The last decade has seen an increasing number of references to quantum mechanics in the humanities and social sciences. This development has in particular been driven by Karen Barad’s agential realism: a theoretical framework that, based on Niels Bohr’s interpretation of quantum mechanics, aims to inform social theorizing. In dealing with notions such as agency, power, and embodiment as well as the relation between the material and the discursive level, the influence of agential realism in fields (...) such as feminist science studies and posthumanism has been profound. However, no one has hitherto paused to assess agential realism’s proclaimed quantum mechanical origin including its relation to the writings of Niels Bohr. This is the task taken up here. We find that many of the implications that agential realism allegedly derives from a Bohrian interpretation of quantum mechanics dissent from Bohr’s own views and are in conflict with those of other interpretations of quantum mechanics. Agential realism is at best consistent with quantum mechanics and consequently, it does not capture what quantum mechanics in any strict sense implies for social science or any other domain of inquiry. Agential realism may be interesting and thought provoking from the perspective of social theorizing, but it is neither sanctioned by quantum mechanics nor by Bohr’s authority. This conclusion not only holds for agential realism in particular, it also serves as a general warning against the other attempts to use quantum mechanics in social theorizing. (shrink)

E. Schrödinger's ideas on interpreting quantum mechanics have been recently re-examined by historians and revived by philosophers of quantum mechanics. Such recent re-evaluations have focused on Schrödinger's retention of space–time continuity and his relinquishment of the corpuscularian understanding of microphysical systems. Several of these historical re-examinations claim that Schrödinger refrained from pursuing his 1926 wave-mechanical interpretation of quantum mechanics under pressure from the Copenhagen and Göttingen physicists, who misinterpreted his ideas in their dogmatic pursuit (...) of the complementarity doctrine and the principle of uncertainty. My analysis points to very different reasons for Schrödinger's decision and, accordingly, to a rather different understanding of the dialogue between Schrödinger and N. Bohr, who refuted Schrödinger's arguments. Bohr's critique of Schrödinger's arguments predominantly focused on the results of experiments on the scattering of electrons performed by Bothe and Geiger, and by Compton and Simon. Although he shared Schrödinger's rejection of full-blown classical entities, Bohr argued that these results demonstrated the corpuscular nature of atomic interactions. I argue that it was Schrödinger's agreement with Bohr's critique, not the dogmatic pressure, which led him to give up pursuing his interpretation for 7 yr. Bohr's critique reflected his deep understanding of Schrödinger's ideas and motivated, at least in part, his own pursuit of his complementarity principle. However, in 1935 Schrödinger revived and reformulated the wave-mechanical interpretation. The revival reflected N. F. Mott's novel wave-mechanical treatment of particle-like properties. R. Shankland's experiment, which demonstrated an apparent conflict with the results of Bothe–Geiger and Compton–Simon, may have been additional motivation for the revival. Subsequent measurements have proven the original experimental results accurate, and I argue that Schrödinger may have perceived even the reformulated wave-mechanical approach as too tenuous in light of Bohr's critique. (shrink)

We clarify Bohr’s interpretation of quantum mechanics by demonstrating the central role played by his thesis that quantum theory is a rational generalization of classical mechanics. This thesis is essential for an adequate understanding of his insistence on the indispensability of classical concepts, his account of how the quantum formalism gets its meaning, and his belief that hidden variable interpretations are impossible.

Bohr’s work in quantum mechanics posed a challenge to philosophers of science, who struggled with the question of whether and to what degree his theories and methods could be considered rational. This paper focuses on Popper, Feyerabend, Lakatos and Kuhn, all of whom recognized some irrational, dogmatic, paradoxical or even inconsistent features in Bohr’s work. Popper, Feyerabend, and Lakatos expressed strong criticism of Bohr’s approach to quantum physics, while Kuhn argued that such criticism was unlikely to be (...) fruitful: progress in science is generally not made through philosophical reflection. Feyerabend’s criticism of Bohr gradually weakened, as he gained a more detailed understanding of the development of Bohr’s views on quantum mechanics, and this went together with an increasingly critical view of normative philosophy of science and was instrumental to his conversion to ‘anarchism’. This paper aims to show that quantum mechanics played a central role in their debates and disagreements on the rationality of science and the possibility of a normative philosophy of science. (shrink)

This article explains why Bohr does not need to discuss the projection postulate or the "problem of measurement". Beginning with a thumbnail sketch of Bohr 's general views, it is argued that Bohr interprets the state function as giving a statistical summary of experimental outcomes. Against the objection that Bohr was too much a microrealist to endorse such an instrumentalist statistical interpretation it is suggested that he rejected the issue of microrealism as not well formed. It is shown that on (...) his statistical interpretation Bohr does not need the projection postulate or face the usual problem of measurement. (shrink)

Steen Brock paints a cross-disciplinary picture of the philosophical and scientific background for the rise of the quantum theory. He accounts for the unity of Kantian metaphysics of Nature, the Helmholtzian principles, and the Hamiltonian methods of modern pre-quantum physics. Brock shows how Planck's vision of a generalization of classical physics implies that the original quantum mechanics of Heisenberg can be regarded as a successful attempt to maintain this modern unity of physics.However, for Niels Bohr, the (...) unity of science and metaphysics did not end in the world of physics. The development of quantum physics had general implications both for other sciences and for various philosophical issues. Brock discusses these matters with respect to recent topics within the philosophy of science and major interpretations of Bohr's ideas. The author invites the reader to follow a long andwinding route of thought which, in the end, culminates in Bohr's ideas of complementarity, culture and Spirit. (shrink)

The present article reports on the finding of the principle behind quantum mechanics. The principle, referred to as genuine fortuitousness, implies that the basic event, a click in a counter, comes without any cause and thus as a discontinuity in spacetime. From this principle, the formalism of quantum mechanics emerges with a radically new content, no longer dealing with things to be measured. Instead, quantum mechanics is recognized as the theory of distributions of uncaused (...) clicks that form patterns laid down by spacetime symmetry and is thereby revealed as a subject of unexpected simplicity and beauty. The departure from usual quantum mechanics is strikingly borne out by the absence of Planck's constant from the theory. The elimination of indeterminate particles as cause for the clicks, which the principle of genuine fortuitousness implies, is analogous to the elimination of the ether implied by the principle of relativity. (shrink)

Bohr’s work in quantum mechanics posed a challenge to philosophers of science, who struggled with the question of whether and to what degree his theories and methods could be considered rational. This paper focuses on Popper, Feyerabend, Lakatos and Kuhn, all of whom recognized some irrational, dogmatic, paradoxical or even inconsistent features in Bohr’s work. Popper, Feyerabend, and Lakatos expressed strong criticism of Bohr’s approach to quantum physics, while Kuhn argued that such criticism was unlikely to be (...) fruitful: progress in science is generally not made through philosophical reflection. Feyerabend’s criticism of Bohr gradually weakened, as he gained a more detailed understanding of the development of Bohr’s views on quantum mechanics, and this went together with an increasingly critical view of normative philosophy of science and was instrumental to his conversion to ‘anarchism’. This paper aims to show that quantum mechanics played a central role in their debates and disagreements on the rationality of science and the possibility of a normative philosophy of science. (shrink)

A review of *Niels Bohr’s Philosophy of Quantum Physics in the Light of the Helmholtzian Tradition of Theoretical Physics *.

The paper argues that Bohr understood his correspondence principle, or at least an aspect of it expressed by the notion of rational generalization, as grounded in Hankel's principle of permanence.

Why does one theory "succeed" while another, possibly clearer interpretation, fails? By exploring two observationally equivalent yet conceptually incompatible views of quantum mechanics, James T. Cushing shows how historical contingency can be crucial to determining a theory's construction and its position among competing views. Since the late 1920s, the theory formulated by Niels Bohr and his colleagues at Copenhagen has been the dominant interpretation of quantum mechanics. Yet an alternative interpretation, rooted in the work of Louis (...) de Broglie in the early 1920s and reformulated and extended by David Bohm in the 1950s, equally well explains the observational data. Through a detailed historical and sociological study of the physicists who developed different theories of quantum mechanics, the debates within and between opposing camps, and the receptions given to each theory, Cushing shows that despite the preeminence of the Copenhagen view, the Bohm interpretation cannot be ignored. Cushing contends that the Copenhagen interpretation became widely accepted not because it is a better explanation of subatomic phenomena than is Bohm's, but because it happened to appear first. Focusing on the philosophical, social, and cultural forces that shaped one of the most important developments in modern physics, this provocative book examines the role that timing can play in the establishment of theory and explanation. (shrink)

It has often been remarked that Bohr's writings on the interpretation of quantum mechanics make scant reference to the mathematical formalism of quantum theory; and it has not infrequently been suggested that this is another symptom of the general vagueness, obscurity and perhaps even incoherence of Bohr's ideas. Recent years have seen a reappreciation of Bohr, however. In this article we broadly follow this "rehabilitation program". We offer what we think is a simple and coherent (...) reading of Bohr's statements about the interpretation of quantum mechanics, basing ourselves on primary sources and making use of and filling lacunas in|recent secondary literature. We argue that Bohr's views on quantum mechanics are more firmly connected to the structure of the quantum formalism than usually acknowledged, even though Bohr's explicit use of this formalism remains on a rather global and qualitative level. In our reading, Bohr's pronouncements on the meaning of quantum mechanics should first of all be seen as responses to concrete physical problems, rather than as expressions of a preconceived philosophical doctrine. In our final section we attempt a more detailed comparison with the formalism and conclude that Bohr's interpretation is not far removed from present-day non-collapse interpretations of quantum mechanics. (shrink)

I reinterpret Bohr's attitude towards quantum mechanical formalism and its empirical content, based on his understanding of the correspondence principle and its approximate applicability. I suggest that Bohr understood complementarity as a limitation imposed by the commutation relations upon the applicability of the idealizations which had grounded the use of the correspondence principle. By discussing this interpretation against the contemporary background of discussions regarding “naïve realism” about operators (as observables), I suggest that a Bohrian view on the empirical (...) content of quantum mechanical operators may provide a middle ground between complete contextualism and an untenable realism about quantum properties. (shrink)

Bohr's complementarity interpretation is represented as the relativization of the quantum mechanical description of a system to the maximal Boolean subalgebra (in the non-Boolean logical structure of the system) selected by a classically described experimental arrangement. Only propositions in this subalgebra have determinate truth values. The concept of a minimal revision of a Boolean subalgebra by a measurement is defined, and it is shown that the nonmaximal measurement of spin on one subsystem in the spin version of the (...) Einstein—Podolsky—Rosen experiment actually selects an appropriate maximal Boolean subalgebra ℛ′ in the logical structure of the composite system, via a minimal revision of the maximal Boolean subalgebra & associated with the preparation of the singlet spin state. This provides an explanation for the determinate truth values of propositions in ℛ′ referring to the second subsystem within the framework of the complementarity interpretation. (shrink)

The aim of this paper is to give an account of the change in Feyerabend's philosophy that made him abandon methodological monism and embrace methodological pluralism. In this paper I offer an explanation in terms of a simple model of 'change of belief through evidence'. My main claim is that the evidence triggering this belief revision can be identified in Feyerabend's technical work in the interpretation of quantum mechanics, in particular his reevaluation of Bohr's contribution to it. (...) This highlights an under-appreciated part of Feyerabend's early work and makes it central to an understanding of the dynamics in his overall philosophy of science. (shrink)

I argue that quantum optical experiments that purport to refute Bohr’s principle of complementarity fail in their aim. Some of these experiments try to refute complementarity by refuting the so called particle–wave duality relations, which evolved from the Wootters–Zurek reformulation of BPC. I therefore consider it important for my forgoing arguments to first recall the essential tenets of BPC, and to clearly separate BPC from WZPC, which I will argue is a direct contradiction of BPC. This leads to a (...) need to consider the meaning of particle–wave duality relations and to question their fundamental status. I further argue that particle and wave complementary concepts are on a different footing than other pairs of complementary concepts. (shrink)

Although Niels Bohr's notion of complementarity is usually referred to in the context of quantum mechanics, it is not of physical origin. Bohr derived it from the philosophical idea of a holistic entanglement of knowledge and action. Bohr's complementarity primarily refers to a key element of the pragmatist tradition, the reflective relation between the immediate experience of an object and the awareness of its objectification. Similar relations have been observed by Kurt Goldstein in his studies of (...) brain-injured patients. From a pragmatic point of view, Goldstein's idea of adequacy in biological knowledge might lead to novel approaches to current ethical questions in medicine as well as biotechnology. (shrink)

We believe that physics education has to meet today’s requirement for a qualitative approach to Quantum Mechanics (QM) worldview. An effective answer to the corresponding instructional problem might allow the basic ideas of QM to be accessed atan early stage of physics education. This paper presents part of a project that aims at introducing a sufficient, simple, and relevant teaching approach towards QM into in-/preservice teacher education, i.e., at providing teachers with the indispensable scientific knowledge and epistemological base (...) needed for a reform of science education along the aforementioned line. The investigation of teacher–learners’ (t-ls’) initial knowledge indicated that their main misconceptions appear to be the result of their pre-/in university traditional instruction, which causes the overlapping/mix-up of the conceptual frameworks of Classical Physics (CP) and QM. Assuming that these misconceptions form by nature epistemological obstacles to the acquisition of QM knowledge, the educational strategy proposed here aims at leading t-ls to form a conceptual structure that includes CP and QM as two totally independent conceptual systems. Accepting, furthermore, that the complete distinction of these systems demands a radical reconstruction of t-ls’ initial knowledge, we present here an instructional model that bases the required reconstruction on the juxtaposition of two models that constitute the signal point of twentieth century’s “paradigm shift”: (a) Bohr’s semiclassical atom model, and (b) the model of the atom accepted by modern physics theory. (shrink)

This study posits that Bohr failed to defend the completeness of the quantum mechanical description of physical reality against Einstein–Podolsky–Rosen’s paper. Although there are many papers in the literature that focus on Bohr’s argument in his reply to the EPR paper, the purpose of the current paper is not to clarify Bohr’s argument. Instead, I contend that regardless of which interpretation of Bohr’s argument is correct, his defense of the quantum mechanical description of physical reality remained incomplete. For (...) example, a recent trend in studies of Bohr’s work is to suggest he considered the wave-function description to be epistemic. However, such an interpretation cannot be used to defend the completeness of the quantum mechanical description. (shrink)

Quantum mechanics has raised in an acute form three problems which go to the heart of man's relationship with nature through experimental science: (r) the public objectivity of science, that is, its value as a universal science for all investigators; (2) the empirical objectivity of scientific objects, that is, man's ability to construct a precise or causal spatio-temporal model of microscopic systems; and finally (3), the formal objectivity of science, that is, its value as an expression of what (...) nature is independently of its being an object of human knowledge. These are three aspects of what is generally called the "crisis of objec tivity" or the "crisis of realism" in modern physics. This crisis is. studied in the light of Werner Heisenberg's work. Heisenberg was one of the architects of quantum mechanics, and we have chosen his writings as the principal source-material for this study. Among physicists of the microscopic domain, no one except perhaps Bohr has expressed himself so abundantly and so profoundly on the philosophy of science as Heisenberg. His writings, both technical and non-technical, show an awareness of the mysterious element in scientific knowledge, far from the facile positivism of Bohr and others of his contemporaries. The mystery of human knowledge and human SUbjectivity is for him an abiding source of wonder. (shrink)

In conventional quantum mechanics, complementarity appears as a remarkable but somewhat useless consequence of the formalism. On the contrary, in Bohr’s view, his notion of complementarity – what I call Bohr’s complementarity – apart from offering a consistent interpretation of QM, was setting the requirement for a ‘thorough revision’ of our common attitude towards ‘physical reality’ and was teaching an ‘epistemological lesson’ transcending the domain of physical sciences. In the present paper, the discussion on the internal rationale of (...) Bohr’s thought from a contemporary philosophical viewpoint permits me to argue that BC stems from a realistic standpoint which starts by accepting an ontology compatible with the non-separable structure of quantum formalism and comes to recognize the necessity of largely revising the epistemological ideas of traditional scientific realism. In this respect, I propose an elaborated form of BC which recognizes the participation of the human perspective in the content of knowledge and, on this basis, attempts to ground scientific objectivity on the notions of ‘perspectival contextuality’ and ‘perspectival plurality’ which integrate reductionistic and holistic epistemological demands in a realistic worldview. The epistemology delineated here creates, I claim, a promising epistemological bridge between physical sciences and humanities. (shrink)

Patrick Aidan Heelan’s The Observable offers the reader a completely articulated development of his 1965 philosophy of quantum physics, Quantum Mechanics and Objectivity. In this previously unpublished study dating back more than a half a century, Heelan brings his background as both a physicist and a philosopher to his reflections on Werner Heisenberg’s physical philosophy. Including considerably broader connections to the contributions of Niels Bohr, Wolfgang Pauli, and Albert Einstein, this study also reflects Heelan’s experience in Eugene (...) Wigner’s laboratory at Princeton along with his reflections on working with Erwin Schrödinger dating from Heelan’s years at the Institute for Advanced Cosmology in Dublin. A contribution to continental philosophy of science, the phenomenological and hermeneutic resources applied in this book to the physical and ontological paradoxes of quantum physics, especially in connection with laboratory science and measurement, theory and model making, will enrich students of the history of science as well as those interested in different approaches to the historiography of science. University courses in the philosophy of physics will find this book indispensable as a resource and invaluable for courses in the history of science. (shrink)

This essay examines various issues surrounding the orthodox interpretation of quantum mechanics. These began with the famous debate between Einstein and Bohr on the topics of quantum uncertainty, wave-particle dualism, and nonlocal interaction. Where Bohr maintained the in-principle ‘completeness’ of orthodox QM - i.e., the conceptual impossibility that it should ever be subject to major revision - Einstein argued that it must be incomplete since it failed to provide any adequate interpretation. Until recently the orthodox doctrine continued (...) to hold sway despite counter-arguments advanced by David Bohm and others of a realist persuasion. In their view there is no reason to accept the veto on supposing particles to possess simultaneous objective values of position and momentum. That we cannot precisely determine those values has to do with certain well-defined limits on our powers of observation/measurement rather than with any intrinsic ‘strangeness’ about microphysical objects and events. Bohm’s theory perfectly matches the established predictive and empirical results while providing a credible realist ontology that avoids any drastic break with the principles of causal realism and inference to the best, most rational explanation. My article discusses the way that Bohm’s heterodox account was often rejected out of hand by proponents of the Copenhagen doctrine. I also review some recent studies - by Beller, Cushing, and Holland - which have either declared strongly in favour of Bohm or challenged the prevailing bias by offering a historically contextualised account of how the orthodox theory took hold. (shrink)

Quantum mechanics, which describes the behavior of subatomic particles, seems to challenge common sense. Waves behave like particles; particles behave like waves. You can tell where a particle is, but not how fast it is moving--or vice versa. An electron faced with two tiny holes will travel through both at the same time, rather than one or the other. And then there is the enigma of creation ex nihilo, in which small particles appear with their so-called antiparticles, only (...) to disappear the next instant in a tiny puff of energy. Since its inception, physicists and philosophers have struggled to work out the meaning of quantum mechanics. Some, like Niels Bohr, have responded to quantum mechanics' mysteries by replacing notions of position and velocity with probabilities. Others, like Einstein and Penrose, have disagreed and think that the entire puzzle reflects not a fundamental principle of nature but our own ignorance of basic scientific processes. Sneaking a Look at God's Cards offers the general reader a deep and real understanding of the problems inherent to the interpretation of quantum mechanics, from its inception to the present. The book presents a balanced overview of current debates and explores how the theory of quantum mechanics plays itself out in the real world. Written from the perspective of a leading European physicist, the book looks extensively at ideas from both sides of the Atlantic and also considers what philosophers have contributed to the scientific discussion of this field. Sneaking a Look at God's Cards sets out what we know about the endlessly fascinating quantum world, how we came to this understanding, where we disagree, and where we are heading in our quest to comprehend the seemingly incomprehensible. (shrink)

Adopting Murdoch’s pragmatist reading of Bohr’s theory of meaning with regard to Bohr’s notion of complementarity, in this paper I try to see Bohr’s post-Como and, in particular, post-EPR philosophy of quantum mechanics in the light of Peircean pragmatism with the hope that such a construal can shed more light to Bohr’s philosophy. I supplement Murdoch’s position on Bohr’s pragmatism by showing that in addition to his complementarity, Bohr’s correspondence principle, instrumentalism and realism can be read on the (...) basis of Peirce’s pragmatic maxim and his notion of indeterminism has commonalities with Peirce’s tychism. Also, Bohr’s practice of applying the correspondence principle can be interpreted in the light of Peirce’s fallibilism. However, when it comes to Bohr’s understanding of the symbolic character of quantum mechanics, Bohr’s philosophy deviates from Peircean pragmatism. Bohr’s philosophy distinguishes between the symbolic language of quantum formalism, which counts as a tool practically useful for prediction, and observation sentences which are visualizable in space and time and refer to the so-called individual phenomena. Such an epistemologically significant distinction is not recognized by Peircean pragmatism. (shrink)

The objective of this article is to demonstrate how the historical debate between materialism and idealism, in the field of Philosophy, extends, in new clothes, to the field of Quantum Physics characterized by realism and anti-realism. For this, we opted for a debate, also historical, between the realism of Albert Einstein, for whom reality exists regardless of the existence of the knowing subject, and Niels Bohr, for whom we do not have access to the ultimate reality of the matter, (...) unless conditioning it to the existence of an observer endowed with rationality, position adopted in the Interpretation of Complementarity – posture that was expanded in 1935 when Bohr assumed a “relationalist” conception, according to which the quantum state is defined by the relationship between the quantum object and the entire measuring device. This is an extremely important debate, as it further consolidates the results of nascent Quantum Mechanics, guaranteeing Bohr the leadership of the orthodoxy based on the interpretation of complementarity. Here, when dealing with Quantum Theory, we will not make any distinction between the terms Quantum Physics, Quantum Theory or Quantum Mechanics. The entire discussion will be held under the name “Quantum Theory”. Theory that tries to analyze and describe the behavior of physical systems of reduced dimensions, close to the sizes of molecules, atoms and subatomic particles. We hope that the reader will appreciate the genius of these two titans in this field of Physics when they magnificently formulate the arguments that support the object of their defenses. (shrink)

The Copenhagen interpretation, which informs the textbook presentation of quantum mechanics, depends fundamentally on the notion of ontological wave-particle duality and a viewpoint called “complementarity”. In this paper, Bohr’s own interpretation is traced in detail and is shown to be fundamentally different from and even opposed to the Copenhagen interpretation in virtually all its particulars. In particular, Bohr’s interpretation avoids the ad hoc postulate of wave function ‘collapse’ that is central to the Copenhagen interpretation. The strengths and weakness (...) of both interpretations are summarized. (shrink)

In this paper, the main outlines of the discussions between Niels Bohr with Albert Einstein, Werner Heisenberg, and Erwin Schrödinger during 1920–1927 are treated. From the formulation of quantum mechanics in 1925–1926 and wave mechanics in 1926, there emerged Born's statistical interpretation of the wave function in summer 1926, and on the basis of the quantum mechanical transformation theory—formulated in fall 1926 by Dirac, London, and Jordan—Heisenberg formulated the uncertainty principle in early 1927. At the Volta (...) Conference in Como in September 1927 and at the fifth Solvay Conference in Brussels the following month, Bohr publicly enunciated his complementarity principle, which had been developing in his mind for several years. The Bohr-Einstein discussions about the consistency and completeness of qnautum mechanics and of physical theory as such—formally begun in October 1927 at the fifth Solvay Conference and carried on at the sixth Solvay Conference in October 1930—were continued during the next decades. All these aspects are briefly summarized. (shrink)

The Copenhagen interpretation, which informs the textbook presentation of quantum mechanics, depends fundamentally on the notion of ontological wave-particle duality and a viewpoint called “complementarity.” In this paper, Bohr's own interpretation is traced in detail and is shown to be fundamentally different from and even opposed to the Copenhagen interpretation in virtually all its particulars. In particular, Bohr's interpretation avoids the ad hoc postulate of wave function ‘collapse' that is central to the Copenhagen interpretation. The strengths (...) and weakness of both interpretations are summarized. ‡I thank Edward Mackinnon, Henry Folse, and Greg Anderson for valuable comments on the penultimate draft. The final responsibility for the paper rests with the author. †To contact the author, please write to: Bhaktivedanta Institute, 2334 Stuart Street, Berkeley, CA; e-mail: [email protected]. I have been unable to achieve a sharp formulation of Bohr's principle of complementarity despite much effort I have expended on it. (Einstein 1949, 674) While imagining that I understand the position of Einstein, as regards the EPR correlations, I have very little understanding of his principal opponent, Bohr. (Bell 1987, 155) Niels Bohr brain-washed a generation of physicists into believing that the problem had been solved fifty years ago. (Gell-Mann 1979, 29) Every sentence I say must be understood not as an affirmation, but as a question. (Niels Bohr, quoted in Jammer 1966, 175) Bohr's interpretation has never been fully clarified. It needs an interpretation itself, and only that will be its defense. (Weizsäcker 1971, 25). (shrink)

The author, a physicist as well as a philosopher, uses the thought of Werner Heisenberg as a focus for examining the epistemological foundations of quantum theory. Though Heisenberg's earliest original insights were stimulated by Plato's Timaeus he soon swung over to Bohr's empiricism in developing and supporting the Copenhagen interpretation of quantum mechanics. His later philosophical reflections are markedly Kantian with irreducible physical invariants playing the role of Kant's necessary and universal laws. As Heelan sees it, (...) an examination of the intentionality-structure of the scientist supplies the critical basis for judging the reality of the objects known through science. Though Heisenberg rejected the naive "empirical objectivity" of pre-quantum interpretations of science, his reflective evaluation of his own achievements is inadequate in explaining the formal objectivity of the objects known. By distinguishing the criterion of reality, rational affirmation, from the meaning of "reality," whatever is defined by the object in its formal sense, Heelan is able to develop a critical realism that assigns an ontological status to fundamental particles. "Main-line" philosophers of science may feel ill at ease with Heelan's phenomenological terminology of "intentionality-structure," "noema," and "horizon" and may object to his treatment of "meaning" and "language." But if they "bracket" these reservations they will find this book an unusually well-informed and penetrating study of the philosophical implications of modern physics.—E. M. M. (shrink)

The interpretation of quantum mechanics has been a problem since its founding days. A large contribution to the discussion of possible interpretations of quantum mechanics is given by the so-called impossibility proofs for hidden variable models; models that allow a realist interpretation. In this thesis some of these proofs are discussed, like von Neumann’s Theorem, the Kochen-Specker Theorem and the Bell-inequalities. Some more recent developments are also investigated, like Meyer’s nullification of the Kochen-Specker Theorem, the MKC-models (...) and Conway and Kochen’s Free Will Theorem. This last one is taken to suggest that the problems that arise for certain interpretations of quantum mechanics are not limited to realist interpretations only, but also affect certain instrumentalist interpretations. It is argued that one may arrive at a more satisfying interpretation of quantum mechanics if one adopts a logic that seems more compatible with the instrumentalist viewpoint namely, intuitionistic logic. The motivations for adopting this form of logic rather than classical logic or quantum logic are linked to some of the philosophical ideas of Bohr. In particular a new interpretation of Bohr’s notion of complementarity is proposed. Finally some possibilities are explored for linking the intuitionistic interpretation of quantum mechanics to the mathematical formalism of the theory. (shrink)

Ever since the beginning of development of Quantum Mechanics there was a metaphysical division between the “macro” world as described in “everyday language” and the “micro” world described by quantum formalism. A discussion is offered of the need to reunite these arbitrarily divided worlds through an overview of the main interpretations of the formalism. Bohr’s Copenhagen interpretation, as well as the problems it faces due to EPR thought experiment, is presented in greater detail. It is claimed that (...) Bohr’s answers to the said experiment demand more than a restriction of everyday descriptive metaphysics, when describing phenomena at the micro-level. Thus, the special place Bohr’s interpretation takes among other interpretations of the formalism is forfeited. It is also shown that MacKinnon’s more detailed schema aiming to connect the theoretical and everyday language cannot be applied to EPR conclusions and Bohr’s reply to those. MacKinnon’s own modifications of the “everyday language” induced by the mathematical conclusions of Quantum Mechanics are considered too radical and too coarse to take the vacated special place among formalism interpretations. (shrink)

In this article, we argue that although Bohr's version of the Copenhagen interpretation is in line with several key elements of logical positivism, pragmatism is the closest approximation to a classification of the Copenhagen interpretation, whether or not pragmatists directly influenced the key figures of the interpretation. Pragmatism already encompasses important elements of operationalism and logical positivism, especially the liberalized Carnapian reading of logical positivism. We suggest that some elements of the Copenhagen interpretation, which are in line with logical (...) positivism, are also supported by pragmatism. Some of these elements are empirical realism, fallibilism, holism, and instrumentalism. However, pragmatism goes beyond logical positivism in espousing some other key elements of the Copenhagen interpretation, though imperfectly, such as the correspondence principle, complementarity, and indeterminism. (shrink)

Niels Bohr’s “correspondence principle” is typically believed to be the requirement that in the limit of large quantum numbers (n→∞) there is a statistical agreement between the quantum and classical frequencies. A closer reading of Bohr’s writings on the correspondence principle, however, reveals that this interpretation is mistaken. Specifically, Bohr makes the following three puzzling claims: First, he claims that the correspondence principle applies to small quantum numbers as well as large (while the statistical agreement of frequencies (...) is only for large n); second, he claims that the correspondence principle is a law of quantum theory; and third, Bohr argues that formal apparatus of matrix mechanics (the new quantum theory) can be thought of as a precise formulation of the correspondence principle. With further textual evidence, I offer an alternative interpretation of the correspondence principle in terms of what I call Bohr’s selection rule. I conclude by showing how this new interpretation of the correspondence principle readily makes sense of Bohr’s three puzzling claims. (shrink)

A recent rethinking of the early history of Quantum Mechanics deemed the late 1920s agreement on the equivalence of Matrix Mechanics and Wave Mechanics, prompted by Schrödinger’s 1926 proof, a myth. Schrödinger supposedly failed to achieve the goal of proving isomorphism of the mathematical structures of the two theories, while only later developments in the early 1930s, especially the work of mathematician John von Neumman (1932) provided sound proof of equivalence. The alleged agreement about the Copenhagen (...) Interpretation, predicated to a large extent on this equivalence, was deemed a myth as well. If such analysis is correct, it provides considerable evidence that, in its critical moments, the foundations of scientific practice might not live up to the minimal standards of rigor, as such standards are established in the practice of logic, mathematics, and mathematical physics, thereby prompting one to question the rationality of the practice of physics. In response, I argue that Schrödinger’s proof concerned primarily a domain-specific ontological equivalence, rather than the isomorphism. It stemmed initially from the agreement of the eigenvalues of Wave Mechanics and energy-states of Bohr’s Model that was discovered and published by Schrödinger in his First and Second Communications of 1926. Schrödinger demonstrated in this proof that the laws of motion arrived at by the method of Matrix Mechanics could be derived successfully from eigenfunctions as well (while he only outlined the reversed derivation of eigenfunctions from Matrix Mechanics, which was necessary for the proof of isomorphism of the two theories). This result was intended to demonstrate the domain-specific ontological equivalence of Matrix Mechanics and Wave Mechanics, with respect to the domain of Bohr’s atom. And although the full-fledged mathematico-logical equivalence of the theories did not seem out of the reach of existing theories and methods, Schrödinger never intended to fully explore such a possibility in his proof paper. In a further development of Quantum Mechanics, Bohr’s complementarity and Copenhagen Interpretation captured a more substantial convergence of the subsequently revised (in light of the experimental results) Wave and Matrix Mechanics. I argue that both the equivalence and Copenhagen Interpretation can be deemed myths if one predicates the philosophical and historical analysis on a narrow model of physical theory which disregards its historical context, and focuses exclusively on its formal aspects and the exploration of the logical models supposedly implicit in it. (shrink)

The centerpiece of Jeffrey Bub's book Interpreting the Quantum World is a theorem (Bub and Clifton 1996) which correlates each member of a large class of no-collapse interpretations with some 'privileged observable'. In particular, the Bub-Clifton theorem determines the unique maximal sublattice L(R,e) of propositions such that (a) elements of L(R,e) can be simultaneously determinate in state e, (b) L(R,e) contains the spectral projections of the privileged observable R, and (c) L(R,e) is picked out by R and e alone. (...) In this paper, we explore the issue of maximal determinate sets of observables using the tools provided by the algebraic approach to quantum theory; and we call the resulting algebras of determinate observables, "maximal *beable* subalgebras". The capstone of our exploration is a generalized version of Bub and Clifton's theorem that applies to arbitrary (i.e., both mixed and pure) quantum states, to Hilbert spaces of arbitrary (i.e., both finite and infinite) dimension, and to arbitrary observables (including those with a continuous spectrum). Moreover, in the special case covered by the original Bub-Clifton theorem, our theorem reproduces their result under strictly weaker assumptions. This added level of generality permits us to treat several topics that were beyond the reach of the original Bub-Clifton result. In particular: (a) We show explicitly that a (non-dynamical) version of the Bohm theory can be obtained by granting privileged status to the position observable. (b) We show that Clifton's (1995) characterization of the Kochen-Dieks modal interpretation is a corollary of our theorem in the special case when the density operator is taken as the privileged observable. (c) We show that the 'uniqueness' demonstrated by Bub and Clifton is only guaranteed in certain special cases -- viz., when the quantum state is pure, or if the privileged observable is compatible with the density operator. We also use our results to articulate a solid mathematical foundation for certain tenets of the orthodox Copenhagen interpretation of quantum theory. For example, the uncertainty principle asserts that there are strict limits on the precision with which we can know, simultaneously, the position and momentum of a quantum-mechanical particle. However, the Copenhagen interpretation of this fact is not simply that a precision momentum measurement necessarily and uncontrollably disturbs the value of position, and vice-versa; but that position and momentum can never in reality be thought of as simultaneously determinate. We provide warrant for this stronger 'indeterminacy principle' by showing that there is no quantum state that assigns a sharp value to both position and momentum; and, a fortiori, that it is mathematically impossible to construct a beable algebra that contains both the position observable and the momentum observable. We also prove a generalized version of the Bub-Clifton theorem that applies to "singular" states (i.e., states that arise from non-countably-additive probability measures, such as Dirac delta functions). This result allows us to provide a mathematically rigorous reconstruction of Bohr's response to the original EPR argument -- which makes use of a singular state. In particular, we show that if the position of the first particle is privileged (e.g., as Bohr would do in a position measuring context), the position of the second particle acquires a definite value by virtue of lying in the corresponding maximal beable subalgebra. But then (by the indeterminacy principle) the momentum of the second particle is not a beable; and EPR's argument for the simultaneous reality of both position and momentum is undercut. (shrink)

Rovelli’s RQM is first characterized by contrast with both Everett’s and Bohr’s interpretations of quantum mechanics. Then, it is shown that a basic difficulty arises from the choice of formulating RQM in a naturalistic framework. Even though, according to Rovelli’s interpretation, statements about the world only make sense relative to certain naturalized observers described by means of quantum mechanics, this very meta-statement seems to make sense relative to a sort of super-observer which does not partake of (...) the naturalized status of ordinary observers. The difficulty is solved by substituting functional reference frames for physical (or naturalized) observers throughout. Instead of being relative to physical observers, statements about the state vector of physical systems are here relative to well-defined projects of probabilistic prediction which may be embodied by several physical observers. (shrink)

Soviet attitude towards Bohr reflects changes in the ideological approach to science. During the last period before Stalin's death danov proclaimed the campaign against Western influence in Soviet philosophy and science. Nevertheless the physicist M. A. Markov tried to introduce complementarity as a materialistic interpretation of quantum-mechanics in 1948. He was officially condemned. This was followed by a period (1948-54) during which heavy attacks were made against the Copenhagen school. In 1958, after a personal exchange of thoughts with (...) Bohr, academician Fock declared complementarity and probability to be irreversible steps towards a new insight into physical reality, at the same time correcting some of Bohr's epistemological conceptions. (shrink)

In this paper, I try to explain the philosophical problems that Niels Bohr felt had been exposed by the discovery of the "quantum of action," and by the emergence of the quantum theory that arose in large part as a result of his efforts. I won't have space to make the case adequately here, but my own view is that we have not yet fully digested the message brought to us by Bohr's "Copenhagen Interpretation" of Quantum (...) Mechanics, and I suspect that it will finally prove to be every bit as revolutionary as Bohr thought it was. (shrink)

The interpretation of quantum mechanics presented in this paper is inspired by two ideas that are fundamental in Bohr’s writings: indivisibility and complementarity. Further basic assumptions of the proposed interpretation are completeness, universality and conceptual economy. In the interpretation, decoherence plays a fundamental role for the understanding of measurement. A general and precise conception of complementarity is proposed. It is fundamental in this interpretation to make a distinction between ontological reality, constituted by everything that does not depend at (...) all on the collectivity of human beings, nor on their decisions or limitations, nor on their existence, and empirical reality constituted by everything that not being ontological is, however, intersubjective. According to the proposed interpretation, neither the dynamical properties, nor the constitutive properties of microsystems like mass, charge and spin, are ontological. The properties of macroscopic systems and space-time are also considered to belong to empirical reality. The acceptance of the above mentioned conclusion does not imply a total rejection of the notion of ontological reality. In the paper, utilizing the Aristotelian ideas of general cause and potentiality, a relation between ontological reality and empirical reality is proposed. Some glimpses of ontological reality, in the form of what can be said about it, are finally presented. (shrink)

The Heisenberg microscope and its analysis by Weizsäcker are used by Grete Hermann in her 1935 essay on the foundations of quantum mechanics to argue her claims about causality in quantum mechanics. In this chapter, I wish to draw a comparison between Hermann’s use of the Heisenberg microscope and another famous use of a very similar thought experiment : Bohr’s analysis of the suspended single slit in his reply to EPR. I shall argue that Hermann’s use (...) of different aspects of the classical pictures in the treatment of the Heisenberg microscope makes her treatment closer to Bohr’s discussion of the suspended slit than to Heisenberg’s own treatment of the microscope. This suggests that Hermann, who equally gave an extensive analysis of complementarity in her 1935 essay, may be an especially acute interpreter of Bohr’s views. I conclude by looking at Hermann’s approach in the context of more general examples of measurement and at possible limitations of the approach. (shrink)

First, this article considers the nature of quantum reality and the concept of realism in quantum theory, in conjunction with the roles of locality, causality, and probability and statistics there. Second, it offers two interpretations of quantum mechanics, developed by the authors of this article, the second of which is also a different theory of quantum phenomena. Both of these interpretations are statistical. The first interpretation, by A. Plotnitsky, “the statistical Copenhagen interpretation,” is nonrealist, insofar (...) as the description or even conception of the nature of quantum objects and processes is precluded. The second, by A. Khrennikov, is ultimately realist, because it assumes that the quantum-mechanical level of reality is underlain by a deeper level of reality, described, in a realist fashion, by a model, based in the pre-quantum classical statistical field theory, the predictions of which reproduce those of quantum mechanics. Moreover, because the continuous fields considered in this model are transformed into discrete clicks of detectors, experimental outcomes in this model depend on the context of measurement in accordance with N. Bohr’s interpretation and the statistical Copenhagen interpretation, which coincides with N. Bohr’s interpretation in this regard. (shrink)

This book concerns the metasemantics of quantum mechanics (QM). Roughly, it pursues an investigation at an intersection of the philosophy of physics and the philosophy of language, and it offers a critical analysis of rival explanations of the semantic facts of standard QM. Two problems for such explanations are discussed: categoricity and permanence. New results include 1) a reconstruction of Einstein's incompleteness argument, which concludes that a local, separable, and categorical QM cannot exist, 2) a reinterpretation of (...) class='Hi'>Bohr's principle of correspondence, grounded in the principle of permanence, 3) a meaning-variance argument for quantum logic, which follows a line of critical reflections initiated by Weyl, and 4) an argument for semantic indeterminacy leveled against inferentialism about QM, inspired by Carnap's work in the philosophy of classical logic. (shrink)

The ArgumentThe aim of this paper is to provide a critical perspective for Einstein's opposition to the Copenhagen interpretation of quantum physics, by analyzing the ingenious rhetoric of Bohr's principle of complementarity. I argue that what Bohr presents as arguments of “inevitability” are in fact merely arguments for the consistency of the quantum-mechanical scheme. Einstein's resistance to being persuaded by this potent technique of argumentation, and his rejection of Bohr's interpretation of quantum physics, appear consequently (...) as an eminently reasonable position and not as a conservative stand, as it is often presented by the adherents of the Copenhagen orthodoxy. (shrink)

We show that Bohr's principle of complementarity between position and momentum descriptions can be formulated rigorously as a claim about the existence of representations of the canonical commutation relations. In particular, in any representation where the position operator has eigenstates, there is no momentum operator, and vice versa. Equivalently, if there are nonzero projections corresponding to sharp position values, all spectral projections of the momentum operator map onto the zero element.

In modern science, established by the scientific revolution in 16th and 17th century, the scientific observation process is understood as a process where the observer directly grasps Nature as the observed and scientific mathematical formulation is understood as a direct description of reality. Husserl criticized this lack of distinction between method and the object of investigation in modern science and emphasized the importance of phenomena in the observation process. A similar approach was used by Bohr in his interpretation of (...) class='Hi'>quantum experiments that seemed inexplicable from the modern science point of view. Many contemporary interpretations of quantum mechanics follow Bohr’s opposition to the realism of modern science. Among them is informational foundations of quantum theory that connects parts of his interpretation with the latest quantum experiments, but due to the complexity and individuality of Bohr’s interpretation, its philosophical consistency is mostly lost. In IFQT there is no direct connection between information and the observed. This ambiguous ontic status of information is often criticised, however, it can be solved by supplementation with Husserl’s philosophical understanding of the observation process. If Husserl’s definition of the relationship between the thing and the phenomenon is transmitted to the relationship between the observed and information in IFQT information can be understood as the direct answer to the question about the observed and thereby the observer’s only knowledge about it. This helps to reject the main criticism of IFQT and to additionally support its explanations of quantum phenomena. (shrink)

Niels Bohr was a central figure in quantum physics, well known for his work on atomic structure and his contributions to the Copenhagen interpretation of quantum mechanics. In this book, philosopher of science Slobodan Perović explores the way Bohr practiced and understood physics, and analyzes its implications for our understanding of modern science. Perović develops a novel approach to Bohr’s understanding of physics and his method of inquiry, presenting an exploratory symbiosis of historical and philosophical analysis that (...) uncovers the key aspects of Bohr’s philosophical vision of physics within a given historical context. -/- To better understand the methods that produced Bohr’s breakthrough results in quantum phenomena, Perović clarifies the nature of Bohr’s engagement with the experimental side of physics and lays out the basic distinctions and concepts that characterize his approach. Rich and insightful, Perović’s take on the early history of quantum mechanics and its methodological ramifications sheds vital new light on one of the key figures of modern physics. (shrink)