Under some well-defined conditions the mathematical formalism of quantum mechanics enables physicists, chemists and other to calculate and predict the outcome of a vast number of experiments. In fact, especially the Schrödinger equation which involves an imaginary quantity describes how a quantum state of a physical system changes with time and is one of the main pillars of modern quantum mechanics. The wave function itself is a determining part of the Schrödinger equation, but the physical meaning of the wave function is still not clear. Altogether, does the wave function represent a new kind of reality? This publication will solve the problem of the physical meaning of the wave function by investigating the relationship between the wave function and the theory of special relativity. It is shown that the wave function is determined by notion co-ordinate time of the special theory of relativity. Moreover, the result of this investigation suggests a new understanding of the wave function, according to which the wave function and co-ordinate time of the theory of special relativity are equivalent. Apparently, based upon the close relationship between time and gravitational field and the normalized relativistic energy-momentum relation, this contribution provides a way to calculate the “mass-equivalent” of a photon in SI units as 7.372 503 726 490 51 * 10^-51 and the “mass-equivalent” of a graviton in SI units as 1.346053370*10^-136 . A necessary mathematical formalism for the quantization of the gravitational field is developed.