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Question

I am curious as to exactly when scientists found out that space is a vacuum and not made up of ether? What year was this and who is credited with the discovery?
Asked by: Nancy Thorgaard

Answer

In 1887, Albert Michelson and Edward Morley conducted an experiment that refuted the concept of and ether wind. They compared the speed of light in one direction with its speed at right angles to that direction. If light were in fact transmitted via an ever present ether, the motion of the Earth through it would result in an ether wind which would affect light's speed into and across its path.

The Michelson-Morley experiment detected no difference in the speed of light, regardless of direction vs. the hypothesized ether wind. Although several attempts were made to explain away the experiment's results, the eventual conclusion was that the proposed ether wind must, therefore, not exist.
Answered by: Paul Walorski, B.A., Part-time Physics/Astronomy Instructor


Originally, the idea of measuring the speed of Earth through the ether came from Maxwell. During correspondence with others, the task fell upon Michelson. Michelson had made the most accurate measurement of the speed of light to date. But then Michelson proceeded to invent a new instrument with accuracy far exceeding that which had been attained to that date, and that instrument is now universally called the Michelson interferometer. In trying to measure the speed of the Earth through the supposed 'ether', you could depend upon one component of that velocity being known - the velocity of the Earth around the sun, about 30 km/s. Using a wavelength of about 600 nm, there should be a shift of about 0.04 fringes as the spectrometer was rotated 360�. Though small, this was well within Michelson's capability. Michelson, and everyone else, was surprised that there was no shift. Michelson's terse description of the experiment: 'The interpretation of these results is that there is no displacement of the interference bands. ... The result of the hypothesis of a stationary ether is thus shown to be incorrect.'

Lord Rayleigh wrote to Michelson, urging him to repeat the experiment with greater accuracy to test these hypotheses. Michelson, with the collaboration of E. W. Morley, constructed a new interferometer with multiple mirrors and a path length about 10 times longer. This device should have given a fringe shift of about 0.4, but they observed less than 0.005 fringe. Although repeated over the next 40 years with ever greater precision and the same negative result, this 1887 experiment is pointed to as one of the experimental foundations of relativity, and earned Michelson the Nobel Prize in 1907.
Answered by: Jason Heidecker, Physics Undergrad, Occidental College, Los Angeles



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