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Source of photon propagation

  1. Nov 13, 2004 #1
    Imagine a massless, classically zero curvature, infinite spacetime in which propagates a single actual photon. What eventually motivated this photon to propagate, and does its trajectory or energy vary due to the spacetime vacuum energy?
  2. jcsd
  3. Nov 13, 2004 #2


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    It's impossible to answer the first question. I believe the answer to the second is that the vacuum energy would be completely irrelevant in a universe without gravity. If the photon actually has a trajectory depends on the state it's in. If it's a momentum eigenstate, its position is smeared out over the entire universe.
  4. Nov 15, 2004 #3
    Given an infinite time, we can use the uncertainty principle to argue that energy is borrowed from the vacuum, a particle-antiparticle pair for example is created and the particles then annihilate into 2 gamma photons which travel in opposite directions, instead of going back into the vacuum. Then, if you want, you can ignore one of them (I wonder if this makes sense!?!). I can't answer the second question.
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