One of the great beauties of science is that failure is as important as success. It is through “failed” experiments that we learn what is not true. This can help eliminate the falsehoods in our thinking, allowing much better decision making in the future.
One great falsehood was the idea of the “luminferous aether.” It was believed by physicists of the 19th century that, just as water waves must have a medium to move across (water), and audible sound waves require a medium to move through (such as air or water), so also light waves require a medium. Because light can travel through a vacuum, it was assumed that the vacuum must contain the medium of light. This theory was put to the test by 1887 by Albert Michelson and Edward Morley at what is now Case Western Reserve University in Cleveland, Ohio.
Their test sent a single source of white light through a half-silvered mirror that was used to split it into two beams travelling at right angles to one another. After leaving the splitter, the beams were reflected back into the middle on small mirrors. They then recombined on the far side of the splitter in an eyepiece, producing a pattern of constructive and destructive interference based on the spent time to transit the arms.
If the Earth is traveling through an aether medium, a beam reflecting back and forth parallel to the flow of ether would take longer than a beam reflecting perpendicular to the ether because the time gained from traveling downwind is less than that lost traveling upwind. The result would be a delay in one of the light beams that could be detected when the beams were recombined through interference. Any slight change in the spent time would then be observed as a shift in the positions of the interference fringes. If the aether were stationary relative to the sun, then the Earth’s motion would produce a fringe shift 4% the size of a single fringe.
This experiment was a completely failure; it did not provide any insight into aether. Instead Michelson and Morley found the shift measurement to be as small as one-fortieth of the expected displacement. Later it was to be determined to be within the range of an experimental error that would allow the speed to actually be zero. Thus we had the first strong evidence that there was no aether.
This experiment was a starting point for many later scientific developments. One primary role was helping support Einstein’s notion of the constancy of the speed of light and encourage the acceptance of special relativity. If this “failure” had not happened, science would not in place it is now. We owe Michelson and Morley a great deal for their failed experiment.
-That is all.