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Photon mass

  1. Oct 18, 2012 #1
    why rest mass of photon is zero? how to prove it by m=m'/√(1-v^2/c^2)?
     
  2. jcsd
  3. Oct 18, 2012 #2

    ZapperZ

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    You cannot prove something like this via analytical methods. Please read the FAQ subforum in the Relativity forum.

    Zz.
     
  4. Oct 18, 2012 #3
    REad about Photon!
     
  5. Oct 18, 2012 #4

    Matterwave

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    How would you prove the mass of the electron with that formula? You can't. Elementary particle masses are experimentally verified, not proved.
     
  6. Oct 18, 2012 #5

    ZapperZ

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    Which part of the photon did you want me to read?

    Zz.
     
  7. Oct 18, 2012 #6
    In addition to the other answers, if photon's mass were different than zero, it should be infinite (according to the formula you have written) because v = c for a photon; its energy would be infinite too. Clearly that is a nonsense.
     
  8. Oct 18, 2012 #7

    bcrowell

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    If the photon's mass is nonzero, then it doesn't have v=c.

    The mass of the photon can only be established experimentally.

    R.S. Lakes, "Experimental limits on the photon mass and cosmic magnetic vector potential", Physical Review Letters , 1998, 80, 1826-1829 http://silver.neep.wisc.edu/~lakes/mu.html

    Luo et al., “New Experimental Limit on the Photon Rest Mass with a Rotating Torsion Balance”, Phys. Rev. Lett, 90, no. 8, 081801 (2003)

    Zz, I'd suggest adding these two references to the FAQ entry.
     
  9. Oct 19, 2012 #8
    Of course. But the answer one can give, can also depend on the level of answer the OP was looking for: starting from the fact that a photon's speed is c, then a photon's mass different than zero generate an impossible situation.
     
  10. Oct 19, 2012 #9
    Just because you cannot divide by zero does not prove that photons must possess a nonzero mass. Einstein's ideas concerning mass and speed are not just idle speculations, they have been verified through experiments. Keeping this in mind:

    Since photons, by definition, travel at the speed of light, if they did possess ANY mass their mass would have to be infinite. A particle the size of a photon with INFINITE mass would create a singularity that would consume everything it touched. Since this is clearly not the case, photons cannot have any mass.
     
  11. Oct 19, 2012 #10

    bcrowell

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    The point is that we don't know that a photon's speed is c. We can only put a lower limit on its speed for a given energy.
     
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