Do photons decay?

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dst
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Main Question or Discussion Point

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?
 

Answers and Replies

Hootenanny
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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.
 
dst
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Bleurgh!

So what constraints do we have on our information apart from this event horizon? Anything time-independant?
 
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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.
 
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From what I gather, even the proton has a probability to break apart after however long.
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.
 
Nabeshin
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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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