Paul Dirac has been undoubtedly one of the central figures of the last century physics, contributing in several and remarkable ways to the development of quantum mechanics; he was also at the centre of an active community of physicists, with whom he had extensive interactions and correspondence. In particular, Dirac was in close contact with Bohr, Heisenberg and Pauli. For this reason, among others, Dirac is generally considered a supporter of the Copenhagen interpretation of quantum mechanics. Similarly, he was considered a physicist sympathetic with the positivistic attitude which shaped the development of quantum theory in the 1920s. Against this background, the aim of the present essay is twofold: on the one hand, we will argue that, analyzing specific examples taken from Dirac's published works, he can neither be considered a positivist nor a physicist methodologically guided by the observability doctrine. On the other hand, we will try to disentangle Dirac's figure from the mentioned Copenhagen interpretation, since in his long career he employed remarkably different—and often contradicting—methodological principles and philosophical perspectives with respect to those followed by the supporters of that interpretation. Quanta 2019; 8: 68–87.
Paul Dirac has been undoubtedly one of the central figures of the last century physics, contributing in several and remarkable ways to the development of quantum mechanics; he was also at the centre of an active community of physicists, with whom he had extensive interactions and correspondence. In particular, Dirac was in close contact with Bohr, Heisenberg and Pauli. For this reason, among others, Dirac is generally considered a supporter of the Copenhagen interpretation of quantum mechanics. Similarly, he was considered a physicist sympathetic with the positivistic attitude which shaped the development of quantum theory in the 1920s. Against this background, the aim of the present essay is twofold: on the one hand, we will argue that, analyzing specific examples taken from Dirac's published works, he can neither be considered a positivist nor a physicist methodologically guided by the observability doctrine. On the other hand, we will try to disentangle Dirac's figure from the mentioned Copenhagen interpretation, since in his long career he employed remarkably different—and often contradicting—methodological principles and philosophical perspectives with respect to those followed by the supporters of that interpretation. Quanta 2019; 8: 68–87.
The Copenhagen Interpretation of quantum mechanics has become the standard way of explaining the physical philosophical meaning of the mathematics of microscopic behavior. It developed from the thought of people who attended the Institute for Theoretical Physics of the University of Copenhagen during the 40 years that Niels Bohr directed it, from 1920 to 1962. Bohr took a large part in developing the Copenhagen Interpretation, he didn't escape all controversy over it (although the quote above is a bit of an exaggeration). Bohr did die before the experimental theoretical developments that have transposed the debate over the appropriateness adequacy of the Copenhagen Interpretation into a new key, he may well have been lucky to have escaped when he did. There is no authoritative codification of CI [the Copenhagen Interpretation], write T Gornitz C. E von Weizsacker of the Max Planck Institute in Starnberg, West Germany in' their formal presentation to the recent Loyola Conference on Mathematical Interpretational Problems in Relativistic Quantum Theory, and under the conditions of its origin there probably could not be one.... All prominent authors of the time who wrote on these questions, like Bohr, [Werner] Heisenberg, [Wolfgang] Pauli, J[ohn] v[on] Neumann on one side, [Albert] Einstein [Erwin] Schrodinger on the other, fell, so we feel, into some stammering when they tried to express their own positions. Nevertheless there is what might be called a Copenhagen attitude. It concentrates on observable phenomena, makes statistics probability central to its understanding, considers quantum mechanics primarily a theory of knowledge or information becomes a kind of physica negativa (analogous to a theologia negativa) in trying not to say too much about things that can't be seen or felt. For example, it doesn't much care whether the orbits of electrons in atoms are real or not and, in fact, tends to regard them as unreal. It appears in most textbooks as the standard way of looking at things.
Of all the many rival interpretations of quantum mechanics, none is more important or influential than the Copenhagen interpretation. Unfortunately, there is no one Copenhagen interpretation of quantum mechanics. If one uses the expression, and everyone does, one should not think of the Copenhagen interpretation as a single consistent interpretation of the theory. Philosophers of physics tend to use the expression ‘the Copenhagen interpretation of quantum mechanics’ as a label covering a variety of different interpretations all of which either originate with Niels Bohr or were invented by him, his colleagues and guests at the Institute for Theoretical Physics in Copenhagen beginning in the middle 1920s. Perhaps one should say that the Copenhagen interpretation in this diffuse sense goes back farther than this, back even before the rise of the new quantum mechanics. Heisenberg tells the story of a boat trip he, Bohr, and some friends took from Copenhagen to the island of Fyn around the time when the then new quantum mechanics was being developed. Bohr, ‘full of the new interpretation of quantum theory’, talked of ‘the difficulties of language, of the limitations of all our means of expressing ourselves’ and of how these limitations had been expressed ‘in the foundation of atomic theory in a mathematically lucid way’. ‘Finally,’ Heisenberg ends the story, ‘one of the friends remarked drily, “But, Niels, this is not really new, you said exactly the same ten years ago”
Niels Bohr and the Philosophy of Physics: Twenty-First-Century Perspectives examines the philosophical views, influences and legacy of the Nobel Prize physicist and philosophical spokesman of the quantum revolution, Niels Bohr. The sixteen contributions in this collection by some of the best contemporary philosophers and physicists writing on Bohr’s philosophy today all carefully distinguish his subtle and unique interpretation of quantum mechanics from views often imputed to him under the banner of the “Copenhagen Interpretation.” With respect to philosophical influences on Bohr’s outlook, the contributors analyse prominent similarities between his viewpoint and Kantian ways of thinking, the views of the Danish philosopher Harald Høffding, and themes characteristic of American pragmatism. In recognizing the importance of Bohr’s epistemological naturalism they examine his defence of the indispensability of classical concepts from a variety of different perspectives. This collection shows us that Bohr’s interpretation of quantum mechanics, now nearly a century old, still has
Niels Bohr and Philosophy of Physics: Twenty-First Century Perspectives examines the philosophical views, influences and legacy of the Nobel Prize physicist and philosophical spokesman of the quantum revolution, Niels Bohr. The sixteen contributions in this collection by some of the best contemporary philosophers and physicists writing on Bohr's philosophy today all carefully distinguish his subtle and unique interpretation of quantum mechanics from views often imputed to him under the banner of the “Copenhagen Interpretation.” With respect to philosophical influences on Bohr's outlook, the contributors analyse prominent similarities between his viewpoint and Kantian ways of thinking, the views of the Danish philosopher Harald Høffding, and themes characteristic of American pragmatism. In recognizing the importance of Bohr's epistemological naturalism they examine his defence of the indispensability of classical concepts from a variety of different perspectives. This collection shows us that Bohr's interpretation of quantum mechanics, now nearly a century old, still has the power to shed light on a variety of issues that have arisen only since his lifetime, as well as decoherence theory and other non-collapse interpretations. Balancing historical themes with contemporary discussions, Niels Bohr and the Philosophy of Physics establishes Bohr's on-going contribution to the philosophy of physics and examines his place in the history of philosophy.
In the 20th century the Copenhagen interpretation of quantum mechanics had the leading position. This interpretation was formulated by N. Bohr and W. Heisenberg in the late twenties and in thirties and was named the orthodox interpretation as it was presented in leading textbooks. The alternative interpretations arose, however they were treated in connection with the problems, which were typical for the orthodox interpretation. In the 21st century the new situation arose. A number of non-orthodox interpretations has been taken under consideration by the physicists, and they have been treated in connection withtheir specific methodological problems. In the present paper we refer to the list of the popular interpretations of quantum mechanics, the list which was compiled on the basis of two sources: 1) a survey of the physicists who participated in the seminar which was organized by the Nobel Prize winner A. Zeilinger, and 2) a review of the literature, provided by the French physicist and the historian of physics F. Laloë. We take under consideration the following interpretations: the Copenhagen interpretation, information interpretation (A. Zeilinger), many-worlds interpretation (H. Everett, B. DeWitt); interpretation of relative states (H. Everett); interpretation of objective collapse (R. Penrose); subjectivist (Bayesian) interpretation.
Göttingen and Copenhagen were the undoubted capitals of the new discipline of quantum mechanics. The expertise in experimental and mathematical physics and in pure mathematics made Göttingen the epicentre of the revolution which was taking place in the mathematical physics of quanta. Whilst this was to remain the case for the next few years, other actors soon appeared on the scene who were to contribute to Born's ‘tangle of interconnected alleys’. What was truly remarkable was how quickly the different approaches to the problems of quantum theory were developed and the rapid assimilation of all of them into a coherent and self-consistent theory of quantum mechanics. Whilst the theory itself was completed relatively quickly, the understanding of its physical content was to take many more years. The new players on the scene included Paul Dirac at Cambridge, Erwin Schrödinger in Vienna and Norbert Wiener at the Massachusetts Institute of Technology. Each of them brought quite new approaches to the development of quantum theory – their innovations were to supersede the matrix mechanics of Born, Heisenberg and Jordan, but there can be no doubt that the success of that theory indicated clearly the route ahead. They were however to involve the introduction of new mathematical techniques into the description of quantum phenomena. Dirac's approach to quantum mechanics Paul Dirac was trained as an electrical engineer at Bristol University, but he had a very strong mathematical bent. He was a solitary character who was notoriously quiet and self-effacing. He simply worked things out on his own.