Undoubtedly the most critical turning point in the history of physics was the Michelson-Morleyexperiment which was carried out by Albert Michelson and Edward Morley in 1887 and repeatedby many others since then with increasing accuracy but ongoing misleading conclusions. Asalready mentioned, before the M-M experiment scientists were happy with Isaac Newton's andJames Maxwell's absolute space and absolute time and believed that the velocity of light in spacewas constant relative to a stationary reference frame. Thus the velocity of light relative to areceiver on the earth would not be constant but would be affected by the earth's complex motionthrough space. Michelson and Morley set out to prove this fact. However, they didn't get the resultthey expected due to the fact that they didn't really understand how their instrument (theMichelson interferometer) actually worked. The experiment they performed was never capable of producing the result they were looking for.
By the late 1800s, physicists generally believed that light was a wave. Therefore, it was thought, it had to travel through some sort of medium, just as sound waves are vibrations in air. Scientists had believed for centuries that a mysterious, ghostly substance, known as the luminiferous ether, must permeate the universe and serve as a medium for the light waves. Various scientists attempted to detect the ether, with no success. Finally, in 1887 Albert Michelson and Edward Morley carried out their famous experiment, which provided strong evidence against the ether. They reported the results in November of that year, but both thought their experiment a failure and continued to cling to their belief in the ether.