The General Theory of Relativity was proposed by Albert Einstein in 1915 – ten years after the publication of his Special Theory of Relativity in the journal

where

and

*Annalen der Physik*. The general theory incorporates gravity and accelerated frames of reference in the special theory, and may be summarized by the celebrated Einstein’s field equations:where

*R*is the Ricci curvature tensor,

_{μν}*R*is the scalar curvature,

*g*is the metric tensor,

_{μν}*Λ*is the cosmological constant,

*G*is the gravitational constant,

*T*is the stress–energy–momentum tensor,

_{μν}and

*μ*,*ν*∈ {0,1,2,3} refer to the four spacetime co-ordinates, one (0) for time and three (1, 2, 3) for space. Since*μ*and*ν*can each take on four values, there is not one but sixteen field equations. The left-hand side of each equation is an expression involving the curvature of spacetime while the right-hand side deals with energy and momentum. You could say that the equations are trying to tell us the following: “Space tells matter how to move, matter tells space how to curve.”