What was the value of redshift $z$ when matter started to dominate the universe?
Is there any way to calculate it without knowing the time?
$\begingroup$
$\endgroup$
1
-
$\begingroup$ $z_{eq} \sim 3000$. It should be easy to calculate if you know the present amount of radiation and matter energy density. $\endgroup$– IhleCommented Nov 1, 2015 at 21:17
Add a comment
|
1 Answer
$\begingroup$
$\endgroup$
0
We can calculate the redshift of matter-radiation equality by using the scaling of the energy density of radiation and matter:
$$ \rho_{\text{matter}} = \rho_{\text{matter}}^0(1+z)^3, $$ $$ \rho_{\text{radiation}} = \rho_{\text{radiation}}^0(1+z)^4, $$ where $\rho^0$ denotes the current enegy density.
This gives us $$ z_{eq} = \frac{\rho_{\text{matter}}^0}{\rho_{\text{radiation}}^0} -1 \sim 3400.$$
The exact current value can be found in Page 16, Planck 2018 results. VI. Cosmological parameters.
