There is no ether (wind or drag by which the speed of light is slower in a given direction). What there is is empty space (and full time) in the sense that particles and their anti-matter counterparts spring from, and back to, nothingness, which amounts to a form of nothingness whether apart, or together - a clue, I guess, to the precise definitions for apart, and together. As explained by Dirac's equation, which trivially, without much explanation, combines relativity, and quantum science. The contemporary view is that the universe, itself, thus springs back, and forth, of nothingness, and, so, continues to be created, and destroyed.
Is it definition of, or, for?
https://english.stackexchange.com/qu...definition-for