General relativity is a theory of space and time. The theory was published by Albert Einstein in 1915. The central idea of general relativity is that space and time are two aspects of spacetime. Spacetime is curved when there is matter, energy, and momentum resulting in what we perceive as gravity. The links between these forces are shown in the Einstein field equations. In general relativity, gravity has no force as Newton put forward. According to Einstein it is a curvature that warps not only space, but also time. (Time dilation)