In order for a scientific explanation of the mass to be accurate and justified at least three conditions should be met. First, it has to be in accordance with experienced fact which is described by Newton's law that \(M = \frac F A\). Second, it has to be in accordance with experimentally confirmed fact that mass of artificially created particles equals \(M = \frac W {c^2}\). Third, it has to be able to qualitatively explain and mathematically prove the law of gravitation \(F = G \frac {M_1 M_2} {R^2}\).

In this paper we will explain and mathematically prove the first two conditions. As for the law of gravitation, for its theoretical and mathematical explanation it is necessary to present a nature of ether in a more detailed manner first, as space gas fluid which fills entire endless space of the Universe, and we will do that in one of subsequent papers. The reader will eventually understand that efforts in explaining of the material Universe with the assumption that ether doesn't exist are more futile than efforts to explain the nature of the ocean on the premises that water doesn't exist.