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CRC Press eBooks

Quantum

Published Aug 1, 2003• 0 citations
Publisher

Abstract

Bohr, Niels There is no quantum world. There is only an abstract quantum physical description. It is wrong to think that the task of physics is to find out how nature is. Physics concerns what we can say about nature.
DOI
10.1201/9781420034677-130

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Seeking 'pictures of reality' beneath the surface of quantum theory may seem anathema to those who concur with Niels Bohr's authoritative remark: '... in the general problem of quantum theory, one is faced ... with an essential failure of the pictures in space and time on which the description of natural phenomena has hitherto been based'. Nevertheless, in the last few decades there has been a resurgence of interest in salvaging from the theory at least some picture of how the microphysical world is, however counterintuitive that may be.

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If you ask Google to search for “no quantum world,” you will get nearly 300 hits. They all give the following quotation (or recognizable corruptions of it): There is no quantum world. There is only an abstract quantum physical description. It is wrong to think that the task of physics is to find out how nature is. Physics concerns what we can say about nature. Over 90% of them attribute the statement to Niels Bohr, with phrases like “Bohr's dictum …,” “Bohr insisted that …,” “Bohr proclaimed …,” “Niels Bohr said, in a frequently quoted passage …,” “Niels Bohr wrote [my emphasis] …,” and even “Explain and evaluate Bohr's philosophy of quantum theory with reference to his assertion ….” Here is yet another example of the power of the internet to enrich our knowledge. There is only one problem. Bohr, who took writing very seriously indeed, never published such an assertion in any of his writings, although he repeatedly refined, reformulated, and often simply repeated his position on the philosophical foundations of the quantum theory. The statement actually comes from an essay by Aage Petersen, “The Philosophy of Niels Bohr” [1], which he published in the Bulletin of the Atomic Scientists shortly after Bohr's death. Petersen introduced the words with When asked whether the algorithm of quantum mechanics could be considered as somehow mirroring an underlying quantum world, Bohr would answer … So what may now be the most celebrated of all Bohr quotations on the nature of the quantum theory is at best an attempt by a close associate to characterize Bohr's general response to the highly problematic notion of a “quantum world,” written too late for Bohr to respond. When you ask Google to list only those pages that also mention the actual author of the words, Petersen, the number of hits drops from 286 to 18. The status of this “quotation” as hearsay is in danger of being lost. I'm particularly sensitive to this risk because in the 1980s I used to enjoy giving physics colloquia on Bell's theorem and its implications for our understanding of quantum mechanics. I was always fond of Petersen's recollection of what Bohr used to say, and I felt that his formulation captured something important about the situation revealed by Bell's theorem.

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In his Reference Frame column “What’s Wrong With This Quantum World?” (Physics Today, Physics Today 0031-9228 57 2 2004 10 https://doi.org/10.1063/1.1688051. February 2004, page 10 ), David Mermin comments on a statement attributed to Niels Bohr by his associate Aage Petersen: When asked whether the algorithm of quantum mechanics could be considered as somehow mirroring an underlying quantum world, Bohr would answer “There is no quantum world. There is only an abstract quantum physical description. It is wrong to think that the task of physics is to find out how nature is. Physics concerns what we can say about nature.” 1 1. A. Petersen, Bull. At. Sci. 19, 8 (1963). Mermin’s column describing different physicists’ reactions to the statement touches on issues that remain central to the understanding of quantum mechanics. Although “quantum world” was not part of Bohr’s terminology, we can imagine that he might have responded as indicated to the question posed. We see the statement in relation to his basic view that the algorithm of quantum mechanics is a purely symbolic formalism accounting for observations that are obtained under specified conditions. That view is illustrated by his advocacy that the word “phenomenon” be used exclusively to refer to “an observation obtained under specified circumstances, including an account of the whole experimental arrangement. In such a terminology, the observational problem is free of any special intricacy, since, in actual experiments, all observations are expressed by unambiguous statements referring, for instance, to the registration of the point at which an electron arrives at a photographic plate.” 2 2. N. Bohr, Essays 1933–1957 on Atomic Physics and Human Knowledge, Ox Bow Press, Woodbridge, CT (1987), p. 64. Interpreted in this manner, the dismissal of a quantum world leaves the particle as an object capable of directly producing the basic event of observation, such as the registration of an electron arriving at a photographic plate or a click produced in a counter. As is evident in the conflicting reactions that Mermin reports, the issue of which world these objects belong to remains controversial.Mermin asks, What’s wrong with this quantum world? Our answer is that the rejection of it in the form described does not go far enough. As we have recently argued, 3 3. A. Bohr, B. R. Mottelson, O. Ulfbeck, Foundations of Physics 34(3), 405 (2004). https://doi.org/10.1023/B:FOOP.0000019621.02554.7e the perceived need to explain the click as being caused by a particle is a remnant from classical imagery, which has obscured the full implications of fortuitousness and thereby the principle underlying quantum mechanics. Thus all experimental evidence is consistent with a complete break with causality in that the click comes without any cause, as a genuinely fortuitous event. The event is recognized as a macroscopic discontinuity in the counter. Thus genuine fortuitousness unavoidably eliminates the particles. Although fortuitousness has been a central innovation of quantum physics, a complete break with causality was beyond the horizon of the pioneers of quantum mechanics. Indeed, if there were no particles producing the clicks, what would the theory be all about?Perhaps surprisingly, the very notion of genuine fortuitousness is powerful in its implications. With particles excluded, only geometry is left on the stage, and the symmetry of spacetime itself, through its representations, provides the mathematical formalism of quantum mechanics. Once that point is recognized, quantum mechanics emerges from the principle of genuine fortuitousness combined with the embodiment of spacetime symmetry, without any reference to degrees of freedom of particles or fields. The theory, exclusively concerned with probability distributions of genuinely fortuitous clicks, thus differs from previous physical theories in that it does not deal with objects to be measured—which eliminates the issue of a quantum world.REFERENCESSection:ChooseTop of pageREFERENCES <<CITING ARTICLES1. A. Petersen, Bull. At. Sci. 19, 8 (1963). Google ScholarCrossref2. N. Bohr, Essays 1933–1957 on Atomic Physics and Human Knowledge, Ox Bow Press, Woodbridge, CT (1987), p. 64. Google Scholar3. A. Bohr, B. R. Mottelson, O. Ulfbeck, Foundations of Physics 34(3), 405 (2004). https://doi.org/10.1023/B:FOOP.0000019621.02554.7e , Google ScholarCrossref© 2004 American Institute of Physics.

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The Description of Nature: Niels Bohr and the Philosophy of Quantum Physics

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Niels Bohr, the founding father of modern atomic physics and quantum theory, was as original a philosopher as he was a physicist. This study explores several dimensions of Bohr's vision: the formulation of quantum theory and the problems associated with its interpretation, the notions of complementarity and correspondence, the debates with Einstein about objectivity and realism, and his sense of the infinite harmony of nature. The author's chief attention is given to Bohr's epistemological lesson, the conviction that all our description of nature is dependent on the words we use and the ways we can unambiguously use them. Against those who would view Bohr as a vague positivist, the author argues here that Bohr is best understood as using transcendental arguments and shaping a kind of descriptive metaphysics in his defence of our abilities to offer a description of the world we live in.

•Jan 1, 1987•108 citations
Seeking 'pictures of reality' beneath the surface of quantum theory may seem anathema to those who concur with Niels Bohr's authoritative remark: '... in the general problem of quantum theory, one is faced ... with an essential failure of the pictures in space and time on which the description of natural phenomena has hitherto been based'. Nevertheless, in the last few decades there has been a resurgence of interest in salvaging from the theory at least some picture of how the microphysical world is, however counterintuitive that may be.
If you ask Google to search for “no quantum world,” you will get nearly 300 hits. They all give the following quotation (or recognizable corruptions of it): There is no quantum world. There is only an abstract quantum physical description. It is wrong to think that the task of physics is to find out how nature is. Physics concerns what we can say about nature. Over 90% of them attribute the statement to Niels Bohr, with phrases like “Bohr's dictum …,” “Bohr insisted that …,” “Bohr proclaimed …,” “Niels Bohr said, in a frequently quoted passage …,” “Niels Bohr wrote [my emphasis] …,” and even “Explain and evaluate Bohr's philosophy of quantum theory with reference to his assertion ….” Here is yet another example of the power of the internet to enrich our knowledge. There is only one problem. Bohr, who took writing very seriously indeed, never published such an assertion in any of his writings, although he repeatedly refined, reformulated, and often simply repeated his position on the philosophical foundations of the quantum theory. The statement actually comes from an essay by Aage Petersen, “The Philosophy of Niels Bohr” [1], which he published in the Bulletin of the Atomic Scientists shortly after Bohr's death. Petersen introduced the words with When asked whether the algorithm of quantum mechanics could be considered as somehow mirroring an underlying quantum world, Bohr would answer … So what may now be the most celebrated of all Bohr quotations on the nature of the quantum theory is at best an attempt by a close associate to characterize Bohr's general response to the highly problematic notion of a “quantum world,” written too late for Bohr to respond. When you ask Google to list only those pages that also mention the actual author of the words, Petersen, the number of hits drops from 286 to 18. The status of this “quotation” as hearsay is in danger of being lost. I'm particularly sensitive to this risk because in the 1980s I used to enjoy giving physics colloquia on Bell's theorem and its implications for our understanding of quantum mechanics. I was always fond of Petersen's recollection of what Bohr used to say, and I felt that his formulation captured something important about the situation revealed by Bell's theorem.
In his Reference Frame column “What’s Wrong With This Quantum World?” (Physics Today, Physics Today 0031-9228 57 2 2004 10 https://doi.org/10.1063/1.1688051. February 2004, page 10 ), David Mermin comments on a statement attributed to Niels Bohr by his associate Aage Petersen: When asked whether the algorithm of quantum mechanics could be considered as somehow mirroring an underlying quantum world, Bohr would answer “There is no quantum world. There is only an abstract quantum physical description. It is wrong to think that the task of physics is to find out how nature is. Physics concerns what we can say about nature.” 1 1. A. Petersen, Bull. At. Sci. 19, 8 (1963). Mermin’s column describing different physicists’ reactions to the statement touches on issues that remain central to the understanding of quantum mechanics. Although “quantum world” was not part of Bohr’s terminology, we can imagine that he might have responded as indicated to the question posed. We see the statement in relation to his basic view that the algorithm of quantum mechanics is a purely symbolic formalism accounting for observations that are obtained under specified conditions. That view is illustrated by his advocacy that the word “phenomenon” be used exclusively to refer to “an observation obtained under specified circumstances, including an account of the whole experimental arrangement. In such a terminology, the observational problem is free of any special intricacy, since, in actual experiments, all observations are expressed by unambiguous statements referring, for instance, to the registration of the point at which an electron arrives at a photographic plate.” 2 2. N. Bohr, Essays 1933–1957 on Atomic Physics and Human Knowledge, Ox Bow Press, Woodbridge, CT (1987), p. 64. Interpreted in this manner, the dismissal of a quantum world leaves the particle as an object capable of directly producing the basic event of observation, such as the registration of an electron arriving at a photographic plate or a click produced in a counter. As is evident in the conflicting reactions that Mermin reports, the issue of which world these objects belong to remains controversial.Mermin asks, What’s wrong with this quantum world? Our answer is that the rejection of it in the form described does not go far enough. As we have recently argued, 3 3. A. Bohr, B. R. Mottelson, O. Ulfbeck, Foundations of Physics 34(3), 405 (2004). https://doi.org/10.1023/B:FOOP.0000019621.02554.7e the perceived need to explain the click as being caused by a particle is a remnant from classical imagery, which has obscured the full implications of fortuitousness and thereby the principle underlying quantum mechanics. Thus all experimental evidence is consistent with a complete break with causality in that the click comes without any cause, as a genuinely fortuitous event. The event is recognized as a macroscopic discontinuity in the counter. Thus genuine fortuitousness unavoidably eliminates the particles. Although fortuitousness has been a central innovation of quantum physics, a complete break with causality was beyond the horizon of the pioneers of quantum mechanics. Indeed, if there were no particles producing the clicks, what would the theory be all about?Perhaps surprisingly, the very notion of genuine fortuitousness is powerful in its implications. With particles excluded, only geometry is left on the stage, and the symmetry of spacetime itself, through its representations, provides the mathematical formalism of quantum mechanics. Once that point is recognized, quantum mechanics emerges from the principle of genuine fortuitousness combined with the embodiment of spacetime symmetry, without any reference to degrees of freedom of particles or fields. The theory, exclusively concerned with probability distributions of genuinely fortuitous clicks, thus differs from previous physical theories in that it does not deal with objects to be measured—which eliminates the issue of a quantum world.REFERENCESSection:ChooseTop of pageREFERENCES <<CITING ARTICLES1. A. Petersen, Bull. At. Sci. 19, 8 (1963). Google ScholarCrossref2. N. Bohr, Essays 1933–1957 on Atomic Physics and Human Knowledge, Ox Bow Press, Woodbridge, CT (1987), p. 64. Google Scholar3. A. Bohr, B. R. Mottelson, O. Ulfbeck, Foundations of Physics 34(3), 405 (2004). https://doi.org/10.1023/B:FOOP.0000019621.02554.7e , Google ScholarCrossref© 2004 American Institute of Physics.
Abstract Quantum theory provides a superb description of physical reality on a small scale, yet it contains many mysteries. Without doubt, it is hard to come to terms with the workings of this theory, and it is particularly difficult to make sense of the kind of ‘physical reality’—or lack of it—that it seems to imply for our world. Taken at its face value, the theory seems to lead to a philosophical standpoint that many (including myself) find deeply unsatisfying. At best, and taking its descriptions at their most literal, it provides us with a very strange view of the world indeed. At worst, and taking literally the proclamations of some of its most famous protagonists, it provides us with no view of the world at all.
Niels Bohr, the founding father of modern atomic physics and quantum theory, was as original a philosopher as he was a physicist. This study explores several dimensions of Bohr's vision: the formulation of quantum theory and the problems associated with its interpretation, the notions of complementarity and correspondence, the debates with Einstein about objectivity and realism, and his sense of the infinite harmony of nature. The author's chief attention is given to Bohr's epistemological lesson, the conviction that all our description of nature is dependent on the words we use and the ways we can unambiguously use them. Against those who would view Bohr as a vague positivist, the author argues here that Bohr is best understood as using transcendental arguments and shaping a kind of descriptive metaphysics in his defence of our abilities to offer a description of the world we live in.