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Best attempts at measuring photon mass?

  1. Dec 9, 2012 #1
    What are the most recent or most accurate attempts at measuring photon mass? Additionally, what are the upper limits, uncertainty or error associated with those measurements?
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  3. Dec 9, 2012 #2


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  4. Dec 9, 2012 #3
    J.D. Jackson in his Classical Electrodynamics states in section 1.2 that the mere existence Schumann resonances in the earth-ionosphere resonant cavity sets a limit mγ < 10-48 kg on the photon mass.

    I have to emphasize, though, that what we call photons (the quanta of the electromagnetic field) are strictly massless in vacuum. As soon as a photon is made to interact with the medium it is propagating through, its dispersion relation may change and the long-wavelength frequency starts of at a non-zero value, which is synonymous to saying that the "dressed" photon acquires a mass. Examples of these include photon propagating through cavities, where the condition of a standing wave in one direction causes the finite zero-wavelength (w.r.t. the other unrestricted directions) frequency, or the propagation of plasma polartions, polaritons, and the Meissner effect in superconductors.
    Last edited: Dec 9, 2012
  5. Dec 9, 2012 #4
    Unfortunately none of referenced papers seem to be free. What I am particularly interested in is error in those measurements and whether there is some of them that do not involve any equations having speed of light as I think that would lead to circular logic, so I'd prefer measurements based on equations without it.
  6. Dec 9, 2012 #5


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    They use "speed of light" as the speed limit of special relativity, I think. A non-zero photon mass would make light slower than this "speed of light" (that name would be bad in that case, of course).
    For recent particle physics publications, try searching for the paper title at arXiv. Usually, you can find (nearly) the same text there for free.

    The uncertainty is always included in the upper limit.
  7. Dec 9, 2012 #6
    Also, if the photon has a mass, it means that the U(1) gauge symmetry associated with the electromagnetic interaction is broken. I don't know if the converse is true, though. So, if an experiment claims a measurement of such a symmetry breaking, then it may be a candidate for a measurement of a non-zero photon mass.
  8. Dec 9, 2012 #7
    I'll try that tomorrow, thanks. In the meantime can anyone explain this part from that Wikipedia article: "A massive photon would have other effects as well. Coulomb's law would be modified..."

    It's not just that I don't see any connection between electric field and photon mass, but what does electric field have anything to do with photons to start with?

    What do you mean? That's what I am afraid of, that having speed of light in equations you are using to measure photon mass you are only ever going to measure nothing but some error. Besides, shouldn't error be expressed as a separate value, like +/- some number?
  9. Dec 9, 2012 #8


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    Photons are the elementary particles of the electromagnetic force - you can describe a static electric field as the exchange of photons between charged objects.
    If those photons have mass, the field gets weaker for large distances (compared to Coulomb's law), you get a Yukawa potential.
    You can see a similar effect for the weak force, which has massive particles (W,Z) and a very limited range as result. The residual strong force in a nucleus has the same effect: It can be described as exchange of massive pions, and its range is very short.
  10. Dec 9, 2012 #9
    I hated that theory, whatever it is, from the second I heard about it. Anyway, aren't those supposed to be virtual rather than actual photons? If they are actual we could, for example, get two permanent magnets close to each other, put some sensor in between and catch some of those photons, but that's not the case, or is it?
  11. Dec 9, 2012 #10


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    Virtual photons, right.
    It is not useful to use this model to describe the force between two magnets, but it is useful to calculate the potential (and many other things) if the force carrier is massive.

    You can detect the electromagnetic field if you put a sensor in between. This is like "catching virtual photons" (but you don't influence the exchange of virtual photons between the magnets, you just add an interaction).
  12. Dec 11, 2012 #11
    After trying to find a free copy of the paper referenced in Wikipedia ("New Experimental Test of Coulomb's Law: A Laboratory Upper Limit on the Photon Rest Mass") regarding inverse square law of the Coulomb's law, the best I could find is just the first page of the paper:


    ...but then I realized in another thread someone gave me perhaps even better paper on the subject, surely far more recent one:

    http://www.princeton.edu/~romalis/PHYS312/Coulomb Ref/TuCoulomb.pdf

    I couldn't quite grasp it on the first read, so I'll make further comments later on when I understand it better, but in the meantime if anyone understands what's that all about and can summarize briefly how this relation between photon mass and electric filed works, please do.
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