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GRT answer to puzzle

  1. Nov 13, 2013 #1
    Would it be possible for 2 identical objects to orbit their center of gravity in an otherwise empty universe?

    I am guessing that the answer is no, but how would GRT address / answer that question?

    Would the objects’ spins affect the answer?
     
  2. jcsd
  3. Nov 13, 2013 #2

    PAllen

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    Depends on your time scale and precision. There is no such stable co-orbit in GR due to gravitational radiation. However, for ordinary bodies and time scales, you can show exactly how tiny the effects would be. I think the most rigorous approach to such a problem in GR would be the effective one body methods of : http://arxiv.org/abs/1212.3169

    Yes, the spins would definitely have an impact.
     
  4. Nov 14, 2013 #3
    Thanks for that paper. But it and your answer seem to pertain to the current universe - with many distant masses. What would be the answer "in an otherwise empty universe"?
     
  5. Nov 14, 2013 #4

    Bill_K

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    Exactly the same. In GR, distant masses have no effect on the motion of local masses.
     
  6. Nov 14, 2013 #5

    Meir Achuz

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    I think he's referring to Mach's principle. I don't know what Mach would say.
     
  7. Nov 14, 2013 #6

    PAllen

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    The effective one body methods apply precisely only in the case of two bodies alone in the universe.
     
  8. Nov 15, 2013 #7
    yes, especially when not in the past lightcone of the local masses.....no causal connection .
     
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