The gravitational force is one of fundamental forces in nature discovered to govern the interaction of material objects. The other three fundamental forces are the electromagnetic force, the strong nuclear force, and the weak nuclear force (which is now usually combined with the electromatic force as the electroweak force). The two nuclear forces are effective only at the subatomic scale. In contrast, the gravitational and electromagnetic forces act on objects from the atomic to extragalactic scales. Progress is also being made to treat gravitation as a side effect of string forces.

Johannes Kepler discovered (circa 1609) that the planets describe ellipses in their circuits about the Sun, with the Sun occupying a focal point of the ellipse. From this discovery scientists like Edmond Halley, Robert Hooke, and others, speculated that the force exerted by the Sun on the planets varied as the inverse square of the distance...