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Does time effect slowed light or not?

  1. Jun 8, 2013 #1
    I really wanted to know if we have managed to slow down light so its speed is not c ?
    and if when its slowed down, if time effects the light or not?
  2. jcsd
  3. Jun 8, 2013 #2


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    Staff: Mentor

    Welcome to PF.

    No, the speed of light in a vacuum is what it is. It is constant.
    Last edited: Jun 9, 2013
  4. Jun 8, 2013 #3


    Staff: Mentor

    Yes, that is how refraction works.

    I am not sure what you mean by this. Classically, light obeys Maxwell's equations both in and out of refractive materials, and Maxwell's equations certainly can be written in a manner which includes time. So I would say that time affects light both in vacuum and in matter. But it is hard to say without some more information about your meaning.
  5. Jun 9, 2013 #4
    So mean, that given light when it is travelling at its normal speed is not subject to time. So time doesn't effect light.
    Is this still true if we slow down light?

    So, you take a light beam, slow it down, then see if time still effects it.
    This is important because if time does effect slowed light then time is separate from light.
    But if it doesn't then it means that time is more universal.

    Hope that is clear
  6. Jun 9, 2013 #5


    Staff: Mentor

    Maxwell's equations disagree.
  7. Jun 9, 2013 #6
    I think what he's trying to say is:

    Since photons travel at c, they do not do not experience time and distance. But if they could be slowed down would this still be the case?
  8. Jun 9, 2013 #7
    How can that be true?

    -Photons oscillate at some frequency.

    -The path of a photon is affected by strong gravitation fields.

    How can a thing have frequency and change of directional without time and distance?
  9. Jun 10, 2013 #8
    Good point, but wouldn't the changes for the photons only apply for an observer?
  10. Jun 10, 2013 #9
    That statement has no meaning as there is no inertial reference frame for light....you can't have clocks and rulers travel at 'c' is one way to look at it.... Here are a few recent comments I saved from another discussion about that:

    Reference frame for a photon?



    In other words, length contraction and time dilation formulas don't apply to massless particles; the Lorentz transforms don't apply at velocities of c and greater.
  11. Jun 10, 2013 #10
    Here is the discussion on 'reference frame for a photon'??


    About the only way to think about issues such as the one posed by the op, is to consider particles moving close to the speed of light.....but you can't extrapolate exactly to 'c'.

    PS: If you observe light approaching a black hole, it will appear to slow down when viewed from a great distance, like earth. But actually that is a coordinate effect, that is a mathematically based appearance; locally, light always moves at velocity c'.

    Another phenomena is phase and group velocity of waves:

    Refraction is a change in the phase velocity of light...but individual photons always move a speed 'c'.....
    There is some current experimental work at Harvard U., I believe, about 'slowing light' quantum mechanically, I can't remember the professors name....

    edit: Her name is Prof. Hau.....three minute youtube video here....

    seems like absorption and emission....individual photons appear to still move at 'c'...but maybe a Bose-Einstein condensate person here can clarify.....
    Last edited by a moderator: Sep 25, 2014
  12. Jun 10, 2013 #11
    That's really remarkable! (that there's scientific work put towards that goal)

    I've seen the "Light slowed down" video of light "propagating" through a coke bottle. That of course was remarkable camera work, not remarkable physics.

    Tickles the (very small) sci-fi geek in me, of course "harnessing" the dimensions is the only route to acceleration without any work being done :tongue2:
  13. Jun 10, 2013 #12
    Thanks Naty, makes sense
  14. Jun 10, 2013 #13
    Not sure just what your mean by that, but if you do a Google type search you'll find she
    began 'slowing light' about 15 years ago.....

    I wonder if anyone has been able to devise a practical application..
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