Aether theories

Aether theories in physics propose the existence of a medium, 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 for the propagation of electromagnetic or gravitational forces. 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. Since the development of special relativity, theories using a substantial aether are not used any more in modern physics, and are replaced by more abstract models.^[2]

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.

Gravitational aether

From the 16th until the late 19th century, gravitational phenomena had also been modeled utilizing an aether. The most well-known formulation is Le Sage's theory of gravitation, although other models were proposed by Isaac Newton, Bernhard Riemann, and Lord Kelvin. None of those concepts is considered to be viable by the scientific community today. Einstein sometimes used the word aether for the gravitational field within general relativity, but this terminology never gained widespread support.^[3]

Quantum vacuum

Quantum mechanics can be used to describe spacetime as being non-empty at extremely small scales, fluctuating and generating particle pairs that appear and disappear incredibly quickly. It has been suggested by some such as Paul Dirac^[4] or Robert B. Laughlin,^[5] that this quantum vacuum may be the equivalent in modern physics of a particulate aether. However, Dirac's aether hypothesis was motivated by his dissatisfaction with quantum electrodynamics, and it never gained support by the mainstream scientific community.^[6]

See also

• Absolute space and time

References

1. ^ "Aether", American Heritage Dictionary of the English Language.
2. ^ Born, Max (1964), Einstein's Theory of Relativity, Dover Publications, ISBN 0-486-60769-0 
3. ^ Einstein, Albert: "Ether and the Theory of Relativity" (1920), republished in Sidelights on Relativity (Methuen, London, 1922)
4. ^ Dirac, Paul: "Is there an Aether?", Nature 168 (1951), p. 906.
5. ^ Laughlin, Robert B. (2005). A Different Universe: Reinventing Physics from the Bottom Down. NY, NY: Basic Books. pp. 120–121. ISBN 978-0-465-03828-2. 
6. ^ Kragh, Helge (2005). Dirac. A Scientific Biography. Cambridge: Cambridge University Press. pp. 200-203. ISBN 0-521-01756-4. 

Further reading

• Whittaker, Edmund Taylor (1910), A History of the theories of aether and electricity (1 ed.), Dublin: Longman, Green and Co., http://www.archive.org/details/historyoftheorie00whitrich 
• Schaffner, Kenneth F. (1972), Nineteenth-century aether theories, Oxford: Pergamon Press, ISBN 0-08-015674-6 
• Darrigol, Olivier (2000), Electrodynamics from Ampére to Einstein, Oxford: Clarendon Press, ISBN 0-19-850594-9 
• Maxwell, James Clerk (1878), "Ether", Encyclopædia Britannica Ninth Edition 8: 568–572, http://en.wikisource.org/wiki/Encyclop%C3%A6dia_Britannica_Ninth_Edition/Ether 
• Harman, P.H. (1982), Energy, Force and Matter: The Conceptual Development of Nineteenth Century Physics, Cambridge: Cambridge University Press, ISBN 0-521-28812-6 
• Decaen, Christopher A. (2004), "Aristotle's Aether and Contemporary Science", The Thomist 68: 375–429, http://www.thomist.org/jour/2004/July/2004%20July%20A%20Dec.htm, retrieved 2011-03-05. 
• Joseph Larmor, "Ether", Encyclopædia Britannica, Eleventh Edition (1911).
• Oliver Lodge, "Ether", Encyclopædia Britannica, Thirteenth Edition (1926).
• "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)
• Epple, M. Topology, Matter, and Space, I: Topological Notions in 19th-Century Natural Philosophy. Arch. Hist. Exact Sci. 52 (1998) 297–392.