Birkhoff's Theorem proves qualities about General Relativity that demonstrate its relation to Newtonian Gravity, i.e., conditions under which the two converge. One consequence is that under GR, isolated, non-rotating, spherically-symmetric masses are equivalent to gravity from a point mass, analogous to what Isaac Newton proved about Newtonian Gravity to make it practical to apply it to the dynamics of the solar system. A corollary to this is that a spherically symmetric pulsation (e.g., a star's pulsating that happens to retain perfect spherical symmetry of its mass) creates no Gravitational Waves. |