Located in the heart of the Case Western Reserve University, this marker commemorates one of the most important experiments in modern science. In a building located near this marker in 1887, physicists Albert A. Michelson and Edward Morley conducted an experiment to try to detect whether their light traveled through matter or whether it traveled in the absence of matter. Scientists had speculated that if waves traveled through matter such as water and air, light should travel through matter as well. People at this time referred to this hypothetical substance as aether or ether. Michelson and Morley's experiments revealed that this theory was untrue: aether did not exist, and light traveled at a constant speed. This discovery was central to the modern understanding of the nature of light and how it travels.
The experiment, which used a device called an interferometer, entailed shining a beam of light through an opaque mirror, which was placed at an angle. The light was split into two beams and traveled to mirrors that reflected them back to the original angled mirror. The beams recombined and bounced to a screen that measured the speed of the now single beam. The results demonstrated that there was virtually no difference in speed between the original and recombined beams, indicating that substance, ether, did not, in fact, exist. This experiment would help later physicists, including Albert Einstein, to formulate the special theory of relativity, which states that the speed of light is constant at all times. Michelson conducted an earlier test in 1881, but the one that took place here was more refined.