The Luminiferous Aether

The Luminiferous Aether

was believed to be the substance that filled up the realms of celestial space and was often identified as the mysterious fifth element, along with air, water, earth, and fire.

To account for the failure of Michelson–Morley experiment which conclusively proved that the earth is stationary, heliocentric science community discarded the existence of Aether and replaced it with space vacuum and the theory of relativity.