Ether
. Ether (physics and astronomy), substance once thought to fill all space, but now known not to exist. Scientists of the late 19th and early 20th centuries believed that the ether was the medium, or substance, that allowed light to travel through space. The theory of relativity of German American physicist Albert Einstein showed that light did not need a medium through which to travel, so belief in the existence of the ether was abandoned. See also Quantum Theory . DEVELOPMENT OF THE ETHER THEORY Physicists have tried for hundreds of years to determine whether light is a stream of particles or a set of waves. In the 1860s and 1870s Scottish physicist James Clerk Maxwell formulated a theory that linked electricity and magnetism, and light, to waves of electromagnetic energy. His theory predicted that waves of varying electric and magnetic fields travel through space in the form of electromagnetic waves. These waves carry energy from place to place. Maxwell showed that these electroma