Numerous approaches to a quantum theory of gravity posit fundamental ontologies that exclude spacetime, either partially or wholly. This situation raises deep questions about how such theories could relate to the empirical realm, since arguably only entities localized in spacetime can ever be observed. Are such entities even possible in a theory without fundamental spacetime? How might they be derived, formally speaking? Moreover, since by assumption the fundamental entities cannot be smaller than the derived and so cannot ‘compose’ them in (...) any ordinary sense, would a formal derivation actually show the physical reality of localized entities? We address these questions via a survey of a range of theories of quantum gravity, and generally sketch how they may be answered positively. (shrink)

This paper deals with the development of, and the current discussion about, the interpretation of quantum mechanics. The following topics are discussed: 1. The Copenhagen Interpretation, 2. Formal Problems of Quantum Mechanics, 3. Process of Measurement and the Equation of Motion, 4. Macroscopic Level of Description, 5. Search for Hidden Variables, 6. The Notion of “Reality” and Epistemology of Quantum Mechanics, 7. Quantum Mechanics and the Explanation of Life.The Bohr‐Einstein dialogue on the validity of the quantum mechanical description of physical (...) reality lasted over two decades. Since the early nineteen fifties, Wiper has provided much of the point and counterpoint of the continuing discussion on the interpretation and epistemology of quantum mechanics. We have explored Wiper's views in some detail against the background of historical development and current debate. (shrink)

This paper argues for a metaphysics of relations based on a characterization of quantum entanglement in terms of non-separability, thereby regarding entanglement as a sort of holism. By contrast to a radical metaphysics of relations, the position set out in this paper recognizes things that stand in the relations, but claims that, as far as the relations are concerned, there is no need for these things to have qualitative intrinsic properties underlying the relations. This position thus opposes a metaphysics of (...) individual things that are characterized by intrinsic properties. A principal problem of the latter position is that it seems that we cannot gain any knowledge of these properties insofar as they are intrinsic. Against this background, the rationale behind a metaphysics of relations is to avoid a gap between epistemology and metaphysics. (shrink)

In this paper, it is argued that the prima facie conflict between special relativity and the quantum-mechanical collapse postulate is only apparent, and that the seemingly incompatible accounts of entangled systems undergoing collapse yielded by different reference frames can be regarded as no more than differing accounts of the same processes and events. Attention to the transformation properties of quantum-mechanical states undergoing unitary, non-collapse evolution points the way to a treatment of collapse evolution consistent with the demands of relativity. r (...) 2002 Elsevier Science Ltd. All rights reserved. (shrink)

Dividing, Separating and Unifying. EPR Without Holism. In the standard interpretation of quantum mechanics parts of composed systems are correlated in a non-causal way, they are ontologically dependent on each other. In this paper I try to defend traditional realism giving a non-holistic interpretation of the EPR-paradox. An analysis of events in the macroscopic world shows that dividing and unifying objects is quite dif-ferent from changing (modifying) objects. In application to quantum mechanics I argue that a measurement at a given (...) single-system changes (modifies) this object, but the EPR-measurement divides the given object. Therefore this given object is an undivided and dividable One and not a composed system. If parts are produced (by EPR-measurement) correlations do not occur. (shrink)

This article summarizes the Quantum Bayesian point of view of quantum mechanics, with special emphasis on the view's outer edges---dubbed QBism. QBism has its roots in personalist Bayesian probability theory, is crucially dependent upon the tools of quantum information theory, and most recently, has set out to investigate whether the physical world might be of a type sketched by some false-started philosophies of 100 years ago (pragmatism, pluralism, nonreductionism, and meliorism). Beyond conceptual issues, work at Perimeter Institute is focused on (...) the hard technical problem of finding a good representation of quantum mechanics purely in terms of probabilities, without amplitudes or Hilbert-space operators. The best candidate representation involves a mysterious entity called a symmetric informationally complete quantum measurement. Contemplation of it gives a way of thinking of the Born Rule as an addition to the rules of probability theory, applicable when an agent considers gambling on the consequences of his interactions with a newly recognized universal capacity: dimension (formerly Hilbert-space dimension). (The word "capacity" should conjure up an image of something like gravitational mass---a body's mass measures its capacity to attract other bodies. With hindsight one can say that the founders of quantum mechanics discovered another universal capacity, "dimension.") The article ends by showing that the egocentric elements in QBism represent no impediment to pursuing quantum cosmology and outlining some directions for future work. (shrink)

Einstein's philosophy of physics was predicated on his Trennungsprinzip, a combination of separability and locality, without which he believed objectification, and thereby "physical thought" and "physical laws", to be impossible. Bohr's philosophy, on the other hand, was grounded in a seemingly different doctrine about the possibility of objective knowledge, namely the necessity of classical concepts. In fact, it follows from Raggio's Theorem in algebraic quantum theory that - within an appropriate class of physical theories - suitable mathematical translations of the (...) doctrines of Bohr and Einstein are equivalent. Thus - upon our specific formalization - quantum mechanics accommodates Einstein's Trennungsprinzip if and only if it is interpreted a la Bohr through classical physics. Unfortunately, the protagonists themselves failed to discuss their differences in this constructive way, since their debate was dominated by Einstein's ingenious but ultimately flawed attempts to establish the "incompleteness" of quantum mechanics. This aspect of their debate may still be understood and appreciated, however, as reflecting a much deeper and insurmountable disagreement between Bohr and Einstein about the knowability of Nature. Using the theological controversy on the knowability of God as a analogy, we can say that Einstein was a Spinozist, whereas Bohr could be said to be on the side of Maimonides. Thus Einstein's off-the-cuff characterization of Bohr as a 'Talmudic philosopher' was spot-on. (shrink)

Einstein regarded as one of the triumphs of his 1915 theory of gravity - the general theory of relativity - that it vindicated the action-reaction principle, while Newtonian mechanics as well as his 1905 special theory of relativity supposedly violated it. In this paper we examine why Einstein came to emphasise this position several years after the development of general relativity. Several key considerations are relevant to the story: the connection Einstein originally saw between Mach's analysis of inertia and both (...) the equivalence principle and the principle of general covariance, the waning of Mach's influence owing to de Sitter's 1917 results, and Einstein's detailed correspondence with Moritz Schlick in 1920. (shrink)

Schrödinger averred that entanglement is the characteristic trait of quantum mechanics. The first part of this paper is simultaneously an exploration of Schrödinger’s claim and an investigation into the distinction between mere entanglement and genuine quantum entanglement. The typical discussion of these matters in the philosophical literature neglects the structure of the algebra of observables, implicitly assuming a tensor product structure of the simple Type I factor algebras used in ordinary Quantum Mechanics . This limitation is overcome by adopting the (...) algebraic approach to quantum physics, which allows a uniform treatment of ordinary QM, relativistic quantum field theory, and quantum statistical mechanics. The algebraic apparatus helps to distinguish several different criteria of quantum entanglement and to prove results about the relation of quantum entanglement to two additional ways of characterizing the classical versus quantum divide, viz. abelian versus non-abelian algebras of observables, and the ability versus inability to interrogate the system without disturbing it. Schrödinger’s claim is reassessed in the light of this discussion. The second part of the paper deals with the relativity-to-ambiguity threat: the entanglement of a state on a system algebra is entanglement of the state relative to a decomposition of the system algebra into subsystem algebras; a state may be entangled with respect to one decomposition but not another; hence, unless there is some principled way to choose a decomposition, entanglement is a radically ambiguous notion. The problem is illustrated in terms a Realist versus Pragmatist debate, the former claiming that the decomposition must correspond to real as opposed to virtual subsystems, while the latter claims that the real versus virtual distinction is bogus and that practical considerations can steer the choice of decomposition. This debate is applied to the fraught problem of measuring entanglement for indistinguishable particles. The paper ends with some remarks about claims in the philosophical literature that entanglement undermines the separability or independence of subsystems while promoting holism. (shrink)

It is widely believed that the development of the general theory of relativity coincided with a shift in Einstein’s philosophy of science from a kind of Machian positivism to a form of scientific realism. This article criticizes that view, arguing that a kind of realism was present from the start but that Einstein was skeptical all along about some of the bolder metaphysical and epistemological claims made on behalf of what we now would call scientific realism. If we read Einstein’s (...) philosophy of science in its proper late nineteenth-and early twentieth-century philosophical context, we find that a kind of Duhemian under determinationist holism and conventionalism was more important to Einstein than either positivism or realism. And, reading his philosophy of science in its proper scientific. (shrink)

Abstract Die moderne Physik besteht nicht nur aus neuen Entdeckungen und Erfindungen durch die Relativitätstheorie und durch die Quantenphysik. Sie besteht auch aus völlig neuen Sichtweisen und flexiblen Denkweisen von Zusammenhängen und Verschränkungen zwischen den Dingen. Die moderne Physik hat sich von dem Klischee des Schwarz-Weiß-Denkens verabschiedet, für das es nur getrennte Dinge, ohne fließende Übergänge gibt. Solche unbeweglichen, dogmatischen schwarzweißen Denkweisen können wir zurückverfolgen bis zu dem griechischen Philosophen Aristoteles. In der Zeit der Klassischen Mechanik hatten sie einen überwältigenden (...) Erfolg. Galilei behauptete, das Buch der Natur sei in der Sprache der Mathematik geschrieben. Das war die sehr kurzgefasste Formulierung der Klassischen Mechanik. Die moderne Physik hat sich keineswegs von der Mathematik verabschiedet, ganz und gar nicht. Doch der heilige Ernst und der starre und absolute Dogmatismus hat nachgelassen. Moderne Denkweisen in der Physik können mit den Begriffen von fließenden Übergängen, von Zwischenstufen, von Zusammenhängen zwischen den Dingen und von Schwingungen gekennzeichnet werden. Seit Faraday und Maxwell hat sich eine Verschiebung der Untersuchungsobjekte ergeben: Seit der Mitte des 19. Jahrhunderts, seit ca 1850, drehen sich die Denkmodelle der modernen Physik nicht mehr um getrennte, isolierten Körper, die im Nichts schwimmen, sondern um die Zwischenräume zwischen den Körpern und um die flexiblen Beziehungsgeflechte zwischen den Dingen und um die Netzwerke, die die Dinge umgeben. Das sind ganz neue physikalische Denkweisen, die durchaus Dunkelzonen und Zweifel und Ungewissheiten kennen, die den Bereich der Exaktheit überschatten. Neue Beiträge der physikalischen Denkweisen sind auch durch eine Flexibilität bei der Bildung von Begriffen gekennzeichnet. Sie lassen sich nicht auf einige wenige Begriffe oder auf eine starre und exakte Festlegung der Wortwahl festnageln. -/- „Jede Philosophie bezieht ihre Farbe von der geheimen Lichtquelle eines Vorstellungshintergrunds, der niemals ausdrücklich in ihrenGedankenketten auftaucht“ (Whitehead) (1) . (shrink)

We present an exegesis of the Einstein-Podolsky-Rosen argument for the incompleteness of quantum mechanics, and defend it against the critique in Fine. (1) We contend,contra Fine, that it compares favorably with an argument reconstructed by him from a letter by Einstein to Schrödinger; and also with one given by Einstein in a letter to Popper. All three arguments turn on a dubious assumption of “separability,” which accords separate elements of reality to space-like separated systems. We discuss how this assumption figures (...) in the literature spawned by the Bell inequalities. (shrink)

Does the quantum state represent reality or our knowledge of reality? In making this distinction precise, we are led to a novel classification of hidden variable models of quantum theory. We show that representatives of each class can be found among existing constructions for two-dimensional Hilbert spaces. Our approach also provides a fruitful new perspective on arguments for the nonlocality and incompleteness of quantum theory. Specifically, we show that for models wherein the quantum state has the status of something real, (...) the failure of locality can be established through an argument considerably more straightforward than Bell’s theorem. The historical significance of this result becomes evident when one recognizes that the same reasoning is present in Einstein’s preferred argument for incompleteness, which dates back to 1935. This fact suggests that Einstein was seeking not just any completion of quantum theory, but one wherein quantum states are solely representative of our knowledge. Our hypothesis is supported by an analysis of Einstein’s attempts to clarify his views on quantum theory and the circumstance of his otherwise puzzling abandonment of an even simpler argument for incompleteness from 1927. (shrink)

Einstein’s unpublished 1927 deterministic trajectory interpretation of quantum mechanics is critically examined, in particular with regard to the reason given by Einstein for rejecting his theory. It is shown that the aspect Einstein found objectionable—the mutual dependence of the motions of particles when the (many-body) wavefunction factorises—is a generic attribute of his theory but that this feature may be removed by modifying Einstein’s method in either of two ways: using a suggestion of Grommer or, in a physically important special case, (...) using a simpler technique. It is emphasized though that the presence or absence of the interdependence property does not determine the acceptability of a trajectory theory. It is shown that there are other grounds for rejecting Einstein’s theory (and the two modified theories), to do with its domain of applicability and compatibility with empirical predictions. That Einstein’s reason for rejection is not a priori grounds for discarding a trajectory theory is demonstrated by reference to an alternative deterministic trajectory theory that displays similar particle interdependence yet is compatible with quantum predictions. (shrink)

In what follows, I examine three main points which may help us to understand the deep nature of Einstein's objections to quantum mechanics. After having played a fundamental pioneer role in the birth of quantum physics, Einstein was, as is well known, far less enthusiastic about its constitution as a quantum mechanics and, since 1927, he constantly argued against the pretention of its founders and proponents to have settled a definitive and complete theory. I emphasize first the importance of the (...) philosophical climate, which was dominated by the Copenhagen orthodoxy and Bohr's idea of complementarity: What Einstein was primarily reluctant to was to accept the fundamental character of quantum mechanics as such, and to modify for it the basic principles of knowledge. I thus stress the main lines of Einstein's own programme in respect to quantum physics, which is to be considered in relation to his other contemporary attempts and achievements. Finally, I show how Einstein's arguments, when dealing with his objections, have been fruitful and some of them still worthy, with regard to recent developments concerning local nonseparability as well as concerning the problems of completeness and accomplishment of quantum theory. (shrink)

The validity of the conclusion to the nonlocality of quantum mechanics, accepted widely today as the only reasonable solution to the EPR and Bell issues, is questioned and criticized. Arguments are presented which remove the compelling character of this conclusion and make clear that it is not the most obvious solution. Alternative solutions are developed which are free of the contradictions related with the nonlocality conclusion. Firstly, the dependence on the adopted interpretation is shown, with the conclusion that the alleged (...) nonlocality property of the quantum formalism may have been reached on the basis of an interpretation that is unnecessarily restrictive. Secondly, by extending the conventional quantum formalism along the lines of Ludwig and Davies it is shown that the Bell problem may be related to complementarity rather than to nonlocality. Finally, the dependence on counterfactual reasoning is critically examined. It appears that locality on the quantum level may still be retained provided one accepts a newly proposed principle of nonreproducibility at the individual quantum level as an alternative of quantum nonlocality. It is concluded that the locality principle can retain its general validity, in full conformity with all experimental data. (shrink)

Instead of the usual asymptotic passage from quantum mechanics to classical mechanics when a parameter tended to infinity, a sharp boundary is obtained for the domain of existence of classical reality. The last is treated as separable empirical reality following d'Espagnat, described by a mathematical superstructure over quantum dynamics for the universal wave function. Being empirical, this reality is constructed in terms of both fundamental notions and characteristics of observers. It is presupposed that considered observers perceive the world as a (...) system of collective degrees of freedom that are inherently dissipative because of interaction with thermal degrees of freedom. Relevant problems of foundation of statistical physics are considered. A feasible example is given of a macroscopic system not admitting such classical reality.The article contains a concise survey of some relevant domains: quantum and classical Bell-type inequalities; universal wave function; approaches to quantum description of macroscopic world, with emphasis on dissipation; spontaneous reduction models; experimental tests of the universal validity of the quantum theory. (shrink)

The difference between the measurement bases of classical and quantum mechanics is often interpreted as a loss of reality arising in quantum mechanics. In this paper it is shown that this apparent loss occurs only if one believes that refined everyday experience determines the Euclidean space as the real space, instead of considering this space, both in classical and quantum mechanics, as a theoretical construction needed for measurement and representing one part of a dualistic space conception. From this point of (...) view, Einstein's program of a unified field theory can be interpreted as the attempt to find a physical theory that is less dualistic. However, if one rgards this dualism as resulting from the requirements of measurements, one can hope for a weakening of the dualism but not expect to remove it completely. (shrink)

This paper addresses arguments that “separability” is an assumption of Bell’s theorem, and that abandoning this assumption in our interpretation of quantum mechanics (a position sometimes referred to as “holism”) will allow us to restore a satisfying locality principle. Separability here means that all events associated to the union of some set of disjoint regions are combinations of events associated to each region taken separately.In this article, it is shown that: (a) localised events can be consistently defined without implying separability; (...) (b) the definition of Bell’s locality condition does not rely on separability in any way; (c) the proof of Bell’s theorem does not use separability as an assumption. If, inspired by considerations of non-separability, the assumptions of Bell’s theorem are weakened, what remains no longer embodies the locality principle. Teller’s argument for “relational holism” and Howard’s arguments concerning separability are criticised in the light of these results. Howard’s claim that Einstein grounded his arguments on the incompleteness of QM with a separability assumption is also challenged. Instead, Einstein is better interpreted as referring merely to the existence of localised events. Finally, it is argued that Bell rejected the idea that separability is an assumption of his theorem. (shrink)

Nagarjuna and Quantum physics. Eastern and Western Modes of Thought. Summary. The key terms. 1. Key term: ‘Emptiness’. The Indian philosopher Nagarjuna is known in the history of Buddhism mainly by his keyword ‘sunyata’. This word is translated into English by the word ‘emptiness’. The translation and the traditional interpretations create the impression that Nagarjuna declares the objects as empty or illusionary or not real or not existing. What is the assertion and concrete statement made by this interpretation? That nothing (...) can be found, that there is nothing, that nothing exists? Was Nagarjuna denying the external world? Did he wish to refute that which evidently is? Did he want to call into question the world in which we live? Did he wish to deny the presence of things that somehow arise? My first point is the refutation of this traditional translation and interpretation. 2. Key terms: ‘Dependence’ or ‘relational view’. My second point consists in a transcription of the keyword of ‘sunyata’ by the word ‘dependence’. This is something that Nagarjuna himself has done. Now Nagarjuna’s central view can be named ‘dependence of things’. Nagarjuna is not looking for a material or immaterial object which can be declared as a fundamental reality of this world. His fundamental reality is not an object. It is a relation between objects. This is a relational view of reality. Reality is without foundation. Or: Reality has the wide open space as foundation. 3. Key terms: ‘Arm in arm’. But Nagarjuna did not stop there. He was not content to repeat this discovery of relational reality. He went on one step further indicating that what is happening between two things. He gave indications to the space between two things. He realised that not the behaviour of bodies, but the behaviour of something between them may be essential for understanding the reality. This open space is not at all empty. It is full of energy. The open space is the middle between things. Things are going arm in arm. The middle might be considered as a force that bounds men to the world and it might be seen as well as a force of liberation. It might be seen as a bondage to the infinite space. 4. Key term: Philosophy. Nagarjuna, we are told, was a Buddhist philosopher. This statement is not wrong when we take the notion ‘philosophy’ in a deep sense as a love to wisdom, not as wisdom itself. Philosophy is a way to wisdom. Where this way has an end wisdom begins and philosophy is no more necessary. A.N. Whitehead gives philosophy the commission of descriptive generalisation. We do not need necessarily a philosophical building of universal dimensions. Some steps of descriptive generalisation might be enough in order to see and understand reality. There is another criterion of Nagarjuna’s philosophy. Not his keywords ‘sunyata’ and ‘pratityasamutpada’ but his 25 philosophical examples are the heart of his philosophy. His examples are images. They do not speak to rational and conceptual understanding. They speak to our eyes. Images, metaphors, allegories or symbolic examples have a freshness which rational ideas do not possess. Buddhist dharma and philosophy is a philosophy of allegories. This kind of philosophy is not completely new and unknown to European philosophy. Since Plato’s allegory of the cave it is already a little known. The German philosopher Hans Blumenberg has underlined the importance of metaphors in European philosophy. -/-. (shrink)

While its applications have made quantum theory arguably the most successful theory in physics, its interpretation continues to be the subject of lively debate within the community of physicists and philosophers concerned with conceptual foundations. This situation poses a problem for a pragmatist for whom meaning derives from use. While disputes about how to use quantum theory have arisen from time to time, they have typically been quickly resolved, and consensus reached, within the relevant scientific sub-community. Yet rival accounts of (...) the meaning of quantum theory continue to proliferate . In this article I offer a diagnosis of this situation and outline a pragmatist solution to the problem it poses, leaving further details for subsequent articles. (shrink)

Rudyard Kipling, the famous english author of « The Jungle Book », born in India, wrote one day these words: « Oh, East is East and West is West, and never the twain shall meet ». In my paper I show that Kipling was not completely right. I try to show the common ground between buddhist philosophy and quantum physics. There is a surprising parallelism between the philosophical concept of reality articulated by Nagarjuna and the physical concept of reality implied (...) by quantum physics. For neither is there a fundamental core to reality, rather reality consists of systems of interacting objects. Such concepts of reality cannot be reconciled with the substantial, subjective, holistic or instrumentalistic concepts of reality which underlie modern modes of thought. (shrink)

A closer look at some proposed Gedanken-experiments on BECs promises to shed light on several aspects of reduction and emergence in physics. These include the relations between classical descriptions and different quantum treatments of macroscopic systems, and the emergence of new properties and even new objects as a result of spontaneous symmetry breaking.

This article examines the implications of the holonomy interpretation of classical electromagnetism. As has been argued by Richard Healey and Gordon Belot, classical electromagnetism on this interpretation evinces a form of nonseparability, something that otherwise might have been thought of as confined to nonclassical physics. Consideration of the differences between this classical nonseparability and quantum nonseparability shows that the nonseparability exhibited by the classical electromagnetism on the holonomy interpretation is closer to separability than might at first appear.

In the present paper, I shall argue that disjunctively construed naïve realism about the nature of perceptual experiences succumbs to the empirically inspired causal argument. The causal argument highlights as a first step that local action necessitates the presence of a type-identical common kind of mental state shared by all perceptual experiences. In a second step, it sets out that the property of being a veridical perception cannot be a mental property. It results that the mental nature of perceptions must (...) be exhausted by the occurrence of inner sensory experiences that narrowly supervene on the perceiver. That is, empirical objects fail directly to determine the perceptual consciousness of the perceiver. The upshot is that not only naïve realism, but also certain further forms of direct realism have to be abandoned. (shrink)

This paper deals with the development of, and the current discussion about, the interpretation of quantum mechanics. The following topics are discussed: 1. The Copenhagen Interpretation, 2. Formal Problems of Quantum Mechanics, 3. Process of Measurement and the Equation of Motion, 4. Macroscopic Level of Description, 5. Search for Hidden Variables, 6. The Notion of “Reality” and Epistemology of Quantum Mechanics, 7. Quantum Mechanics and the Explanation of Life.The Bohr‐Einstein dialogue on the validity of the quantum mechanical description of physical (...) reality lasted over two decades. Since the early nineteen fifties, Wiper has provided much of the point and counterpoint of the continuing discussion on the interpretation and epistemology of quantum mechanics. We have explored Wiper's views in some detail against the background of historical development and current debate. (shrink)

I discuss a rarely mentioned correspondence between Einstein and Swann on the constructive approach to the special theory of relativity, in which Einstein points out that the attempts to construct a dynamical explanation of relativistic kinematical effects require postulating a fundamental length scale in the level of the dynamics. I use this correspondence to shed light on several issues under dispute in current philosophy of spacetime that were highlighted recently in Harvey Brown’s monograph Physical Relativity, namely, Einstein’s view on the (...) distinction between principle and constructive theories, and the consequences of pursuing the constructive approach in the context of spacetime theories. r 2008 Elsevier Ltd. All rights reserved. (shrink)

— Niels Bohr, 19231 “There must be quite definite and clear grounds, why you repeatedly declare that one must interpret observations classically, which lie absolute ly in thei r essenc e. . . . It must belong to your deepest conviction—and I cannot understand on what you base it.”.

In the May 15, 1935 issue of Physical Review Albert Einstein co-authored a paper with his two postdoctoral research associates at the Institute for Advanced Study, Boris Podolsky and Nathan Rosen. The article was entitled “Can Quantum Mechanical Description of Physical Reality Be Considered Complete?” (Einstein et al. 1935). Generally referred to as “EPR”, this paper quickly became a centerpiece in the debate over the interpretation of the quantum theory, a debate that continues today. The paper features a striking case (...) where two quantum systems interact in such a way as to link both their spatial coordinates in a certain direction and also their linear momenta (in the same direction). As a result of this “entanglement”, determining either position or momentum for one system would fix (respectively) the position or the momentum of the other. EPR use this case to argue that one cannot maintain both an intuitive condition of local action and the completeness of the quantum description by means of the wave function. This entry describes the argument of that 1935 paper, considers several different versions and reactions, and explores the ongoing significance of the issues they raise. (shrink)

The line of argument pursued in this paper is to proceed from Einstein’s fundamental problem situation to a consideration of scientific representation with respect to the Special theory of relativity (STR). Einstein’s fundamental problem situation, which is Kantian in spirit, is how the conceptual freedom of the scientist is compatible with the need for an objective representation of an independently given material world. To solve this philosophical issue Einstein employs a number of constraints, which are central to the STR. The (...) issue of scientific representation leads to a consideration of the notion of reality and to the realistic commitments implied in the STR. From this point of view, the paper concludes that Einstein was committed to a kind of ‘structural’ realism. (shrink)

This paper argues for a metaphysics of relations based on a characterization of quantum entanglement in terms of non-separability, thereby regarding entanglement as a sort of holism. By contrast to a radical metaphysics of relations, the position set out in this paper recognizes things that stand in the relations, but claims that, as far as the relations are concerned, there is no need for these things to have qualitative intrinsic properties underlying the relations. This position thus opposes a metaphysics of (...) individual things that are characterized by intrinsic properties. A principal problem of the latter position is that it seems that we cannot gain any knowledge of these properties insofar as they are intrinsic. Against this background, the rationale behind a metaphysics of relations is to avoid a gap between epistemology and metaphysics. (shrink)

In a recent paper, David Albert has suggested that no quantum theory can yield a description of the world unfolding in Minkowski spacetime. This conclusion is premature; a natural extension of Stein's notion of becoming in Minkowski spacetime to accommodate the demands of quantum nonseparability yields such an account, an account that is in accord with a proposal which was made by Aharonov and Albert but which is dismissed by Albert as a ‘mere trick’. The nature of such an account (...) is clarified by an extension to a relativistic quantum context of David Lewis' picture of objective chances evolving in time. 1 Introduction 2 Classical relativistic becoming 3 Relativistic quantum becoming, without collapse 4 Relativistic quantum becoming, with collapse 5 Objective chance, conditional probability, and definite properties 6 The nature of the wave function 7 Conclusion. (shrink)

In the context of stochastic hidden variable theories, Howard has argued that the role of separability—spatially separated systems possess distinct real states—has been underestimated. Howard claims that separability is equivalent to Jarrett‘s completeness: this equivalence should imply that the Bell theorem forces us to give up either separability or locality. Howard's claim, however, is shown to be ill founded since it is based on an implausible assumption. The necessity of sharply distinguishing separability and locality is emphasized: a quantitative formulation of (...) separability, due to D'Espagnat, is reviewed and found unsatisfactory, in that it basically conflates separability and locality in a single notion. Finally, the possibility of an ‘Einsteinian’ nonseparable realism, envisaged by Shimony, is reviewed and found also to be implausible. (shrink)

At first sight the Aharonov- Bohm effect appears nonlocal, though not in the way EPR/Bell correlations are generally acknowledged to be nonlocal. This paper applies an analysis of nonlocality to the Aharonov- Bohm effect to show that its peculiarities may be blamed either on a failure of a principle of local action or on a failure of a principle of separability. Different interpretations of quantum mechanics disagree on how blame should be allocated. The parallel between the Aharonov- Bohm effect and (...) violations of Bell inequalities turns out to be so close that a balanced assessment of the nature and significance of quantum nonlocality requires a detailed study of both effects. (shrink)

Recent studies have shown that Einstein did not write the EPR paper and that he was disappointed with the outcome. He thought, rightly, that his own argument for the incompleteness of quantum theory was badly presented in the paper. We reconstruct the argument of EPR, indicate the reasons Einstein was dissatisfied with it, and discuss Einstein's own argument. We show that many commentators have been misled by the obscurity of EPR into proposing interpretations of its argument that do not accurately (...) represent Einstein's own views. Finally, we evaluate Einstein's own incompleteness argument, concluding that recent experimental findings have likely shown it to be unsound. (shrink)

We first examine Howard's analysis of the Bell factorizability condition in terms of 'separability' and 'locality' and then consider his claims that the violations of Bell's inequality by the statistical predictions of quantum mechanics should be interpreted in terms of 'nonseparability' rather than 'nonlocality' and that 'nonseparability' implies the failure of spacetime as a principle of individuation for quantum-mechanical systems. We will argue that his argument for the first claim is less than compelling and that any argument for the second (...) claim will be interpretation-dependent and, hence, not generally valid. (shrink)

This paper attempts to build a bridge between the interpretation of quantum theory and the philosophy of mind. In contrast to other such attempts, the bridge which this paper suggests does not consist in extending features of quantum theory to the philosophy of mind. The argument of this paper is that the discussion about a revision of the Cartesian tradition in current philosophy of mind is relevant to the interpretation of quantum theory: taking this discussion into account sharpens up the (...) task for the interpretation of quantum physics as far as the scope of what is known as quantum holism is concerned. In particular, considering this discussion makes out a strong case against the interpretation that considers quantum holism to be universal in the physical realm. (shrink)

Algebraic quantum field theory (AQFT) puts forward three ``causal axioms'' that aim to characterize the theory as one that implements relativistic causation: the spectrum condition, microcausality, and primitive causality. In this paper, I aim to show, in a minimally technical way, that none of them fully explains the notion of causation appropriate for AQFT because they only capture some of the desiderata for relativistic causation I state or because it is often unclear how each axiom implements its respective desideratum. After (...) this diagnostic, I will show that a fourth condition, local primitive causality (LPC), fully characterizes relativistic causation in the sense of fulfilling all the relevant desiderata. However, it only encompasses the virtues of the other axioms because it is implied by them, as I will show from a construction by Haag and Schroer (1962). Since the conjunction of the three causal axioms implies LPC and other important results in QFT that LPC does not imply, and since LPC helps clarify some of the shortcomings of the three axioms, I advocate for a holistic interpretation of how the axioms characterize the causal structure of AQFT against the strategy in the literature to rivalize the axioms and privilege one among them. (shrink)

Wave function realism is an interpretative framework for quantum theories which recommends taking the central ontology of these theories to consist of the quantum wave function, understood as a field on a high-dimensional space. This paper presents and evaluates three standard arguments for wave function realism, and clarifies the sort of ontological framework these arguments support.

The violation of Bell’s inequality has shown that quantum theory and relativity are in tension: reality is nonlocal. Nonetheless, many have argued that GRW-type theories are to be preferred to pilot-wave theories as they are more compatible with relativity: while relativistic pilot-wave theories require a preferred slicing of space-time, foliation-free relativistic GRW-type theories have been proposed. In this paper I discuss various meanings of ‘relativistic invariance,’ and I show how GRW-type theories, while being more relativistic in one sense, are less (...) relativistic in another. If so, the initial claim that GRW-type theories have a greater compatibility with relativity is unwarranted: both type of theories violate relativity, one way or another. (shrink)

I argue against the claim -- advocated by Albert Einstein, Bernard Williams, and Ted Sider, among others -- that a description is objective only if it says how the world is in itself. Instead, I argue for the claim -- inspired by comments of Niels Bohr -- that a family of descriptions is objective only if they co-vary with their respective descriptive contexts. Moreover, I claim that "there is a shared objective reality" simply means that it is possible to satisfy (...) this kind of covariance requirement. (shrink)

I assess various proposals for the source of the intuition that there is something problematic about contextuality, ultimately concluding that contextuality is best thought of in terms of fine-tuning. I then argue that as with other fine-tuning problems in quantum mechanics, this behaviour can be understood as a manifestation of teleological features of physics. Finally I discuss several formal mathematical frameworks that have been used to analyse contextuality and consider how their results should be interpreted by scientific realists. In the (...) course of this discussion I obtain several new mathematical results—I demonstrate that preparation contextuality is a form of fine-tuning, I show that measurement contextuality can be explained by appeal to a global constraint forbidding closed causal loops, and I demonstrate how negative probabilities can arise from a classical ontological model together with an epistemic restriction. (shrink)

I address the view that the classical electromagnetic potentials are shown by the Aharonov–Bohm effect to be physically real. I give a historico-philosophical presentation of this view and assess its prospects, more precisely than has so far been done in the literature. Taking the potential as physically real runs prima facie into ‘gauge-underdetermination’: different gauge choices represent different physical states of affairs and hence different theories. This fact is usually not acknowledged in the literature, neither by proponents nor by opponents (...) of the potentials view. I then illustrate this theme by what I take to be the basic insight of the AB effect for the potentials view, namely that the gauge equivalence class that directly corresponds to the electric and magnetic fields is too wide, i.e., the Narrow Equivalence Class encodes additional physical degrees of freedom: these only play a distinct role in a multiply-connected space. There is a trade-off between explanatory power and gauge symmetries. On the one hand, this narrower equivalence class gives a local explanation of the AB effect in the sense that the phase is incrementally picked up along the path of the electron. On the other hand, locality is not satisfied in the sense of signal locality, viz. the finite speed of propagation exhibited by electric and magnetic fields. It is therefore intellectually mandatory to seek desiderata that will distinguish even within these narrower equivalence classes, i.e. will prefer some elements of such an equivalence class over others. I consider various formulations of locality, such as Bell locality, local interaction Hamiltonians, and signal locality. I show that Bell locality can only be evaluated if one fixes the gauge freedom completely. Yet, an explanation in terms of signal locality can be accommodated by the Lorenz gauge: the potentials propagate in waves at finite speed. I therefore suggest the Lorenz gauge potentials theory—an even narrower gauge equivalence relation—as the ontology of electrodynamics. (shrink)

The paper discusses the Kantian legacy in modern views about scientific theories. The aim of this paper is to show how Einstein's philosophy of science, which was inspired by his physics, offers a specialized version of the Kantian synthesis of Empiricism and Rationalism. In modern physical theories Kant's a priori conditions become “constraints,” as shown in Einstein's use of principle theories. Einstein's use of principle theories shows how constraints are used to steer the mapping of the rational onto the empirical (...) elements of scientific theories. (shrink)

QBism is an interpretation of quantum mechanics that posits quantum probabilities as subjective Bayesian probabilities, whence its name. By avoiding experientially unfulfilled speculations about what exists prior to measurement, QBism seems to make a close encounter with the phenomenological method. What follows is an interview with QBism’s founder and principal champion, the physicist Christopher Fuchs.

In this paper, I accomplish a conceptual task and a historical task. The conceptual task is to argue that (1) Einstein’s Principle of Separability (henceforth “separability”) is not a supervenience principle and that (2) separability and entanglement are compatible. I support (1) by showing that the conclusion of Einstein’s incompleteness argument would still follow even if one assumes that the state of a composite system does not supervene on the states of the subsystems, and by showing that what Einstein says (...) in “Quantum Mechanics and Reality” (1948) strongly suggests that separability is not a principle about how subsystem states relate to the state of composite systems. I support (2) by showing that if separability was incompatible with entanglement, then Einstein’s argument would be incoherent in a trivial way. Thus, by arguing for (1) and (2) I directly challenge what has been, and still is, a very common reading of separability. The historical task is to offer the first detailed review of the different ways in which separability has been defined by physicists and philosophers in the last 60 years. Among other things, such a review distinguishes three different definitions of the principle, and shows that since the 1990s and up until the present date, it became standard to take separability (as presented by Einstein) to be a supervenience principle. (shrink)

There is a long tradition of preferring local theories to ones that posit lawful or causal influence at a spacetime distance. In this paper, we argue against this preference. We argue that nonlocality is scientifically unobjectionable and that nonlocal theories can be known. Scientists can gather evidence for them and confirm them in much the same way that they do for local theories. We think these observations point to a deeper constraint on scientific theorizing and experimentation: the (quasi‐) isolation of (...) causal or lawful influence. We argue that this requirement ought to replace the locality desideratum in science. We then explore the possibility that the order of explanation has been reversed: perhaps it is isolatable influence that determines what counts as local in the first place. (shrink)