The Tausk Controversy on the Foundations of Quantum Mechanics: Physics, Philosophy, and Politics

Abstract

In 1966 the Brazilian physicist Klaus Tausk (1927-2012) circulated a preprint from the International Centre for Theoretical Physics in Trieste, Italy, criticizing Adriana Daneri, Angelo Loinger,and Giovanni Maria Prosperi’s theory of 1962 on the measurement problem in quantum mechanics. A heated controversy ensued between two opposing camps within the orthodox interpretation of quantum theory, represented by Léon Rosenfeld and Eugene P. Wigner. The controversy went well beyond the strictly scientific issues, however, reflecting philosophical and political commitments within the context of the Cold War, the relationship between science in developed and Third World countries, the importance of social skills, and personal idiosyncrasies.

This chapter is based on the paper with the same title, co-authored by Osvaldo Pessoa Jr., Olival Freire Jr., and Alexis De Greiff, Physics in Perspective 10 (2008) 138–162. The original text had its format fitted to the editorial guidelines for this book. References were updated. Acknowledgements are in the original paper.

Appendix: Summary of Tausk’s Arguments

Tausk’s arguments against Daneri, Loinger, and Prosperi’s (DLP’s) theory may be summarized as follows:

DLP’s Theory Deals Only with the Statistical Case

Tausk presents the reduction or projection postulate for an individual, “pure” case, and contrasts it with a statistical version, which he calls the “weak reduction postulate.” He then argues that what DLP derive in their paper is not the projection postulate in the pure case, but in the statistical case (Tausk 1966, p. 4). If so, then the “measurement problem” is not solved, and DLP’s theory fails. Bohm accepted this argument in his letter to Tausk of October 1, 1966 (op. cit.), and Bub developed it in his paper of 1968 (Bub 1968).

DLP’s Analysis Is Circular

Tausk argues that DLP’s description of measurement as occurring in two stages is circular. His argument, however, seems to follow from an incorrect reading of DLP’s theory, which Jauch said was one of the “many details with which I disagree.”⁵⁹

The Ergodic Hypothesis Plays No Role in DLP’s Theory

Tausk (1966, p. 20) suggests that the use of the ergodic hypothesis in DLP’s theory plays only a “purely psychological role,” a view that is based upon some sort of misunderstanding.

Negative-Result Measurements Refute DLP’s Theory

This argument, which we have examined above, is correct in that it shows that amplification is not necessary for state reduction. However, as we noted, contrary to what one might expect, the existence of negative-result measurements does not refute DLP’s theory, which, as Loinger (1968, pp. 246–248) argued, does not explicitly mention amplification. In any case, after Tausk presents his argument, he gives an example of his not very elegant style of writing that contributed to the negative reception of his preprint, declaring that: “To our mind, this argument shows that all attempts to fulfil [sic] the program of DLPI belong to the realm of wishful thinking or, occasionally, of just wishing” (Tausk 1966, p. 23).

Tausk made three additional points in his 1966 preprint and in his 1967 doctoral thesis, as follows:

The Conservation of Angular Momentum Paradox

In Sect. 5 of his preprint and in his thesis,⁶⁰ Tausk raises an apparent paradox concerning the angular momentum of an atom that passes through a Stern-Gerlach apparatus. Assuming that before detection the component of its angular momentum along the line joining the two magnets is zero, immediately after detection it is nonzero, either “up” or “down,” depending upon which of the two detectors is triggered. Tausk asks how this apparent violation of conservation of angular momentum can be explained. A few years later, however, he realized that it could be explained by assuming that angular momentum is transferred to the Stern-Gerlach magnets.⁶¹

Critique of Heisenberg’s Epistemic Conception of Reduction

In his book, Physics and Philosophy of 1958, Heisenberg (1958, pp. 54–55) claimed that state reduction expresses nothing more than an increase of our knowledge of a quantum-mechanical system. Tausk (1966, p. 32) criticizes this view and suggests that quantum mechanics requires a completely new foundation.

No-Signaling Theorem

In his doctoral thesis, Tausk proved that an ensemble of two correlated particles, I and II, prepared in the same composite state, can never be used to transmit information at a speed greater than the speed of light (Tausk 1967, pp. 29–31). This probably is the first time that a physicist proved this rather simple result, which is known in the literature as a no-signaling theorem and is attributed to Philippe Eberhard (1978, on 416–417).

Finally, it is curious that Tausk continues by analyzing the famous Einstein-Podolsky-Rosen paper of 1935 (Einstein et al. 1935), stating that they do not make use of the reduction postulate. That is incorrect: they do make explicit use of it. This illustrates both some of the shortcomings of Tausk’s work and, because this error remained in his thesis even after he defended it, shows that the Brazilian community of physicists was still not well prepared to understand and discuss such philosophical subtleties as we have noted above on the foundations of quantum mechanics.