Scalar-field cosmology
= Scalar-field cosmology
A homogeneous canonical <scalar field> contributes <energy density> $\rho=\dot\varphi^2/2+V$ and <pressure> $P=\dot\varphi^2/2-V$. When it is the only source in a spatially flat <FLRW metric>, the <Friedmann equation> is $3M_{\rm Pl}^2H^2=\rho$, and its evolution follows the <scalar field equation of motion>. Positive <energy density> implies $w\ge-1$ because $\rho+P=\dot\varphi^2\ge0$, even if the <scalar potential> is negative.