Talk:Photon/Photons and Mass Debate5

message: It's easy to recognize that there are many really smart people here, who have devoted much time and effort to understanding light and photons.  I think we'll all be happier and more productive, however, if we confine our remarks to physics and the best methods for explaining it to Wikipedia's readers, all the while keeping those two topics distinct.
Believe it or not, I think we all now agree on the physics, specifically that (1) the rest mass of a system is increased when it absorbs energy in any form; and (2) the rest mass of a system is not changed if the form of its internal energy is changed.  One example is that of the equilibrating blackbody box mentioned above.  Perhaps a simpler example would be a box initially filled with a plasma of positrons and electrons and no photons; the electrons and positrons will gradually annihilate each other, forming photons, but the rest mass of the box — as seen from outside — will not change.  This is a good example because the electrons and positrons have rest mass, whereas the photons are massless.
Since (I think) we all agree that this is true, we can safely drop the discussion of the physics, and turn to the pedagogy (next section, stay tuned). Willow 14:15, 11 August 2006 (UTC)
replies: text: But I doubt we all agree that this is true. We now Atti if he's willing to sign off on the idea that a box which contains a positron-electron pair which anihilate, does not change mass, inertia, and weight now that it contains two photons instead. SBHarris 15:18, 11 August 2006 (UTC)
replies: text: Sure , as long as you phrase it correctly to say that now the box contains the energy 2E where E is the energy of one photon and you do not attempt to say that the mass of each photon is E/c^2Ati3414 15:27, 11 August 2006 (UTC)
replies: text: We never said the mass of each photon is E. We said the mass of the 2 photon SYSTEM is 2E.  Which it is, box or not. SBHarris 15:31, 11 August 2006 (UTC)
replies: text: Ati, if you want to be constructive, you need to criticize what the text actually says, and provide an alternative encyclopedic sentence or paragraph that you believe is better.  Criticizing it for what it does not say, calling it "junky", and asking for it to be deleted is not constructive in helping to get to a version that we can all agree is clear and correct.  In this section, you could just say you agree with the physics as present above (if you do), and then move you issues with the pedagogy to the next section.  If you're not willing to do this, you should be written off as uncooperative and the rest of us should move on. Dicklyon 16:48, 11 August 2006 (UTC)
replies: text: I did, all that needs to be done is to take out the parens in "For example, a mirrored box containing a gas of photons, or even a single photon, with total energy E will have greater rest mass (by Δm = E/c²) than if the box did not contain this energy." Ati3414 17:15, 11 August 2006 (UTC)
replies: text: Oh, I see, it's the amount of mass corresponding to the photon energy that is in question.  Is it that the energy is undefined?  Or that the mass added is not energy over c^2?  Or what?  I still remain perplexed abokut how this E/c² bothers you; I thought we were in agreement on the physics, but maybe not. Dicklyon 17:26, 11 August 2006 (UTC)
replies: text: "For example, a mirrored box containing a gas of photons, or even a single photon, with total energy E will have greater rest mass than if the box did not contain this energy." OK? I wrote this for you about 10 times. This is the corrected  statement Ati3414 17:27, 11 August 2006 (UTC)
replies: text: And why do you object to quantifying the amount of mass that the energy E adds? Dicklyon 19:46, 11 August 2006 (UTC)

text: His objection to the inclusion of the parenthetical "(by Δm = E/c²)" seems to be based on the idea that someone might use the incorrect value for E (like using 3E where the correct number is sqrt(8)E for his example).  Ati, is there more to it than that? Should be easy to clarify if that's all it is. Dicklyon 21:21, 11 August 2006 (UTC)
thread_title: A way out of the labyrinth (part 1: physics)

message: ::My try is in place, except I wasn't quite sure what to do about the "Molecular absorbtion" section, which has some now-redundant language.  The "box" section I simply removed, since I think, as Xerces pointed out long ago, it's not really about photons per se. Feel free to put the "box" section back if you think it's useful, but please consider keeping the rest of the edit, including the miscellaneous copyedits (removal of scare quotes, "nonzero mass" rather than simply "mass" when "nonzero" is what's meant, removal of piped links when wiki syntax makes them unnecessary, stuff like that). --Trovatore 07:11, 12 August 2006 (UTC)
replies: text: I think it's OK, though I never understood why the "box" as composite system was a stumbling block.  I made a few edits to it to clarify the relationship, as I understand it, to the more modern formulation that doesn't have the notion of relativistic mass in it.  Please check it. Dicklyon 19:24, 12 August 2006 (UTC)
replies: text: Well, there wasn't anything really wrong with the "box" section; it's just not clear that it belonged in an article called "Photon". It's not really about photons; it's about mass and relativity.  The "composite systems" section, it seems to me, has the same problem. --Trovatore 19:44, 12 August 2006 (UTC)
replies: text: Just the fact that a photon can add mass to a system seems very relevant to me, especially in light of the extent to which some people have a hard time accepting it. In that sense, a photon is the standin for massless particles more generally. Dicklyon 21:03, 12 August 2006 (UTC)

text: Oh, here's another thought -- how about moving "box" to mass in special relativity? It might be a more natural fit there. Note to anyone who does this: Please make sure you note in the edit summary that the text came from this article. Otherwise there's no record of authorship, which is likely a violation of the GFDL. --Trovatore 07:39, 12 August 2006 (UTC)
thread_title: implemented way out

message: I think Ati had some kind of break and was threatening another user and got himself blocked. Thus, we can write whatever we like about the mass of a collection of photons. I suggest we write the truth. Two wrongs don't make a right, but three lefts do. Life is complicated. That's no reason to dumb it down to child level. Photons have no mass, but some residual of their energy shows up AS MASS, in systems which contain 2 or more of them traveling in different directions. That mass can be calculated. There we are. SBHarris 05:43, 14 August 2006 (UTC)
replies: text: I suspect he'd be having a fit over the new section "Transfer of invariant mass between systems", as it makes the mistake he warns against, of essentially attributing the relativistic mass E/c^2 to the photon without being careful about the different frames that make the E values possibly different at emission and absorption.  At least, that's what I think his issues may have at their root.  Anyway, I edited it; someone please check and see if I'm right. Dicklyon 04:57, 16 August 2006 (UTC)
thread_title: Ati no longer with us

message: Hi, I'm OK with not having a full section describing the application of "relativistic mass" to photons, but I do think we need to clarify for Wikipedia's readers which definition of mass is "mainstream", don't you agree?  
Based on the survey of standard physics textbooks I carried out above, the usage in early literature by Einstein, Planck and others of that era, and my own familiarity with the modern scientific literature, it seems fair to say that the "relativistic mass" of a photon is not now — and never has been — a mainstream concept in physics.  I have not found a single instance of it by name, although perhaps others will be able to cite such instances in Phys. Rev. or similar sources.  So that's why I'm uncomfortable with calling it an "older concept, not much used anymore"; that phrasing suggests that it was once a mainstream concept that has now fallen from favor.  Based on my reading, it was never even mainstream to apply  "relativistic mass" to massive particles such as electrons (a handful of physicists adopted that approach), to say nothing  of massless particles such as the photon.
The FAQs cited at mass in special relativity and the quotes from textbooks contained therein, also support this viewpoint.
However, I'm willing to listen to other viewpoints — particularly if they cite scientific references! ;)  Perhaps my wording was strong, but I do favor being accurate at the expense of a few extra words, as I think you do, too, from what you said above.  Let's find a good compromise. :) Willow 23:06, 15 August 2006 (UTC)
replies: text: The wording of the footnote as of this writing (and even the mere fact that the text is in a footnote, as opposed to the main text) should be adequate to indicate which one is "mainstream". The fact that physicists are not very fond of the usage is not really a fact about photons; it's a "meta" sort of consideration, and distracting. It would be different if it actually made a difference whether you describe things in terms of invariant mass or relativistic mass, but since it doesn't, let's just describe the two usages and be done with it. What readers do need to know is what unqualified "mass" means in scientific literature, but that is adequately covered by the current text. --Trovatore 23:17, 15 August 2006 (UTC)
thread_title: Wording of footnote, serenely ;)