2 00 6 The road not considered . . . the question of photon mass

It is well-known that a conflict between Galilean relativity and Maxwell equations of electromagnetic equations was apparent by the end of the 19th century. Equally well-known is the fact that Einstein resolved the conflict by pointing out that the principle of relativity and Maxwell equations can both be correct if the notion of absolute time is abandoned. The rest is history. The purpose of this article is not to recount that history. Rather, we wonder about a question which, it seems, should have been asked in the process, but apparently was not. Newtonian formulation of dynamics was firmly established by the nineteenth century, proving its worth in all sorts of questions that were addressed within its framework. Einstein’s introduction of Special Theory of Relativity required a reformulation of the laws of dynamics. Newtonian dynamics became only an approximation, valid in the regime of small speeds. Maxwell equation of electrodynamics, however, remained unaffected. And this is where the question comes. In the times of great upheavals, it is natural to re-examine everything conventional. Newtonian dynamics was indeed re-examined and replaced by a more sophiticated alternative with the advent of special relativity. Why wasn’t there any serious discussion about any modification or reformulation of Maxwell equations at the same time? It almost seems like a vain question. Wasn’t the entire conflict created by the presence of the quantity c in Maxwell equations, implying that the speed of electromagnetic waves in the vacuum is independent of the observer? And didn’t Einstein absorb this statement as a postulate in his system, thus assuming the immutability of Maxwell equations in the basic structure of his Special Theory? Yes, it is undeniable that the Maxwell equations contained a fundamental quantity which has the dimension of velocity. This is most apparent if we write the equations in Gaussian units, where the electric and the magnetic fields are assumed