Well. Do they have mass or not? How is the investigation nowadays? Anybody knows?
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.
Any data about the upper mass bound? it should be very small,I suppose.
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.)
Thank you chroot, you have understand me even my bad english!
Does somebody know the upper mass bond of a photon?
Due to Louis de Broglie the photon also has a mass, and I believe that this is a reasonable assumption.
The upper bound is 2×10-16 ev.
No, de Broglie's hypothesis was made in regards to matter waves, not photons.
I believe that it is an unreasonable assumption.
A photon mass would imply, among other things, that the electrostatic force is not really an inverse square law, but rather derived from a Yukawa potential. It would also destroy gauge invariance. Both of these things are well tested.
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?
Also I had another question you may know something about. Lineweaver said that the predicted temperature of the cosmic neutrino background (left over from baryon-genesis at a certain stage in the cooling of the early universe) was 1.9 kelvin.
I don't know how far people are from being able to detect neutrinos well enough to determine if there is a cosmic background of neutrinos(and if so what temperature it is).
Or even if such a thing is in principle measurable given all the other neutrinos in the foreground. Do you know anything about this?
edit: I just did a google search for cosmic neutrino background and came up with a recent article by a german physicist at DESY
"How to detect the cosmic neutrino background?"
Also for what its worth a 1999 AIP abstract:
Number 425 (Story #1), April 28, 1999 by Phillip F. Schewe and Ben Stein
THE COSMIC NEUTRINO BACKGROUND can in principle be detected. There are almost as many neutrinos loose in the universe as photons, and almost as much energy vested in neutrinos as in photons. Yet, owing to the extreme reticence of neutrinos to interact with other particles, detecting the neutrino background is not easy as detecting the cosmic photon (microwave) background. Indeed, dedicated neutrino detectors struggle just to record a handful of incoming neutrinos from potent nearby sources like the sun. Nevertheless, there might be a chance to map the background indirectly. The pattern of lumps in the microwave background, which will be measured by the upcoming MAP and PLANCK orbiting detectors, encodes information about the neutrino background. Scott Dodelson of Fermilab (630-840-2426), Michael Turner and Robert Lopez of the University of Chicago, and Andrew Heckler of Ohio State show these measurements will accurately establish the time at which slow-moving matter (protons and later atoms) became predominant over fast-moving radiation (photons and neutrinos), and that this in turn determines precisely how much early annihilation energy (arising from electrons and positrons smashing up) was apportioned among photons and neutrinos. (Lopez et al., Physical Review Letters, 17 May 1999.)
The first observatory able to make a neutrino map is working now!
It has its basis at the Antartida
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".
But, disappointingly, Amanda cannot detect neutrinos of the cosmic background. The article I mentioned discusses the reasons for this
(How to detect the cosmic neutrino background, by Ringwald of DESY)
and gives estimates of the original energy when the neutrinos were released and their presentday energy and number density.
According to Ringwald the neutrinos were released when the universe was about 1 second old and they had energies on the order of 1 MeV.
Now they have energies on the order of 10-4 eV
says ringwald. It is much too low for the detector to see.
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)."
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.
OK, I wasn't aware of that. How did he "show" this?
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.
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.
The appoach of de Broglie to QM was discarted by Bohr and Heisenberg during the Solvay conference 1927 in Brussels. De Broglie gave up at the time, but later he restarted his version of quantum theory (wich has some relation to the one of David Bohm).
To my knowledge the approach of de Broglie was never reevalued again by the physical community. But it has certain abilities. For instance is it quite easy to determine the parameters of the electron in a classical way if the model of de Broglie is used. Normally the electron is used as the chief witness for the (believed) fact that elementary particles can only be descibed by QM.
They are proven accurate to the extend the experiments can provide. You can only give some kind of an upper bond by an experiment.
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.
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.
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.
It may be true that both what are not the same? Real and virtual photons?
I don't know if this has been asked,
but does anyone know why originally
they were thought to have no rest mass?
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.
Nuetrinos....... sorry I didn't
have time to read all of the thread
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".
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.
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) this statement about the photon fits to it.
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.
To come back to your original point: The exchange particle of the electric field may be different from real 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.
Does that mean that you really do not know that deBroglie showed what you claimed he showed?
If particles are not waves in his theory, then why does he postulate that particles have a wavelength?
So you keep saying.
My question is the same: How? How? How?
Notice a pattern here?
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.
They are certainly different from real photons. Real photons have kμkμ=0, whereas virtual photons do not.
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.
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 in
The idea of de Broglie is that every particle has an internal oscillation. Its frequency is the de Broglie frequency. As every particle has a type of interaction it must have a field around. This field is, due to the internal oscillation, an alternating field of the same frequency. The field moves with the particle, and the oscillating field has the wavelength as it is assigned to that particle in its motion state.
This field causes the seeming wave behaviour of the particle. At a double slit this fields builds an interference pattern which guides the particle though the slit and which causes the known scattering distribution.
This model of de Broglie has a striking consequence which was not seen by him. From the Dirac function it follows that the internal oscillation (in that case restricted to the electron) takes place with the speed of light c. If this behaviour is not only assumed for leptons but also for quarks, then special relativity is an immediate consequence of this model without Einstein's assumptions about space and time. - So we have a unique model which explains both, QM and SR, at the same time.
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):
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.
His conclusion has by the way a very interesting consequence. If also a photon behaves like a lepton and a quark mentioned above then relativity can be derived from the structure of elementary particles without Einstein's assumptions about time and space.
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?
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.
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:
1. No one can measure an absolute speed to that accuracy
2. We do not even know what the correct speed c numerically is. We only know photons. The internal speed within an electron, which should be the genuine c according to Dirac, can not at all be measured with a reasonable accuracy
3. Precision measurements of photon speeds (like Michelson) are generally performed by an interference method. But at interference one compares the speed of a photon with the speed of another photon of the same wavelength. This does not provide the information wanted.
4. But: I have read the astronomers have found that photons of different wavelength need slightly different time to travel though the universe. This could be an experimental hint that de Broglie is right.
Do you mean that it can be used to determine c? Such a decay experiment has normally a precision in the region of percent. Even if it is much better than this there is no chance to check the hypothesis of de Broglie by such an experiment.
No I don't think neutrinos or the Beta decay can be used to measure c. It was just that the mass energies of the observable properties seemed to balance, so it looked like the neutrino wasn't carrying any mass away, so they said mass = 0. As you remarked this kind of decay isn't very sensitive and "mass small" would have been a better take.
Anyway, for years it was mass=0 and therefore from relativity speed = c. This is a firm conclusion of relativity and unlike you, the physicists have confidence in it. Basically they know the Lorentz transformation work in their experiments and the design of their accelerators. The Lorentz transformations give you mass=0 => speed = c right away.
On your fourth item, I think you are referring to the claim of LQG that light of different frequencies would have tiny differences of speed through the foam, leading to dispersal which might be detected. The amount of variation is appropriate to the planck scale of the foam, and in no way supports any gross variations in c.
Separate names with a comma.