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If the scale factor $a(t)$ is 0 at the start of the universe, what would the scale factor at the end of the Planck epoch (t=Tp) be?

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  • $\begingroup$ In the standard Friedmann-Robertson-Walker Universe, the scale factor at the start of the Universe is $a=0$. $\endgroup$ – Virgo Nov 5 '16 at 21:27
  • $\begingroup$ Oh, ok. What would it be, in theory, at one Planck time? Surely, it'd be near 0, obviously. Don't seem to be pushy, btw lol. $\endgroup$ – Ringo Hendrix Nov 5 '16 at 21:35
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The temperature of the CMB today is about 3K. While the Planck temperature is about $10^{32}$ K. Ignoring some minor changes due to some out of equilibrium phases, $T\propto a^{-1}$. We can therefore conclude at the Planck era $a\sim 10^{-32}$.

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