Energy density
= Energy density
{title2=$\rho$}
{wiki}
The energy density is energy per unit volume. A homogeneous particle species with one-particle energy $E(\mathbf p)$ has
$$
\rho=g\int\frac{d^3p}{(2\pi)^3}E(\mathbf p)f(\mathbf p).
$$
= Energy density
{title2=$\rho$}
{wiki}
The energy density is energy per unit volume. A homogeneous particle species with one-particle energy $E(\mathbf p)$ has
$$
\rho=g\int\frac{d^3p}{(2\pi)^3}E(\mathbf p)f(\mathbf p).
$$