Author: Jaume Navarro is an Ikerbasque Research Professor at the University of the Basque Country
In 1951, the physicist Paul A.M. Dirac called for the re-introduction of the æther in an oft-quoted letter to Nature. His was an attempt to resuscitate an epistemic object that most scientists at the time, as much as today, judged to be dead and buried. By using the old-fashioned spelling, Dirac was making a statement against the track quantum electrodynamics had taken and which he regarded as ‘ugly and incomplete’. From his point of view, the problems of the theory resided in it being founded on the notion of individual, point-like electrons inevitably leading to the problem of infinities. Instead, he argued, one should take the electromagnetic field with certain mathematical properties as a starting point and deduce electrical charges from those properties. In other words, Dirac was suggesting that the fundamental entity in quantum electrodynamics should be ‘a space with properties’, analogous to what Maxwell had done almost a century before with the æther.
What was the Victorian ether or æther? Simply put, the ether was an imponderable fluid or medium that permeated the whole universe, whose interactions with ordinary matter were the origin of electric and magnetic phenomena, not least the transmission of light, which Maxwell came to explain as electromagnetic waves in the ether. It was the only remnant of a tradition of imponderable fluids that in the eighteenth century separately accounted for phenomena like electricity, magnetism, heat, or even life. By the time Dirac wrote his paper, however, the ether was mostly regarded as a relic of times gone by, an entity that had been fully rejected.
Indeed, for decades, the received view of the falsification of the ether was the same story that Einstein himself had elaborated in his pedagogical explanations of special relativity, and which Karl Popper used for his philosophy of science. That narrative relied on the negative results of Michelson and Morley’s experiments in the 1880s in their quest to determine the absolute speed of the earth in the ether. Certainly, that story, while still popular among some physicists, teachers and science popularisers, has long been problematized by historians of science. Neither was the Michelson Morley experiment a turning point in experimental or theoretical physics, nor was the ether abandoned by the beginning of the twentieth century, not even by Einstein himself.
The historiography of the demise of the ether is, thus, an episode in search of a fuller account. A recent international research project soon to be published by Oxford University Press analysed the status of the ether in the early twentieth century and challenged a number of general assumptions, three of which will be discussed in this article: the misleading separation between classical and modern physics, the role of authority in preserving scientific ideas, and the resurgence of pluralism as a legitimate stance in philosophy of science.
The misleading separation between classical and modern physics
In the last decade, historians of physics have become increasingly critical about the existence of a clear-cut divide between classical and modern physics. The heroic and revolutionary stories about the origins of Relativity and Quantum Physics are slowly giving way to a more nuanced and continuous development of science in which the new emerged from the old rather than appearing out of the blue by some epistemic miracle. In the old historiographical framework, the ether was presented as the symbol of classical, old physics. And the battle seemed to be one between progressive against reactionary physicists, the latter holding on to the ether almost irrationally. This simplistic account contrasts, for instance, with the role the ether played in the explanations of wireless technologies, indeed a very modern subject in the early twentieth century.
In 1922, with the creation of the BBC, the British public suddenly became directly engaged with a technology that was radically transforming communications: wireless broadcasting. Amateurs, engineers and the public at large were keen to have simple and clear explanations of the intricacies of the new gadgets. Wireless waves were, precisely, waves; and the analogy with water or air waves called for a medium: the ether. Indeed, radio was for the first time materialising the ether in every household, in every workshop and in every store where radio sets were used, fixed and sold. Moreover, such explanations gained particular strength when they were broadcasted in popular talks given by no other than Sir Oliver Lodge, an influential physicist, electrical engineer and public face of science. The argument was clear: the reason why you can hear my voice through the radio set is that between the sender and the receiver there is a medium through which electromagnetic waves travel. The absence of such medium would make this broadcasting literally impossible.
Modernist artists also relied on the ether in their explanations of their new representational experiments. Challenges to the continuity of space in cubism have long been related to the fashion of relativity and quantum physics in the early decades of the twentieth century. But so was the ether, together with X-rays, electrons and radioactivity. As Gillian Beer showed years ago, the values of modernism found in the complexities and contradictions of modern physics such as wireless action or wave-particle puzzles a fertile ground for the development of new artistic languages; in literature, as much as in the plastic and performing arts.
The role of authority in preserving scientific ideas
Authority is as important in science as arguments, internal logic and empirical results. The prestige of figures such as Lodge and Arthur Eddington in Britain, Phillip Lenard in Germany, Henri Poincaré in France, or the astronomer Dayton Miller in the USA, all defendants of the ether (albeit in different guises and for different reasons) was instrumental to keeping the ether alive in the public sphere. But so was Einstein and his theories. Indeed, the popularity of general relativity after its highly-advertised confirmation in 1919 triggered a decade of debates to which scientists, philosophers and dilettantes equally contributed. In these disputes, the ether took centre stage in ways that transcended the limits of esoteric physics. At stake was, not only the existence of this imponderable medium, but also what physics was or had to be.
A highly controversial example was the case of a number of German men of science who created the ‘Society in Defence of the Ether and Universal Science’ in the 1920s and 1930s. Certainly, in the nationalistic and anti-semitic mood of the times in Germany, part of this defence of the ether was motivated by an opposition to anything related to Einstein, but that is not the full story. Abandoning the ether was, for the members of this society, tantamount to challenging stability and continuity, promoting chaos, and diminishing the role of science to that of mere mathematical results without deeper explanations.
The resurgence of pluralism
For some defendants of relativity and quantum physics, the ether was not only irrelevant but also a relic of the past. For others such as Eddington, and also Einstein to a certain extent after 1920, the ether could be preserved, although its meaning modified –which, by the way, is a common strategy in the history of science. For many engineers and wireless amateurs, the ether was a much-needed medium to make sense of the waves they were working with. And the question almost naturally arises as to which of these three groups of people was right. Let me suggest that the three stances were legitimate in their own way, thus providing us with a case of scientific pluralism.
The ether qua absolute reference framework and quasi-material universal substratum had indeed been stabbed to death by Einstein’s special relativity, the replication of Michelson-Morley-type experiments, and the long-known internal contradictions of such a concept. But, as Eddington put it, one could not do away with the ether while keeping notions such as particles, force or action at a distance. General relativity did indeed formulate a new physics without any such concepts, and the whole conceptual apparatus was intrinsically consistent; but trying to preserve, for instance, the notion of action at a distance without a medium was at least as mysterious as keeping a conceptually contradictory ether. Thus, the wireless amateur could preserve an ether that the relativist did not need since their epistemic needs were different. In the same way, as quite a number of physics have recently claimed, in ways that remind us of the failed attempt of Dirac in 1951, talk about ‘space with properties’, which is what current quantum field theories do, is not that far from some of the epistemological roles the ether of old played. Rather than a battle between champions and opponents to the ether, a more pluralistic physics might allow for the co-existence of both stances, albeit each limited to particular phenomena and epistemic needs.
Geoffrey N. Cantor and Michael J. S. Hodge, Conceptions of Ether. Studies in the History of Ether Theories, 1740-1900. (Cambridge: Cambridge University Press, 1981).
Jaume Navarro (ed)., Ether and Modernity (Oxford: Oxford University Press, 2018, forthcoming)
Ludwik Kostro, Einstein and the Ether (Montreal: Apeiron, 2000).
Richard Staley, “On the Co-Creation of Classical and Modern Physics”, Isis, 96 (2005), 530-558.