Relativity and Electrodynamics

Abstract

This chapter is deliberately not called “relativistic” electrodynamics, because there really has never been a “nonrelativistic” precursor. Maxwell’s theory has always been relativistic in Einstein’s sense, though no one before Einstein realized this. To be precise, the formal transformations (of the coordinates and of the electric and magnetic field vectors) leaving Maxwell’s equations invariant had already been found by Lorentz and others (and this was the origin of the “Lorentz transformations”), but it simply was not understood that these transformations had a physical significance, namely that they related actual measurements made in different inertial frames. Since the physically relevant coordinate transformation was thought to be the Galilean transformation, Maxwell’s theory was in fact thought to be strictly true in only one inertial frame—that of still ether.