Ether, in physics, was once believed to be a substance that filled all space. By the late 1600’s, some physicists believed that light traveled in waves. They knew that light could travel through artificially created vacuums and through the void of outer space. But they could not explain how light could travel without a medium (substance) to travel through. As a result, they assumed the presence of a luminiferous (light-carrying) ether, a substance that differed from all other matter. It could not be seen, felt, or weighed and was present in vacuums, outer space, and all matter. The ether was stationary, and Earth and other bodies in space moved through it.
In 1864, the British physicist James Clerk Maxwell correctly suggested that light waves are electromagnetic and travel as disturbances of an electromagnetic field. Therefore, they do not need a medium to travel through. But Maxwell and other physicists still believed in the existence of ether.
In 1887, two American scientists, Albert A. Michelson and Edward W. Morley, conducted an experiment to measure the speed of Earth relative to the ether. Their findings suggested that Earth did not move through ether. However, Hendrik A. Lorentz, a Dutch physicist, explained the finding by assuming that ether affected matter in a complicated way. In 1905, the German-born physicist Albert Einstein published his special theory of relativity, which shows how light behaves and does not rely on the existence of ether.
