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Do photons decay?

  1. Apr 12, 2008 #1


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    From what I gather, even the proton has a probability to break apart after however long.

    Is this valid for photons as well? Supposing they did decay, then would there be a second "cosmic event horizon" by which light from a certain distance can't reach us regardless of time?
  2. jcsd
  3. Apr 12, 2008 #2


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    No, as far as I know photons cannot decay. But as you say, even if there was some mechanism by which a photon could decay, due to time dilation the decay would never be observed in any reference frame.
  4. Apr 12, 2008 #3


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    So what constraints do we have on our information apart from this event horizon? Anything time-independant?
  5. Apr 12, 2008 #4
    If a photon would decay into massive particles, then it would violate momentum or energy conservation: a massless particle always has more momentum than an equal energy massive particle.
  6. Apr 13, 2008 #5
    although this was not the main part of your question, I would like to provide a clarification to this point.

    there exist some theories that the proton might decay, but until now there is no experimental evidence for this. the guys at the super-kamiokande detector herded quite a lot of protons together, watched them, and - nothing happened !

    so all we can say at the moment is, that there is a lower boundary for the half-life of the proton (I think its 10^35 years, could anybody confirm / correct this number ?). but it might very well be that the half-life is in fact infinite, i.e. the proton might not decay at all.
  7. Apr 13, 2008 #6


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    Yeah I've read (I believe in a book by Martin Rees) that the lower bound is somewhere around 10^35 years for decay of a proton.
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