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Question about a photon's momentum.

  1. Oct 22, 2012 #1
    When light travels in a medium, its speed is less than c.

    Thus the lorentz factor is not infinite. Since photons have zero rest mass, does this also imply that the photons have zero momentum?
  2. jcsd
  3. Oct 22, 2012 #2
    The 'speed of light' in a medium is a complex subject that has been discussed at length in these forums. but individual photons still travel at 'c' in such a medium. the overall travel is slower than c. For example information transmission in fiber optic cable is a bit slower than in a vacuum.

    Photons always have momentum.

    In a medium there is a complex scattering and absorption interaction between photons , the phonons of of atomic structures such as lattices and atomic particles.

    There is a FAQ on this, but it is not so 'crystal clear' to me.....

    and from another discussion:

    Oh - hang on, found a FAQ:

    https://www.physicsforums.com/showpost.php?p=899393 [Broken]

    But see:
    http://physics.stackexchange.com/que...-through-glass [Broken]
    http://physics.stackexchange.com/que...qed-snells-law [Broken]
    ... many objections in the FAQ are addressed in these.
    Last edited by a moderator: May 6, 2017
  4. Oct 24, 2012 #3
    Last edited: Oct 24, 2012
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