Mass of Photon: Consequences & Experiments - L.C. Tu et al (2004)

[Nereid]

If the photon were found to have a non-zero mass, experimental physicists would go wild! (not an original point, Zapper made it much earlier).

At least it would point to some potentially very, very interesting 'new physics', and within a decade or three no doubt some other quite curious or intriguing things would be discovered by the experimentalists. The most frustrating scenario would be if all this 'new physics' remained at the very edge of detectability, with large error bars, and results that were really not much more than hints.

The exciting thing is that there's absolutely no way to predict how it would turn out - a dramatic new world that makes the early years of last century look like pure tedium? some almost trivial, subtle modifcation to existing theories that ties up all loose ends? pure validation for one of today's 'fringe' ideas? a slow, hard slog that eventually leaves either M-Theory or LQG the last theory standing?

 

[Andrew Mason]

Special Relativity rests on two postulates as well as many currently credible background assumptions.

No assumptions - other than the two postulates.

Not so long ago neutrinos were taken as massless and now non zero masses are being measured. If that were to happen to light, light would no longer have the maximal speed; but, as another poster pointed out, the postulate of a maximal speed would remain intact.

If photons have rest mass the speed of light would depend on the speed of its source. So it would destroy Einstein's second postulate.

Einstein did not postulate that c is the maximum speed attainable. He postulated that the speed of light depended only upon properties of space and so was independent of the motion of its source. He showed how this postulate with the principle of relativity leads to the conclusion that the speed of light cannot be exceeded. The speed of light can be exceeded if an inertial frame of reference can be attached to a photon. So the discovery of photon rest mass would negate the postulates of relativity.

Consequently the principle of relativity is logically independent from the speed of light and remains intact no matter what speed light has.

SR is inextricably tied to the speed of a photon in free space being the same for all inertial observers. This would be completely destroyed if photons have rest mass, no matter how small an amount. The essential conclusion of SR is not that there is some maximum speed. It is that the speed of a photon cannot be exceeded. So I think your suggestion is incorrect.

AM

 

[Andrew Mason]

If the photon were found to have a non-zero mass, experimental physicists would go wild! (not an original point, Zapper made it much earlier).

At least it would point to some potentially very, very interesting 'new physics', and within a decade or three no doubt some other quite curious or intriguing things would be discovered by the experimentalists. The most frustrating scenario would be if all this 'new physics' remained at the very edge of detectability, with large error bars, and results that were really not much more than hints.

The exciting thing is that there's absolutely no way to predict how it would turn out - a dramatic new world that makes the early years of last century look like pure tedium? some almost trivial, subtle modifcation to existing theories that ties up all loose ends? pure validation for one of today's 'fringe' ideas? a slow, hard slog that eventually leaves either M-Theory or LQG the last theory standing?

I agree completely. I think the theoretical physicists would go wild too.

And I should say that agree with the fundamental point that Zapperz was making at the beginning of this thread, which is that any theory, relativity included, is subject to physical evidence, so experimental testing is always valid. I just think he was understating a little the impact the discovery of photon mass would have.

AM

 

[ZapperZ]

I agree completely. I think the theoretical physicists would go wild too.

And I should say that agree with the fundamental point that Zapperz was making at the beginning of this thread, which is that any theory, relativity included, is subject to physical evidence, so experimental testing is always valid. I just think he was understating a little the impact the discovery of photon mass would have.

AM

No, I'm not trying to understate anything. I'm trying to counter your argument that any discovery of the photon mass, no matter how "weak" the violation is, will AUTOMATICALLY result in the "overhaul" of SR. I disagree with this "automatic" thing. I brought up a few examples where fundamental violation of perceived symmetry of our universe did not require any such overhaul.

Now I'm not saying there won't be one. I'm saying you can't tell based on previous similar instances - after all, the history of such events are all we have to go by. Moreover, the current form of SR already works! That is the biggest "evidence" we have right now that this form has a lot of validity to it! It is the claim that automatically, SR must be over haul with any kind of photon mass discovery. That is what I was arguing against.

Zz.

 

[Rob Woodside]

No assumptions - other than the two postulates.
Reply:
Where does the notion that space-time is made of events come from? Point particles? Worldlines?, Extended bodies?, World tubes?, etc. Then there are the mathematical assumptions behind a manifold that is supposed to descrbe space-time. If those postulates were the only assumptions, the theory would be vaccuous. Your first postulate uses the notion of inertial frame ("all inertial frames are equivalent"), but never tells you what an inertial frame is. The second postulate doesn't say what light is. Without some major assumptions the postulates read: 1)All glorps are equivalent; 2) The speed of zilch in a glorp is independant of the emitter or absorber. People are always using implicit assumptions and should be aware of it.

Quote = Andrew Mason
If photons have rest mass the speed of light would depend on the speed of its source. So it would destroy Einstein's second postulate.

Reply:
Quite so. Are we frozen in history with only Einstein's words to guide us or has special relativity developed in any way in the last century? What is the second postulate really about? If you think it is about light and it turns out experimentally that light has a rest frame, then the second, not the first, postulate fails. Einstein was trying to give mechanics and electromagnetism the SAME space-time. The first postulate was a boulder of truth that came from mechanics and the second from electromagnetism under the natural (since Maxwell) assumtion that light was electromagnetic in origin. Instead of "light" Einstein could have used "changes in the electromagnetic field". Today we could use "changes in space-time curvature" on a flat background, but Einstein's point was to put mechanics and E/M on the same footing. That "something's" speed in an inertial frame is a constant independant of its emitter or absorber seems like a tame and testable assumption and that is probably why Einstein chose it. Logically that assumption leads to the "something" having a maximum invariant velocity. Why not take that as the second postulate? Then if light does have a rest frame, the well tested special relativity remains valid.

 

[ohwilleke]

The argument Rob is trying to make, is essentially similar to an aether argument. Certainly, no one disputes that photons do not necessarily travel at the speed c in a non-vacuum. This is no big deal. We have c which is commonly called the speed of light in a vacuum, and use it in theories, and life goes on, even thought light doesn't always move at this speed as we observe it. If what seemed to be a vacuum was not actually a vacuum, but an aether, there would be a discrepency between "c" and the speed of light. (Indeed the terminology "permissivity of free space" for a key electromagnetic constant implies such an interpretation, although the aether concept that underlies the terminology is no longer in vogue.)

The trouble is that unlike the neutrino, the speed of light in a vacuum flows over via Maxwell's Equations (at the classical level) into essentially all properties of electromagentic phenomena. It is a keystone. And, this keystone is not easily divorced from the physical phenomena of traveling photons because photons are the mechanism by which Maxwell's Equations are effective. If photons have mass, then electrodynamics laws would work differently than they do, and electrodynamics is the most rigorously empirically tested laws known.

 

[Rob Woodside]

The argument Rob is trying to make, is essentially similar to an aether argument.
Reply:
Arghh! You put words in my mouth. My belief is that light has no rest frame. This will not change until a couple of independent and credible experimental groups publish otherwise in a refereed journal. Who knows what would follow from such a finding. Speculating wildly, space-time could loose its Lorentz invariance. I do not think this is inevitable as Andrew Mason does. It should be clear that local inertial frames can still have Lorentz invariance with a massive photon. That was all I was trying to say.

 

[jcsd]

I agree completely. I think the theoretical physicists would go wild too.

And I should say that agree with the fundamental point that Zapperz was making at the beginning of this thread, which is that any theory, relativity included, is subject to physical evidence, so experimental testing is always valid. I just think he was understating a little the impact the discovery of photon mass would have.

AM

Andrew it's just that your making too many assumptions about would happen, cleraly something would change, but it's not necessarily what you think would change. (which is basically what Rob Woodside has said).

No invariance is absolutely sacred, if that was held true we'd never of replaced Gallielan invaraince with Lorentz invaraince, so it could conceivably turn out that future theories are not Lorentz invariant in some fundamental way (I think I remember doubly-special relativity isn't Lorentz invaraint, but from what I understand it is just a toy theory really). Experimentation tells us though that any theory that wants to explain nature must approximate to a Lorentz invaraint theory with a very high degree of accuracy in a very, very wide range of physical situations.

 

[Andrew Mason]

If those postulates were the only assumptions, the theory would be vaccuous.

He had evidence that the laws of electrodynamics were valid in at least one inertial frame. He did not have to postulate that. Since he did not have evidence that these laws were valid in all inertial frames, he had to assume it to be true, without proof, in order to develop his theory.

Your first postulate uses the notion of inertial frame ("all inertial frames are equivalent"), but never tells you what an inertial frame is.

An inertial reference frame is a defined term: the frame of reference whose origin is an observer experiencing no acceleration. No postulate needed.

The second postulate doesn't say what light is.

The laws of physics describing the electromagnetic nature of light had been verified by experiment. He did not have to postulate what light was. He could rely on evidence.

Are we frozen in history with only Einstein's words to guide us or has special relativity developed in any way in the last century? What is the second postulate really about? If you think it is about light and it turns out experimentally that light has a rest frame, then the second, not the first, postulate fails.

Either the first postulate fails and we go back to the concept of 'luminiferous aether" or we modify Maxwell's equations so that they take into account the the absolute motion of the source. I don't see any other way around it. Either way, the laws of electrodynamics become frame dependent and the concept of equivalence of all inertial frames goes out the window.

That "something's" speed in an inertial frame is a constant independant of its emitter or absorber seems like a tame and testable assumption and that is probably why Einstein chose it. Logically that assumption leads to the "something" having a maximum invariant velocity. Why not take that as the second postulate?

He was not postulating that. It is not such an obvious thing to assume. One usually postulates something that is reasonable and then sees where it leads. He was postulating that the speed of light in a vacuum depends only upon the properties of space and not upon the speed of the source. This was reasonable and was supported by the Michelson Morley experiment, for example.

If that postulate is correct, and if the first postulate is correct, the properties of the vacuum which determine the speed of light are valid in all inertial frames. Hence the speed of light is invariant in all inertial frames. This necessarily means that no inertial observer can ever reach the speed of a photon - the photon will always appear to be traveling at c relative to every inertial frame of reference.

Then if light does have a rest frame, the well tested special relativity remains valid.

I don't see how that follows from your postulate. In order for light to have an invariant speed in all inertial frames, it cannot be at rest in ANY inertial frame. If the photon has rest mass or inertia, the photo defines an inertial frame in which it is at rest. By definition then, it cannot be traveling at speed c relative to that frame. It would also necessarily follow that the rules for translating between inertial frames apply to the frame of reference of the photon and this means that the speed of light would be different in different inertial frames.

AM

 

[Andrew Mason]

Yes, but your not asking yourself whether the postulates can be altered in minor amost superficial ways, to make them independent of light or any theory of light, the answer is yes as long that theory of light is Lorentz covaraint.

And just how would you maintain Lorentz covariance if light has a rest frame? The laws of physics would predict results for the same event that are different in the inertial frame of the photon than in any other coinciding inertial frame (ie, the photon would not move in the rest frame of the photon but would move in the co-inciding frame). Would that not destroy Lorentz covariance?

AM

 

[donjennix]

AM seems to be totally correct!

 

[jcsd]

And just how would you maintain Lorentz covariance if light has a rest frame? The laws of physics would predict results for the same event that are different in the inertial frame of the photon than in any other coinciding inertial frame (ie, the photon would not move in the rest frame of the photon but would move in the co-inciding frame). Would that not destroy Lorentz covariance?

AM

No not necessarily! Does the fact that an electron is at rest in one frame but moving in others mean that the electron cannot be described by a Lorentz covaraint theory? The answer is no! Your giving the photon a special role that it may not necessarily have.

 

[selfAdjoint]

If the postulate that all inertial frames see the same speed of light is abandoned you don't have special relativity anymore. And if the photon were to have a rest frame it could see its own speed as zero while others saw it as moving, so the postulate would have to go.

 

[jcsd]

Selfadjoint, my point is that that's only ONE formualtion of SR, we could of quite easily of refrered to any massless particle or just postulated the existence of a finite maximum speed.

 

[jcsd]

Put it this way: forget about the postulates of relativity and where they came from, does there exist a proof that the any possible em theory where the photon has a non-zero rest mass is incompatible with SR?

 

[Andrew Mason]

No not necessarily! Does the fact that an electron is at rest in one frame but moving in others mean that the electron cannot be described by a Lorentz covaraint theory? The answer is no! Your giving the photon a special role that it may not necessarily have.

There is a big difference between an electron, or any massive object, and a photon. If Maxwell's equations are valid in all frames of reference, the speed of a photon is frame independent. There is no law of physics that requires the speed of an electron to be frame independent.

I did not give the photon a special role. Nature (and Einstein) did.

AM

 

[Andrew Mason]

Selfadjoint, my point is that that's only ONE formualtion of SR, we could of quite easily of refrered to any massless particle or just postulated the existence of a finite maximum speed.

What other massless particle could you use? SR says that all particles with 0 rest mass travel at the same speed, c. Gluons are thought to have 0 rest mass, but they also don't travel very far so their speeds are hard to measure. Neutrinos appear to have rest mass so you can't use those. The photon (of any energy) is all there is.

It is not just a matter of postulating a finite maximum speed. Ultimately it has to be based on evidence. The existence of c as the maximum speed is a simple, logical consequence of observed fact that the speed of light does not depend on the speed of its source but only on properties of space that are frame independent. Since light must move at speed c in all frames of reference, speed c can never reached.

AM

 

[jcsd]

There is a big difference between an electron, or any massive object, and a photon. If Maxwell's equations are valid in all frames of reference, the speed of a photon is frame independent. There is no law of physics that requires the speed of an electron to be frame independent.



I did not give the photon a special role. Nature (and Einstein) did.

AM

We are talkign about if a photon does have mass so the distinction is no longer there. Maxwell's equations do not describe a massive photon they must be modified, what I am arguing against is the pre-emptive nature of what you think those modifications would be (though thie possible forms have been studied for exmaple in http://www.iop.org/EJ/abstract/0034-4885/68/1/R02 (but special relativity has always been assumed to still hold AFAIK).

What it comes down to is this: you are saying null geodesics are important becasue photons travel along them, whereas I am saying that these interesting properties of the photon comes from the fact that it travels along a null geodesic.

 

[jcsd]

What other massless particle could you use? SR says that all particles with 0 rest mass travel at the same speed, c. Gluons are thought to have 0 rest mass, but they also don't travel very far so their speeds are hard to measure. Neutrinos appear to have rest mass so you can't use those. The photon (of any energy) is all there is.

I'm not talking about practical necessity I'm talking about theoretical necessity. Imagine the existence of some other massless particle let's call it the hypethicon 9as indeed special rleativty places no limit on the varities of massless particles), now there called be an alien race in some distant part of the universe who have formulated speical relativity around the Lorentz invaraince of the speed of the hypethicon without any refernce to the photon. Does the human theory of special relativity depend on whetehr the hypethicon has mass? Does the Klargon theory of special relativity depnd on whether the photon has mass?

It is not just a matter of postulating a finite maximum speed. Ultimately it has to be based on evidence. The existence of c as the maximum speed is a simple, logical consequence of observed fact that the speed of light does not depend on the speed of its source but only on properties of space that are frame independent. Since light must move at speed c in all frames of reference, speed c can never reached.

AM

But again your seeing mixing up the historical cirvcumstances with theoreticla necessities, let's say before special relativity had been devloped we had devolped travel at signifcant fractions of the speed of light, we may of noticed the way that spaceships constantly accelerating asympotically approached c, or we may of observed effects such as time dialtion or Lorentz-Fitzgerald contraction.

The keyb point being that special relativity and infact theories in general can be derived using different sets postulates.

 

[ZapperZ]

It is not just a matter of postulating a finite maximum speed. Ultimately it has to be based on evidence. The existence of c as the maximum speed is a simple, logical consequence of observed fact that the speed of light does not depend on the speed of its source but only on properties of space that are frame independent. Since light must move at speed c in all frames of reference, speed c can never reached.

AM

But again, as I have pointed out, and as jcsd is also trying to get across, is that it isn't AUTOMATIC that SR needs to be overhaul if we ever discover a non-zero photon mass. Again, let me reiterate that I do NOT expect to see such a thing especially at the macroscopic scale. There are simply waaaaay to many experimental evidence to indicate that photons are massless.

However, once you get close to the Planck scale, anything can happen! Why? Because once you get close there, then our notion of how we define a LENGTH comes into play. Clearly, it is a valid question on how we actually measure the speed of anything! So the issue here isn't the fact that a photon has mass, and therefore, moves at slightly lower than c, but rather the uncertainty in our MEASUREMENT will cause an apparent shift in a photon's property. The "vacuum" dispersion curve can easily NOT look like the ordinary dispersion of photons in vacuum. We have already seen this for ordinary particles in many-body interactions. An electron can appear to have a mass 200 times its bare mass! Again, the issue at hand is that at such a scale, our methodology in determining the quantity called "speed" will affect our measurement.

This is what I called a "weak violation" that occurs only in certain circumstance at certain times. Similar to CP violation which does NOT require us to overhaul all our fundamental symmetries of the universe, any possible violation of Lorentz symmetry at the Planck scale will be VERY weak and very confined to such scale in such a way that it certainly requires no overhaul of SR.[1] This is certainly a plausible scenario. But the issue here isn't trying to validate this possible violation. The issue here is that by presenting such a scenario, one can already see that any variation in c and the photon mass do NOT necessarily require a complete overhaul of SR. You still have your cherised postulates. It's just that, when "space" and "time" are not well-defined concepts, you will have a trouble with preserving your Lorentz symmetry.

Zz.

1. V.A. Kostelecky, ed., "CPT and Lorentz Symmetry I" (World Scientific, 2002).

 

[Nereid]

Just another little comment ... what is 'a photon'? It's as much a theoretical construct as 'mass'. The3-decades-after-the-discovery-of-the-non-zero-'photon'-mass resolution may be that the concept of a 'photon' was off-base ... maybe it is, 'in fact', an illusion (a beautiful but complex superposition of 10^600 different types of 10^20 dimensional entities, interacting in a breath-takingly elegant fashion, describable by math that's today only vaguely known to a dozen or so folk engaged in what everyone else thinks of as just too arcane to even comment on).

Also, if the 'photon' has mass, then EM theory will need some revision. Also2, if SR needs some modification, then so will GR ... maybe leading to an entirely different view of the first microsecond of the Big Bang?

 

[Andrew Mason]

But again, as I have pointed out, and as jcsd is also trying to get across, is that it isn't AUTOMATIC that SR needs to be overhaul if we ever discover a non-zero photon mass.

Well, let me put it this way. Since
1.the SR postulates would have to be replaced,
2. the speed of light would be frame dependent and
3. the concept of a limiting speed (c) would have to be changed from the speed of light to the speed which light and everything else can approach but never reach,

our understanding of WHY there is a limiting speed at all and why relativistic effects occur (and which you see every day in your work at the Advanced Photon Source (synchrotron)) would be lost. The insight provided by SR would be lost.

However, once you get close to the Planck scale, anything can happen! Why? Because once you get close there, then our notion of how we define a LENGTH comes into play. Clearly, it is a valid question on how we actually measure the speed of anything! So the issue here isn't the fact that a photon has mass, and therefore, moves at slightly lower than c, but rather the uncertainty in our MEASUREMENT will cause an apparent shift in a photon's property. ...

It's just that, when "space" and "time" are not well-defined concepts, you will have a trouble with preserving your Lorentz symmetry.

I agree that effects observed on the Planck scale as you describe would not invalidate SR. But the existence of such effects would also not imply that all photons have rest mass.

AM

 

[ZapperZ]

I agree that effects observed on the Planck scale as you describe would not invalidate SR. But the existence of such effects would also not imply that all photons have rest mass.

AM

Correct. Only SOME photons will have "rest mass"! These are the ones we are "measuring" over the Planck scale. The rest of the photons that we are observing in the macroscopic universe are behaving the way we are familiar with.

In NONE of the papers postulating violation of the Lorentz invariance was there ever any mention of overhauling SR. In fact, none of them even claim that the discovery of such violation would require SR to be modified.[1,2] Again, I am not arguing for the validity of these idea. I am arguing the fact that even when variation to such properties of the photon/Lorentz transformation are proposed, SR is still valid! If such a scenario can exist and be thought of, then the claim that SR needs to be automatically overhaul is not correct.

Zz.

1. V.A. Kostelecky and S. Samuel, Phys. Rev. D v.63, p.111101 (2001).
2. V.A. Kostelecky and R. Potting, Phys. Rev. D v.41, p.3923 (1995).

 

[Andrew Mason]

In NONE of the papers postulating violation of the Lorentz invariance was there ever any mention of overhauling SR. In fact, none of them even claim that the discovery of such violation would require SR to be modified.[1,2] Again, I am not arguing for the validity of these idea. I am arguing the fact that even when variation to such properties of the photon/Lorentz transformation are proposed, SR is still valid! If such a scenario can exist and be thought of, then the claim that SR needs to be automatically overhaul is not correct.

Of course you could simply insert a correction term into SR. A tweaked SR would no doubt 'work'. While it would still be useful in predicting results, as a theory to explain nature, it would provide little insight.

... I am reminded of Lorentz' attempt to explain the Michelson Morely result by an arbitrary tweak to Newtonian mechanics (suggesting that motion physically shrinks distances in the direction of motion by \sqrt{1-v^2/c^2}^{-1}). But he could offer no fundamental explanation why this would be so. The importance of Einstein was that he explained the result.

AM

 

[ZapperZ]

Of course you could simply insert a correction term into SR. A tweaked SR would no doubt 'work'. While it would still be useful in predicting results, as a theory to explain nature, it would provide little insight.

... I am reminded of Lorentz' attempt to explain the Michelson Morely result by an arbitrary tweak to Newtonian mechanics (suggesting that motion physically shrinks distances in the direction of motion by \sqrt{1-v^2/c^2}^{-1}). But he could offer no fundamental explanation why this would be so. The importance of Einstein was that he explained the result.

AM

But we're NOT arguing about "insight". We're arguing your assertion that by simply having ANY non-zero mass (no matter how weak, or under what circumstances it appears), that automatically, SR cannot be salvaged and must be overhaul. I have repeated this many times that this is what I disagree.

What bothers me here is that it appears you haven't read the paper that I cited that started this thread. If you have, you would have immediately realized that there ARE formulations and adjustments made to both Maxwell equation and SR to allow for such mass. The Proca equations have been mentioned here in this thread, and in the paper in question:

The effects of a nonzero photon rest mass can be incorporated into electromagnetism straightforwardly through the Proca equations, which are the simplest relativistic generalization of Maxwell’s equations.

Furthermore:

γ Phase invariance (U(1) invariance) is lost in Proca theory, but the Lorentz gauge is automatically held, and this is indispensable to charge conservation, i.e. the Lorentz condition becomes a condition of consistency for the Proca field.

Again, I will repeat. The issue here isn't the validity of any of these things. The issue here is the claim that any such discovery on the photon mass will automatically imply an overhaul of SR, and that Lorentz symmetry cannot be salvage. If you have read this paper that started this thread, you would not have made such knee-jerk statement, because this clearly show a possibility that none of those overhauls are called for.

Zz.

 

[jcsd]

Of course you could simply insert a correction term into SR. A tweaked SR would no doubt 'work'. While it would still be useful in predicting results, as a theory to explain nature, it would provide little insight.

... I am reminded of Lorentz' attempt to explain the Michelson Morely result by an arbitrary tweak to Newtonian mechanics (suggesting that motion physically shrinks distances in the direction of motion by \sqrt{1-v^2/c^2}^{-1}). But he could offer no fundamental explanation why this would be so. The importance of Einstein was that he explained the result.

AM

Is simply restricting the set of possible postulates of SR really altering SR in any important way? I would sya not.

The explanatory power of physicasl theories lies entirely in predicting results (Lorentzian and special relativity were not strictly the same, or at least that's what I've lawas beeen led to believe).

 

[Rob Woodside]

If the postulate that all inertial frames see the same speed of light is abandoned you don't have special relativity anymore. And if the photon were to have a rest frame it could see its own speed as zero while others saw it as moving, so the postulate would have to go.

Reply:
Try replacing the second postulate with the demand of a maximum invariant speed and say nothing about light. This produces a purely mechanical special relativity that just happens to give the space-time arena required by electromagnetism- either Maxwell theory OR Proca theory.

Originally Einstein wanted to call S.R. the German equivalent of "Invariant Theory" for the invariance of light speed as required by Maxwell theory. There was not then and there is not now any physical reason to suspect that light has a rest frame. Clever theorists like Proca can play a "what if" game and people can rummage around inside error bars looking for proof. The situation is comparable to abandoning a global vector potential and looking for Dirac monopoles.

 

[Rob Woodside]

There is a big difference between an electron, or any massive object, and a photon. If Maxwell's equations are valid in all frames of reference, the speed of a photon is frame independent. There is no law of physics that requires the speed of an electron to be frame independent.

I did not give the photon a special role. Nature (and Einstein) did.

AM

Reply: Yes you did! You were claiming that if the photon had mass then BOTH postulates of Special Relativity were wrong. The great divide between massive and massless objects would not necessarily disappear if the photon had mass.

 

[Andrew Mason]

But we're NOT arguing about "insight".

Well I guess that is where we differ. I am. If a theory loses its ability to explain WHY things are the way they are, we need another theory.

You could say that Ptolemy's cycloids were a valid theory of the solar system because they 'worked'. But as a theory it offered no insight into why planets and the sun moved that way. Ptolemy needed an overhaul.

What bothers me here is that it appears you haven't read the paper that I cited that started this thread.

Your link gives me "access forbidden" so if you want me to read it, you'll have to give me a way of accessing it. Besides, you explained its essential point. The important point is the null result for the rest mass of the photon.

If you have read this paper that started this thread, you would not have made such knee-jerk statement, because this clearly show a possibility that none of those overhauls are called for.

I can assure you it is not a 'knee-jerk' reaction. It is based on about 35 years of thinking about and studying relativity. Now I may have not learned anything in those 35 years, but that is what my reaction is based on. I guess we will just have to disagree on the meaning of 'overhaul'.

I have looked at the very recent paper cited by jcsd, BTW, on the "Mass of the Photon" and find this passage illuminating:

"In the limit \omega \rightarrow \infty, the group velocity will approach the constant c, which is consistent with Einstein's assumption that there is a unique limiting velocity c for all phenomena. Therefore, a new postulate must be introduced in order to restore the features of special relativity theory for photons of nonzero mass. The postulate is as follows (Goldhaber and Nieto 1971b): given any two inertial frames, the first moving at velocity v with respect to the second, there exists a frequency \omega_0 depending on |v| and the desired accuracy \epsilon, such that any light wave of frequency greater than \omega_0 will have a speed between c and c - \epsilon in both frames.

A nonzero photon mass implies that the speed of light is not a unique constant but is a function of frequency. In fact, the assumption of the constancy of the speed of light is not necessary for the validity of special relativity, i.e. special relativity can instead be based on the existence of a unique limiting speed c to which speeds of all bodies tend when their energy becomes much larger than their mass (Kobzarev and Okun 1968, Goldhaber and Nieto 1971b). Then, the velocity that enters in the Lorentz transformation would simply be this limiting speed, not the speed of light."​

The authors say the validity of SR can maintained by changing the assumptions behind SR (BTW, Einstein did not assume the constancy of the speed of light as a unique limiting speed - he found that SR predicts that result). They offer no explanation as to what would cause the new limiting speed to exist. Would you not see the need for some new theory if that were to occur?

AM

 

[jcsd]

Andrew, Einstein did assume that the speed of light was constant, that is why it is called the second postulate, after all from a theoretical point of view a postulate is an assumption offered without explanation. And what explanation did Einstein offer for a finite constant speed of light in all inertial frames?