Abstract

According to conventional wisdom, Poincar? failed to derive a relativity theory mainly as a result of his stubborn adherence to the ether. In (1905) Einstein constructed a relativity theory that was based on the assertion that the ether was superfluous. In 1908 Minkowski formulated the theory of the ?absolute world?. The nineteenth century ether no longer existed. A new kind of ether (space-time) came into being. One could keep on maintaining the ether, and at the same time strip it of the notion of absolute rest. Einstein seemed to agree, and after 1916 he returned to the ether. In 1920 he combined Minkowski?s absolute world concept and Mach?s ideas on rotational movements: in order to cancel action-at-a-distance, the inertial interactions between matter and fixed stars should be mediated by a medium. Einstein called Mach?s medium ?Mach?s ether?. In this paper I demonstrate that Einstein?s 1920 reasoning hardly differed from the one Poincar? had presented prior to 1905. Thus, whil Einstein was a hero because he did away with the ether, this situation lasted a few years only. This is not to underestimate the magnitude of Einstein?s achievement, but to emphasize the limits of simplistic comparisons between Einstein and Poincar?.