one: Well, that's because I wanted to point at the absolute component of a given photon's color. Had this color been relative only - i.e one dependent on the reference frame only - without any absoloute component, then we couldn't have explained why this photon's color shown to us from a red rose was not the same as the other photon's color shown to us from a green bean, even though both photons were watched in the same reference frame. In other words, the fact those colors are different even though they are watched in the same reference frame, proves a given photon's color has also an absoloute component - not dependent on any reference frame.

As to your second comment: I'm only pointing, both at an absolute component of the photon's color, and at a relative component of the photon's color, whereas only the relative component depends on the reference frame. These different components have reminded me the absoloute value of the electron's energy (being its rest mass) and the relative electron's energy (being its relativistic mass), so I'm asking whether - we actually notice an analogy between an electron's energy and a photon's energy - once we notice that both kinds of energy have two components: an absolute one and a relative one. HOTmag (talk) 00:41, 11 December 2023 (UTC)[reply]

With relativity, proper mass is reference frame invariant and the fundamental bosons' energies are not, from that perspective and paradigm, thus the analogy breaks down (from my understanding of it). Modocc (talk) 01:28, 11 December 2023 (UTC)[reply]

Please notice, that the photon's "absolute" ("basic"/"fundamental") energy has been defined in my old thread as the photon's energy (=frequency) when measured in the system emitting the photon (according to DickLyon's first response which rules out photons not emitted from any system), just as the electron's absolute ("basic"/"fundamental") energy is defined as the electron's energy (=mass) when measured in the electron's reference frame. Please notice, that according to this definition in my old thread, both the photon's absolute energy and the electron's absolute energy are invariant, because they don't let you choose where to measure this "absolute" energy. HOTmag (talk) 01:48, 11 December 2023 (UTC)[reply]

Ok, so the photon's energy with respect to the emission frame is in accord with mass-energy equivalence and with what is known, which is a safe place to land your query as any other. Still, thanks for reminding me of why I am here (at all). Modocc (talk) 02:11, 11 December 2023 (UTC)[reply]

My point, is not the way I define the electron's absolute energy as its mass when measured in the electron's reference frame, but rather the full analogy between - the electron's absolute/relative energy and the photon's absolute/relative energy respectively - as defined in my old thread. HOTmag (talk) 09:44, 11 December 2023 (UTC)[reply]

Feel free to eject me from this thread entirely if I'm missing the point, but it seems like you are treating the "reference frame" like it is a box containing the observer, that phenomena may enter from "outside". There is a reason it is not called the reference box. The reference frame, to the best of my understanding, is not a physical entity, as stated above—but moreover, is simply an abstraction encapsulating the relativistic effects throughout all spacetime, and assigning it to a discrete object that can be neatly talked about.

The distinction you are making between "absolute" and "relative" components is not warranted—I do not understand what you are isolating as "absolute" when you compare the measured wavelengths of two photons. Both were subject to the same fundamentally relativistic dynamics on their way to your eye. Remsense留 02:08, 11 December 2023 (UTC)[reply]

As opposed to what you ascribe to me, I don't consider a reference frame to be a reference box. I do agree a reference frame is only an abstraction encapsulating the relativistic effects throughout all spacetime.

As to your last comment about the distinction I'm making between "absolute" and "relative" components: Actually when referring to what I call the color's "absolute" component, I'm referring to what makes the difference between a given photon's color and another photon's color - when both photons are watched in the same reference frame. I call this difference an "absolute" one, just to remind - it doesn't depend on the reference frame - but rather on what photon we choose from a set of two different photons. On the other hand when referring to what I call the color's "relative" component, I'm referring to the difference between - a given photon's color when measured in one reference frame - and this photon's color when measured in another reference frame. I call this difference a "relative" one, just to remind - it does depend on the reference frame - rather than on the photon's "identity" (so to speak). To sum up: the color's "absolute" component refers to two different photons whose colors are measured in the same reference frame, whereas the color's "relative" component refers to two different reference frames measuring colors of the same photon. However, when referring to two different photons measured in two different reference frames, we're actually referring to two components of a given photon's color: the color's "absolute" component and the color's "relative" component. HOTmag (talk) 09:44, 11 December 2023 (UTC)[reply]

In my view, even if it is just a definition for convenience, your use of "absolute" and "relative" to label this distinction constitutes a misnomer, one that seems to be doing a lot of the work in confusing all of us.

In fact, there still seems to be an unstated assumption you are making that certain measurements are somehow privileged over others or provide more valuable information—given your attempts with labels such as "fundamental", "basic", "absolute"—the core conceit of relativity is that this is not justified. No point in spacetime is privileged in any given measurement. Remsense留 09:59, 11 December 2023 (UTC)[reply]

In my view, the way we label new concepts is not that important. I give you my permission to replace "absolute" by "delicious" or whatever.

My analysis begins with the "absolute" value (or "delicious" value if you want) of the electron's energy, being its rest mass, i.e. its mass when measured in the electron's reference frame, as opposed to the electron's "relative" energy dependent on the arbitrary reference frame we choose. That said I continue with an analogy between, the electron's absolute/relative energy, and the photon's absolute/relative energy respectively - as defined in my old thread. My original question in that thread was whether this analogy made sense. If you don't want to refer to my old thread in the current thread, you can respond on my talk page. HOTmag (talk) 10:24, 11 December 2023 (UTC)[reply]

HOTmag, your belief that there is an "absolute component of a given photon's color" is perhaps the main source of your confusion. There is no such component. Everything is relative. For example, if we have two stream of photons (or EM plain waves) with two different wavelengths, one longer than the other, there will be another frame in which they are the same wavelength, and another in which the order is reversed (except maybe not for the special case where their wavevectors have exactly the same direction). You can characterize a photon in any reference frame, e.g. the emitter's or the observer/absorber's, or any other, and can get any wavelength you like that way, but there's no absolute. Dicklyon (talk) 05:39, 11 December 2023 (UTC)[reply]

I'm talking about photons moving in the same direction. When referring to what I call the color's "absolute" component, I'm referring to what makes the difference between a given photon's color and another photon's color - when both photons are watched in the same reference frame. I call this difference an "absolute" one, just to remind - it doesn't depend on the reference frame - but rather on what photon we choose from a set of two different photons. On the other hand when referring to what I call the color's "relative" component, I'm referring to the difference between - a given photon's color when measured in one reference frame - and this photon's color when measured in another reference frame. I call this difference a "relative" one, just to remind - it does depend on the reference frame - rather than on the photon's "identity" (so to speak). To sum up: the color's "absolute" component refers to two different photons whose colors are measured in the same reference frame, whereas the color's "relative" component refers to two different reference frames measuring colors of the same photon. However, when referring to two different photons measured in two different reference frames, we're actually referring to two components of a given photon's color: the color's "absolute" component and the color's "relative" component. Don't you agree? Of course, provided that you accept the definition of "absolute" and of "relative". HOTmag (talk) 09:44, 11 December 2023 (UTC)[reply]

Phase diagrams of the noble gases

Does anyone know where I can find up-to-date phase diagrams of the noble gases with the high-pressure phases (e.g. metallisation of Xe)? Double sharp (talk) 13:00, 4 December 2023 (UTC)[reply]

Possible lead-ref: doi:10.1038/nchem.445 (from 2009). DMacks (talk) 14:22, 4 December 2023 (UTC)[reply]

As a failed chemist, I thought 'that has to be fairly complicated': yep: Diamond anvil cell. Nice. MinorProphet (talk) 15:46, 4 December 2023 (UTC)[reply]

Thanks! Looking through the cites at metallization pressure, it seems that experiments are available only for Xe (and that that's the only one that we can metallise with current technology, though Kr should be close). As it turns out (doi:10.1016/0375-9601(89)90503-3) metallisation happens because the outer d-subshells drop down in energy under pressure and become available for bonding: per calculations (and experiment for Xe), Ar, Kr, and Xe first turn from fcc to hcp (with some intermediate close-packed structure for Xe), then metallise. Neon is weird here as it doesn't have a 2d to drop down, so it should require much, much greater pressure (terapascals rather than gigapascals) because it needs to use 3d instead: it also seems to stay fcc all the way.

Helium is interesting. Per doi:10.1103/PhysRevLett.71.2272, solid ⁴He also goes through a fcc-hcp transition; it's just that at cryogenic temperatures fcc is bypassed altogether and hcp is the first solid phase. Apparently it stays hcp pretty much up to the terapascal pressure it takes to metallise (still seems lower than Ne, though).

I can't find anything (even theoretical) about radon. Not that I expected to, though. Presumably it would follow the trend from Ar onward. Double sharp (talk) 17:04, 4 December 2023 (UTC)[reply]

Blimey. My maths is even worse than my chemistry, but I suspect that the mere 150 Gpa to metallise Xe is approximately 15,295,000 tons/m². I imagine you would need something like this to achieve those sort of pressures. MinorProphet (talk) 19:33, 4 December 2023 (UTC)[reply]

December 6

Mixing foods into poison

A fairly common folk belief is that certain combinations of foods are unhealthy - even poisonous - to eat in close sequence to each other. For example, a Newfoundlander friend of mine once warned me not to eat ice cream after eating shellfish as it would give me a stomach ache. And a Turkish friend commented today that eating yogurt and unfresh fish (such as canned fish or smoked fish) would "make poison" in your stomach if eaten together. Curiously, both of these are not too far from the Jewish food laws. I've always assumed these are nothing more than superstitions, but I thought I'd ask the overarching question: is there any combination of foods that, although perfectly healthful on their own, have harmful effects if eaten together? Just to be clear, I'm not talking about eating too much of something or of combinations that might taste gross eaten together, but straightforward: A is fine and B is fine but eating A+B in the same meal could be dangerous.

I guess technically the opposite might be true: not including the sodium in your table salt is unlikely to have health benefits. Matt Deres (talk) 02:49, 6 December 2023 (UTC)[reply]

I googled "foods unsafe to eat together", and several entries arose that are merely about getting too fat from them or whatever (such as burgers and fries), but some possible answers came up, including this one from Hindustantimes.com: "'Banana should not be eaten with milk, curds, or buttermilk because the combination can diminish digestion and produce toxins in the body. Eating this combination can lead to cold, cough, and allergies,' says the Ayurveda expert. Curds can cause swelling and aggravate blood (rakta), pitta, and kapha." I can't vouch for the accuracy of this claim, but it looks like there are at least some possibilities of things not to eat together. ←Baseball Bugs ^{What's up, Doc?} carrots→ 06:44, 6 December 2023 (UTC)[reply]

Banana milkshake is almost a staple of the American diet, but we have seen few reports of a resulting vāta–pitta–kapha imbalance. --Lambiam 08:57, 6 December 2023 (UTC)[reply]

Even more common in the American diet (or at least it was when I was a child) is sliced bananas in a bowl of breakfast cereal (Cheerios, Corn Flakes, etc) and milk.--User:Khajidha (talk) (contributions) 13:56, 6 December 2023 (UTC)[reply]

And on this side of the Atlantic, there's banana custard. Alansplodge (talk) 18:00, 6 December 2023 (UTC)[reply]

What side is that? Wikipedia doesn't reside on any particular side of the Atlantic. Are we supposed to go to your userpage to figure out that you meant the British side? Dhrm77 (talk) 18:20, 6 December 2023 (UTC)[reply]

"a staple of the American diet", followed by "common in the American diet" sort of sets the scene for "And on this side of the Atlantic". Think of an Anglophone country on the opposite side of the Atlantic to the USA, there aren't that many to choose from. Martin of Sheffield (talk) 20:59, 6 December 2023 (UTC)[reply]

While rhubarb leaves are already poisonous, cooking them with baking soda can make them more poisonous. --Lambiam 09:13, 6 December 2023 (UTC)[reply]

I guess it all comes down to chemical reactions. Which happens all the time with food, such as in cooking or digesting. For instance, citric acid in lemon juice will react with some components of tea, possibly the tanins, to form something else, equally harmless. To find 2 foods that shouldn't mix, you need to find 2 naturally occurring chemicals in foods that can react with each other to form a form of poison, or strong toxin. Lots of food already have mild toxins, such as some uncooked beans, rhubarb leaves, potatoes growing above ground (green), some nuts. It might just be a matter of somehow increasing their potency, or decreasing the ability of the human body to deal with them. Dhrm77 (talk) 14:02, 6 December 2023 (UTC)[reply]

One classic example is not strictly a "food" but a well-known traditional medicine: St John's wort. Our article covers the issues quite well. Some of the components may have health benefits but others can, in combination with other foods or medicines, have unwanted and sometimes serious side-effects. Grapefruit can have similar problems. Mike Turnbull (talk) 14:24, 6 December 2023 (UTC)[reply]

Yes, I was curious if grapefruit would come into this as it has many well-known impacts with drugs (our article is not exactly short...). It doesn't seem to have any significant interactions with other foods, though. Matt Deres (talk) 15:35, 6 December 2023 (UTC)[reply]

I noticed years ago that pizza plus ice cream bother my gut more than over-indulging on one or the other alone. Something about the combination of fats, I guess. —Tamfang (talk) 18:27, 6 December 2023 (UTC)[reply]

Eating ink-cap fungi in combination with alcohol makes one ill. This has been utilised to help alcoholics desist in their addiction. See Coprinopsis atramentaria#Toxicity_and_uses. JMCHutchinson (talk) 14:06, 7 December 2023 (UTC)[reply]

(edit conflict) In past years I have gorged on hot cross buns. These usually appear in the shops at the beginning of January, irrespective of the date of Easter (31 March this year, although a table at Wikipedia:Reference desk/Archives/Humanities/2023 November 28#The Reichenau Primer (opposite Pangur Bán) indicates 5 May). I'm not referring to the table that's there now, but to a second table which has disappeared. Recently I've not bought them because they started to make me very ill. Could the culprit be cinnamon, which is made from tree bark? Camphor is also made from trees, and it's extremely dangerous. 92.12.76.4 (talk) 14:10, 7 December 2023 (UTC)[reply]

What a bizarre non sequitur! Do you avoid forks because they're made of steel and so are bazookas? Matt Deres (talk) 18:56, 7 December 2023 (UTC)[reply]

If there were a food combination that worked in the way the OP suggests, then Agatha Christie would be the one who would have used it! Mike Turnbull (talk) 14:33, 7 December 2023 (UTC)[reply]

Not quite "makes poison", but but an interesting related topic is antinutrient. DMacks (talk) 15:11, 7 December 2023 (UTC)[reply]

Wow, this sounds like a question I would ask. And yes, medications can contraindicate other medicines, and some foods like grapefruit does contraindicate. In any event, so far no 1 said antacids, which can react with acidic foods, but likely not in any bad ways. 170.76.231.162 (talk) 19:13, 8 December 2023 (UTC).[reply]

Bird head movements

My bird feeder is usually swinging a little in the wind or from the momentum of birds landing and taking off. Some birds, such as robins, when perched on the feeder (or on a branch) make their heads remain still while their body is rocking along with the perch. Other birds, such as tits, won't bother with this and just allow their whole body to rock. Why do some birds do this and does this behaviour have a name? I am not talking about the back and forth head movements exhibited by walking fowl, nor the side to side movements by raptors to enhance their depth perception. All my Googling only brings up those types of movement. Shantavira|^{feed me} 12:23, 6 December 2023 (UTC)[reply]

My take on this is that the european robin is principally a groundfeeding bird, so, unlike the great and blue tits, which are both woodland birds, they will not be adapted to a moving target. Unfortunately, I've not yet found a source to back up my OR. Mikenorton (talk) 12:42, 6 December 2023 (UTC)[reply]

It's possible that the stabilizing behavior is a necessity in some hovering birds that isn't learned in ground feeding species, per your conjecture and an article I found with less than 20 citations. ^[1] Reconrabbit (talk) 23:04, 6 December 2023 (UTC)[reply]

Might it be that the tits are just too small to bother trying to compensate? NadVolum (talk) 12:45, 6 December 2023 (UTC)[reply]

The great tit is, however, almost exactly the same size and weight as the robin. Mikenorton (talk) 13:28, 6 December 2023 (UTC)[reply]

Probably not the first exchange we've had here about tit size. —Tamfang (talk) 18:53, 10 December 2023 (UTC)[reply]

Head-bobbing in birds, easily observed in walking chickens and pigeons, has the same function as the phenomenon of saccades in human vision, namely to fix the image seen by the eye between movements. When a head-bobber is not walking but swaying, so does its head but in contrary motion so as to fix the image.^[2] "The best examples are seen in ground feeding birds, which need a clear field of view to the side while foraging, in order to recognize small items of food."^[3] This provides a source to back up Mikenorton's hypothesis that the difference lays in one species being a ground feeder while the other is not. --Lambiam 08:35, 7 December 2023 (UTC)[reply]

"Head stabilization" would be the phrase to look for.^[2] Shyamal (talk) 08:49, 7 December 2023 (UTC)[reply]

Thanks, I've tried that specifically for the great tit and blue tit, but found very few results and nothing useful. What would appear to be unusual in these birds is not having noticeable head stabilization during feeding, which seems to be the norm in birds. I'll have to look more carefully at the birds in my garden - I get all three species on a daily basis. Mikenorton (talk) 21:05, 7 December 2023 (UTC)[reply]

References

^ Su, Jian-Yuan & Ting, Shang-Chieh & Chang, Yu-Hung & Yang, Jing-Tang. (2011). Aerodynamic trick for visual stabilization during downstroke in a hovering bird. Physical review. E, Statistical, nonlinear, and soft matter physics. 84. 012901. 10.1103/PhysRevE.84.012901.
^ [https://www.cell.com/current-biology/pdf/S0960-9822(09)00668-X.pdf Bird head stabilization]

Glacier models

Has anyone developed formulas or models that describe the behaviour of a radial ice cap with a given insolation, wind, temperature profile, precipitation and bedrock slope? Jo-Jo Eumerus (talk) 16:11, 6 December 2023 (UTC)[reply]

@Jo-Jo Eumerus, I found a paper on continental ice sheet simulation. Here's a link to it - https://arxiv.org/pdf/1711.09947.pdf Leoneix _(talk) 17:22, 6 December 2023 (UTC)[reply]

This is a model of the Vestfonna ice cap. Mikenorton (talk) 17:28, 6 December 2023 (UTC)[reply]

The summary of this paper tells us that knowledge of basal conditions such as friction is important and that these conditions can be variable. A realistic model is sensitive to such variation in the basal conditions. --Lambiam 08:08, 7 December 2023 (UTC)[reply]

Is there a model or formula for a given friction law? Jo-Jo Eumerus (talk) 17:14, 7 December 2023 (UTC)[reply]

That paper says that it assumes no basal melting and uses a linear friction law, which it describes as a Weertman type sliding law with a Robin type boundary condition, citing Greve and Blatter (2009), which I'm unable to look at the relevant parts of on Google Books. It does say that values for the basal friction parameter are inferred from surface velocity observations, for what it's worth. Mikenorton (talk) 21:56, 7 December 2023 (UTC)[reply]

December 7

"I'm Julian and this is..."

I just came across this website [4]. It explains what the Julian date is, but it also has a "Julian Date Calendar 2023", which is the day of the year mapped on to the date. As there are no weekdays we can't tell whether this is Julian or not, but in 2020 Tesco said this was Gregorian [5]. There is a reference to "food service industries". Who is right? 92.29.73.147 (talk) 13:21, 7 December 2023 (UTC)[reply]

That weird website conflates Julian date and Julian calendar, which are not the same thing. The calendar that we usually use is the Gregorian calendar. The Julian calendar is similar to the Gregorian one in that is uses months and days within the month, just with different rules for leap years, which causes an increasing difference between the two. The Julian date is simply the number of days since 1st January, 4713 BC. What Tesco uses is simply the number of the day within the (Gregorian) year — I don't know whether people call this a "Julian date" (imho they shouldn't...). --Wrongfilter (talk) 13:55, 7 December 2023 (UTC)[reply]

See Julian day#Terminology: "The term Julian date may also refer, outside of astronomy, to the day-of-year number (more properly, the ordinal date) in the Gregorian calendar, especially in computer programming, the military and the food industry". Martin of Sheffield (talk) 15:12, 7 December 2023 (UTC)[reply]

Yes, it's extremely common in the food industry for manufacturers to stamp the "julian code" on products, especially shelf-stable ones where there's no need for a best-before date. They avoid stamping the date itself as customers would balk at perfectly safe food that was "old", so it's very handy that so many vendors use the same methodology as people in the industry can readily read them. Matt Deres (talk) 19:00, 7 December 2023 (UTC)[reply]

A useful concept, but a terrible misnomer. -- Jack of Oz ^{[pleasantries]} 21:35, 7 December 2023 (UTC)[reply]

I'm not sure I see why, unless your astronomy lab has some stock boys inadvertently using their julian date definition where they oughtn't. Matt Deres (talk) 15:54, 8 December 2023 (UTC)[reply]

It's based on the day of the year in the Gregorian calendar. Not the Julian or the Mayan or the Jewish or the Islamic or anything else. The only saving grace is that in 97 years out of 100 the day of the year is always the same in both Julian and Gregorian calendars, and in the other 3 years it's the same for the first 59 days. That's about a 97.79% correspondence, but it's wrong in principle. They've taken the term "Julian day" - which starts with 1 at a point where the 3 cycles of the Julian calendar coincided before historical times, and adds 1 for every subsequent day, continuing forever, not being reset to 1 each year - and applied a similar-sounding terminology to the Gregorian calendar, but without any regard to (a) the incommensurability between the calculation of Julian days and so-called Julian dates, which are reset every January 1, and never exceed 366, or (b) the complete inappropriateness of using the word "Julian" anywhere in the name. That's why it's a terrible misnomer. Also, approximately 97.79%^{[citation needed]} of stock boys have never even heard of the Julian calendar; all they know is "the calendar" (= the Gregorian). -- Jack of Oz ^{[pleasantries]} 17:02, 8 December 2023 (UTC)[reply]

No no no! In 397 out of 400 years the length of the year is the same. For the Revised Julian calendar (now there's a name to play with) the corresponding figure is 893 in 900. For Gregorian v Revised Julian the figure is 3587 in 3600. 2A00:23C7:9CD1:3901:7762:1B1D:468A:BF09 (talk) 17:46, 8 December 2023 (UTC)[reply]

You seem to have misread my post. I said "the day of the year", not "the length of the year". -- Jack of Oz ^{[pleasantries]} 08:07, 9 December 2023 (UTC)[reply]

I see your point, though grocers at least do not use their system as a calendar. Matt Deres (talk) 22:40, 9 December 2023 (UTC)[reply]

Implicitly "hello! I'm Julian and this is my friend Sandy!" . . A dated catchphrase. . dave souza, talk 22:56, 9 December 2023 (UTC)[reply]

Atmospheric pressure changes and water boiling

Do changes in atmospheric pressure, as reported in weather forecasts, affect the boiling point of water at ground level (e.g. increasing or decreasing it, ultimately affecting the boiling time in a kettle)? 212.180.235.46 (talk) 14:23, 7 December 2023 (UTC)[reply]

Any changes in atmospheric pressure (measurable at ground level with, say, a barometer) would affect the boiling point of water according to its phase diagram (refer to Water (data page) for specifics). However, even at the absolute extremes in atmospheric pressure differences, the boiling point would only decrease by ~~4.3 °C (39.7 °F)~~ 4.3 °C (7.7 °F) (at 25.69 inches of mercury (0.859 atm)) or increase by ~~1.9 °C (35.4 °F)~~ 1.9 °C (3.4 °F) (at 32.03 inches of mercury (1.070 atm)). I don't think you would end up saving more than 30 seconds compared to normal atmospheric pressure. Reconrabbit (talk) 14:46, 7 December 2023 (UTC)[reply]

You seem to have made an error in your unit conversions. A difference of 4.3 °C is equal to a difference of 7.7 °F, not 39.7 °F, and a difference of 1.9 °C is a difference of 3.4 °F, not 35.4 °F. You don't add 32 when you're converting a temperature difference, as opposed to an absolute temperature. CodeTalker (talk) 19:14, 7 December 2023 (UTC)[reply]

My bad, I was using the automatic conversions, which assume absolute units. Reconrabbit (talk) 19:24, 7 December 2023 (UTC)[reply]

If you're using the {{Convert}} template, you can use the unit "C-change" rather than "C" to convert a temperature difference. CodeTalker (talk) 19:30, 7 December 2023 (UTC)[reply]

At the top of Mount Everest, the boiling point of water is about 68°C (154°F) due to the decrease in atmospheric pressure with height above sea level. Philvoids (talk) 19:41, 7 December 2023 (UTC)[reply]

December 8

Bee in balloon

If a standard bumblebee was placed inside of a standard party balloon, the balloon was pumped up with air and fully inflated, picked up, and then released in mid-air, could the bee fly into the walls of the balloon and thus move the balloon around the room, as if the balloon was flying around the room? Ignoring any negative effects that the pressure inside the balloon could have on the bee. (I am aware this is a bit of an unusual question.)

Any insights would be greatly appreciated!

User:Heyoostorm^_talk! 04:35, 8 December 2023 (UTC)[reply]

According to the Waikato Domestic Beekeepers Association, a honeybee "can bring back half her weight, i.e. 0.05g, though sometimes she brings back only 0.02g." A generic-looking filled balloon weighed in at 3.5 grams.[6] That seems like too much for one bee to manage. Clarityfiend (talk) 09:18, 8 December 2023 (UTC)[reply]

As the poor bumblebee bounces back, the balloon will get a jolt forward, but it won't move out farther than its diameter. The centre of mass of the system formed by balloon + bumblebee does not budge and however far the balloon moves, it will keep this centre of mass inside. If the bumblebee is much heavier than the balloon, the centre of mass of the system will in fact be inside the bumblebee, so the bumblebee flying will hardly move the bumblebee itself, but mainly cause the balloon to bumble around while remaining confined to a rather limited space. This is only a first-degree approximation, though. The full story is more complex, because the movements of the balloon will be subject to friction with the air in the room, transferring momentum (and causing air currents), so balloon + bumblebee is not a fully closed system. Because of this friction the balloon will make more of a subtle Brownian motion and – purely theoretically – a fully situation-aware bumblebee might be able to impart a bias on this motion. --Lambiam 09:39, 8 December 2023 (UTC)[reply]

But if the bee stings the balloon in frustration – loud pop and the bee flies away. Martin of Sheffield (talk) 09:49, 8 December 2023 (UTC) [reply]

A bee powers its flight by pushing air backwards and down, which pushes itself up and forwards by Newton's 2nd Law of Motion. Here the momentum of the air pushed back is equal and opposite to the bee moving forward, and if the momentum of that air didn't then distribute in all directions (still equal and opposite in all directions btw) it would propagate straight backwards, hit the back wall of the balloon, and bounce forward again (if there's any elasticity in the collision) while the balloon wall is bounced backward. The bee, meanwhile, continues forward to the front wall of the balloon, where is hits with the same momentum and bounces back. Or image the bee pressed up against the front wall of the balloon flapping with all their might -- the backward-moving air will again push off the back wall and counteract the forward force. As Lambiam notes above, this is what a closed system looks like, and we can simplify it by looking only at the center of mass and forces acting outside the system. The bee and balloon can sadly only move relative to each other.

Now let's say it wasn't a bee in the balloon, but a micro spacecraft using some ion thruster where only a the outgoing ions take a long time to all collide with the surrounding air, and they pass cleanly through the balloon. Then your bee-balloon system is no longer a closed system -- your spacecraft pushes out exhaust that travels beyond the balloon walls, giving your spacecraft as much forward force relative to the surrounding air as they have fuel for (and taking the balloon with it when it hits the walls). Note that the ions leaving the balloon-spacecraft system are a loss of mass from the system as well as energy.

(On a mechanical sidenote: from the sounds of it you probably want your balloon floating steady in the air, in which case you'd want it to have equal density (the balloon + the air it contains) which means it has to offset the weight of the balloon by having a bit of helium mixed in the air, or having the outside air be comparatively very cold, or something like that.) SamuelRiv (talk) 11:04, 8 December 2023 (UTC)[reply]

A major correction -- an error of intuition we're frequently making with these simple pedagogy problems (which is why we should work them out thoroughly at all angles before presenting them in a classroom). The bee is pushing on the balloon can moving it very slowly back and forth in the surrounding air -- if the surrounding air (the environment surrounding the closed bee-balloon system) were actually a vacuum, everything I said above about it having no net movement would be correct. However, in cases like this, a relatively small object moving through a fluid slowly (so the fluid looks very viscous, very low Reynolds number), when the bee collides with the front wall of the ballon, the balloon is jolted forward ever so slightly (thanks again Lambian) overcoming the static friction necessary to move the air out of the way, but then is ground to a halt from the dynamic friction of the viscous air. Meanwhile, that rearward motion of the bee and the air, with equal momentum, dissipates into a much more gradual push backward which almost certainly will not be enough to overcome the viscosity of the air and move the balloon backward at all (and even if it did, it would be slower and stopped from friction much sooner). Thus the bee, if it is banging on the front wall instead of pushing on it continuously like a tractor, can ratchet it forward millimeter by millimeter using the viscosity of the air as a brake. SamuelRiv (talk) 12:33, 8 December 2023 (UTC)[reply]

As an aside, when we first study physics or teach intro classes we are encouraged to abstract into the largely frictionless world of Newton's Laws. But for most normal humans, the everyday experience of air and water means that intuitive physics is fluid physics. So perhaps our intro physics classes -- the ones trying to explain that math describes the world we actually see and feel around us (not just throwing a baseball or trains on a track) -- should actually begin with, dare I say, a modernized Aristotle? Carlo Rovelli 2013 argues a compelling case on the subject. SamuelRiv (talk) 12:39, 8 December 2023 (UTC)[reply]

For something similar, once the balloon has landed somewhere, there are Mexican jumping beans, in addition to Hamster balls. Modocc (talk) 11:09, 8 December 2023 (UTC)[reply]

Great examples! A jumping bean, when it jumps on the ground, is of course not a closed-bug-bean-system anymore because the force the bug exerts downward is countered by an opposite normal force from the ground (which can be arbitrarily large, thus the bug can jump with all its might and not merely be pushing its the shell backwards). An analogy with our bee-balloon system would only occur if the bee is flying up against the wall of the balloon (or pushing air against it) that is then adjacent to a hard surface. If the balloon is resting flat on the horizontal ground, and the bee is flying against the wall of the balloon in a horizontal direction (i.e. parallel to the ground) nothing changes from the above. However, if the balloon instead flies at any angle toward the ground, diagonal or whatnot, or if the ground were diagonally sloped, then there would be a contribution of a normal force from the ground, outside the bee-balloon system, and the system could actually start moving.

To take the hamster wheel, rolling works on a similar principle of having a normal force outside the system, which is necessary for a wheel to roll on the ground. Given that, the wheel in the abstract can roll smoothly indefinitely (but of course in the real world it has rolling resistance). SamuelRiv (talk) 11:51, 8 December 2023 (UTC)[reply]

In the limit we can have the bee enclosed in a very thin rubber suit (super 🐝 with 🅱️ on the chest?) and flying the '🎈 balloon' along so there's more to it than just the conservation laws 😁 NadVolum (talk) 12:07, 8 December 2023 (UTC)[reply]

When the bee is encased in rubber, the rubber-encased wings now flap against the outside air and it flies as normal. The point of the exercise of the spherical balloon enclosing the bee is that there is no way for the balloon, with only air and a bee moving slowly inside it, to push the outside air around it with a steady net force in some direction. SamuelRiv (talk) 12:18, 8 December 2023 (UTC)[reply]

A common similar "teaching example" is the motion of a balloon in a closed car as the car accelerates and decelerates. DMacks (talk) 12:52, 8 December 2023 (UTC)[reply]

A close analogy, perhaps easier to visualise, would be if a person inside a rowing boat, entirely sealed by a tarpaulin (so no interaction with the outside air or water, or ability to throw mass out of the boat), were to try to move the boat by pushing on the inside of the bow, or by bumping themself against it. {The poster formerly known as 87.81.230.195} 90.199.215.44 (talk) 14:34, 8 December 2023 (UTC)[reply]

As anyone who has rowed knows, this does significantly move the boat ("check"), and can be used to impart net momentum. Hence my corrected reply above. SamuelRiv (talk) 14:45, 8 December 2023 (UTC)[reply]

If the balloon is on the ground and can slide forward or back, then the trick with static friction works. The bee alternates fast rearward accelerations with slow forward accelerations. The reaction force on the balloon alternates between a large forward force, enough to overcome static friction, and a small rearward force, not enough to overcome static friction, so the balloon slides forward. But that only works for a balloon sliding over a surface. In case of fluids, there's no static friction, no threshold before any movement happens. But there may still be a way to move.

Suppose the bee alternates fast forward moves with slow rearward moves, both over the same distance. By conservation of momentum, the balloon makes the reverse movement: fast rearward moves and slow forward moves, with durations inversely proportional to the speed. The drag will, during each move, apply an impulse proportional to drag times time interval. Assuming the drag increases quadratically with speed (high Reynolds number), this impulse is proportional to speed, so more impulse is applied during the rearward move of the balloon, providing net forward propulsion.

The thing breaks down when the drag is proportional to speed (low Reynolds number). Now the impulse applied during the forward move is of equal magnitude and opposite direction as the impulse applied during the rearward move and there can be no net change of momentum.

In general, a bee in a balloon (or a person on a boat) can provide propulsion using drag, without directly interacting with the surrounding medium but just moving back and forth, if and only if the drag isn't proportional to velocity.

PiusImpavidus (talk) 17:45, 8 December 2023 (UTC)[reply]

Note that for a boat well below the hull velocity, it's a pretty good approximation to say that drag is proportional to speed – except that for an asymmetrical hull the constant of proportionality is different for a forward move compared to a rearward move. PiusImpavidus (talk) 17:54, 8 December 2023 (UTC)[reply]

In a jolt, an object's position undergoes an appreciable change of position in a very small time, as when integrating the Dirac delta function.

Δ s

may be small, but

Δ t

is very small, so

Δ s /Δ t

is – very briefly – quite high. Even with the low Reynolds number of air, if the velocity is high enough we may no longer ignore the nonlinearity of the drag. But the bumblebee needs to keep hitting in the same direction for a net effect, which is why I wrote it had to be fully situation-aware. --Lambiam 18:42, 8 December 2023 (UTC)[reply]

I'm surprised that no-one has mentioned the Birds in a truck riddle yet. Mitch Ames (talk) 02:03, 10 December 2023 (UTC)[reply]

Cylinder capacity

In an un-reffed source, a 6-cylinder engine is claimed to have a swept capacity of 6.191 litres, but the cylinder dimensions are not stated. How might have this particular figure been arived at?
The engine manufacturer definitely used π = 355÷113, thus π/4 = 0.78539823, but other approximations like 3.14 and 22/7 may have been used. The manufacturer almost always increased bore and stroke in 5 mm increments, eg 100 * 110, 100 * 115, 100 * 120, 105 * 130 etc., and only once used a cylinder of 100 * 106 in various 4, 6, 8, and 12-cylinder designs. Big differences in the dimensions (eg 90 * 140) are unlikely, as are oversquare dimensions (eg 110 * 100).

Capacity in litres = (bore² (mm) * stroke (mm) * π/4 * no. of cylinders) ÷ 1,000,000
The closest I can get to the claimed 6.191 litres is with π = 355÷113 and a bore & stroke of 100 * 130 = 6.126 litres: taking π as 3.14 results in 6.123; with 22/7 = 6.128 litres. (I hate doing maths in public, there are probably some errors). Other possible dimensions taking π = 355÷113:

105 * 110 = 5.714 litres

100 * 125 = 5.890

105 * 115 = 5.974

105 * 117 = 6.078 (unlikely, just to check)

100 * 130 = 6.126, closest to 6.191 litres: taking π as 3.14 = 6.123; 22/7 = 6.128

105 * 118 = 6.130 (again unlikely)

105 * 120 = 6.234

105 * 130 = 6.754

Apologies for any mistakes. Any thoughts? MinorProphet (talk) 15:33, 8 December 2023 (UTC)[reply]

If bore and stroke are whole multiples of 1 mm you can only get there (assuming cylinders with a circular cross section) when both bore and stroke are allowed not to be multiples of 5 mm:

(99 mm)² × 134 mm × ((22/7) / 4) × 6 / 1000000 = 6.1914... L.

--Lambiam 20:30, 8 December 2023 (UTC)[reply]

Dimensions don't have to be, and often aren't, whole numbers. I doubt any modern manufacturer takes pi as anything other than whatever their software uses. 21:50, 8 December 2023 (UTC) Greglocock (talk) 21:50, 8 December 2023 (UTC)[reply]

Many thanks for your kind reply, L. Going with the pattern of 5mm increments it seems possible that the dimensions were indeed 100 * 130, which might indicate that some error or fanciful notion has probably crept in to the claimed figure of 6.191 litres. Thanks again for all your replies. MinorProphet (talk) 22:46, 8 December 2023 (UTC)[reply]

All the above calculations seem to assume that the top surfaces of the piston and cylinder are flat. Is it not the case that they are sometimes somewhat domed? This would introduce small variations from purely cylindrical volume calculations. {The poster formerly known as 87.81.230.195} 90.199.215.44 (talk) 22:29, 10 December 2023 (UTC)[reply]

Isn't the swept capacity still the same, by a variation on Cavalieri's principle (divvying up the swept volume lengthwise into many thin columns instead of cutting across into thin slices)? --Lambiam 23:26, 10 December 2023 (UTC)[reply]

Thanks for everyone's continued interest. I have finally found a reliable source which says that the engine in question had a bore & stroke of 105 * 120 mm which results (taking π = 355÷113) in a capacity of approx. 6.234 litres,^[1] one of the possibilities I mentioned in my OP. The engine is a Maybach HL62 (Table not updated yet...) designed in 1935: a technical drawing of the similar HL42 shows flat piston heads.^[2] Later diesel I-6 and fuel-injected V-12s definitely had (concave-)shaped pistons.^[3] MinorProphet (talk) 00:09, 11 December 2023 (UTC)[reply]

References

^ Zima 2021, p. 360.
^ Zima 2021, p. 356.
^ Zima 2021, pp. 362, 364, 369, 370.

Zima, Stefan (2021) [1992]. "Hochleistungsmotoren 1933 bis 1950". In Eckermann, Erik; Treue, Wilhelm; Zima, Stefan (eds.). Technikpionier Karl Maybach - Antriebssysteme, Autos, Unternehmen. [Originally published as 'Hochleistungsmotoren - Karl Maybach und sein Werk', ed. Zima & Treue] (in German) (3rd ed.). Wiesbaden, Germany: Springer. ISBN 978-3-658-25118-5. Edit for link if interested.

Resolved

A space probe to move Asteroid Apophis in 2029?

Will NASA or some companies send a space probe to move and guide the Asteroid Apophis away from Earth in the year 2029 ? 45.58.92.17 (talk) 20:53, 8 December 2023 (UTC)[reply]

Unlikely, given information at 99942 Apophis. Mike Turnbull (talk) 22:32, 8 December 2023 (UTC)[reply]

December 9

Evolutionary adaptation time and survival

Seemingly some complex adaptations, like evolving capsaicin in pepper to deter seed-destroying rodents, require quite a long time (possibly longer than some simple adaptations). If I understand correctly, the successful evolution of such traits require a more or less stable population over time. But in such cases detrimental factors that drive evolutionary adaptation seem to constantly diminish the overall population, thus reducing the probabilistic chances to evolve a beneficial trait - e.g. rodents eating early pre-capsaicin peppers were regularly damaging seeds, thus diminishing evolutionary chances for next-generation peppers - especially considering high reproduction rate of rodents that overwhelms pepper seeds. As the result, there should have been peppers with very few intact seeds which looks unsufficient to evolve a beneficial deterring trait over time.

On the other hand, if I understand correctly, the evolutionary pressure - that is detrimental factors - should be strong and persistent enough to produce such a beneficial trait, otherwise it may not evolve at all. How do organisms overcome this? Brandmeister^talk 09:00, 9 December 2023 (UTC)[reply]

Many detrimental factors are not so strong that they would lead to extinction; they are compatible with a stable population, allowing beneficial adaptations sufficient time to evolve. Other possible adaptations of herbaceous plants to seed-destroying rodents are to grow taller, so that the berries are not in easy reach of ground dwellers, as well as to grow more berries. Such simple adaptations develop in a shorter time, buying more time for more complex adaptations. --Lambiam 11:22, 9 December 2023 (UTC)[reply]

It appears there should be a fine balance in the strength of evolutionary pressure to produce a required trait in that regard - not so strong and not so weak, which, given the multitude of successful adaptations, honestly leads me to the fine-tuning argument. Brandmeister^talk 14:50, 9 December 2023 (UTC)[reply]

Found some papers that suggest this is indeed a challenge in evolutionary biology: [7], [8]. Brandmeister^talk 15:05, 9 December 2023 (UTC)[reply]

My understanding is that an evolutionary pressure killing one in a thousand is quite strong enough to lead to evolution in response. This is why if some gene hangs around that has some detremental effect it is always worth having a good look for what its other effects might be. Evolution normally proceeds on a number of genes at once so single mutations only have a minor effect unless they really do help or harm. NadVolum (talk) 16:59, 9 December 2023 (UTC)[reply]

Correct, most known natural selection pressures are so subtle that they are barely detectable statistically. A 1% selection pressure is considered crazy high. Abductive (reasoning) 20:17, 9 December 2023 (UTC)[reply]

Coumaric

Why are the coumaric acids called "coumaric"? How are they related to coumarin? --Lambiam 11:53, 9 December 2023 (UTC)[reply]

In the 1800s when coumarin was first isolated, one of the standard steps to work out what it was would be to hydrolyse it with e.g. NaOH. In that case, the lactone ring would open, giving the hydroxy cinnamate (although not initially the trans isomer). Naming would then follow, even if the complete structure was not then known. Mike Turnbull (talk) 12:12, 9 December 2023 (UTC)[reply]

December 10

Why is the top quark more massive than the Higgs boson?

I only have a beginner level understanding of particle physics and such, but I was wondering why the top quark had more mass than the Higgs boson? Shouldn’t the Higgs boson be the most massive particle there, since it’s the quantum excitation of the Higgs field? UniversalAlien (talk) 00:19, 10 December 2023 (UTC)[reply]

The Higgs mechanism only explains the massivity of some gauge bosons, which include the quarks but not the Higgs boson itself, since it is a scalar boson. No way is currently known of calculating the masses of the various elementary particles from accepted underlying theory such as the Standard Model and QCD, except that those moving at the speed of light are massless. Theses masses can therefore only be determined by experimental measurement and we have no clue why they are as they are found to be. --Lambiam 11:52, 10 December 2023 (UTC)[reply]

Lambiam, if I can parlay someone else's question into a query of your take on a tangentially related topic: are you someone who finds it worthwhile to ponder the hypothetical significance of dimensionless constants, e.g. the fine structure constant? As a comparative layperson, I find both extreme positions—that such questions are axiomatically meaningless, or that they are of singular importance and most likely "hold the key" to the door to further understanding—to be unsatisfying, but beyond that I can't decide where I fall. Remsense留 00:46, 11 December 2023 (UTC)[reply]

It is conceivable that some future theoretical physicist develops a testable theory of the quantum foam of the vacuum from which the value of the fine structure constant emerges as the limit of a summation over an infinitude of Feynman diagrams. So there might be an answer to question why

\alpha

has the value that is has. An open-minded scientist would not assert that the question is necessarily meaningless, but one should accept the possibility that there is no explanation other than that it is where it happened to become frozen in some symmetry breaking process. --Lambiam 09:06, 11 December 2023 (UTC)[reply]

Tadpoles that never grew up

I remember watching an arte documentary once about alluminium. A German-speaking researcher was interviewed there who showed in his laboratory that tadpoles apparently did not undergo metamorphosis when exposed to aluminium. Does anyone know about this study? 2A02:8071:60A0:92E0:290F:A41:F8B0:B100 (talk) 12:34, 10 December 2023 (UTC)[reply]

A Google scholar search for the obvious keywords gives lots of hits, of which a well-cited article was this one from 1986. That probably isn't your researcher if the documentary was a recent one. In particular, it says the tadpoles took longer to undergo metamorphosis, not that they never did, but that may depend on the aluminium dose. Mike Turnbull (talk) 15:04, 10 December 2023 (UTC)[reply]

Their growth was aluminum foiled. ←Baseball Bugs ^{What's up, Doc?} carrots→ 18:25, 10 December 2023 (UTC)[reply]

Witzelsucht is a sad condition. --jpgordon^{𝄢𝄆𝄐𝄇} 21:18, 10 December 2023 (UTC)[reply]

Can stratospheric water vapour be measured through ice cores?

That is, prehistoric stratospheric water vapor which tends to end up in Antarctic ice cores. Jo-Jo Eumerus (talk) 17:00, 10 December 2023 (UTC)[reply]

I don't think there is a way to determine whether an H₂O molecule in Antarctic ice spent some time in the stratosphere after evaporation before ending up in the ice. --Lambiam 23:16, 10 December 2023 (UTC)[reply]

Yes, ice cores can be used to indirectly infer past stratospheric water vapor levels through analysis of oxygen isotopes in the ice.^[9] -- 136.54.106.120 (talk) 02:24, 11 December 2023 (UTC)[reply]

December 11

What's the product of a collision between a neutrino and an anti-neutrino, when their combined energy is not sufficient for creating the Z boson's rest mass?

Please notice the product of that collision can't be any massless particle, i.e. neither photons nor gluons, because neutrinos only react to the weak force and to the gravitational force, whereas gravitons have never been detected so their very existence is only theoretical for the time being.

Really, I'm not sure, but I do suspect, this kind of collision between matter and antimatter will have no effect: It will be like every "regular" elastic collision between two ping pong balls. Am I right? If I am, then this "regular" collision will be an extraordinary collision between matter and antimatter, right? HOTmag (talk) 01:19, 11 December 2023 (UTC)[reply]

Does it have to be a Z boson? Can't the energy be carried off by photons, possibly with an intermediary step of the creation of a virtual electron–positron pair? --Lambiam 10:21, 11 December 2023 (UTC)[reply]

What about a collision between a neutrino and an anti-neutrino whose combined energy is not suffcient for creating the new pair you suggest? HOTmag (talk) 10:38, 11 December 2023 (UTC)[reply]

The annihilation cross section for the process suggested by Lambiam will be very small, but there is no lower energy threshold when virtual particles are involved. --Wrongfilter (talk) 10:56, 11 December 2023 (UTC)[reply]

Thank you for this clarification. By mistake, I overlooked the word "virtual" in Lambiam's response. Anyway, I still wonder if the first step after any collision between matter and antimatter may be virtual particles that are not gauge bosons. HOTmag (talk) 11:13, 11 December 2023 (UTC)[reply]

[1] Su, Jian-Yuan & Ting, Shang-Chieh & Chang, Yu-Hung & Yang, Jing-Tang. (2011). Aerodynamic trick for visual stabilization during downstroke in a hovering bird. Physical review. E, Statistical, nonlinear, and soft matter physics. 84. 012901. 10.1103/PhysRevE.84.012901.

[2] [https://www.cell.com/current-biology/pdf/S0960-9822(09)00668-X.pdf Bird head stabilization]

[FOOTNOTEZima2021360-3] Zima 2021, p. 360.

[FOOTNOTEZima2021356-4] Zima 2021, p. 356.

[FOOTNOTEZima2021362,_364,_369,_370-5] Zima 2021, pp. 362, 364, 369, 370.

[1]

[2]

[1]

[2]

[3]

@@ Line 377: / Line 377: @@
 ::What about a collision between a neutrino and an anti-neutrino whose combined energy is not suffcient for creating the new pair you suggest? [[User:HOTmag|HOTmag]] ([[User talk:HOTmag|talk]]) 10:38, 11 December 2023 (UTC)
 :::The annihilation cross section for the process suggested by Lambiam will be very small, but there is no lower energy threshold when virtual particles are involved. --[[User:Wrongfilter|Wrongfilter]] ([[User talk:Wrongfilter|talk]]) 10:56, 11 December 2023 (UTC)
+::::Thank you for this clarification. By mistake, I overlooked the word "virtual" in Lambiam's response. Anyway, I still wonder if the first step after any collision between matter and antimatter may be virtual particles that are not gauge bosons. [[User:HOTmag|HOTmag]] ([[User talk:HOTmag|talk]]) 11:13, 11 December 2023 (UTC)