CHAPTER 1 - THE PRINCIPLE OF RELATIVITY

Abstract

This chapter presents the principle of relativity. According to this principle, all the laws of nature are identical in all inertial systems of reference. In other words, the equations expressing the laws of nature are invariant with respect to transformations of coordinates and time from one inertial system to another. This means that the equation describing any law of nature, when written in terms of coordinates and time in different inertial reference systems, has one and the same form. The combination of the principle of relativity with the finiteness of the velocity of propagation of interactions is called the principle of relativity of Einstein, formulated by Einstein in 1905, in contrast to the principle of relativity of Galileo, which was based on an infinite velocity of propagation of interactions. The idea of an absolute time is in complete contradiction to the Einstein principle of relativity. For this, it is sufficient to recall that in classical mechanics, based on the concept of an absolute time, a general law of combination of velocities is valid, according to which the velocity of a composite motion is simply equal to the (vector) sum of the velocities which constitute this motion. This law, being universal, should also be applicable to the propagation of interactions. The principle of relativity leads to the result that time is not absolute. Time elapses differently in different systems of reference.