Einstein and the Ether
(Apeiron, Montreal, 2000)
"Whether gravitational, electrical, and nuclear
interactions can be encompassed within a unified
theoretical structure, and whether such a structure
will be conceived as a plenary space with physical
properties, remains to be seen. But if the history of
the successive dynasties of aether is any guide,
we can eventually proclaim:
The luminiferous aether is dead!
Long live the aether!" (Owen Gingerich)
Nowadays, nobody talks any longer about the ether in scientific ortohodox books, in higher school or university classes, etc., yet this concept has been one of the corner stones of many rational interpretation of natural phaenomena for a great long time - to such an extent that a good physicist recently wrote to us that all XIXth century physics tried to "prove the existence of the ether which was later proved not to exist".
If we ask why the ether has disappeared from the major scenes of our knowledge of Nature, everybody will answer that Einstein has proved, with his celebrated theory of relativity, that the ether does not exist. This was one of those concepts that old physicists were accustomed to use in their "primitive" speculations, but today, luckily, it has been completely overthrown, together with other similar relics of "superstition", by XXth century scientists. It was in that time that mankind has realized the greatest achievements of ever in science and technology, which can be interpreted as the goal of a long walk, that began thanks to such men like Copernic, Galilei, Descartes, Newton,... just sprung out from the darkness of Middle Ages.
Thus, "common people", and even the "common scientist", would be surprised in reading this book (about 240 pp.), written by the physicist and philosopher Ludwik Kostro, and intended for physicists as well as for historians of science, philosophers, or in general for any people interested in the development of scientific culture. As a matter of fact, it is entirely dedicated to the troublesome relationships between the greatest scientist of all times - or at least many people think so! - and the elusive ether.
Let us see the question with the author's own words (Introduction):
"In the eyes of most physicists and philosophers, Albert Einstein has acquired a reputation for abolishing the concept of the ether as a medium filling space (or identified with it), which was responsible for carrying electromagnetic, gravitational and other interactions. Today, this notion is echoed in textbooks, encyclopaedias, and scientific reviews. However, it does not fully reflect the historical truth, and in a sense even represents a distortion [...] Einstein denied the existence of the ether for only 11 years - from 1905 to 1916. Thereafter, he recognized that his attitude was too radical and even regretted that his works published before 1916 had so definitely and absolutely rejected the existence of the ether."
The author proves this assertion directly referring to the opinions which Einstein himself expressed during his life, in a book which is therefore full of quotations and precise bibliographical references (up to the point of quoting even the original Deutsch passages in a special appendix). Here they are some examples of Einstein's thoughts:
"It would have been more correct if I had limited myself, in my earlier publications, to emphasizing only the nonexistence of an ether velocity, instead of arguing the total nonexistence of the ether, for I can see that with the word ether we say nothing else than that space has to be viewed as a carrier of physical qualities."
" [...] in 1905 I was of the opinion that it was no longer allowed to speak about the ether in physics. This opinion, however, was too radical, as we will see later when we discuss the general theory of relativity. It does remain allowed, as always, to introduce a medium filling all space and to assume that the electromagnetic fields (and matter as well) are its states. [...] once again 'empty' space appears as endowed with physical properties, i.e., no longer as physically empty, as seemed to be the case according to special relativity [...] ".
"This word ether has changed its meaning many times in the development if science [...] Its story, by no means finished, is continued by relativity theory."
It seems interesting to quote even the following passages by Eistein, where he somehow admits the rational necessity of the ether, that is to say, the necessity of conceiving a space which cannot be thought of but endowed with physical properties:
"There is an important argument in favour of the hypothesis of the ether. To deny the existence of the ether means, in the last analysis, denying all physical properties to empty space."
"The ether hypothesis was bound always to play a part even if it is mostly a latent one at first in the thinking of physicists."
So we have seen the description of one of the main themes of Einstein's research, going on through a complex route which Kostro aims to carefully reconstruct, as the Index of his book clearly shows:
Chap. 1 - Einstein's views on the ether before 1905
Chap. 2 - Einstein denies the existence of the ether (1905-1916)
Chap. 3 - Einstein introduces his new concept of the ether (1916-1924)
Chap. 4 - Development of Einstein's ether concept (1925-1955)
Chap. 5 - Physical meaning of Einstein's relativistic ether
Appendix - Original quotations
[the Bibliography lists more than 250 items!]
We could stop here this presentation, but we feel necessary to add some more words discussing the opinion, shared by the author, that general relativity could be truly conceived of as a theory of a dynamical ether. Indeed, it is perhaps appropriate to emphasize that the general opinion about Einstein discarding the ether is in some sense not absolutely groundless, since a relativistic ether - as we must theorize the physical space according to the relativistic conceptions of space and time - is quite different for instance from the Descartes's ether. This relativistic ether cannot have the same meaning, and role, of the "old" mechanical ether in a rational description of the universe: otherwise, it cannot be properly defined a "true ether". Einstein's 4-dimensional ether, if we wish to call it so, cannot provide the same natural causal explanations which, on the contrary, could be supplied by the introduction of a physical "fluid", filling up the whole 3-dimensional space. The action, and properties, of this universal medium could, in principle, rationally explain all physical phaenomena by means of a simple mechanical analogy (in which, for instance, a force can be interpreted only as a vis a tergo, a field as a perturbation of the space, etc.). Einstein's ether, instead, cannot be thought of but in four dimensions, which means that time must be included in the structure of "space" itself (which is in fact more properly called space-time). This circumstance implies that it is absolutely impossible for the human mind to make an intuitive image of it, and to give any simple meaning for instance to expressions like: "dynamical ether", which would have, vice versa, an easy interpretation with respect to a 3-dimensional fluid ether. As a matter of fact, an ether "moving" with respect to what time? (modern cosmological models are indeed able to introduce a kind of universal time, but it is by no means a simple concept to talk about).
Relativity definitively denies any possibility of human understanding of natural phaenomena, that is to say of any real explanation - it destroys for instance the tomistic proposal of describing science as adaequatio intellectus et rei. It seems more realistic, as far as the widespread attitude of contemporary natural philosophy is concerned, the opinion expressed by Richard P. Feynman (see Episteme N. 1, Umberto Bartocci, "Della natura 'ambigua' della luce"), which exhorts men to resign to the idea that Nature is absurd for their minds:
"The theory of quantum Electrodynamics describes Nature as absurd from the point of view of common sense. And it agrees full with experiment. So I hope you can accept Nature as She is - absurd" (QED - The strange theory of light and matter, Princeton University Press, 1985, p. 10).
Summing up, this would seem one of those cases1 in which the "public opinion" is more concrete, in accepting a lesson, than the teacher himself, with all his doubts, after thoughts, hesitations. As a matter of fact, it does not seem extreme to notice that, after all, ether disappeared as a possible protagonist in the very moment when the european physicist élite dealt with the study of quantum properties of microphysical world, and that all counterintuitive "complications" of quantum mechanics seem due exactly to this absence. Ether could have been, in principle, very well assumed for being the responsible of quantum fluctuations, mysterious interference patterns, etc., but this possibility has never been thoroughly investigated, exactly because of the negative relativistic influence2.
Then, at last, the essential questions remain open: is really general relativity's formalistic and abstract approach a satisfactory answer to the fundamental questions regarding the nature of physical space? Or was all the XXth century theoretical physics on the wrong track, and we should completely change direction, resurrecting perhaps some old suggestions, too hastily considered as dead??
1Another one is concerning Newton's own attitude towards the ether, which was rather multifarious (perhaps even a bit ambiguous?!), and which generated accordingly multiple theories of light: but people (like the "newtonian" Bradley himself, the discoverer of astronomical annual aberration) generally remember him only for the corpuscular theory, which is more coherent with the hypothesis of an empty space.
2For instance, according to the physicists B.H. Lavenda and E. Santamato: "Quantum indeterminism is explainable in terms of the random interactions between quantum particles and the underlying medium in which they supposedly move" ("The Underlying Brownian Motion of Nonrelativistic Quantum Mechanics", Foundations of Physics, Vol. 11, N. 9/10, 1981, p. 654); "It might perhaps be possible to develop a completely classical formulation of quantum mechanics based upon the irregular motion of a single Brownian particle immersed in a suspension of lighter particles" ("Stochastic Interpretations of Nonrelativistic Quantum Theory", Int. J. of Th. Physics, Vol. 23, N. 7, 1984).