We clarify the conditions for Birkhoff’s theorem, that is, time independence in general relativity. We work primarily at the linearized level where guidance from electrodynamics is particularly useful. As a bonus, we also review how the equivalence principle results from general relativity. The basic time-independent solutions due to Schwarzschild and Kerr provide concrete illustrations of the theorem. Only familiarity with Maxwell’s equations and tensor analysis is required.

1.
R.
Arnowitt
,
S.
Deser
, and
C. W.
Misner
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The dynamics of general relativity
,” in
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, New York,
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)
R.
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2.
For the history and a modern derivation, see
S.
Deser
and
J.
Franklin
, “
Schwarzschild and Birkhoff a la Weyl
,”
Am. J. Phys.
73
(
3
),
261
264
(
2005
)
S.
Deser
and
J.
Franklin
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3.
Roy P.
Kerr
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Gravitational field of a spinning mass as an example of algebraically special metrics
,”
Phys. Rev. Lett.
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(
5
),
237
238
(
1963
).
4.
Robert H.
Boyer
and
Richard W.
Lindquist
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Maximal analytic extension of the Kerr metric
,”
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281
(
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5.
Charles W.
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Kip S.
Thorne
, and
John
Archibald Wheeler
,
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(
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J.
Franklin
and
P. T.
Baker
, “
Linearized Kerr and spinning massive bodies: An electrodynamics analogy
,”
Am. J. Phys.
(to be published).
7.

The transformation that takes us back to Cartesian coordinates in this case is: x=r2+a2sinθcosϕ, y=r2+a2sinθsinϕ, and z=rcosθ.

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