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The Quest for the Ether
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12545 |
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Section : |
NATURAL SCIENCE
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| Issue
Date : |
7 / 1987 |
3,867 Words |
| Author
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Arthur I. Miller
Arthur I. Miller is professor of philosophy and history at the
University of Lowell in Lowell, Mass., and Associate of the
Physics Department at Harvard University. |
In 1880, Albert A. Michelson conceived of an optical instrument striking in its simplicity and breathtaking in its precision. Michelson's interferometer opened up new fields of research and led to his being the first American Nobel laureate for any scientific achievement (1907). Yet, ironically, he is best known to many scientists for an experiment that failed.
In July 1887, Michelson and Edward W. Morley attempted to measure the velocity at which the earth moves relative to the medium that was assumed to transmit light, the ether. Their failure was considered to be nothing short of extraordinary. It became a puzzle that would preoccupy physicists for almost two decades, and that is still discussed today. Why? To some extent the reply resides in how the puzzle was resolved. On the one hand, the eminent Dutch physicist H.A. Lorentz proposed a detailed explanation for the dilemma, while on the other hand, Albert Einstein declared that there was no puzzle at all because this was the way the experiment should have turned out. There is also speculation about the place that this experiment has taken in the history of ideas - namely, as a crucial experiment that was the catalyst for Einstein's invention of the special theory of relativity. In the centennial year of what is considered to be one of the most significant experiments ever conducted, it is appropriate to recall its origins, intent, reception, and current interpretation.
Background
By the middle of the nineteenth century, physicists had agreed that light travels in waves, just as sound does. Sound waves require a medium, like air or water, for their transmission; waves are a form of energy that propagate, for example, by progressively compacting and expanding the medium without permanently moving or altering it. Physicists argued that light waves must require a similar medium, and they called this hypothetical substance the ether.
Many experiments were devised in an attempt to detect the presence of the ether. These experiments were collectively called "ether-drift" experiments, for they attempted to show the influence of the ether on the velocity of light. The intent of these experiments can be demonstrated with the following "thought experiment."
Suppose that a light wave is emitted from a source that is at rest on the ground. The velocity of a marked point on the wave relative to the source is c. After the wave has been emitted, an observer originally at rest begins
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