We calculate “deflection of light by the Sun." First, we define a first-order action for a massless particle moving in a gravitational field, and then we calculate the motion of light on a geodesic as motion of light in a medium with a small, position-dependent index of refraction, giving the light deviation for small angles. Then we redo the calculation from the Hamilton–Jacobi formalism by first defining the Hamilton–Jacobi equation for light motion and then solving it. This gives the nonperturbative light deviation that matches the previous calculation at small angles. We end by comparison with the deflection of light by the Sun in special relativity, which is different by a factor of 2.

We define general relativity. We first consider intrinsically curved spaces and the notion of metric. Einstein's theory of general relativity is defined, based on the two physical assumptions, that gravity is geometry, and that matter sources gravity, and leading to general coordinate invariance and the equivalence principle. Kinematics, specifically tensors, Christoffel symbol and covariant derivatives, is defined. The motion of a free particle in a gravitational field is calculated.