General theory of relativity
The general theory of relativity explains the phenomena of gravity as a an artifact of the geometry of space and time, which is not simply a Euclidean geometry but a Riemannian geometry that varies from location to location as it is affected by the presence of massive objects. The theory was proposed by Albert Einstein in 1915. An historical sketch of the theory and its experimental verification is found in the Introduction of Hughston and Tod. The work of Robert Pound provided the first experimental confirmation of the theory.