Proof of light speed invariance and relative velocity invariance

In this paper, we will explain and prove in detail Einstein's postulate with respect to the invariance of light speed. The "mysterious" invariance of light speed is a very normal natural phenomenon, but it is impossible to dominate time and space. The two observers on two relative motion reference frames have opposite views regarding which reference frame is stationary. We also give the precise definition of invariance of light speed, and explain the postulate of maximum speed.

This paper also derives the principle of invariance of relative velocity, which is the physical reason of the principle of relativity. In fact, Newtonian mechanics and Maxwell's equations are based on relative motion. We give the precise definitions of relative velocity

Distinguishing physical time and mathematical time, and distinguishing physical space and mathematical space are the key to understand the reason of invariance of light speed. All motions are relative. All motion velocities are based on a reference frame we define. We don't have an absolutely stationary reference frame in the universe.