1The Invariant Truth Principle

Abstract. A single postulate, called the Invariant Truth Principle, is proposed. It imposes that, in principle, the happening of a physical event in a given frame has to be acknowledged in any other frame whatever their relative motion be. That postulate could replace the two principles on which Special Relativity is based. ____________________ If “kinematic ” were a qualifying adjective, I would say that the way used by Einstein to introduce Special Relativity seems too “kinematic ” as far as I am using “kinematic ” as a synonym of “descriptive”. I mean that one could think that if we did not need a group of transformations (from one frame to another) which was the same both in the mechanics and in the electromagnetism, we would not need the theory of Special Relativity. This amounts to saying that Special Relativity and its successful results seem due almost exclusively to the new vision of space and time or, if we like, of space-time. It has to be acknowledged that this new vision exerted a great deal of “fascination ” during some decades following the publication of the Einstein’s article “On the Electrodynamics of Moving Bodies ” but, because in everyday life we experience only velocities which are very low compared to the velocity of light, such a vision is kept in mind mainly by scientists who use the contents of Special Relativity and by students facing this part of physics for the first time. It’s no accident that Einstein himself starts his book “The Meaning of Relativity ” with the sentence: The theory of relativity is intimately connected with the theory of space and time.1 That space-time is the fundamental element we need to describe the natural processes is extremely obvious; nevertheless we have to keep in mind that the effects of