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Strong Equivalence Principle

  1. Dec 6, 2008 #1
    Ok so I was answering a question about a spacecraft accelerating through deep space with observer A in the front and observer B in the rear. I was asked to explain why a phton sent from A to B would appear blue shifted to B - simple enough I just plugged in a positive velocity to the relativistic doppler shift equation. I was then asked to explain the significance of the blue shift in terms of the strong equivalence principle and, well frankly, I can't see the connection. any ideas??? also an explanation of the use of the strong EP would be really helpful!
    thanks for any help
    latentcorpse
     
  2. jcsd
  3. Dec 6, 2008 #2

    atyy

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    Pound-Rebka?
     
  4. Dec 6, 2008 #3

    Fredrik

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    Do you understand why the rear is moving faster than the front? If not, I suggest you read up on Born rigidity, e.g. by checking out what I've been saying about it in this forum the last few months: https://www.physicsforums.com/search.php?searchid=1377913
     
  5. Dec 7, 2008 #4
    What is the Strong Equivalence Principle?
     
  6. Dec 7, 2008 #5

    Hey that link you posted doesn't seem to be working - it just says "sorry no matches were found". erm..i amen't really sure about why the rear is moving faster than the front??? could u post the link again
     
  7. Dec 7, 2008 #6

    Fredrik

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    It was a link to the results of a search I just made. I guess it was a bit optimistic of me to expect that the link would work long enough to be useful. (It worked when I previewed). Click "search" at the top of this window. Choose "advanced search" (under "search forums", not under "search blogs"). Type "fredrik" in the user name field. Type "born rigid" in the "keyword(s)" field. Change "find posts from" to "3 months ago" (and newer). Highlight "special & general relativity" in the "search in forum(s)" field. Change "show results as" from "threads" to "posts". Then click "search now".
     
  8. Dec 7, 2008 #7
    Last edited: Dec 7, 2008
  9. Dec 7, 2008 #8

    Jonathan Scott

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    There are two basic ways to look at this case.

    Firstly, the spaceship is accelerating, so by the time the photon from the front reaches the back, it is moving faster, so relativistic doppler shift applies, as already mentioned.

    Secondly, by the Strong Equivalence Principle, you can consider the environment inside the spaceship to be equivalent to a static situation in a gravitational field, so the photon is being emitted at a higher potential and hence apparently has a higher frequency when it reaches the bottom, as in the Pound-Rebka experiment (previously mentioned by atyy). As this sounds like a homework question, I'll leave the trivial calculation of the result and the check that it matches the other view to the student.
     
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