Lorentz ether theory

defunct theory of electromagnetism

What is now often called Lorentz ether theory (LET) has its roots in Hendrik Lorentz's "theory of electrons", which was the final point in the development of the classical aether theories at the end of the 19th and at the beginning of the 20th century.


  • The approach of Einstein differs from that of Lorentz in two major ways. There is a difference of philosophy, and a difference of style.
    The difference of philosophy is this. Since it is experimentally impossible to say which of two uniformly moving systems is really at rest, Einstein declares the notions ‘really resting’ and ‘really moving’ as meaningless. For him only the relative motion of two or more uniformly moving objects is real. Lorentz, on the other hand, preferred the view that there is indeed a state of real rest, defined by the ‘aether’, even though the laws of physics conspire to prevent us identifying it experimentally. The facts of physics do not oblige us to accept one philosophy rather than the other. And we need not accept Lorentz’s philosophy to accept a Lorentzian pedagogy. Its special merit is to drive home the lesson that the laws of physics in any one reference frame account for all physical phenomena, including the observations of moving observers. And it is often simpler to work in a single frame, rather than to hurry after each moving object in turn.
    The difference of style is that instead of inferring the experience of moving observers from known and conjectured laws of physics, Einstein starts from the hypothesis that the laws will look the same to all observers in uniform motion. This permits a very concise and elegant formulation of the theory, as often happens when one big assumption can be made to cover several less big ones. There is no intention here to make any reservation whatever about the power and precision of Einstein’s approach. But in my opinion there is also something to be said for taking students along the road made by Fitzgerald, Larmor, Lorentz and Poincaré. The longer road sometimes gives more familiarity with the country.
  • Well, what is not sufficiently emphasized in textbooks, in my opinion, is that the pre-Einstein position of Lorentz and Poincare, Larmor and Fitzgerald was perfectly coherent, and is not inconsistent with relativity theory. The idea that there is an aether, and these Fitzgerald contractions and Larmor dilations occur, and that as a result the instruments do not detect motion through the aether - that is a perfectly coherent point of view.
    • John S. Bell, interview in The Ghost in the Atom: A Discussion of the Mysteries of Quantum Physics (1986) edited by P. C. W. Davies and Julian R. Brown
  • Even though the Lorentz theory is no longer generally accepted today, it is worthwhile to study it in some detail, not only because it helps to provide an appreciation of the historical context out of which the theory of relativity arose, but much more because it helps us to understand the essential content of Einstein’s new approach to the problem. Indeed, a critical examination of the Lorentz theory leads one, on the basis of already familiar and accepted physical notions, to see clearly what is wrong with the Newtonian concepts of space and time, as well as to suggest a great many of the changes needed in order to avoid the difficulties to which these concepts lead.
    Lorentz began by accepting the assumption of an ether. However, his basic new step was to study the dependence of the process of measurement of space and time on the relationship between the atomic constitution of matter and the movement of matter through the ether.
  • An experimental decision between Lorentz's and Einstein's theories was thus not possible; it was seen that between them there could fundamentally be no experimentum cruris. The advocates of the new doctrine accordingly had to appeal—an unusual spectacle in the history of physics—to general philosophical grounds, to the advantages over the assumption of Lorentz which the new doctrine possessed in a systematic and epistemological respect.
    • Ernst Cassirer, Substance and Function: Einstein's theory of relativity (1923)
  • Although the contraction hypothesis successfully accounted for the negative result of the experiment, it was open to the objection that it was invented for the express purpose of explaining away the difficulty, and was too artificial. However, in many other experiments to discover an ether wind, similar difficulties arose, until it appeared that nature was in a “conspiracy” to thwart man by introducing some new phenomenon to undo every phenomenon that he thought would permit a measurement of u. It was ultimately recognized, as Poincaré pointed out, that a complete conspiracy is itself a law of nature! Poincaré then proposed that there is such a law of nature, that it is not possible to discover an ether wind by any experiment; that is, there is no way to determine an absolute velocity.
    • Richard Feynman, in Richard P. Feynman, Robert B. Leighton, Matthew Sands, The Feynman Lectures on Physics (1963)
  • Lorentz's new theory not only accounted for the negative results of the Michelson-Morley experiment; it also accounted for any conceivable experiment designed to detect changes in the speed of light as a result of an ether wind. Its equations for variations in length and time were worked out in such a way that every possible method of measuring the speed of light, from any frame of reference, would always give the same result. It is easy to understand why physicists were unhappy with this theory. It was ad hoc in the full sense of the word. It seemed little more than a weird effort to patch up the rents that had developed in the ether theory.
  • If the ether as an absolute reference system could be demonstrated, the notion of absolute space could be saved. Indeed, one of the most important experiments to this end, the Michelson-Morley experiment, was in 1904 interpreted by Lorentz in this sense. His interpretation fulfilled all physical requirements. As is well known, according to Lorentz every body moving with reference to the motionless ether or absolute space undergoes a certain contraction in the dimension parallel to the motion. However, the Michelson-Morley experiment served as the starting point for the development of the theory of relativity and was interpreted by Einstein on entirely different lines, adverse to the acceptance of absolute space. It was understood that both interpretations give a complete explanation of all observations known at the beginning of the twentieth century. An experimenturn cruris could not decide between these two theories.
  • The same point can be made at least equally effectively in reverse: there is no such thing as research without counterinstances. For what is it that differentiates normal science from science in a crisis state? Not, surely, that the former confronts no counterinstances. On the contrary, what we previously called the puzzles that constitute normal science exist only because no paradigm that provides a basis for scientific research ever completely resolves all its problems. The very few that have ever seemed to do so (e.g., geometric optics) have shortly ceased to yield research problems at all and have instead become tools for engineering. Excepting those that are exclusively instrumental, every problem that normal science sees as a puzzle can be seen, from another viewpoint, as a counterinstance and thus as a source of crisis. Copernicus saw as counterinstances what most of Ptolemy’s other successors had seen as puzzles in the match between observation and theory. Lavoisier saw as a counterinstance what Priestley had seen as a successfully solved puzzle in the articulation of the phlogiston theory. And Einstein saw as counterinstances what Lorentz, Fitzgerald, and others had seen as puzzles in the articulation of Newton’s and Maxwell’s theories. Furthermore, even the existence of crisis does not by itself transform a puzzle into a counterinstance. There is no such sharp dividing line. Instead, by proliferating versions of the paradigm, crisis loosens the rules of normal puzzle-solving in ways that ultimately permit a new paradigm to emerge. There are, I think, only two alternatives: either no scientific theory ever confronts a counterinstance, or all such theories confront counterinstances at all times.
    • Thomas Kuhn, The Structure of Scientific Revolutions (1962)
  • Though a true experimental decision between the theory of Lorentz and the theory of relativity is indeed not to be gained, and that the former, in spite of this, has receded into the background, is chiefly due to the fact that, close as it comes to the theory of relativity, it still lacks the great simple universal principle, the possession of which lends the theory of relativity an imposing appearance.

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