In this paper it is proposed that the mass of the bodies has its origin and nature in the reciprocal gravitational interactions between them; and also by some kind of effect over the size of the celestial bodies due to the very big distances in space, as seemed each other at a distance. In a Dynamic Theory of Gravitation , it is proved that the fundamental velocity is the escape velocity due to the apparent size of the interacting heavenly bodies, which is the medium used by gravity to transmit its effects like propagating force of Nature . Given that is the greatest speed of the Universe, the celestial bodies interact between them in a reciprocal way . Because of that dynamical process all those bodies have an intrinsic property called mass. Then, the mass of any body is a kind of parameter by means of which a measure of the inertial effects can be obtained. That property is different from weight. It is a consequence of the gravitational interactions between any body and all the rest of the heavenly bodies of the Universe, and also by some deep characteristic of the space that separate them.
Fierros Palacios, A. (2015). The Small Deformation Strain Tensor as a Fundamental Metric Tensor. Journal of High Energy Physics, Gravitation and Cosmology, 1, 35-47.