= Photon-only matter-radiation equality
{title2=$1+z_{m\gamma}=\Omega_{m0}/\Omega_{\gamma0}$}
Nonrelativistic matter density grows as $(1+z)^3$, whereas freely redshifting <photon> <energy density> grows as $(1+z)^4$. Their equality gives the displayed redshift. Radiation inferred solely from a <cosmic microwave background> <temperature> excludes the relic <neutrino> <energy density>, so the resulting redshift differs from total matter-radiation equality. Comparing density parameters at one epoch is equivalent to comparing the densities because their common critical-density denominator cancels.
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