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Tolman surface brightness test - need help!

  1. Feb 8, 2007 #1
    Tolman surface brightness test -- need help!

    Richard Tolman derived that in an expanding universe with any arbitrary geometry, the surface brightness of a set of identical objects will decrease by (1+z)^4.

    I have two questions:

    1) The surface brightness is the same as the flux (W/m^2), right?
    2) My understanding so far has been that the received flux decreases with the distance squared, so reading that it will decrease by a factor of (1+z)^4 is a bit confusing. Is it perhaps a factor that is ignored when the distance from Earth is relatively small (because z is so small)?

    Need help urgently!
    Last edited: Feb 8, 2007
  2. jcsd
  3. Feb 8, 2007 #2
    Oh, and another question. Some sources say the SB will decrease by (1+z)^2 instead of (1+z)^4 in an expanding universe. Which is correct?
  4. Feb 9, 2007 #3
    I've received answers to the first two questions already, so no need for anyone to bother with them. The question in my second post is still unanswered, though.
  5. Feb 10, 2007 #4


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