Results from a Michelson-Morley experiment were wrongly interpreted and Albert Einstein puffed his pipe and proclaimed, “The Ether is not necessary.” (Background: Our Friend, The Ether (Part 5), Ersjdamoo’s Blog entry of October 17, 2013.)
Albert Abraham Michelson (surname pronunciation anglicized as “Michael-son”, December 19, 1852 – May 9, 1931) thought The Ether might be detectable via an “ether wind.” Of course, since The Ether is at absolute rest in absolute space, there would be no “ether wind” as such. However because the earth travels through The Ether at roughly 67,000 miles per hour, this might result in effectively an “ether wind.”
The light waves are carried by The Ether. But would an “ether wind” make any difference on how fast the light waves traveled? You probably know that if you ride your bicycle into the wind, that can slow you down. Maybe a beam of light traveling against the “ether wind” would be slowed down as well, pondered Michelson.
Yet right there we have a preliminary problem: An ordinary wind has friction, which you can perceive riding a bicycle into it. But Michelson merely assumed an “ether wind” would also have friction which would influence the speed of a beam of light. However The Ether is an extremely rarified gas and might not have any friction to speak of. This caveat was delved into by Sir Oliver Lodge, in his book, The Ether of Space: “Not only can our bodies move through it [i.e., The Ether], but much larger bodies, planets and comets, can rush through it at what we are pleased to call a prodigious speed without showing the least sign of friction. I myself [i.e. Sir Oliver Lodge], indeed, have designed and carried out a series of delicate experiments to see whether a whirling mass of iron could to the smallest extent grip the ether and carry it around, with so much as a thousandth part of its own velocity… The answer is, no; I cannot find a trace of mechanical connection between matter and ether, of the kind known as viscosity or friction.”
Yet undeterred by this consideration that an “ether wind” might have no appreciable effect on the speed of a beam of light, Michelson nonetheless designed an experiment. Michelson teamed up with Edward Williams Morley (January 29, 1838 – February 24, 1923) and they constructed what is since called an “interferometer.”
A beam of light was sent into the interferometer. The single beam was split into two beams traveling at right angles to each other by a half-silvered mirror. Those two beams traveled on, until they were both returned by a mirror. One of the two light beams must have been effected by an “ether wind”, it was presumed. And yet, no effect of an “ether wind” upon the two light beams was detected. “Michelson and Morley made thousands of observations over many months, and in July, 1887, finally announced their conclusion. There was no ether wind!” (Source: Understanding Physics (Vol. 2, chapter 6), by Isaac Asimov.)
Yet Michelson and Morley had jumped to conclusions. They had assumed “viscosity” (friction) involved with their “ether wind.” Consider this as well: One of the split light beams journeys out, traveling into the “ether wind”; on its return journey, the light beam now has the “ether wind” at its back: therefore the two situations, into the “ether wind” and with the “ether wind” at its back, would cancel each other out and no effect of an “ether wind” would have been detected.
George Francis FitzGerald (1851 – 1901) also considered something a bit more complicated: The FitzGerald Contraction. Here again, “the two effects of the ether wind cancel perfectly” due to all objects “growing shorter” in the direction of their absolute motion. “The distance covered by the beam of light moving with-and-against the ether wind is now decreased by foreshortening to just exactly the extent that would allow the beam to cover the distance in the same time as was required by the beam traveling crosswind.” (Asimov, op. cit.)
Bottom line: The Michelson-Morley experiment did not disprove the existence of The Ether. Michelson-Morley assumed there would be friction caused by their “ether wind.” Furthermore, even if there were friction, the outgoing and incoming frictions would have canceled each other out. The FitzGerald Contraction also undermines the conclusion of Michelson-Morley.