# Hubble expansion and superluminality

28 Nov 2012Why do we observe light from galaxies if their recession velocity exceeds the speed of light? At what redshift in a \(\Lambda\)CDM cosmology would a galaxy move as fast as light? Why isnâ€™t that a problem with special relativity?

bonus question: Can you show the property \(\Gamma(x+1) = x\Gamma(x)\) of the \(\Gamma\)-function which is defined by \(\Gamma(x)\equiv \int_0^\infty\mathrm{d}t\:t^{x-1}\mathrm{e}^{-t}\)?