Non-exact solutions in general relativity
# Non-exact solutions in general relativity

Non-exact solutions in general relativity are solutions of Albert Einstein's field equations of general relativity which hold only approximately. These solutions are typically found by treating the gravitational field, $g$, as a background space-time, $\gamma$, (which is usually an exact solution) plus some small perturbation, $h$. Then one is able to solve the Einstein field equations as a series in $h$, dropping higher order terms for simplicity.

A common example of this method results in the linearised Einstein field equations. In this case we expand the full space-time metric about the flat Minkowski metric, $\eta _{\mu \nu }$:

       $g_{\mu \nu }=\eta _{\mu \nu }+h_{\mu \nu }+{\mathcal {O}}(h^{2})$,

and dropping all terms which are of second or higher order in $h$.

