Einstein’s formulation of general relativity represents one of the great triumphs of modern physics and provides the currently accepted classical theory that unifies gravitation, inertia, and geometry. The Einstein equations are the mathematical embodiment of this theory.
The definitive form of the equations,
was attained in November 1915; this was the final act of Einstein’s eight-year struggle to generalize his principle of relativity so as to encompass gravitation, which had been described in the earlier “Newtonian” theory by the Poisson equation
for the potential and ...