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Slowing Down a Photon

  1. Nov 3, 2007 #1
    Slowing down a photon


    Does a single unique photon ever not travel at c in the same inertial frame?
    I'm stuck on the apparent problems with applying the Lorentz transformation to a photon. I don't think it makes sense physically to apply them to a photon. Talking about moving photons from rest to c, I don't think happens or even makes sense. When light is slowed down, isn't that really the group velocity of the EM field that gets slowed from which photons are emitted.
    Anyway, enough rambling help!
  2. jcsd
  3. Nov 3, 2007 #2

    Meir Achuz

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    A photon always travels at c.
    If you Lorentz transform, you will still get c.
  4. Nov 4, 2007 #3
    Ok, so I got through the photons always have velocity c in any inertial frame part, which includes photons created inside a semi-conductor laser or in some EIT material,
    I'm now stuck on how to reconcile photon velocity and the speed light slowing in EIT experiments. More specifically, is it proper to talk of the EM field taking up and giving back mass from the energy of the photons, and that the taking up and giving back by the field acts as a curvature of space-time? Is that even possible?
  5. Nov 4, 2007 #4


    Staff: Mentor

    The speed of light* is only equal to c in vacuum. In other materials the speed of light can be less than c.

    *Classical Maxwell-type speed of light, I don't know about for individual photons in a QM type analysis.
    Last edited: Nov 4, 2007
  6. Nov 4, 2007 #5


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    Staff: Mentor

    Post #4 of the Physics Forums FAQ may be of interest here.
  7. Nov 5, 2007 #6
    In a superfluid light can be slowed to a few miles per hour. As for if you mean in a vacuum yes in all frames of reference, except of course the photons own frame of reference it will be travelling at c.
  8. Nov 5, 2007 #7
    I have heard physics profs say many a times that using Minkowski's space to understand such things is more profitable. It clears most of the so-called paradoxes.

  9. Nov 23, 2007 #8
    the speed of an individual photon is always c. when a photon travels through a material it can take a zig zag path to the other side as its affected by the atoms in the material so it will take longer to get to the other side and is effectively slowed down.
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