This article considers the concepts of reality, observer, and complementarity in Pauli and Bohr, and the similarities and, especially, differences in their understanding of these concepts, differences defined most essentially by their respective views of the role of the human observer in quantum measurement. These differences are significant even in the case of their respective interpretations of quantum phenomena and quantum mechanics, where the influence of Bohr's ideas on Pauli's understanding of quantum physics is particularly strong. They become especially strong and even radical in the case of their overall philosophical visions, where the impact of Jungean psychology, coupled to that of the earlier archetypal thinking of such figures as Kepler and Fludd, drives Pauli's thinking ever further away from that of Bohr.
This article considers the concepts of reality, observer, and complementarity in Pauli and Bohr, and the similarities and, especially, differences in their understanding of these concepts, differences defined most essentially by their respective views of the role of the human observer in quantum measurement. These differences are significant even in the case of their respective interpretations of quantum phenomena and quantum mechanics, where the influence of Bohr's ideas on Pauli's understanding of quantum physics is particularly strong. They become especially strong and even radical in the case of their overall philosophical visions, where the impact of Jungean psychology, coupled to that of the earlier archetypal thinking of such figures as Kepler and Fludd, drives Pauli's thinking ever further away from that of Bohr.
This article explores Bohr's argument, advanced under the heading of 'complementarity,' concerning quantum phenomena and quantum mechanics, and its physical and philosophical implications.In Bohr, the term complementarity designates both a particular concept and an overall interpretation of quantum phenomena and quantum mechanics, in part grounded in this concept.While the argument of this article is primarily philosophical, it will also address, historically, the development and transformations of Bohr's thinking, under the impact of the development of quantum theory and Bohr's confrontation with Einstein, especially their exchange concerning the EPR experiment, proposed by Einstein, Podolsky and Rosen in 1935.Bohr's interpretation was progressively characterized by a more radical epistemology, in its ultimate form, which was developed in the 1930s and with which I shall be especially concerned here, defined by his new concepts of phenomenon and atomicity.According to this epistemology, quantum objects are seen as indescribable and possibly even as inconceivable, and as manifesting their existence only in the effects of their interactions with measuring instruments upon those instruments, effects that define phenomena in Bohr's sense.The absence of causality is an automatic consequence of this epistemology.I shall also consider how probability and statistics work under these epistemological conditions.
This article reconsiders the concept of physical reality in quantum theory and the concept of quantum measurement, following Bohr, whose analysis of quantum measurement led him to his concept of a (quantum) "phenomenon," referring to "the observations obtained under the specified circumstances," in the interaction between quantum objects and measuring instruments. This situation makes the terms "observation" and "measurement," as conventionally understood, inapplicable. These terms are remnants of classical physics or still earlier history, from which classical physics inherited it. As defined here, a quantum measurement does not measure any preexisting property of the ultimate constitution of the reality responsible for quantum phenomena. An act of measurement establishes a quantum phenomenon by an interaction between the instrument and the quantum object or in the present view the ultimate constitution of the reality responsible for quantum phenomena and, at the time of measurement, also quantum objects. In the view advanced in this article, in contrast to that of Bohr, quantum objects, such as electrons or photons, are assumed to exist only at the time of measurement and not independently, a view that redefines the concept of quantum object as well. This redefinition becomes especially important in high-energy quantum regimes and quantum field theory and allows this article to define a new concept of quantum field. The article also considers, now following Bohr, the quantum measurement as the entanglement between quantum objects and measurement instruments. The argument of the article is grounded in the concept "reality without realism" (RWR), as underlying quantum measurement thus understood, and the view, the RWR view, of quantum theory defined by this concept. The RWR view places a stratum of physical reality thus designated, here the reality ultimately responsible for quantum phenomena, beyond representation or knowledge, or even conception, and defines the corresponding set of interpretations quantum mechanics or quantum field theory, such as the one assumed in this article, in which, again, not only quantum phenomena but also quantum objects are (idealizations) defined by measurement. As such, the article also offers a broadly conceived response to J. Bell's argument "against 'measurement'".
This paper examines the transformation of Bohr's interpretation of quantum phenomena and quantum mechanics, known as complementarity, from the version presented in his famous Como lecture (1927), which introduced complementarity, to a new version that was developed by Bohr shortly thereafter, in part under the impact of his intervening exchanges with Einstein. While the existence of more than one version of Bohr's complementarity (and of still different versions of the Copenhagen interpretation by others) has been noted, Bohr's rethinking itself of complementarity has rarely been adequately addressed. Apart from refining and indeed correcting the Como argument, the transformation in question was, I argue, defined by a shift from a more philosophical to a more experimental argument. My aim is to explore both this shift and the complexity of the relationships between physics and philosophy in Bohr's thinking in order to understand better the beginnings and the ends, also in the sense of aims, of Bohr's complementarity.
Abstract In this paper, I suggest that a closer look at Bohr’s analogies to psychology helps us to better understand his interpretation of quantum measurement and how he conceived of the role of the subject in quantum physics. This focus helps us to pinpoint how Bohr’s view on quantum measurement differed from John von Neumann’s and Wolfgang Pauli’s understandings of it. I argue that Bohr’s interpretation of quantum measurement was about ensuring that quantum mechanics is an objective description of quantum phenomena. For Bohr, objective knowledge meant knowledge that can be communicated unambiguously, which requires that there is a sharp division between subject and object. He was adamant that in physics, there is such a sharp division, including in quantum physics. Therefore, he argued, there is no measurement problem in quantum physics.
The argument of this article is grounded in the irreducible interference of observational instruments in our interactions with nature in quantum physics and, thus, in the constitution of quantum phenomena versus classical physics, where this interference can, in principle, be disregarded. The irreducible character of this interference was seen by N. Bohr as the principal distinction between classical and quantum physics and grounded his interpretation of quantum phenomena and quantum theory. Bohr saw complementarity as a generalization of the classical ideal of causality, which defined classical physics and relativity. While intimated by Bohr, the relationships among observational technology, complementarity, causality and the arrow of events (a new concept that replaces the arrow of time commonly used in this context) were not addressed by him either. The article introduces another new concept, that of quantum causality, as a form of probabilistic causality. The argument of the article is based on a particular interpretation of quantum phenomena and quantum theory, defined by the concept of 'reality without realism (RWR)'. This interpretation follows Bohr's interpretation but contains certain additional features, in particular the Dirac postulate. The article also considers quantum-like (Q-L) theories (based in the mathematics of QM) from the perspective it develops. This article is part of the theme issue 'Thermodynamics 2.0: Bridging the natural and social sciences (Part 2)'.
Complementarity and Deconstruction: Plotnitsky's Analysis and Beyond Makoto Katsumori Akita University The philosophical thought of the modern physicist Niels Bohr (1885–1962), which revolves around the concept of complementarity, has long been a major subject of historical and philosophical inquiry. Many prior studies of Bohr's complementarity, however, seem to be limited by the fact that they largely proceed within the conceptual frames of the "mainstream" philosophy of science. This being the case, his radical questioning of traditional scientific and philosophical notions—such as the unambiguity of concepts and words—has not been adequately addressed, insofar as these notions are uncritically presupposed by the commentators themselves. In other words, Bohr's thought has often been interpreted under certain tacit premises of scientific rationality that are precisely of the kind targeted by his epistemological critique. In recent years, however, there have emerged new approaches to Bohr's idea of complementarity that place it in different, less conventional, philosophical contexts. Among the most notable of these is Arkady Plotnitsky's endeavor to connect Bohr's complementarity with Jacques Derrida's project of deconstruction. In the present article, based on my recent doctoral dissertation,1 I take up this contribution by Plotnitsky as a suitable point of reference from which to [End Page 435] explore anew Bohr's thought with its radical philosophical implications. After outlining Bohr's complementarity argument and Plotnitsky's reading thereof (in the first and second sections, respectively), I will examine a series of problems that seem to face, or to be left unsolved by, Plotnitsky's account (in the third section). This critical appraisal will finally lead me to sketch a new interpretive approach of my own (in the fourth section), which both extends and delimits the intersections between complementarity and deconstruction. As regards the historical development of Bohr's complementarity, I will largely restrict myself to the period between 1927 and 1950, in which the most crucial of his innovative ideas seem to have been presented. I. Bohr's Idea of Complementarity In his 1927 lecture delivered in Como, Italy, entitled "The Quantum Postulate and the Recent Development of Atomic Theory," Niels Bohr introduced the concept and framework of complementarity as a pivotal idea in his interpretation of quantum theory. From then on, he continually developed the idea of complementarity with regard not only to quantum theory but to other fields of knowledge as well. In what follows, I will first outline his complementarity argument in its "early" period, stretching from 1927 to the mid-thirties,—or, more precisely, until just before his 1935 debate with EPR.2 Bohr starts by noting that "our usual description of physical phenomena is based entirely on the idea that the phenomena concerned may be observed without disturbing them appreciably."3 This notion of physical phenomena as undisturbed by observation underlies all of classical physics and is still maintained in the theory of relativity. However, Bohr continues, a new situation has arisen with the development of quantum theory, specifically with "the so-called quantum postulate, which attributes to any atomic process an essential discontinuity, or rather individuality, completely foreign to the classical theories"; this "individuality" implies that "any observation of atomic phenomena will involve an interaction with the [End Page 436] agency of observation not to be neglected" (PWNB, 1: 53–54.). In more specific terms, any observation aimed at space-time coordination brings about an exchange of momentum and energy with the measuring rods and clocks. It is crucial here that this interaction between the object and the instrument of observation is not simply unavoidable, but "uncontrollable," which represents a "feature of irrationality" brought into the description of nature (PWNB, 1: 68, 91). For insofar as the measuring instruments are to fulfill their purpose, the interaction itself cannot be taken into account, and thus the magnitude of the disturbance always remains unknown. It follows, in Bohr's view, that "an independent reality in the ordinary physical sense can neither be ascribed to the phenomena nor to the agencies of observation...