Assume that we live in a Robertson-Walker universe with matter, radiation and curvature. The present mass density is ρm = 3Ω0H20/(8πG), where H0 = 100 h km s-1 Mpc-1 and Ω0(1+ρr,0/ρm;0) ≤ 1 (i.e., k ≤ 0). The present radiation temperature is T0 = 2.725 K.
Assume that only photons, with present...