Spacetime. Computer illustration showing the curvature of a squared piece of spacetime due to the presence of a star, leading to the formation of a gravitational well. Spacetime is shown here on a two-dimensional grid, with gravitational potential represented by a third dimension. A product of Einstein's theory of relativity, spacetime describes any event using four coordinates - three giving the position in space and one the time. In the presence of a gravitational field spacetime becomes curved. This curvature means that the shortest distance between two points is not usually a straight line but a curve. The curvature due to gravity results in light bending when it passes by a massive object.