Past exam of the relativistic Astrophysics and Cosmology course of the University of Cambridge / 2012 / Paper 1 / 2 / c

Comparing photons with the constant vacuum density gives ${\Omega }_{\gamma 0}(1+z{)}^4=0.7$, soMatter dominates both at this crossing: its density in units of today's critical density is $0.3(10.98735{)}^3\simeq 398$, compared with $0.7$ for each of the other components. radiation-vacuum density equality therefore does not itself mark a switch in the dominant component.