Einstein’s Article of 1905

This chapter firstly aims to show that Einstein began his research on the electrodynamics of moving bodies between mid-May and the end of June 1905. It will then be shown that, using a purely kinematicKinematic approach consisting of writing the equations for the propagation of a light signal in a moving reference frame with respect to a stationary one, Einstein succeeded in establishing the transformation of coordinates and time leaving invariant the four Maxwell’sMaxwell, James Clerk equations. However, unlike Poincaré, he did not immediately give it the LorentzLorentz, Hendrik Antoon name. He was, however, able to deduce from it the new relativistic velocity addition lawRelativistic velocity addition law. This kinematicKinematic approach also enabled him to extend the Doppler-Fizeau effectDoppler-Fizeau effect to electromagnetic waves, thus demonstrating the Relativistic Doppler effect. Finally, it will be shown that while Poincaré tried to “save” Lorentz’s theory of electronsLorentz (Theory of electrons), Einstein planned to develop a new theory, soon to be known as the special theory of relativitySpecial theory of relativity.