If we know that the temperature of photons was apprx. 3000 K at recombination and the temperature of the CMB is apprx. 2.725 K today, how can we extrapolate the value of the scale factor at recombination?(adsbygoogle = window.adsbygoogle || []).push({});

I know that recombination happens at a matter-dominated era, such that the density goes a^-3 ****(not a^-4) and that at this era a(t) goes t^2/3

But this doesn't tell me how a(t) is related to temperature....

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# How to find scale factor at recombination?

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