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Can a photon last forever?

  1. May 28, 2008 #1
    If there's nothing to interact with, will the photon attenuate and disappear after some distance, or will it continue to exist and travel forever?

    For example, in a hypothetical universe where all matter is within a sphere and spacetime continues outside the sphere without limits, if a photon exits the sphere will it last forever?
     
    Last edited: May 28, 2008
  2. jcsd
  3. May 28, 2008 #2
    In your scenario it will indeed last forever, although it will be gravitational redshifted while moving away from the sphere.
     
  4. May 31, 2008 #3
    That red-shift denotes a decrease in the photons original frquency over time and through it's pasages through gravitational influences.
    I believe that what is not known at this time is if a photon decreases in frequency without gravitational influence.
    Does a photon eventually "flat-line" by virtue of extended travel without any other influence?
    I've heard that this is a good question with no experimental evidence to suggest an answer at this time.
     
  5. May 31, 2008 #4
    If it decreases in frequency, ie if the e/m wave is getting closer and closer to dc, then this is not equivalent to going out of existence, is it.

    Does the gravitational bending of spacetime extend all the way to infinity? Or does gravity, consisting of particles that cannot have less energy than a quantum quantity, disappear completely after some distance?
     
  6. Jun 1, 2008 #5
    This is the "Tired Light" idea, you might be interested in the wikipedia article http://en.wikipedia.org/wiki/Tired_light and especially the corresponding discussion http://en.wikipedia.org/wiki/Talk:Tired_light (the discussion is very "lively", if you want to see it in a positive way - including the identification of a sockpuppet :biggrin:)

    my personal opinion is, that at the moment there exists no credible mechanism that would predict such a "tiring" effect.
     
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