On the Naturalness and Generality of the Relativity Principle

Special relativity theory postulates that the laws of physics are the same in all inertial frames of reference (the relativity postulate), and that the velocity of light in vacuum has the same value c in all inertial frames of reference (constancy of c postulate). We show, based on basic principles, that nature is endowed with symmetry with respect to its laws, such that the principle of relativity is a genuine property of nature, which is independent on the constant velocity of light, or on any other constant. We also show that the principle of relativity is associated with spatial asymmetry, such that the direction of relative motion matters. For frames of reference departing from each other, an observer in one frame will measure time and distance extension, with respect to the time and distance measured in the other frame, while for reference frames approaching each other, the same observer will measure time and distance contraction with respect to the same occurrence. No less important, we show that the principle of relativity is valid for all physical systems, independently of the type of information carrier utilized in the system, and is not specific to systems in which information between reference frames is transmitted by light, or other electromagnetic waves.