The force of attraction that exists between any two masses, whether they be stars, microscopic particles or any other bodies with mass. It is by far the weakest of the four fundamental forces (the others being the electromagnetic force, the strong nuclear force and the weak nuclear force), and yet, because it is a consistent force operating on all bodies with mass, it is instrumental in the formation of galaxies, stars, planets and black holes. It was approximately described by Sir Isaac Newton’s Law of Universal Gravitation in 1687, and more accurately described by Albert Einstein’s General Theory of Relativity in 1916.