Angular diameter distance in a flat power-law universe
= Angular diameter distance in a flat power-law universe
{title2=$d_A(t_e,t_0)=ct_e^p(t_0^{1-p}-t_e^{1-p})/(1-p)$}
For $R=At^p$, $0<p<1$, integrate the radial <photon> path from emission to reception and multiply by the <scale factor> at emission. This gives the displayed <angular diameter distance>. The arbitrary normalization $A$ cancels, and the distance is not obtained by multiplying light speed by elapsed <cosmic time>.