# Density Parameter for radiation dominated universe

by ibysaiyan
Tags: density, dominated, parameter, radiation, universe
 P: 442 Greetings everyone , Can anyone point me into the right direction on how to come out with a value/ expression for the density parameter of a radiation dominated universe. Things that I know of/ can recall are: Friedmann equation : $$8/3 \pi G ρ R^2 -kc^2$$ Also when radiation dominates matter then we get ρ = 1/R^4 ( I think) Density parameter : So what am I missing to give me the density parameter ? $\Omega_{m}$ = $\rho / \rho_{critical}$ where $\rho_{critical}= (3H^2 q / 4Pi G)$ Any sort of help is appreciated. -ibysaiyan
 Mentor P: 8,316 Your post doesn't make much sense. Your Friedmann 'equation' is not an equation, since you do not have an equals sign. You don't define R, or any of your other variables. But it's not really clear what you want to find -- an expression for $\Omega_R$ in terms of what?
 Quote by cristo Your post doesn't make much sense. Your Friedmann 'equation' is not an equation, since you do not have an equals sign. You don't define R, or any of your other variables. But it's not really clear what you want to find -- an expression for $\Omega_R$ in terms of what?