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A photon's time

  1. Jul 19, 2011 #1
    From thousands of galaxies dotting Hubble deep sky photographs, photons have been traveling for say, ten billion years before they reach the telescope's lens. But by definition when something travels at the speed of light the passage of time slows down to zero. So is it accurate to say that in their own reference frame, these photons over the course of 10 billion years have actually had not even a second elapse?
  2. jcsd
  3. Jul 19, 2011 #2
    I don't think you can define a proper frame moving at the speed of light relative to another inertial reference frame.
  4. Jul 19, 2011 #3
    I think this is correct, the gamma factor goes to infinity, so I think that’s what the Lorentz equations tell us. That does bring up some weird ideas, like when a photon gets red shifted away by its perspective it never had time to exist so how did it have time to redshift?
  5. Jul 19, 2011 #4
    redshifted relative to whom?
  6. Jul 20, 2011 #5
    Dickfore is absolutely correct here. It is meaningless to talk about a photon frame in the context of special relativity (or any existing theory that I can think of)
  7. Jul 20, 2011 #6
    I agree that it may be meaningless to talk about a photon's frame of reference from a mathematical point of view, as 'Frames of Reference are used for a specific purpose in relativity.

    But I don't see why it is meaningless to discuss what happens to photon from creation to absorption. This is after all, a real situation. Particularly if it helps the OP grasp a concept. Even Einstein imagined travelling along side a light beam, which we know is meaningless, but it certainly helped him.

    So why is it that it is not valid to talk about what happens to a photon from the time we create one to the time we would observe it being absorbed?

    So maybe another way of asking the OP’s question might be this.

    If I switch my torch on and point it to a particular area of the sky, is it possible that in 10 billion years or so, assuming we are still around, that someone may detect that photon. EDIT: And obviously assuming life elsewhere.

    If so, then in 100 years time, if my grandson repeats our family tradition of shining bright torches in a particular direction in the sky, is it possible that the same device that detected my photon, could detect my grandson’s photon simultaneously, from their frame of reference?
  8. Jul 20, 2011 #7


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    Who says that THAT is meaningless? We consider that ALL THE TIME! But we consider that in our reference frame, not the photon's!

    What is meaningless is to do a Lorentz transformation to the photon's frame. Don't believe me? Try it!

    To the OP: Please read the FAQ subforum here.

  9. Jul 20, 2011 #8
    Been there, tried that lol. Yes that was my point, but phrased a lot better. :)thanks.
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