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20 - John Bell's Varying Interpretations of Quantum Mechanics: Memories and Comments
- from Part IV - Nonlocal Realistic Theories
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- By H. Dieter Zeh, Heidelberg University
- Edited by Mary Bell, Shan Gao, Chinese Academy of Sciences, Beijing
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- Book:
- Quantum Nonlocality and Reality
- Published online:
- 05 September 2016
- Print publication:
- 19 September 2016, pp 331-343
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Summary
Abstract
Various interpretations of quantum mechanics, favored (or neglected) by John Bell in the context of his nonlocality theorem, are compared and discussed.
Varenna 1970
I met John Bell for the first time at the Varenna conference of 1970 [1]. I had been invited on the suggestion of Eugene P. Wigner, who had already helped me to publish my first paper on the concept that was later called decoherence – to appear in the first issue of Foundations of Physics a few months after the conference [2]. This concept arose from my conviction, based on many applications of quantum mechanics to composite systems under various conditions, that Schrödinger's wave function in configuration space, or more generally the superposition principle, is universally valid and applicable. In particular, stable narrow wavepackets can represent classical configurations, while their superpositions define novel individual properties – such as “momentum,” defined as a plane wave superposition of different positions. Superpositions of macroscopically different properties, on the other hand, are regularly irreversibly “dislocalized” (distributed over many degrees of freedom) by means of interactions described by the Schrödinger equation. The corresponding disappearance of certain local superpositions (“decoherence”) seems to explain the phenomenon of a classical world as well as the apparent occurrence of quantum jumps or stochastic “events” – see Sect. 20.4 or [3] for a historical overview of the conceptual development of quantum theory. So I had never felt any motivation to think of “hidden variables” or any other physics behind the successful wave function.
Therefore, I was very surprised on my arrival in Varenna to hear everybody discuss Bell's inequality. It had been published a few years before the conference, but I had either not noticed it or not regarded it as particularly remarkable until then. As this inequality demonstrates that the predictions of quantum theory would require any conceivable reality possibly underlying the nonlocal wave function to be nonlocal itself, I simply found my conviction that the latter describes individual reality confirmed. For example, I had often discussed the conservation of total spin or angular momentum in an individual decay process, which requires nonlocal entanglement between the fragments at any distance in a form that was later called a “Bell state”.
6 - The wave function: it or bit?
- from Part III - Quantum reality: theory
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- By H. Dieter Zeh, Universität Heidelberg
- Edited by John D. Barrow, University of Cambridge, Paul C. W. Davies, Macquarie University, Sydney, Charles L. Harper, Jr
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- Book:
- Science and Ultimate Reality
- Published online:
- 29 March 2011
- Print publication:
- 22 April 2004, pp 103-120
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Summary
Introduction
Does Schrödinger's wave function describe physical reality (“it” in John Wheeler's terminology (Wheeler 1994)) or some kind of information (“bit”)? The answer to this question must crucially depend on the definition of these terms. Is it then merely a matter of words? Not quite – I feel. Inappropriate words may be misleading, while reasonably chosen terms are helpful.
A bit is usually understood as the binary unit of information, which can be physically realized in (classical) computers, but also by neuronal states of having fired or not. This traditional physical (in particular, thermodynamical) realization of information (“bit from it”) has proven essential in order to avoid paradoxes otherwise arising from situations related to Maxwell's demon. On the other hand, the concept of a bit has a typical quantum aspect: the very word quantum refers to discreteness, while, paradoxically, the quantum bit is represented by a continuum (the unit sphere in a two-dimensional Hilbert space) – more similar to an analog computer. If this quantum state describes “mere information,” how can there be real quantum computers that are based on such superpositions of classical bits?
The problematic choice of words characterizing the nature of the wave function (or a general “quantum state”) seems to reflect the common uneasiness of physicists, including the founders of quantum theory, about its fundamental meaning. However, it may also express a certain prejudice.