Aether

In physics and philosophy, aether (also spelt ether) was a substance supposed to fill all of space. Aristotle included it as a fifth element on the principle that nature abhored a vacuum.

See also luminiferous aether for the late 19th-century invocation of this concept by physicists as an attempt to reconcile electromagnetic theory and Newtonian physics.

The term derives from the Aither of Greek mythology. This was the fiery upper air breathed by the gods on Mount Olympus, sometimes personified into a deity.