Aether theories: Encyclopedia - Aether theories

Aether theories

Aether theories - Definition

In natural philosophy, aether (a.k.a. "ether") might be considered "the stuff of space", or "the medium" (lit: "that which is between") that carries signals between objects separated by vacuum. "The aether" was sometimes considered to be "the fifth element" (see: "quintessence"), in addition to Earth, Air, Fire and Water.

Although it is tempting to talk about "the aether", a number of fairly different theories have been presented over the years that assign "the aether" different properties. When someone talks about proving or disproving the existence of "the aether", it is often a good idea to ask which aether is being discussed. Here are a few of the better-known variants:

Aether theories - History

• Isaac Newton disproved the aether "vortex theory" of planetary motion ...
• ... but later proposed a "new" aether, exceptionally fluid, whose density was affected by the local density of matter and local gravitational field strength (see: Optiks). Newton also said that he did not know whether his new aether should be particulate or not - if it was particulate, the particles would have to be incredibly small, even smaller than light-corpuscles.

Aether theories - Theories and experiments

• Absolute aether models assumed that the density and flow of the medium was wholly unaffected by the motion of particles through it.

• dragged aether models assumed that moving material pulled light along with it to some extent ("fully-dragged aether", "partially dragged aether"). Fresnel proposed one of these, and his prediction of dragging effects was apparently validated experimentally by Fizeau.

During the 19th century, a large number of aether theories were produced, with slightly different combinations of absoluteness or relativeness, different degrees of dragging, and different rules for how matter should interact with light. The number of competing theories made keeping track of all the different predictions rather difficult. As with string theory today, there seemed to be too many options, and with the right choice of theory and choice od coefficient values, it seemed that one could predict almost any conceivable result, and as a consequence the credibility of the subject began to suffer.

Attempts to measure the motion of the earth through an absolute aether by measuring offsets in the speed of light ("aether wind") produced a "null" result (Michelson-Morley experiment). Since it was improbable that an absolute aether was locked to the state of motion of the rotating, circling earth, this effectively ruled out a simple absolute aether.

• "Lorentzian ether theory" or Lorentzian electrodynamics (1904), made use of the Fitzgerald-Lorentz contraction hypothesis - it suggested that an object moving through the aether was contracted in its direction of motion by a special ratio now named after Lorentz: According to this theory, an inertial observer would be incapable of measurng their absolute motion, so that their measurements would comply with the principle of relativity ("PoR").

• acceleration effects still implied the existence of some physical property to spacetime, and if (like Mach), one decided that acceleration and rotation effects should be the result of interactions between distant masses, acceleration and rotation also had to be capable of distorting light-beam geometry, and, by implication, distorting spacetime itself. If these properties were absolute, then the properties of spacetime forced behaviours onto matter without accepting any back-reaction (like a form of "absolute" aether), a behaviour that Einstein referred to as "an inherent epistemological defect". But if the effects were purely relative, then forcing matter to move in a way that spacetime did not like should cause a distortion in spacetime ("space tells matter how to move, matter tells space how to bend").

Aether theories - Modern physics and the aether

• "The aether of general relativity" was a phrase used by Einstein in a lecture on general relativity and aether theory. Einstein said that general relativity's gravitational field parameters could be said to have all the usual properties of an aether except one: it was not composed of particulate bodies that could be tracked over time, and so it could not be said to have the property of motion.

• Quantum mechanics can be used to describe spacetime as being "bitty" at extremely small scales, fluctuating and generating particle pairs that appear and disappear incredibly quickly. Instead of being "smooth", the vacuum is described as looking like "quantum foam". It has been suggested that this seething mass of virtual particles may be the equivalent in modern physics of a particulate aether.

Aether theories - Reference literature

ASPDEN, Harold, Physics without Einstein - A Centenary Review (i.e. Chapter IV: "The Way Forward - The Aether: A Preliminary Note; Analysis of Aether Structure; ..."), 2005, pdf

ASPDEN, Harold, The Physics of Creation (i.e. Chapter 7: "Aether Structure"), 2003, pdf

Aether theories - Aether conceptions

• Aether (classical element)
• Aether and general relativity
• Aether drag hypothesis
• Aetherometry
• Etheric plane
• Luminiferous aether
• Timeline of luminiferous aether

Aether theories - Aether experiments

• Kennedy-Thorndike experiment
• Lorentz ether theory
• Lorentz-FitzGerald contraction hypothesis
• Trouton-Noble experiment
• Michelson-Gale-Pearson experiment
• Michelson-Morley experiment
• Fresnel drag coefficient
• Newton's aether model

See also

• History of special relativity
• Preferred frame

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