Looking
back in time :
density of radiation, rrad µ 4sT4/c3
number of
photons conserved , but due to
cosmological
redshift they lose energy by (1+z)
\ rrad µ (1 + z)4
density of
matter rmµ (1 + z)3
Trad µ 2.75 x (1 + z)
at
present, matter dominates
mass-energy
of universe. Earlier, radiation dominated