Abstract

In 1905, as is well known A. Einstein began to deny the existence of an ether as it was conceived in 19th-century physics, in particular of Lorentz's ether, which was in the first place a privileged reference frame. He denied its existence because it violated his principle of relativity, according to which there is no privileged reference fram for the formulation of the laws of nature. Nevertheless, in 1916, after the definitive formulation of the general theory of relativity, Einstein proposed a completely new conception of the ether. In this conception, the new ether does not violate the principle of relativity because the space-time of the theory of relativity is conceived, in it, as a material medium sui generis that can in no way constitute a frame of reference.