### Birkhoff's theorem

(shows GR qualities of a spherically-symmetric mass)

**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.

(*mathematics,physics*)
http://en.wikipedia.org/wiki/Birkhoff's_theorem_(relativity)

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