Lessons From the Michelson-Morley Experiment

This year marks the centenary of one of the most important scientific experiments ever performed It was in Cleveland, Ohio in 1887 that Albert A. Michelson and Edward W Morley undertook a measurement that was a milestone in man's effort to understand the way in which light travels through space. Physicists regard this work as a crucial step in our journey toward an understanding of the very nature of space and time itself Had the results of this measurement been different, Einstein's theory of relativity would not have been tenable. The Michelson-Morley experiment was remarkable in many ways. Not only did it set the stage for Lorentz, Fitzgerald, Poincare, and finally Einstein to establish the mathematical framework that described the propagation of light through space and time, it also marked a turning point for science in the New World. The year 1887 can be said to mark the birth of modern physics in America. Perhaps the most astonishing feature of the Michelson-Morley experiment was the precision with which it was performed. The design of the apparatus was such that it would easily have been possible to detect a change of one part in one hundred million in the average speed with which light traveled along one of the arms of the interferometer! This extraordinary feat was accomplished by splitting a beam of light in two, and then sending each half on a 22-meter journey be fore recombining them into a single beam. Michelson and Morley claimed the ability to detect whether one of the half-beams was lagging behind the other by as little as one-fiftieth of the wavelength of light. This claim would result in an even greater precision of one part in a billion! As we look back on the experiment we can note a number of lessons for modern-day scientists. One immediate observation is it is evidently possible for a great collaboration to occur even when the two partners have markedly dissimilar personalities. Morley was a staid individual whose family had lived in New England since the 17th century, and who was a licensed minister of the Congregational Church. Michel soil, on the other hand, was a much more dashing and colorful figure. The strikingly handsome former Naval officer pursued his science (and, on occasion, the opposite sex) with forcefulness and determination. This contrast in personalities did not pre vent the two great scientists from undertaking a series of intensely fruitful collaborations, culminating in their great ether-drift experiment Another point to note is that Cleveland in the late 19th century provided an environment in which scientific talent was recognized and appreciated. Such industrialists as machine-tool makers Worcester Warner and Ambrose Swasey took a close interest in and gave support to research on the campuses of both Case School of Applied Science, where Michelson worked, and Western Reserve University, where Morley was a professor. Charles Brush, developer of the arc light, supported both scientists, and even co authored a couple of papers with Morley. Then, as now, a close and supportive relationship between science and industry was a significant factor in facilitating the development of new ideas. Perhaps the most timely lesson for 1987 can be learned by a comparison of the simple elegance of the Michelson-Morley experiment with the work that Michelson under took later in his life. His last experiment involved a measurement of the speed of light in a partial vacuum. A corrugated iron tube, 1 mile long and 3 feet in diameter, was built and then equipped with pumps, mirrors and lamps. In its day this surely was the largest piece of physics apparatus ever constructed. It is tempting to think of it as the forerunner of the enormous systems of evacuated pipes in which modern high-energy physics experiments are conducted. While the huge iron tube allowed Michel son's team to make a useful measurement of the velocity of light in a vacuum, the significance of that work pales beside the importance of the tabletop Michelson-Morley experiment performed in 1887. Today we are conscious of the need for ever-larger machines with which to explore the fundamental properties of matter on a smaller and smaller scale. At the same time we should remain awake to the fact that profound and beautiful physics can be found in experiments conducted on a smaller scale. On October 30 we at Case Western Re serve University will be holding a symposium with the title "Modern Physics in America" to mark the centenary of the Michelson-Morley experiment. We will learn of some of the results that big-machine physics has brought us, but will also remember that the simplest of apparatus can, in the hands of a truly creative scientist, lead to the very deepest of insights. Taylor is executive director of the Michel son-Morley Centennial Celebration and is a professor of physics at Case Western Re serve University, Cleveland, OH 44106. For a description of the experiment, by Michelson's daughter, see p. 24.

Lessons From the Michelson-Morley Experiment

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