Thermodynamics and the Crisis of Classical Physics

By the late nineteenth century, most physicists assumed that light, like sound, needed a medium to travel through, a hypothetical substance filling all of space called the luminiferous ether. In 1887, Albert Michelson and Edward Morley, working in Cleveland, built an extremely sensitive interferometer designed to detect the Earth's motion through this ether by comparing the speed of light in perpendicular directions. The experiment found no difference whatsoever, a null result so unexpected that it became one of the most consequential failed experiments in the history of science, eventually forcing a rethinking of space, time, and motion.