P. Lenard. On the Principle of Relativity, the Ether, and Gravitation. (A Critique of the Theory of Relativity.) Edited by Prof. A. K. Timiryazev. 58 pp. State Publishing House. Moscow, 1922.

This little book makes a strange impression. A distinguished physicist, whose name and works are known to everyone, has set himself the goal, come what may, of refuting the general theory of relativity, and he tries to achieve this not so much by means of objections of a scientific character as by a bad polemical tone. The whole booklet is permeated with the latter; here are several examples.

Note on p. 5. A “relativist” is defined as “a person who strives not so much for the knowledge of reality as one who defends, or at least wishes to portray in the most favorable possible light, the principle of which he is an ‘adherent’”...

Note on p. 7. “The ‘boldness’ sometimes ascribed to the natural scientist in reality consists in a fairly unceremonious confidence in his impunity, and this, of course, does not at all contribute to the purity of scientific literature. Such boldness is not among the German qualities.”

Note on p. 51. “I was, in the end, amazed at how little prepared Mr. Einstein seemed to be to answer my questions... In spite of this, he and another specialist, with complete certainty, created among newspaper readers the impression of the unconditional superiority of his theory in comparison with the circle of ideas advanced by me.”

If one adds to this that Lenard’s chief argument is an appeal to “simple common sense,” the very same to which the holy fathers, the Jesuits, appealed when objecting to Copernicus and Galileo, then I think the general tone of this booklet—unique in scientific literature on physics—will have been sufficiently outlined. It seems that since Dühring¹ so much polemic had not been introduced into pure science.

Let us now turn to Lenard’s work on its merits. In it one may distinguish (apart from the bad polemic) two aspects: the criticism of the theory of relativity and the author’s own “theory of dynamids,” which is supposed to replace Einstein’s theory of gravitation. But since this theory of dynamids was only proclaimed by the author and not developed scien—

¹ History of Mechanics.

so that one could compare its results with the results of the general theory of relativity, it seems premature for us to discuss it. But one must dwell on the criticism of the theory of relativity. Lenard objects not to the special theory of relativity, but to its generalization to non-uniform motions, with the exception of uniformly accelerated rectilinear motion. It must be noted that such a restriction of the general principle gives nothing in the fundamental sense; for even in this case one has to sacrifice all “traditional views” (p. 21), for example Euclidean geometry (if we wish to regard a light ray as a straight line—i.e., in precisely the same conditions in which such a sacrifice is necessary in the general theory). Secondly, Lenard’s direct objections are not only unsatisfactory, but sometimes simply incomprehensible. “I insist” (p. 20) “on the universal significance of the proposition: a system in which the action of inertia takes place is in a state of non-uniform motion”... With respect to what, Lenard does not stipulate at all, and thus it turns out that he does not recognize Mach’s well-known remark. And further, on the same page: “Likewise rotational motion, as a special case of non-uniform motion, can be absolutely detected by the action of inertia”... “The heralds of the general principle of relativity... foist upon (just so!) their readers the reasoning that the experiment with Foucault’s pendulum would proceed in exactly the same way both in the case of the earth’s rotation about its axis and in the case of the rotation of the whole world about the earth. I do not know whether they notice, in doing so, that... the formulation of this alternative means an inadmissible logical experiment... since in this case one would have to ascribe to the heavenly bodies... a speed of motion... exceeding the speed of light... and the mere possibility of such speeds would be equivalent to proof of the invalidity of the simple principle of relativity.” I apologize for the length of the quotation1, but I wanted to show the reader sufficiently clearly the groundlessness of Lenard’s criticism. Let us note, first, that speeds exceeding \(3\cdot 10^{10}\) must also be admitted by Lenard if he agrees to recognize the extension of the principle of relativity to uniformly accelerated systems. Secondly, the generalized theory does not contradict the special theory, but includes it, in the manner in which non-Euclidean geometry includes Euclidean geometry; therefore doubts about the admissibility of the above-mentioned logical experiment must fall away. In any case, this logical experiment is in principle no worse than other logical experiments in physics. Lenard’s objections concerning the non-uniform motion of a train have been analyzed by Einstein; but Lenard remained unconvinced.

The comparison of the general theory with experiment cannot as yet be considered complete; but Lenard’s indication of the possibility that rays are bent near the sun as a result of atmospheric refraction, after Emden’s work, must be regarded as untenable, and Lenard ought to have known this.

Every physicist studying the theory of relativity knows that it cannot yet be considered complete; but reading Lenard’s booklet will not advance him in the least in understanding and criticizing the theory of relativity; he has no need of this booklet. For the nonspecialist reader this booklet is harmful. It should not have been translated into Russian; at the very least, in the interests of truth, it should have been supplied with explanatory notes and the polemical attacks softened or altogether removed; the editor of the Russian translation not only failed to do this, but in one of his few notes misleads the reader concerning Einstein’s views on the ether. Einstein does not regard his ether as “absolutely immobile” (p. 13); here are Einstein’s own words1: “one may not think of this ether as consisting of parts that can be followed in time; only ponderable matter possesses such a property; likewise, the concept of motion cannot be applied to it.” It would be far too naive to understand the last phrase as an assertion of the immobility of the ether, and an absolute one at that; it is clearly expressed here that the attribute of motion and its special case—rest—the ether simply does not have, as something distinct from ponderable matter.

Nik. Andreev.

1. Einstein. Ether and the Theory of Relativity. Petrograd, 1921, pp. 26–27. ↩↩