On Saturday we talked about including some definitions of ether in the newsletter that we’re making. As a concept that some of us have found challenging since Geoff’s radio workshop we thought we might have a look at how the meaning of the word ether has changed – possibly by constructing a timeline of definitions. I actually found this http://en.wikipedia.org/wiki/Timeline_of_luminiferous_aether on Wikipedia but it would be nice to put together a few concise definitions, maybe including some of our own. The following are taken from books that I had at home but they were all written relatively recently so are quite consistent – if anyone can find a much older definition to compare, that would be great.
ether clear sky, upper air. (The Little Oxford Dictionary, 1994)
ether n. Clear sky, upper air; medium formerly assumed to permeate space and transmit electromagnetic radiation; ethereal a. light, airy, of unearthly delicacy of substance etc., heavenly (The Oxford Handy Dictionary, 1978)
ether, a hypothetical substance formerly supposed to pervade the whole of space and be the medium in which light travelled. The Michelson-Morley experiment, which used interferometry to detect the presence of this luminiferous ether and to measure the movement of the Earth with respect to the ether, has led to the abandonment of this hypothesis and the acceptance that electromagnetic radiation is a wave motion without a medium. (Oxford Illustrated Encyclopedia of the Universe, 1992)
Michelson-Morley experiment An experiment performed by A.A. Michelson and E.W. Morley in 1881 in an attempt to demonstrate the existence of the luminiferous ether by measuring the earth’s velocity relative to it. They used a Michelson interferometer to obtain interference fringes and then rotated the apparatus through 90 degrees expecting to find a shift in the fringes, since the velocity of light would be different in the two directions. This difference would result from the earth’s motion through the ether. However, no shift was detected. This negative result led to the downfall of the ether theory and was explained by Einstein’s theory of relativity in 1905. (The Macmillan Encyclopedia,1988)
Michelson, Albert Abraham (1852-1931) American physicist, of German extraction, who is mainly remembered for his work on the velocity of light. Using his interferometer (invented in 1881), he and Edward W. Morley showed in 1887 that the speed of light in a vacuum is the same in all inertial reference systems (coordinate systems moving at constant velocity relative to each other). It had been held since the days of Huygens that light travels through a stationary substance filling the whole of space (the so-called ether), but Michelson and Morley’s experiments proved that there was no such thing. This led directly to the development of the special relativity theory by Lorentz and Einstein. (Who Did What, 1974)