Aether (science)

Light is a wave, and the luminiferous aether (or ether) is defined to be whatever medium transmits the light waves.

The Michelson-Morley experiment in 1887 failed to detect any motion of the aether relative to the Earth. Henri Poincaré conjectured that the aether may be unobservable, and invented special relativity based on the notion that the aether may be superfluous. Albert Einstein published conflicting opinions on whether the aether exists.

Quantum electrodynamics (QED) teaches that when light goes through a vacuum, it is really going through a sea of virtual particles. Cosmologists say that the vacuum is really filled with dark energy, and it is unknown whether that has any relation to the aether concept. According to these theories, there is no such thing as empty space. The aether describes space when it is as empty as possible.

The existence of luminiferous aether is a counterexample to relativity as it is sometimes described, as it is sometimes said that Einstein abolished the aether.