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MMX in Accelerating frame

  1. Nov 3, 2006 #1
    We start with a non accelerating long rocket having a clock C1 and photon source S at the front and a mirror M at the rear - photons are emitted at timed intervals recorded on C1 and their return is measured by C1 - so the round trip time for the rest frame is established. The rocket is then accelerated with uniform thrust and the experiment repeated - now the photon going from S to M will take less time than before and the reflected photon will take longer, both for the same reason as the one-way Sagnac effect. The difference in the time between the round trip with no acceleration and with acceleration can be used to determine the acceleration. Next, the rocket thrusters are turn off and the rocket is placed in a uniform G field that has the same intensity as the acceleration developed by the thrusters - the experiment is repeated - the equivalence principle predicts that the same time difference would be measured - but in the case of the rocket under thrust, the time difference was consequent to the fact that the photon traveled a different distance going and coming - in the G field the distance is the same - but the time should be equal to the result obtained when the rocket was accelerated. In both cases involving acceleration, the photon arrives back at the source at the same gravitational potential - so there is no change in frequency - so is the second experiment properly interpreted as an indication that the local velocity of light is affected by gravity?
  2. jcsd
  3. Nov 3, 2006 #2
    How do you conclude that the distance is the same?
  4. Nov 3, 2006 #3

    have please a critical look at
    arXiv.org > physics > physics/0609118

    Physics, abstract
    From: Stefan Popescu [view email]
    Date: Thu, 14 Sep 2006 09:13:24 GMT (357kb)
    Radar echo, Doppler Effect and Radar detection in the uniformly accelerated reference frame
  5. Nov 3, 2006 #4


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    Science Advisor

    The coordinate velocity of light is affected by gravity, but the local velocity of light is not.

    If you use local rulers and local clocks, the speed of light locally is still 'c', as long as one uses a short enough distance.

    I have to run now, there's probably more to say about this.
  6. Nov 4, 2006 #5
    In the first case the rocket is an inertial frame and the total time t* over and back is 2L/c where L is the distance from the C1 to M. In the second case when the rocket is undergoing acceleration "a" the time t' from C1 to M is L/(c-at') and the return time t" from M to C1 is L/(c+at"). When the rocket is placed in a uniform gravitational field "g" where (g = a) should not the round trip time in the g field equal (t' + t") > t* as per what might be expected when the rocket was accelerated. And if the round trip time in the "g" filed is the same as in the "a" field, why do we not have an indication of the effect of g upon local light velocity. I welcome your correction.

    Bernard - for some reason my acrobat reader cannot read your paper - I will try again
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