Ether (physics)

In physics, the ether (also spelled aether) is a concept that was made obsolete by Einstein's theory of special relativity of 1905. The idea of an ether is due to René Descartes (around 1630) and it became especially predominant in the 19th century by the work of Fresnel in the 1810s on light and Maxwell in the 1860s on electromagnetic fields. In order to explain stellar aberration Fresnel had to assume a medium in a state of absolute rest relative to the fixed stars, and Maxwell showed that EM (electromagnetic) waves are transverse (perpendicular to the propagation direction) vibrations.

In the 19th century it was known that transverse waves are not possible in a gas or a liquid, but only in a solid. It was believed that light, and electromagnetic waves in general, must be interpreted as a vibratory process in a medium that filled up universal space. Thus, one arrived at a picture of the ether as a quasi-rigid (not completely rigid, because it could vibrate) luminiferous (light carrying) medium that is a massless transparent solid at rest with respect to the Earth and the stars.

Today, the concept of ether does not play a role any longer in physics, but in daily life it is still used in connection with radio and television signals, which commonly are said to be transmitted "through the ether".