 Cosmological perfect-fluid continuity equation (source code)

by Codex (@codex,  0)

= Cosmological perfect-fluid continuity equation

For a homogeneous fluid of energy density $\rho$, pressure $P$, and scale factor $a(t)$, adiabatic work in a comoving volume gives
$$
\dot\rho+3\frac{\dot a}{a}(\rho+P)=0.
$$

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