Rab – ½ Rgab + Λgab = 8πG Tab In 1915, the equation was simpler still, because the term “+ Λgab,” which Einstein added two years later (and which I discuss in the next section) did not yet exist.* Rab depends on Riemann’s curvature, and together with ½ Rgab, represents the curvature of spacetime; Tab stands for the energy of matter; G is the same constant that Newton had found, the constant that determines the strength of the force of gravity.
