On Einstein's distrust of the electromagnetic theory: The origin of the lightvelocity postulate

Abstract

The constancy of light velocity is a consequence derivable from the application of the relativity postulate to Maxwell's equations. Therefore, Lorentz and Poincare felt no necessity for introducing the light-velocity postulate independently of the relativity postulate. On the other hand, Einstein, who had already developed the theory of light quantum, knew the inadequacy of Maxwell's electromagnetic theory in the microscopic sphere. Therefore, he felt it necessary to set up the light-velocity postulate independently in order to make the electromagnetic foundation of physics compatible with Planck's radiation formula. This point constitutes the essential difference between the theories of Lorentz-Poincare and Einstein. In other words, the Lorentz-Poincare theory lacks the kinematical part essential for the special theory of relativity. The reqson that students of the history of the special theory of relativity hitherto overlooked this obvious fact might lie in a crucial error contained in Einstein's Autobiographical notes in their first and second editions. The correction, introduced for the first time in the German edition of 1955, the year of Einstein's death, revealed that the first core ingredient of Einstein's research program was thermodynamics. His letters to his fiancee as well as his works in his early years permit us to more about his research program. This program conformed to the chemico-thermal research tradition to which he belonged. The latter tradition made postulates of the relativity and the light-velocity accessible to him, and was also important in the receptive process of the special theory of relativity.