Special relativity from classical gedanken experiments involving electromagnetic forces : a contribution to relativity without light

Abstract

Our goal is to present a derivation of Lorentz’s transformations from gedanken experiments with electromagnetic forces without having to assume Einstein’s postulate of the constancy of the speed of light. Instead, we propose a different second postulate, namely that electric charge is independent of the state of motion of the system, and we restrict the first postulate in order to state the relativity of electromagnetic forces only. We argue that assuming that charge is invariant is much more intuitive than assuming that light speed is constant. In this derivation, furthermore, the constancy of a limit speed c is obtained as a result of the velocity addition rule. Finally, we discuss the epistemological and didactic implications of this formulation.