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Well. Do they have mass or not? How is the investigation nowadays? Anybody knows?
Any data about the upper mass bound? it should be very small,I suppose.Originally posted by mathman
Current evidence is that neutrinos (there are 3 kinds) have mass, since the observations seem to show that neutrinos change from one kind to another. This could not happen if they were massless.
The upper bound is 2×10^{-16} ev.Originally posted by Albrecht
Does somebody know the upper mass bond of a photon?
No, de Broglie's hypothesis was made in regards to matter waves, not photons.Due to Louis de Broglie the photon also has a mass,
I believe that it is an unreasonable assumption.and I believe that this is a reasonable assumption.
Warren can you give a brief indication of how WMAP and 2dF data can serve to establish that upper bound, or how the bound is arrived at?Originally posted by chroot
The sum of the masses of all neutrino species (most likely three) is less than or equal to 0.79 eV, with 95% confidence. (WMAP 2003 in conjunction with 2dFGRS 2003.)
- Warren
Meteor, thanks for the reference to the South Pole neutrino detector "Amanda". This led me to several interesting articles about Amanda and the improved version called "Ice Cube".
edit: I just did a google search for cosmic neutrino background and came up with a recent article by a german physicist at DESY
arxiv.org/hep-th/0301157
"How to detect the cosmic neutrino background?"
De Broglie wrote in Comptes rendus (1923):No, de Broglie's hypothesis was made in regards to matter waves, not photons. -
This assumption makes it easy to understand that a photon has a momentum and a (relativistic) mass as well.I believe that it is an unreasonable assumption.
OK, I wasn't aware of that. How did he "show" this?Originally posted by Albrecht
De Broglie wrote in Comptes rendus (1923):
"I showed elsewhere ... that the atom of light should be considered as a moving object of a
very small mass (< 10^-50 g) that moves with a speed very nearly equal to c (although slightly less)."
Right, so what evidence is there that the inverse square law or gauge invariance are not accurate? See, what I consider a "reasonable assumption" is something that is necessary to account for experimental results. Postulation of quarks and neutrinos were "reasonable assumptions" by that standard. The only reason you've offered here is that it clears up the conceptual difficulty of "massless momentum", but I don't think that alone warrants the assumption. There has got to be *some* necessitation from experiment.This assumption makes it easy to understand that a photon has a momentum and a (relativistic) mass as well.
Whether one finds a conflict to the inverse square law in a measurement depends on the numeric deviation from mass=0 or v=c.
De Broglie was the first one who created the idea of the wave properties of a particle. And he developed a model to descibe this phenomenon mathematically. From his model his assumption about the photon followed as a consequence.OK, I wasn't aware of that. How did he "show" this?
They are proven accurate to the extend the experiments can provide. You can only give some kind of an upper bond by an experiment.Right, so what evidence is there that the inverse square law or gauge invariance are not accurate?
But my question was how did he show this. And how can the photon mass be simultaneously an "assumption" and a derived "consequence". That makes no sense to me.Originally posted by Albrecht
De Broglie was the first one who created the idea of the wave properties of a particle. And he developed a model to descibe this phenomenon mathematically. From his model his assumption about the photon followed as a consequence.
Yes, I know that. My point is that there is currently no observational falsification of Classical ED or QED, such that a photon mass is required. In fact, a photon mass would make a right mess of things, so again I say that it is unreasonable to assume it. That is unless de Broglie has shown that the photon mass is a necessary implication of his theory of matter waves. You claim that he did, but as I said I'm still waiting on the details of the proof.They are proven accurate to the extend the experiments can provide. You can only give some kind of an upper bond by an experiment.
It may be true that both what are not the same? Real and virtual photons?The other pre-condition for this conclusion is that the photon is in fact the exchange particle representing the electric field. This is of course a convenient assumption. But it may also be true that both are not the same.
Are you talking about neutrinos or photons? I ask because there are actually 2 conversations going on here: The actual topic, and this tangent discussion about light.Originally posted by Ace-of-Spades
I don't know if this has been asked,
but does anyone know why originally
they were thought to have no rest mass?
Sorry if I was not careful with words. I mean the following: His model is of course an "assumption" as every model. If his model is accepted than the conclusion is a "consequence".Tom wrote:
But my question was how did he show this. And how can the photon mass be simultaneously an "assumption" and a derived "consequence". That makes no sense to me.
You don't have to type it all out here; a reference will do.
I think we have meant real photons here. Virtual photons a subject to QED. And QED is in fact open in respect to its physical meaning. - I have read a statement in a textbook of Richard Feynman:It may be true that both what are not the same? Real and virtual photons?
Still makes no sense, and now for a different reason. You say it is that the photon mass logically follows from de Broglie's hypothesis on matter waves. Acceptance by other people has nothing to do with whether or not the former logically follows from the latter.Originally posted by Albrecht
Sorry if I was not careful with words. I mean the following: His model is of course an "assumption" as every model. If his model is accepted than the conclusion is a "consequence".
Does that mean that you really do not know that deBroglie showed what you claimed he showed?He gave in the mentioned paper the following reference:
Journal de Physique, 6c serie, t.3, 1922, p.422.
I did not try to read it as I do not understand French.
If particles are not waves in his theory, then why does he postulate that particles have a wavelength?But if you follow the whole idea of how de Broglie understood the existence and the properties of particles (which are not waves in his theory)
So you keep saying.this statement about the photon fits to it.
With Feynman's remark taken out of context like that, I am hard pressed to infer what he means, so I withold agreement or disagreement on your interpretation for now.I think we have meant real photons here. Virtual photons a subject to QED. And QED is in fact open in respect to its physical meaning. - I have read a statement in a textbook of Richard Feynman:
(double translated to German and now back)
" The laws of QED are presented in the following, but we do not have a justification for them at present"
That means for my understanding that QED works well (like QM), but we do physically not know, why.
They are certainly different from real photons. Real photons have k_{μ}k^{μ}=0, whereas virtual photons do not.To come back to your original point: The exchange particle of the electric field may be different from real photons.-
Neutrinos were thought to be massless because a massive neutrino implies a phenomenon called neutrino oscillations. I can post more about that later, but the answer to your question is that this phenomenon had not been detected until very recently. When it was detected, the massless neutrino hypothesis was falsified.Originally posted by Ace-of-Spades
I don't know if this has been asked,
but does anyone know why originally
they were thought to have no rest mass?
I refer you again to his most important article in "Comptes rendus" of 1923. (It belongs to the collection of papers of 1922 and 1923 for which he received the Nobel price.) You find an English translation inTom wrote:
If particles are not waves in his theory, then why does he postulate that particles have a wavelength?
I cannot read the French paper to which de Broglie refers. But I understand his logic in the following way (and you will surely do if you read the article referred above):So you keep saying. My question is the same: How? How? How?
I have not yet read the article linked above (doing that in a moment), but can you provide any experimental data supporting the above-quoted claim that a photon has a speed that is less than c?Originally posted by Albrecht
A photon is an elementary particle like all others. So it has an internal oscillation. The speed of this oscillation can only be c as a maximum. So the entire particle must necessarily (due to speed vector addition) have a speed less than c.
From the context of de Broglie one can conclude that the speed of the photon may deviate from the true speed c by a portion of 10^-15 to 10^-20. Such a small deviation can presently not be experimentally verified by the following reasons:LURCH wrote:
I have not yet read the article linked above (doing that in a moment), but can you provide any experimental data supporting the above-quoted claim that a photon has a speed that is less than c?
Self adjoined wrote:
The neutrino was first hypothesize by Pauli to account for missing momentum and spin in the beta decay interaction. The simplest particle that could do this would be a fermion that moved at c. Moving at c = massless.