Testing the quality factor with some approximate solutions to Einstein's equations (Q1110829)

The quality factor of a metric, defined by Bel as a measure of its approximation to a solution of Einstein's equations, is tested with several well-known approximate solutions. Whereas for some metrics such as the linearized plane wave solutions the quality factor leads to some intriguing results, for others such as the Newtonian and post-Newtonian approximations for the one and two body systems, and also the linearized perturbations of the Friedmann-\(Robertson\)-\(Wal\ker\) metrics, it seems to lead to very reasonable results.