In 1887 two American scientists, physicist Albert Michelson and physical chemist Edward Morley, performed an experiment that was designed to detect the motion of the Earththrough a hypothetical medium known as the luminiferous ether which was thought to be present throughout space. They made their measurements with a very sensitive optical instrument now called a Michelson interferometer. Their observations showed no indication of movement through the predicted ether. This outcome was unexpected and has become one of the fundamental experimental results in support of the theory of special relativity, developed by Albert Einstein in 1905.

During the 1800s scientists had become convinced that light was composed of waves, as opposed to a theory that light was made up of particles proposed more than a century earlier by Isaac Newton. They based their belief on experiments that demonstrated phenomena such as interference--the change in intensity caused by mixing two...