What was the total mass energy density at the time of recombination? Has it has it been measured by WMAP? (Edit: I think it's 4.28x10(adsbygoogle = window.adsbygoogle || []).push({}); ^{-18}kg/m^{3}from the # of photons/volume in a 2979K blackbody, x baryon:photon ratio x proton mass x (1+ dark:baryon ratio) divided by the 0.755 matter fraction at the time.)

Assuming a flat Universe, in times before dark energy was significant, I think the critical density as a function of time was 3H^{2}/(8 pi G), where

1) H = 1/(2t) during energy-domination (very early times), and

2) H = 2/(3t) during matter-domination.

Thus during matter-domination, the critical density was 1/(6 pi Gt^{2}), and it was 9/16 of that during energy -domination.

I might expect the total energy density (matter + energy) at the time of recombination to be between the matter-dominated and energy-dominated numbers. (Edit: the WMAP appears to be between those numbers. Matter-dominated would be 5.43x10^{-18}kg/m^{3}) However, when I use a differential eq to solve it directly, I'm only getting 0.291 of the matter-dominated value of 1/(6 pi Gt^{2}) where t is the recombination time. (Edit: I don't do math good. Sorry.)

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# Critical density in Early Times

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