Parametrized post-Newtonian light deflection
= Parametrized post-Newtonian light deflection
{title2=$\alpha=2(1+\gamma_{\rm PPN})GM/(bc^2)$}
The leading <Schwarzschild light deflection> of a distant ray passing an isolated spherical <mass> is $\alpha=2(1+\gamma_{\rm PPN})GM/(bc^2)$. Thus measurements of angular displacement can constrain $\gamma_{\rm PPN}$ rather than merely detect a nonzero <gravitational field>. In <general relativity> this becomes the <Schwarzschild light deflection> $4GM/(bc^2)$.