2. The mutual attraction existing between all objects with mass.
Newton's law of gravitation states that the force of attraction between two bodies varies as the product of the two masses and, inversely, as the square of the distance between them.
Einstein's theory of general relativity views the attraction as being a result of the curving of space and time by a massive object.
Quantum gravity considers the force to be the result of the exchange of particles known as gravitons.