aether theories

Aether theories in physics propose the existence of a medium, the aether (also spelled ether, from the Greek word , meaning "upper air" or "pure, fresh air"), a space-filling substance or field, thought to be necessary as a transmission medium for the propagation of electromagnetic or gravitational forces. The assorted aether theories embody the various conceptions of this "medium" and "substance". This early modern aether has little in common with the aether of classical elements from which the name was borrowed. Since the development of special relativity, theories using a substantial aether fell out of use in modern physics, and were replaced by more abstract models.