= Scalar field equation of motion
{title2=$\Box\varphi-V'(\varphi)=0$}
For a canonical real <scalar field> with <metric signature> $(-,+,+,+)$ and <scalar potential> $V$, variation of its minimally coupled <action> gives the displayed equation. A homogeneous field in an <FLRW metric> therefore obeys $\ddot\varphi+3H\dot\varphi+V'(\varphi)=0$ in <natural units>. Its <energy density> is $\dot\varphi^2/2+V$ and its <pressure> is $\dot\varphi^2/2-V$, which satisfy the <cosmological continuity equation>.
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