General Relativity

General relativity (or general theory of relativity) is the geometric theory of gravitation published by Albert
Einstein in 1915 and the current description of gravitation in modern physics. General relativity generalizes special relativity and Newton's law of universal gravitation, providing a uni ed description of gravity as a geometric property of space and time, or spacetime. In particular, the curvature of space-time is directly related to the energy and momentum of whatever matter and radiation are present. The relation is speci ed by the Einstein  eld equations, a system of partial di erential equations. Albert Einstein's general theory of relativity is one of the towering achievements of 20th-century physics. Einstein proposed that objects such as the sun and
the Earth change this geometry. In the presence of matter and energy it can evolve, stretch and warp, forming ridges, mountains and valleys that cause bodies moving through it to zigzag and curve. So although Earth appears to be pulled towards the sun by gravity, there is no such force. It is simply the geometry of space-time around the sun telling Earth how to move. The general theory of relativity has far-reaching consequences. It not only explains the motion of the planets; it can also describe the history and expansion of the universe, the physics of black holes and the bending of light from distant stars and galaxies.