Abstract

It is a dictum of Einstein?s Special Relativity Theory (SRT) that the strictly inertial motion of any physical system cannot be detected without some reference external to the system. This dictum has been tested through the years by a variety of optical experiments. Usually, the motivation has been to re-open the case with regard to the concept of a ?luminiferous aether?, which had dominated much of scientific thought in the century before Einstein?s revolution. Results have generally been proclaimed ?null?, although in actuality they have sometimes been rather ambiguous, and the more so the more recent the work is. But aversion to anything like the old ?luminiferous aether? still hinders acknowledgment of any such results. It is my belief that any linear velocity with respect to which an optical system can be reversed can indeed be sensed, but that the proper inference to be drawn from that fact does not concern any kind of ?luminiferous aether?, or even modern ?physical ether?. Instead, the proper inference is that revision of Einstein?s light speed postulate is needed. A modified postulate, different but still ether-free, is shown to lead to observed results.