Ether theory

A theory assuming existence of an all-pervasive substance ("ether") filling all space and yet undetectable by direct measurement. Ether theory was originally proposed to explain the fact that the velocity of light is the same regardless of the system of reference: light was supposed to have a constant velocity with respect to ether. The theory of Special relativity has made ether theories obsolete. Modern proponents of ether theories are usually opposed to special relativity on philosophical grounds. Special relativity is now universally accepted by the physics community, unlike General Relativity which is still insufficiently confirmed by experiment to exclude certain alternative theories of gravitation.