Einstein, Michelson, and the "Crucial" Experiment

THE HIGHEST ACHIEVEMENTS in science are of quite different kinds: the bold theoretical generalization, breathtaking by virtue of its sweeping synthetic power, and the ingenious experiment, sometimes called "crucial," in which the striking character of the result signals a turning point. Albert Einstein's special theory of relativity as first published in 1905 is a supreme example of the first kind, and A. A. Michelson's experiments in the 1880's to find the effect of ether drift on the speed of light are often cited as prototypical examples of the second kind. Even if these two achievements had nothing whatsoever to do with each other, each would continue to be remembered and studied on its own merit. But these two cases have in fact held additional interest for historians and philosophers of science; for, as we shall see, it has been the overwhelming preponderance of opinion over the last half century that Michelson's experiments and Einstein's theory have a close genetic connection, one which may be stated most simply in the words of the caption under Michelson's photograph in a recent publication of a scientific society (see frontispiece): Michelson "made the measurements on which are based Einstein's Special Theory of Relativity." A more detailed account of the experimental origins of relativity theory is attempted in R. A. Millikan's essay "Albert Einstein on his Seventieth Birthday." It was the lead article in a special issue in Einstein's honor of the Reviews of Modern Physics, and the early parts are worth quoting: