More than sixty years after the general acceptance of Quantum Mechanics, and notwithstanding its enormous practical success, the nature of the fundamental objects appearing in its framework is unclear, and the debate concerning its conceptual foundations still goes on. This paper tries to examine what may be claimed to be one of the most ‘properly quantic’ ( Lévy-Leblond 1977 ) approaches to this problem, namely ‘no-collapse’ versions of the non-relativistic quantum mechanics of closed systems: Everett’s theory and the ‘pilot wave’.
More than sixty years after the general acceptance of Quantum Mechanics, and notwithstanding its enormous practical success, the nature of the fundamental objects appearing in its framework is unclear, and the debate concerning its conceptual foundations still goes on. This paper tries to examine what may be claimed to be one of the most ‘properly quantic’ ( Lévy-Leblond 1977 ) approaches to this problem, namely ‘no-collapse’ versions of the non-relativistic quantum mechanics of closed systems: Everett’s theory and the ‘pilot wave’.
Quantum mechanics is our most successful physical theory. It underlies our very detailed understanding of atomic physics, chemistry, and nuclear physics, and the many technologies to which physical systems in these regimes give rise. Additionally, relativistic quantum mechanics is the basis for the standard model of elementary particles, which very successfully gives a partial unification of the forces operating at the atomic, nuclear, and subnuclear levels. However, from its inception the probabilistic nature of quantum mechanics, and the fact that “quantum measurements” in the orthodox formulation appear to require the intervention of non-quantum mechanical “classical systems,” have led to speculations by many physicists, mathematicians, and philosophers of science that quantum mechanics may be incomplete. Among the Founding Fathers of quantum theory, Einstein and Schrödinger were both of the opinion that quantum mechanics is in some way unsatisfactory, and this view has been amplified in more recent profound work of John Bell, among others. In an opposing camp, many others in the physics, mathematics, and philosophy communities have attempted to provide an interpretational foundation in which quantum mechanics remains a complete and self-contained system. Among the Founding Fathers, Bohr, Born, and Heisenberg maintained that quantum mechanics is a complete system, and a number of recent proposals have been made to improve upon or to provide alternatives to their “Copenhagen Interpretation.” The debate continues, and has spawned an enormous literature.
Abstract The conceptual foundations of quantum mechanics have been the object of intense interest and debate for both physicists and philosophers ever since the birth of the theory. Providing a coherent and comprehensive interpretation of the non-relativistic quantum algorithm has proved to be an ongoing challenge, and the vast literature on the subject is a testament to both the perennial fascination of the problem and to the absence of any durable consensus about how best to understand the theory.
The purpose is, first, to review the occurrences which led to the acceptance by the bulk of physicists of the instrumentalist approach to quantum mechanics (QM) as the only one worth considering as truly rendering nature at the atomic level. Formulated soon after the creation of QM it outright refused the local realist interpretation. Next, to bring out the successive waves of dissenting voices, which still go on unabated. Finally, to recall that – in spite of the pervading dominance of the Copenhagen reading of quantum phenomena – the manifold questions concerning the interpretation of QM continue to be the subject-matter of forceful interventions claiming that the foundational basis of QM is far from being definitely closed.
Some two centuries before the quantum revolution, Newton (1) suggested that corpuscles of light generate waves in an aethereal medium like skipping stones generate waves in water, with their motion then being affected by these aether waves. Times have changed. Light corpuscles are now known as photons, and the majority of physicists have dispensed with the notion of aether. Nevertheless, certain features of Newton's metaphor live on in one particular version of quantum mechanics. According to pilot wave theory, first proposed by de Broglie (2) and later developed by Bohm (3) with Einstein's encouragement, microscopic elements such as photons and electrons consist of both particle and wave, the former being guided by the latter. Although this physical picture has not been widely accepted, it has had some notable proponents, including Bell (4). Its principal appeal is that it restores realism and determinism to quantum mechanics, its weakness that the physical nature of the guiding wave field remains unclear. At the time that pilot wave theory was developed and then overtaken by the Copenhagen interpretation as the standard view of quantum mechanics, there was no macroscopic pilot wave analog to draw upon. Now there is.
In 1976, a conference called "Fifty Years of Quantum Mechanics" was held at the University of Louis Pasteur, Strasbourg. It was attended by more than a dozen physicists, including a young French scientist, Jean Marc Levy-Leblond. Wheeler's presentation was called, `"Include the Observer in the Wave Function?'' Wheeler had a history of vacillating on Everett's theory, but now, 20 years after he had endorsed it in Reviews of Modern Physics, he rejected Everett's inclusion of the observer in the wave function, essentially upholding the Copenhagen interpretation. In 1977, Jean Marc Levy-Leblond wrote a letter to Everett, including a copy of a paper he had presented at the conference that compared DeWitt's and Everett's views. Everett responded by agreeing with Levy-Leblond's analysis of the differences between the two views. Everett especially liked the short spoof of foundational writing in physics (on "zipperdynamics'') that LeBlond had tacked onto the end of his paper. This document is the published version of Levy-Leblond's paper, which appeared in the journal Dialectica 30 (2/3) in 1976.