Trace-reversed metric perturbation
= Trace-reversed metric perturbation
{title2=$\bar h_{\mu\nu}$}
In four dimensions, the trace-reversed perturbation is
$$
\bar h_{\mu\nu}=h_{\mu\nu}-\frac12\eta_{\mu\nu}h,
\qquad h=\eta^{\rho\sigma}h_{\rho\sigma}.
$$
Trace reversal simplifies the linearized Einstein equations.