Equivalence Principle and Ether: Two Revolutionary Kernels of Einstein’s General Relativity

Abstract

Einstein’s discovery of the Equivalence Principle is to be considered as the most fundamental concept at the origin of his General Relativity. I highlight that the ether problem is related with Enstein’s conception of gravitational waves as a perturbation of the space-time curvature, formalized as a specific space-time process, and not as the effect of a whatever supporting medium. Quite differently, the nineteenth century field theory of gravitation supported by physicists such as Maxwell, Heaviside, and Hertz, w as based on a search for substantial ether, and on a parallelism with Maxwell’s theory of electromagnetic waves. The negative results of their theories proved that parallelism was a wrong approach. Einstein’s genius superseded their approach by considering that it was not a matter of the ether’s constitution, but of a fundamental change in the role and nature of physics. In my paper I refer to Einstein’s different approaches to ether since his 1905 Special Relativity up to his 1950’ views. I argue that his different attempts were symptoms of the difficulty of his revolutionary innovation.