Wikipedia:Reference desk/Archives/Science/2023 December 4

= 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)
 * 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. fiveby(zero) 04:10, 4 December 2023 (UTC)


 * 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)

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)
 * 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)
 * 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)
 * Didn't you just answer your own question? --OuroborosCobra (talk) 13:42, 4 December 2023 (UTC)
 * Where? HOTmag (talk) 13:51, 4 December 2023 (UTC)
 * Reference frames. --OuroborosCobra (talk) 15:46, 4 December 2023 (UTC)
 * 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)
 * 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)
 * 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)
 * 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)
 * 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)
 * 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)
 * 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)
 * 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)
 * 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)
 * 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)
 * 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)
 * 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)
 * 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)
 * 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)
 * 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)
 * 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)
 * 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)
 * None. Modocc (talk) 18:26, 4 December 2023 (UTC)
 * I'm sad. HOTmag (talk) 18:33, 4 December 2023 (UTC)
 * I'm patient. Thanks. Modocc (talk) 19:00, 4 December 2023 (UTC)
 * 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)
 * 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)
 * 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)
 * 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)
 * 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)
 * See my response to NadVolum, below. HOTmag (talk) 18:30, 4 December 2023 (UTC)
 * 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)
 * 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)
 * 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)
 * 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)
 * 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)
 * 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)
 * 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)
 * 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)
 * 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)
 * 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)
 * 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)

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)
 * 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)
 * 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)
 * 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)
 * 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)
 * 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)
 * 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)
 * 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)
 * 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)
 * Agreed. HOTmag (talk) 19:32, 4 December 2023 (UTC)
 * 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)
 * 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)
 * 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)
 * You can do it reasonably well with a prism and some detectors behind it. NadVolum (talk) 12:36, 5 December 2023 (UTC)
 * Stone walls balls do not a prism break ... -- Jack of Oz   [pleasantries]  20:14, 5 December 2023 (UTC)
 * Stone walls balls do not a prism break ... -- Jack of Oz   [pleasantries]  20:14, 5 December 2023 (UTC)

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

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)
 * 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)

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