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Homework Help: Time taken for light to circle the universe.

  1. Mar 26, 2009 #1
    1. The problem statement, all variables and given/known data

    if a(t) = a0(t/t0)^(alpha) how long does it take for a light ray to circle the universe if K = 1

    2. Relevant equations

    The LFRW metric

    3. The attempt at a solution

    it involves that metric and an integral at theta = pi/2 , phi [0,2pi], l [?] and ...... and something about proper time.

    also we know that for null geodesics Guv*dXu*dXv = 0

    very interesting question but i cant seem to start it, any suggestions?
    Last edited: Mar 26, 2009
  2. jcsd
  3. Mar 28, 2009 #2
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