Curvature radius of an open FLRW universe
= Curvature radius of an open FLRW universe
{title2=$r_c=c/[H_0\sqrt{1-\Omega_m}]$}
Normalize the present <scale factor> to one. In a dust-only open cosmology with no <cosmological constant>, the <Friedmann equation> gives $-kc^2=H_0^2(1-\Omega_m)$. The present comoving and physical curvature radii are therefore $r_c=c/[H_0\sqrt{1-\Omega_m}]$. At another epoch the physical curvature radius is $a r_c$.
// Target: cosmic-microwave-background-anisotropy.bigb