The Active Ether
During most of the nineteenth century the existence of an all-encompassing ether as a substitute for a true void was taken for granted. According to the successful electromagnetic ether theory based upon Maxwellian electrodynamics, the ether was endowed w
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The Active Ether
Abstract During most of the nineteenth century the existence of an all-encompassing ether as a substitute for a true void was taken for granted. According to the successful electromagnetic ether theory based upon Maxwellian electrodynamics, the ether was endowed with energy and hence very different from nothingness. Oliver Lodge thought that its energy density was enormous, about 1033 erg cm−3 . The active ether of the fin-de-siècle period was in some respects surprisingly similar to the later quantum vacuum, yet it was based fully on classical physics. Keywords Ether · Electromagnetism · Vortex theory · Oliver Lodge In spite of the opinion of Boyle, many later natural philosophers assumed the existence of a rare and penetrating “subtle matter” that was present also in a void. Although some physicists accepted the vacuum as a passive nothingness, this was not the generally held view. The period from Newton to Maxwell saw a bewildering variety of ethers which in many cases were introduced for specific purposes, such as explaining electricity, magnetism, light, gravitation, nervous impulses, and chemical action (Cantor and Hodge 1981). In an article on the ether for the Encyclopaedia Britannica, Maxwell (1965, p. 763) noted that “To those who maintained the existence of a plenum as a philosophical principle, nature’s abhorrence of a vacuum was a sufficient reason for imagining an all-surrounding æther.” The fact that some of these phenomena were easily transmitted in empty space indicated that their associated ethers were part of even a perfect vacuum. Maxwell continued: “Æthers were invented for the planets to swim in, to constitute electric atmospheres and magnetic effluvia, to convey sensations from one part of our bodies to another, and so on, till a space had been filled three or four times with æthers.” As he implied here, the many hypothetical ethers were ad hoc and therefore unsatisfactory from a methodological point of view. Yet Maxwell was himself not only a believer in the ether; his field theory of electromagnetism was instrumental in introducing a new and unified kind of ether, one which was electrodynamical rather than mechanical in nature. Since the early decades of the nineteenth century the ether had become increasingly associated with optics and seen as the medium in H. S. Kragh and J. M. Overduin, The Weight of the Vacuum, SpringerBriefs in Physics, DOI: 10.1007/978-3-642-55090-4_2, © The Author(s) 2014
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which light propagated. Following the pioneering work of Thomas Young in England and Augustin Fresnel in France, by the 1820s the corpuscular theory of light was abandoned and replaced by a theory of transverse waves. The new “luminiferous” ether pervaded the universe and, according to most physicists, behaved like an elastic solid that—strangely—did not interact with other matter. Although it had the form of a solid, and was sometimes likened to steel, the planets and comets passed through it without noticing any resistance. Strange indeed! In a postscr
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