The theory of relativity presented to the scientific community at the beginning of the last century made a splash. Its author, A. Einstein, for decades to come defined the main directions of physical research. However, do not forget that the German scientist in his works used the numerous achievements of his predecessors, including the famous principle of relativity Galileo - the famous Italian scientist.
The Italian scientist devoted a significant part of his life to the study of mechanics, becoming one of the founders of such a branch of physics as kinematics. Galileo's experiments allowed him to conclude that there are no fundamental differences in the states of rest and uniform movement - the point is what point of reference will be accepted. The famous physicist pointed out that the laws of mechanics are valid not for any one chosen coordinate system, but for all systems. Such a principle went down in history as the Galilean principle of relativity, and systems began to be called inertial.
The scientist with pleasure confirmed his theoretical calculations with numerous examples from life. The example with the book on board the ship was especially popular: in this case, it is at rest relative to the ship itself, and relative to the observer on the shore, it moves. Galileo’s principle confirms his position that there is no difference between peace and movement.
The Galileo principle of relativity formulated in this way made a real sensation among his contemporaries. The thing is that before the publication of the works of the Italian scientist, everyone was convinced of the truth of the teachings of the ancient Greek scientist Ptolemy, who claimed that the Earth is an absolutely motionless body, with respect to which other things are moving. Galileo destroyed this idea, opening new horizons for science.
At the same time, it is impossible in any case to idealize either Galileo's principle of relativity or the law of inertia. After all, based on this formulation, we can conclude that all these positions apply absolutely for any parameters of speed and distance between bodies, but this is not so. The first step from the Galileo-Newton theory to the theory of relativity was the development by Gauss, Gerber and Weber of the theoretical foundations of the phenomenon, which was called "potential delay."
Neither Galileo nor Newton, due to the level of knowledge existing at that time, could even guess that when the body’s speed approaches the speed of light, the laws of inertia simply cease to act. And, in general, the Galilean principle of relativity is ideally suited only for those systems that consist of two bodies, that is, the influence of other objects and phenomena on them is so insignificant that it can be neglected. The movement in such a system (the rotation of the Earth around the Sun can serve as an example ) was subsequently called absolute, all other movements were called relative.