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Thought experiment for general rel., I can't remember how it goes

  1. Dec 22, 2011 #1
    There is a thought experiment pertaining to general relativity that involves a signal traveling from the front to the back of an accelerating space ship, if I remember correctly. I'm sorry for being so vague, but this is something I saw browsing in a library years ago, and I really wanted to think about it, but it slipped out of my mind and now I'm not sure how it goes. I believe that astronaut 1 in the front of the ship sends a pulse of light towards astronaut 2 in the back of the ship. The question is, I believe, how does the transit of this pulse compare to the same pulse in a ship that is moving at a constant velocity instead of accelerating. I'm not sure how much of this I have right but there is a thought experiment with a signal involving two astronauts in the front and back of a space ship that is accelerating. Can someone lead me to this thought experiment and a discussion? Thank you so much. Sorry for the vagueness. ericqb
  2. jcsd
  3. Dec 22, 2011 #2


    Staff: Mentor

    I think you are interested in the proof of gravitational time dilation using the equivalence principle. If a light of a certain frequency is emitted at the front of an accelerating rocket then by the time the light reaches a detector at the back of the rocket the detector will be going a different velocity and by the Doppler effect will detect a higher frequency. Therefore, by the equivalence principle a rocket sitting vertically in a gravity field will also detect blueshift for light emitted at the front and detected at the back.
  4. Dec 22, 2011 #3
  5. Jan 6, 2012 #4
    Dear DaleSpam,

    Thank you for your help. Sorry it took me so long to reply.

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