Stories from the Archives

The Michelson Morley Experiment

It's hard not to notice that the names Albert Michelson and Edward Morley seem to be everywhere here at Case Western Reserve. There is the Michelson-Morley Monument that is reminiscent of Freud, and nearby is the now defunct Morley Chemistry Building. There is the Michelson House dormitory, which allegedly has a large time capsule somewhere in its walls. At least three plaques on campus commemorate their work, as well as at least two mock apparatuses of their interferometer. Clearly their work was, and to some extent still is, a great source of pride for the university.

To understand their importance, however, you have to go back in time. In fact, a very, very long time.

It all begins with a little man from 5th century BC Greece who they called Plato. He theorized that there were five elements that constituted everything. The ones we are familiar with are Earth, Wind, Water and Fire. For example, a rain cloud was made of Wind and Water, whereas a pot was Fire and Earth. The fifth element, the quintessence, was not Milla Jovovich, but something called Aether. Aether was the stuff of celestial bodies and the air of immortals. After many centuries of reasoning, this became what filled the space between planets.

What's unusual about this theory is that aether lived on for more than two millennia afterwards. The interpretation of aether changed to be the medium through which light traveled. Just as sound requires air to transmit across a distance, light needed aether to spread through the heavens. Aether theory also requires something called aether winds, which are the ebb and flow of aether. Without going into too much theory, aether wind is required to give you a point of reference in an otherwise empty universe. Without the aether winds, you have no frame of reference. If you want to know a little more about aether theory, please see the sources down below.

By now I am sure you are now wondering what a very old and now largely non-existent theory has to do with two guys named Edward Morley and Albert Michelson. You may have also stopped reading, which makes this statement rather paradoxical. In 1887, Michelson and Morley were faculty at Case Institute of Technology and Western Reserve University, respectively. Michelson wanted to measure the speed of this aether wind, but his lab had burned down and saw that Morley was the only one who could support the experiment.

The existence of an aether wind has two important implications. The first is that the aether wind must have a directionality when viewed from the surface of the Earth. The second, which is a little subtler, is that depending on which direction a beam of light travels, the time it takes for light to travel a certain distance will vary. If the light travels in the same direction as the aether wind, it will go faster than the light that travels perpendicular to the wind which is without aether wind assist.

The implications of an aether wind therefore made for a relatively clever experiment using a device called an interferometer. Again, to avoid making this into a physics lesson, I will avoid the theory involved in the experiment. What Michelson and Morley thought they would see were differing patterns of light depending on which way the interferometer was oriented relative to the aether wind. What happened, however, was that no matter how they oriented their interferometer, it never changed the light pattern. This was both baffling and disturbing, in the fact that the results seem to indicate either the Earth was perfectly stationary relative to the aether wind, or that aether did not exist.

With these unexpected results, there were two possible conclusions. Having the aether winds move perfectly in sync with the Earth justifies Michelson and Morley's findings, but would make physics radically different depending on from what planet you were observing. If the alternative was true, that aether did not exist, that raises the issue that all the research over the centuries involving aether have to be rethought. Either way, the implications of this experiment were troubling.

Or, at least, they were to Morley. Morley repeated the experiment several times, working with Dayton Miller. The results were always the same, all across the world: no interference pattern. Michelson, on the other hand, was more apathetic to the matter. Until he met Albert Einstein in 1931, Michelson thought the results of his experiment were inconclusive and remained set in aether theory. He moved on to other projects but never investigated aether drift again.

Experiments that have a negative result rarely make the news, but they do remain important. Almost twenty years later Einstein would propose his theory of relativity, in which there is no aether but rather a constant speed of light. The experimental results by Michelson and Morley were the experimental proof for Special Relativity, opening the world to the era now known as Modern Physics. While Michelson and Morley went on to make other scientific discoveries in their lives, the interferometer experiment is commemorated for it's contribution to dispelling old theories and bringing in new ones.

-Greg Wu (gregory dot wu at case dot edu)

Sources: Fabric of the Cosmos, by Brian Greene (the first few chapters are a very good explanation of later aether theory)
Case Western Reserve: A History, by C.H. Cramer