Ether, in physics and astronomy, the name given to an imaginary substance once assumed to fill the otherwise empty space between the stars and planets. Its presence in space was thought to be necessary to provide a carrier for light waves and radio waves. In the 19th century, physicists and astronomers tried to demonstrate ether's existence. An experiment carried out by two United States physicists, Albert Abraham Michelson and Edward Williams Morley, convinced scientists that the presumed ether did not exist. The term is still sometimes used by laymen in referring to the transmission of radio waves.