Aether (also spelled ether) is a concept used in ancient and medieval science as a substance. The aether was believed to be the substance which filled the region of the universe above the terrestrial sphere. Aristotle included it as a fifth element distinct from the other four, Earth, Water, Air, and Fire. Aether was also called quintessence (from quinta essentia, "fifth element").
The word aether () in Homeric Greek means "pure, fresh air" or "clear sky", imagined in Greek mythology to be the pure essence where the gods lived and which they breathed, analogous to the aer breathed by mortals (also personified as a deity, Aether, the son of Erebus and Nyx). It corresponds to the concept of akasha in Hindu philosophy. It is related to "to incinerate"Pokorny, Julius (1959). Indogermanisches Etymologisches Wörterbuch, s.v. ai-dh-., also intransitive "to burn, to shine" (related is the name Aithiopes (Ethiopians), meaning "people with a burnt (black) visage". See also Empyrean.
Aristotle added aether to the system of the classical elements of Ionic philosophy as the "fifth element" (the quintessence), on the principle that the four terrestrial elements were subject to change and moved naturally in straight lines while no change had been observed in the celestial regions and the heavenly bodies moved in circles. In Aristotle's system aether had no qualities (was neither hot, cold, wet, nor dry), was incapable of change (with the exception of change of place), and by its nature moved in circles.G. E. R. Lloyd, Aristotle: The Growth and Structure of his Thought, Cambridge: Cambridge Univ. Pr., 1968, pp. 133-139, ISBN 0-521-09456-9. Medieval scholastic philosophers granted aether changes of density, in which the bodies of the planets were considered to be denser than the medium which filled the rest of the universe.E. Grant, Planets, Stars, & Orbs: The Medieval Cosmos, 1200-1687, Cambridge: Cambridge Univ. Pr., 1994, pp. 422-428, ISBN 0-521-56509-X. Robert Fludd stated that the aether was of the character that it was "subtler than light". Fludd cites the 3rd century view of Plotinus, concerning the aether as penetrative and non-material.Robert Fludd, "Mosaical Philosophy". London, Humphrey Moseley, 1659. Pg 221.
Modern understanding of electromagnetism including Einstein's particle theory of light and various scientific experiments of general relativity has removed the need for a substance like aether to fill the otherwise empty parts of the universe. Newton's and Maxwell's aether model (the latter being a "classic static aether") were both developed from this classical element. However, the null result of the Michelson-Morley experiment led (from 1887 onwards) to the decline of an aether model's wide acceptance. Albert Einstein, in an interpretation he offered for his theory of special relativity, dismissed it, as per Occam's razor; and, though he later reinstated a logical need for an aether in a commentary on his theory of general relativity, most modern theories do not include this classical element.
Alchemy | Astrology | Obsolete scientific theories | Aether theories
Quintessenz (Philosophie) | Éter (física) | Quintessenza | Eteren | Пятый элемент
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"Aether (classical element)".
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