An Etymological Dictionary of Astronomy and Astrophysics

In → general relativity, the → action that yields → Einstein’s field equations. It is expressed by:
S_{EH</SUB = (1/2κ)∫d⁴x (-g)^1/2R + S^m,
where κ ≡ 8πG and S^m is the matter part of the action.}

See also: → Einstein; → Hilbert space; → action.