As of 2014, science remains uncertain about what causes gravity, which is the attraction between two bodies. However, one theory is that small particles called gravitons are responsible for the force. Scientists continue to search for gravitons and gravitational waves to further the understanding of gravity's cause.
In the late 1600s, Sir Isaac Newton shared his theory of universal gravitation with the public. This theory defines the gravitational force between two objects as the product of the masses of the objects multiplied by the gravitational constant and divided by the square of the distance between the objects. Unless one of the bodies is massive, the force of gravity is relatively small.
In the early 20th century, Einstein turned his attention toward gravitation. He saw gravity as a curve in the time-space continuum, not as a force. However, neither Newton nor Einstein provided a complete understanding of gravity.
Although the precise cause of gravity is uncertain, its attraction keeps humans from flying off Earth and into space. Objects thrown into the air, fall back to the surface of the earth at a predictable rate. Some scientists believe that the particle accelerators can provide the answer to the cause behind gravity by allowing them to isolate gravitons or gravity waves.