We're currently working on perturbations within cosmology. There is something I have not heard before which has cropped up, that is: a reference to the term "the background equations".
Are these just the Friedmann equations, without any perturbations present?
The specific question which refers to this is:
Determine the values of $a_{0}$ and $\rho_{0}$ for $\epsilon=0$, the background equations.
Where:
$$ a(t)=a_{0}+\epsilon\delta{a_{1}}(t) \rho(t)=\rho_{0}+\epsilon\delta{\rho_{1}}(t) $$$$ a(t)=a_{0}+\epsilon\delta{a_{1}}(t) $$ $$ \rho(t)=\rho_{0}+\epsilon\delta{\rho_{1}}(t) $$
So, yes, just what are the background equations?
