Vacuum-dominated doubling time
= Vacuum-dominated doubling time
{title2=$t_2=(\log2)\sqrt{3c^2/(8\pi G\epsilon)}$}
In a spatially flat universe dominated by a positive constant <energy density> $\epsilon$, the <Friedmann equations> give $H^2=8\pi G\epsilon/(3c^2)$. On the expanding branch $a(t)=a_i e^{H(t-t_i)}$, so the <scale factor> doubles after $(\log2)/H$. This concerns a linear length scale; the enclosed physical volume grows by a factor of eight over the same interval.