摘要：The law of universal attraction has been used widely. However, how two objects attract each other is still a riddle. Hypotheses, such as gravitons, universal repulsion, sub-photon seas, etc., all have flaws, and do not deal with the basic reason why there is such a law. In this paper, suppose: (1) microparticles at a certain speed, moving like thermal motion of molecules, are distributed in space; (2) the objects are not continuous in microstructure, but there are gaps between the particles comprising the objects, allowing some microparticles to pass through; (3) momentum transferred from microparticles to the objects is proportional to mass of the objects. This theory of momentum exchange between objects and microparticles may interpret the source of universal attraction more reasonably as well as providing a formula to be used as a basis for calculation. Universal attraction is an equivalent expression for momentum exchange between objects and microparticles. This generates the force acting along the line of centers of the two objects which are close to each other. The universal attraction constant G is accurate only for astronomical bodies near the earth. Universal attraction between two objects is related to an intermediary between them. There is no graviton.
