See also the disambiguation page for Aether.

Alchemy, natural philosophy, and early modern physics proposed the existence of a medium of the ęther (also spelled ether, from the Greek word () aether, meaning "upper air" or "pure, fresh air" ), 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 Ęther 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, magnetic and gravitational potentials 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 Ęther at the relevant location, analogous to the way that gaseous, liquid and solid media affect the propagation of sound waves.

The Ęther 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 Ęther 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. 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, lots of problems are solved more easily by imagining the existence of an aether.

Luminiferous ęther

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. 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 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. Unfortunately, modern scientists believe it is not vain to do with little what requires more, so they say the luminiferous aether fell to Occam's Razor.

See also: History of special relativity

Gravitational aether

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"http://www.tu-harburg.de/rzt/rzt/it/Ether.html was a title 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. The general attitude to this amongst physicists today seems to be that Einstein's comments don't count because they stretch the idea of aether theory too far: it is argued that a "non-particulate" aether theory is not really an aether theory, or at least, it doesn't correspond to the idea of "historical" aether theory that is currently taught.

Such a view, however, contradicts the continuum concept of space-time and fields and Einstein's statements in "Aether and the Theory of Relativity", May 5th, 1920:

"More careful reflection teaches us, however, that the special theory of relativity does not compel us to deny ether." and "To deny the ether is ultimately to assume that empty space has no physical qualities whatever".

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.

References

• "Aether", American Heritage Dictionary of the English Language.
• "A Ridiculously Brief History of Electricity and Magnetism; Mostly from E. T. Whittaker?s A History of the Theories of Aether and Electricity". (PDF format)
  • Ibid.
• Maxwell, James Clerk, "On Physical Lines of Force". 1861.
• Albert Einstein, "Ether and the Theory of Relativity" May 5th, 1920, University of Leyden. (ed. this version is from "Collected Papers of Albert Einstein")
• Epple, M. Topology, Matter, and Space, I: Topological Notions in 19th-Century Natural Philosophy. Arch. Hist. Exact Sci. 52 (1998) 297?392.

Further reading

• Kenneth F. Schaffner: Nineteenth-century aether theories, Oxford : Pergamon Press, 1972. (contains several reprints of original papers of famous physicists)
• Oliver Lodge, "Ether", Encyclopędia Britannica, Thirteenth Edition (1926).
• Oliver Lodge, "The Ether of Space". ISBN 1-4021-8302-X (paperback) ISBN 1-4021-1766-3 (hardcover)
• Oliver Lodge, "Ether and Reality". ISBN 0-7661-7865-X
• "Aether", Encyclopędia Britannica, Eleventh Edition (1910?1911). Volume Vol. 1, Page 297.
• James Clerk Maxwell, "Ether", Encyclopędia Britannica, Ninth Edition (1875-89).
• Albert Einstein, "Aether and the theory of relativity" (1920) translated in Sidelights on relativity (Dover, NY, 1983; ISBN 0-486-24511-X), pp.1-24 (ed. was an address delivered on May 5th, 1920, in the University of Leyden; classes general relativity as a form of (nonparticulate) aether theory)
• Albert Einstein, The Investigation of the State of Aether in Magnetic Fields, 1895. (PDF format)
• Edmund Whittaker, "''A History of the Theories of Aether and Electricity, from the Age of Descartes to the Close of the Nineteenth Century''". 1910 (1953).
• Lord Kelvin (Sir William Thomson), "On Vortex Atoms". Proceedings of the Royal Society of Edinburgh, Vol. VI, 1867, pp. 94-105. (ed., Reprinted in Phil. Mag. Vol. XXXIV, 1867, pp. 15-24.)

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