Gravity is an attractive force between all pairs of massive objects in the universe.
An important point is that gravity is an attractive force, tending to bring objects closer together, rather than a repulsive force. The gravitational force of a single object is no more real than the sound of one hand clapping. Newton was able to express the gravitational force between a pair of objects in the form of a single equation, given in the section below. Gravitational force varies directly with the mass of each object, and inversely as the square of the distance between their centers. For instance, if you doubled the mass of the Earth, and kept its radius constant, you would double the gravitational force experienced by every object on the Earth's surface.