Aether theories

Alchemy, natural philosophy, and early modern physics proposed the existence of a medium of the aether (also spelled ether, from the Greek word (αἰθήρ), meaning "upper air" or "pure, fresh air" ^[1]), a space-filling substance or field, thought to be necessary as a transmission medium. The assorted aether theories embody the various conceptions of this "medium" and "substance". This early modern aether has little in common with the aether of classical elements from which the name was borrowed.

Although hypotheses of the aether vary somewhat in detail they all have certain characteristics in common. Essentially it is considered to be a physical medium occupying every point in Space, including within material bodies. A second essential feature is that its properties gives rise to the electric and magnetic phenomena and determines the propagation velocity of their effects. Therefore the speed of light and all other propagating effects are determined by the physical properties of the aether at the relevant location, analogous to the way that gaseous, liquid and solid media affect the propagation of sound waves.

The aether is considered the over-all reference frame for the Universe and thus velocities are all absolute relative to its rest frame. Therefore, in this view, any physical consequences of those velocities are considered as having an absolute, i. e. real effects.

Recent aether theories (see section below on protoscience links) of velocity effects, phenomenon of gravitation and planetary motion (i.e. the angular momentum), creation of proton, of stars (neutron stars too) and planets, etc., exist but are not generally accepted by the mainstream scientific community.

John Bell, interviewed by Paul Davies in "The Ghost in the Atom" has suggested that an aether theory might help resolve the EPR paradox by allowing a reference frame in which signals go faster than light^[2]. He suggests Lorentz contraction is perfectly coherent, not inconsistent with relativity, and could produce an aether theory perfectly consistent with the Michelson-Morley experiment. Bell suggests the aether was wrongly rejected on purely philosophical grounds: "what is unobservable does not exist" [p.49]. Einstein found the non-aether theory simpler and more elegant, but Bell suggests that doesn't rule it out. Besides the arguments based on his interpretation of quantum mechanics, Bell also suggests resurrecting the aether because it is a useful pedagogical device. That is, many problems are solved more easily by imagining the existence of an aether.

Luminiferous aether

In the 19th century, luminiferous aether (or ether), meaning light-bearing aether, was the term used to describe a medium for the propagation of light (electromagnetic radiation). However, a series of increasingly complex experiments had been carried out in the late 1800s like the Michelson-Morley experiment in an attempt to detect the motion of earth through the aether, and had failed to do so. A range of proposed aether-dragging theories could explain the null result but these were more complex, and tended to use arbitrary-looking coefficients and physical assumptions. Hendrik Lorentz and George Francis FitzGerald offered within the framework of Lorentz ether theory a more elegant solution to how the motion of an absolute aether could be undetectable (length contraction), but if their equations were correct, Albert Einstein's 1905 special theory of relativity could generate the same mathematics without referring to an aether at all. This led most physicists to conclude that the classical notion of aether was not a useful concept.

See also: History of special relativity

Gravitational aether

Main article: Mechanical explanations of gravitation

From the 16th until the late 19th century, gravitational phenomena had also been modeled utilizing an aetherial concept. The most well-known concept is Le Sage's theory of gravitation. Other concepts were made by Isaac Newton, Bernhard Riemann, Lord Kelvin etc.

Aether and general relativity

"Aether and the theory of relativity"[3] was a title used by Einstein in a lecture on general relativity and aether theory. Einstein said that according to general relativity space is endowed with physical properties (the metric field), and one could use the word "ether", if one wished, to refer to this metric field, although he acknowledged that this meaning of the word "differs widely from that of the ether of the mechanical undulatory theory of light". In particular, the metric field of spacetime has no mechanical properties at all, not even a state of motion or rest. Its parts cannot be tracked over time. ^[4] The general attitude to this amongst physicists^[who?] today is that although it is purely a matter of semantics, Einstein's comments stretch the word "aether" too far: it is argued that an "aether" with no mechanical properties doesn't correspond to the historical idea of aether, and so it is potentially misleading to apply this name to the spacetime field of general relativity.^{[citation needed]}

Aether and quantum mechanics

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.

Modern derivatives

In physics there is no concept considered exactly analogous to the aether. However, dark energy is sometimes called quintessence due to its similarity to the classical aether. Modern physics is full of concepts such as free space, spin foam, Planck particles, quantum wave state (QWS), zero-point energy, quantum foam, and vacuum energy.