Principle of Relativity

Based on a thought experimentThought experiment devised by Galileo, this chapter aims to explain the principle of relativityPrinciple of relativity as simply as possible. The main consequence is the invariance of physical phenomena, whether mechanical or electromagnetic. In other words, the laws of physics are the same for all observers in uniform rectilinear motion, i.e., moving in a straight line at constant speed relative to each other. We’ll show that to ensure this invarianceInvariance, physicists have devised a change of coordinates, known as Galileo’s transformation that allows us to move from a fixed to a moving reference frame. We’ll then see that the classical velocity addition lawVelocity addition law, which is a consequence of the principle of relativity, discovered by Galileo was invalidated by the failure of experiments attempted to demonstrate the Earth’s motion around the Sun. This brings us to the problem of special theory of relativitySpecial theory of relativity.