At the beginning of last century, physicists tried to solve the problem: to find a way through electrical interaction to get some small (compared to electric) force acting always at the attraction. The calculation of forces for Einstein velocity addition formula. Since the dependence on the size and shape of the body we are not interested, then we consider the space of the body assumed to be sufficiently distant. Then instead of the bodies have the right consider the notion of material point. Must make two statements: 1. In the "rest" all the material points scatter with some low speed -.
(We assume that this rate corresponds to the speed recession of galaxies in terms of 1 meter). 2. Must take into account the electric interaction of charged particles that make up the body (leptons, quarks, etc.). This statement is not necessary to prove – it is usual superposition of fields. Consider, for neutralizing the electrical interaction of two different particles with a charged particle. We show that it remains small (compared to electric) interaction, directed always at the attraction. This attraction is, apparently, is the gravitational interaction. Recession (this is not proof, but one possible explanation) can be explained by the curvature of space.
Suppose that our three-dimensional space is described by Euclidean geometry. Resting on the line, we choose the material points. Now, consider these points in space, describes the geometry of . Then they rest described parallel lines (world lines). Now imagine that this space is not flat, as described by the metric of the – something like this comes in general relativity.