Since the dispute over the theory of relativity has begun to die down over the last several years and the new theory has been even more successfully worked through, the most recent attacks upon it have come from the flank from which it was the least expected. They are not attacks on the philosophical motivation, and thereby not the well-known reproaches that the theory is “inconceivable” or “incompatible with common senses”; rather, we are now confronted with a physical experiment that stands in explicit contradiction to an assertion of the theory of relativity. This experiment was conducted by the American D. C. Miller at Mount Wilson and was published in the Proceedings of the National Academy, Washington (11, 382, 1925).

It concerns the so-called Michelson experiment, one of the most foundational pillars upon which the theory of relativity is constructed. This experiment traces back to the ideas of Maxwell, but it was Michelson, a scholar famous for his precision in optical measurement, who first carried it out. Michelson had already begun his investigation in the seventies in Berlin as an assistant to Helmholtz, and carried it out in the eighties in America. We can describe the experiment in schematic form in the following way (Fig. 13.1): two rigid arms are placed at right angles with mirrors S1 and S2 fixed perpendicularly to the arms at their end points.