Weyl lensing potential
= Weyl lensing potential
{c}
{title2=$\Psi=(\phi+\psi)/2$}
The average of the two <conformal Newtonian gauge> potentials controls scalar <gravitational lensing>. A conformal rescaling makes the spatial optical metric flat and its time component $1+4\Psi$ to first order. Vanishing <scalar anisotropic stress> makes $\phi=\psi$ in general relativity, but lensing depends on their sum even when they differ.