Published in Annalen der Physik in 1916, this paper is Einstein’s full account of the general theory of relativity, drawing together work he had presented to the Prussian Academy of Sciences the previous November. It extends his earlier theory from observers moving at constant velocity to those undergoing acceleration.

The starting point is the equivalence principle: that being at rest in a gravitational field cannot be distinguished, by any local experiment, from being accelerated in empty space. From this Einstein argued that gravity is not a force acting across space but an effect of the curvature of space and time, produced by the presence of mass and energy. Setting this out required the tensor methods of Riemannian geometry, which occupy much of the paper.

Three tests were proposed: the orbit of Mercury, the bending of starlight by the Sun, and the shifting of light towards the red in a gravitational field.