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!