This essay is a discussion of the philosophical and foundational issues that arise in non-relativistic quantum theory. After introducing the formalism of the theory, I consider: characterizations of the quantum formalism, empirical content, uncertainty, the measurement problem, and non-locality. In each case, the main point is to give the reader some introductory understanding of some of the major issues and recent ideas.

Classical physics states that physical reality is local--a point in space cannot influence another point beyond a relatively short distance. However, In 1997, experiments were conducted in which light particles (photons) originated under certain conditions and traveled in opposite directions to detectors located about seven miles apart. The amazing results indicated that the photons "interacted" or "communicated" with one another instantly or "in no time." Since a distance of seven miles is quite vast in quantum physics, this led physicists to (...) an extraordinary conclusion--even if experiments could somehow be conducted in which the distance between the detectors was half-way across the known universe, the results would indicate that interaction or communication between the photons would be instantaneous. What was revealed in these little-known experiments in 1997 is that physical reality is non-local--a discovery that Robert Nadeau and Menas Kafatos view as "the most momentous in the history of science." In The Non-Local Universe, Nadeau and Kafatos offer a revolutionary look at the breathtaking implications of non-locality. They argue that since every particle in the universe has been "entangled" with other particles like the two photons in the 1997 experiments, physical reality on the most basic level is an undivided wholeness. In addition to demonstrating that physical processes are vastly interdependent and interactive, they also show that more complex systems in both physics and biology display emergent properties and/or behaviors that cannot be explained in the terms of the sum of parts. One of the most startling implications of non-locality in human terms, claim the authors, is that there is no longer any basis for believing in the stark division between mind and world that has preoccupied much of western thought since the seventeenth century. And they also make a convincing case that human consciousness can now be viewed as emergent from and seamlessly connected with the entire cosmos. In pursuing this groundbreaking argument, the authors not only provide a fascinating history of developments that led to the discovery of non-locality and the sometimes heated debate between the great scientists responsible for these discoveries. They also argue that advances in scientific knowledge have further eroded the boundaries between physics and biology, and that recent studies on the evolution of the human brain suggest that the logical foundations of mathematics and ordinary language are much more similar than we previously imagined. What this new knowledge reveals, the authors conclude, is that the connection between mind and nature is far more intimate than we previously dared to imagine. What they offer is a revolutionary look at the implications of non-locality, implications that reach deep into that most intimate aspect of humanity--consciousness. (shrink)

The problem of representing a single localized particle has played a crucial role in the historical development of quantum theories. In particular, the failure to construct a relativistically invariant position eigenstate was a contributing factor in the demise of the so-called relativistic quantum mechanics, in favor of quantum field theories. Nevertheless, non-locality which stems from standard accounts of Single-particle localization still presents itself as a problem in the form of Gerhard Hegerfeldt's eponymous theorem of 1974. Accepting that a link may (...) be maintained between invariance and 'objectivity,' it is shown how Hegerfeldt's paradoxical result arises in relativistic theories from a failure of objectivity of localization-the so-called 'Jericho effect'. (shrink)

In a preceding paper, I studied the significance of Jarrett's and Shimony's analyses of 'factorisability' into 'parameter independence' and 'outcome independence' for clarifying the nature of non-locality in quantum phenomena. I focused on four types of non-locality; superluminal signalling, action-at-a-distance, non-separability and holism. In this paper, I consider a fifth type of non-locality: superluminal causation according to 'logically weak' concepts of causation, where causal dependence requires neither action nor signalling. I conclude by considering the compatibility of non-factorisable theories with relativity (...) theory. In this connection, I pay special attention to the difficulties that superluminal causation raises in relativistic spacetime. My main findings in this paper are: first, parameter-dependent and outcome-dependent theories both involve superluminal causal connections between outcomes and between settings and outcomes. Second, while relativistic deterministic parameter-dependent theories seem impossible on pain of causal paradoxes, relativistic indeterministic parameter-dependent theories are not subjected to the same challenge. Third, current relativistic non-factorisable theories seem to have some rather unattractive characteristics. (shrink)

In this paper and its sequel, I consider the significance of Jarrett's and Shimony's analyses of the so-called factorisability (Bell-locality) condition for clarifying the nature of quantum non-locality. In this paper, I focus on four types of non-locality: superluminal signalling, <span class='Hi'>action</span>-at-a-distance, non-separability and holism. In the second paper, I consider a fifth type of non-locality: superluminal causation according to 'logically weak' concepts of causation, where causal dependence requires neither <span class='Hi'>action</span> nor signalling. In this connection, I pay special attention (...) to the difficulties that superluminal causation raises in relativistic space-time. I conclude by evaluating the relevance of Jarrett's and Shimony's analyses for clarifying the question of the compatibility of quantum non-locality with relativity theory. My main conclusions are, first: these analyses are significant for clarifying the questions of superluminal signalling in quantum phenomena and for the compatibility of these phenomena with relativity. But, second, by contrast: these analyses are not very significant for the study of <span class='Hi'>action</span>-at-a distance, superluminal causation, non-separability and holism in quantum phenomena. (shrink)

This book uses the formal semantics of counterfactual conditionals to analyze the problem of non-locality in quantum mechanics. Counterfactual conditionals enter the analysis of quantum entangled systems in that they enable us to precisely formulate the locality condition that purports to exclude the existence of causal interactions between spatially separated parts of a system. They also make it possible to speak consistently about alternative measuring settings, and to explicate what is meant by quantum property attributions. The book develops the possible-world (...) semantics of quantum counterfactuals using David Lewis's famous approach as a starting point but modifying it significantly in order to achieve compatibility with the demands of the special theory of relativity as well as quantum mechanics. There have been several attempts to use counterfactuals semantics to strengthen Bell's theorem and its cognates such as the GHZ and Hardy theorems. These are critically evaluated in the book. Finally, a counterfactual reconstruction of the EPR argument and Bell's theorem is proposed that sheds a new light on their philosophical consequences regarding the relations between realism and local causation. (shrink)

In this paper I do a bit of theoretical work in neo-Bohrian interpretation quantum mechanics, making explicit and clarifying a concept that does important work in Bohr's own discussions of quantum theory and complementarity, and has been discussed by certain of Bohr's contemporary interpreters. It is not an attempt at Bohr exegesis, but an attempt to make a contribution to foundations of physics that begins from Bohr's suggestive and insightful, though sometimes murky, ideas.

This is an excellent book, by one of the philosophy of quantum theory's brightest stars. It combines a clear presentation of determinism, probability and non-locality in several current interpretations of quantum theory, with a good deal of detailed analysis, both reporting other people's and Dickson's own results, and developing his own ideas|which are often heterodox, but always well-defended and thought-provoking. The treatment is often concise, especially when reporting standard material or others' results. There are also frequent changes of gear; both (...) because the issues are complexly related to each other, and because Dickson sensibly does not aim for a de nitive treatment of issues that are at present so controversial|accordingly, he weaves about, not forcing his material into some single line of argument. So this is a monograph, not a textbook for teaching or a treatise summing up a conquered eld. But the style is clear and vigourous; the book is packed with information (sometimes about ancillary issues); and as we shall see, Dickson does have some provocative main claims, if not an overarching single line of argument. In this short space, I can only praise the book's general virtues and state some of the main claims. (shrink)

EPR experiments demonstrate that standard quantum mechanics exhibits the property of nonlocality , the enforcement of correlations between separated parts of an entangled quantum systems across spacelike separations. Nonlocality will be clarified using the transactional interpretation of quantum mechanics, and the possibility of superluminal effects (e.g., faster-than-light communication) from nonlocality and non-linear quantum mechanics will be examined.

This book examines in detail two of the fundamental questions raised by quantum mechanics. First, is the world indeterministic? Second, are there connections between spatially separated objects? In the first part, the author examines several interpretations, focusing on how each proposes to solve the measurement problem and on how each treats probability. In the second part, the relationship between probability (specifically determinism and indeterminism) and non-locality is examined, and it is argued that there is a non-trivial relationship between probability and (...) non-locality. The author then re-examines some of the interpretations of part one of the book in the light of this argument, and considers how they fare with regard to locality and Lorentz invariance. The book will appeal to anyone with an interest in the interpretation of quantum mechanics, including researchers in the philosophy of physics and theoretical physics, as well as graduate students in those fields. (shrink)

We argue that any superluminal theory Tis empirically equivalent to a non-superluminaltheory T , with thefollowing constraints onT : T preservesthe spacetime intervals between events as entailedby T, T is naturalistic (as longas T is), and all the events which have causesaccording to T also have causes according toT. Tim Maudlin (1996) definesstandard interpretations of quantum mechanicsas interpretations `according to which there wasa unique set of outcomes in Aspect's laboratory,which outcomes occurred at spacelike separation, andMaudlin claims that standard interpretations must (...) benon-local in the sense that there are superluminalinfluences. We show (even assuming Aspect's experimentis ideal) that Maudlin's claim is false. (shrink)

In this essay I examine various aspects of the nearcentury-long debate concerning the conceptualfoundations of quantum mechanics and the problems ithas posed for physicists and philosophers fromEinstein to the present. Most crucial here is theissue of realism and the question whether quantumtheory is compatible with any kind of realist orcausal-explanatory account which goes beyond theempirical-predictive data. This was Einstein's chiefconcern in the famous series of exchanges with NielsBohr when he refused to accept the truth orcompleteness of a doctrine (orthodox QM) (...) which ruledsuch questions to be strictly inadmissible. I discussthe later history of quantum-theoretical debate withparticular reference to the issue of nonlocality,i.e., the phenomenon of superluminal(faster-than-light) interaction betweenwidely-separated particles. Then I show how thestandard `Copenhagen' interpretation of QM hasinfluenced current anti-realist orontological-relativist approaches to philosophy ofscience. Indeed, there are clear signs that somephilosophers have retreated from a realist positionvery largely in response to just these problems. So itis important to ask exactly why – on what scientificor philosophical grounds – any preferred alternative(causal-realist) construal should have been ruled outas a matter of orthodox QM wisdom. Moreconstructively, my paper presents various arguments infavour of one such alternative, the `hidden-variables'theory developed since the early 1950s by David Bohmand consistently marginalised by proponents of theCopenhagen doctrine. (shrink)

It seems to me that it is among the most sure-footed of quantum physicists, those who have it in their bones, that one finds the greatest impatience with the idea that the ‘foundations of quantum mechanics’ might need some attention. Knowing what is right by instinct, they can become a little impatient with nitpicking distinctions between theorems and assumptions. —John Stewart Bell [4, p. 33].

I present a thought experiment in quantum mechanics and tease out some of its implications for the doctrine of “peaceful coexistence”, which, following Shimony, I take to be the proposition that quantum mechanics does not force us to revise or abandon the relativistic picture of causality. I criticize the standard arguments in favour of peaceful coexistence on the grounds that they are question-begging, and suggest that the breakdown of Lorentz-invariant relativity as a principle theory would be a natural development, given (...) the general trend of physics in this century. (shrink)

A variation of Bell's theorem that deals with the indeterministic case is formulated and proved within the logical framework of Lewis's theory of counterfactuals. The no-faster-than-light-influence condition is expressed in terms of Lewis would counterfactual conditionals. Objections to this procedure raised by certain philosophers of science are examined and answered. The theorem shows that the incompatibility between the predictions of quantum theory and the idea of no faster-than-light influence cannot be ascribed to any auxiliary or tacit assumption of either determinism (...) or the related idea that outcomes of unperformed measurements are determinate within nature. In addition, the theorem provides an example of an application of Lewis's theory of counterfactuals in a rigorous scientific context. (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)

Bell’s theorem in its standard version demonstrates that the joint assumptions of the hidden-variable hypothesis and the principle of local causation lead to a conflict with quantum-mechanical predictions. In his latest counterfactual strengthening of Bell’s theorem, Stapp attempts to prove that the locality assumption itself contradicts the quantum-mechanical predictions in the Hardy case. His method relies on constructing a complex, non-truth functional formula which consists of statements about measurements and outcomes in some region R, and whose truth value depends on (...) the selection of a measurement setting in a space-like separated location L. Stapp argues that this fact shows that the information about the measurement selection made in L has to be present in R. I give detailed reasons why this conclusion can and should be resisted. Next I correct and formalize an informal argument by Shimony and Stein showing that the locality condition coupled with Einstein’s criterion of reality is inconsistent with quantum-mechanical predictions. I discuss the possibility of avoiding the inconsistency by rejecting Einstein’s criterion rather than the locality assumption. (shrink)

In the paper, the proof of the non-locality of quantum mechanics, given by Bedford and Stapp (1995), and appealing to the GHZ example, is analyzed. The proof does not contain any explicit assumption of realism, but instead it uses formal methods and techniques of the Lewis calculus of counterfactuals. To ascertain the validity of the proof, a formal semantic model for counterfactuals is constructed. With the help of this model it can be shown that the proof is faulty, because it (...) appeals to the unwarranted principle of “elimination of eliminated conditions” (EEC). As an additional way of showing unreasonableness of the assumption (EEC), it is argued that yet another alleged and highly controversial proof of non-locality of QM, using the Hardy example, can be made almost trivial with the help of (EEC). Finally, a general argument is produced to the effect that the locality condition in the form accepted by Stapp and Bedford is consistent with the quantum-mechanical predictions for the GHZ case under the assumption of indeterminism. This result undermines any future attempts of proving the incompatibility between the predictions of quantum theory and the idea of no faster-than-light influence in the GHZ case, quite independently of the negative assessment of the particular derivation proposed by Stapp and Bedford. (shrink)

This book uses the formal semantics of counterfactual conditionals to analyze the problem of non-locality in quantum mechanics. Counterfactual conditionals enter the analysis of quantum entangled systems in that they enable us to precisely formulate the locality condition that purports to exclude the existence of causal interactions between spatially separated parts of a system. They also make it possible to speak consistently about alternative measuring settings, and to explicate what is meant by quantum property attributions. The book develops the possible-world (...) semantics of quantum counterfactuals using David Lewis's famous approach as a starting point but modifying it significantly in order to achieve compatibility with the demands of the special theory of relativity as well as quantum mechanics. There have been several attempts to use counterfactuals semantics to strengthen Bell's theorem and its cognates such as the GHZ and Hardy theorems. These are critically evaluated in the book. Finally, a counterfactual reconstruction of the EPR argument and Bell's theorem is proposed that sheds a new light on their philosophical consequences regarding the relations between realism and local causation. (shrink)

In this paper I do a bit of theoretical work in neo-Bohrian interpretation quantum mechanics, making explicit and clarifying a concept that does important work in Bohr's own discussions of quantum theory and complementarity, and has been discussed by certain of Bohr's contemporary interpreters. It is not an attempt at Bohr exegesis, but an attempt to make a contribution to foundations of physics that begins from Bohr's suggestive and insightful, though sometimes murky, ideas.

This is an excellent book, by one of the philosophy of quantum theory's brightest stars. It combines a clear presentation of determinism, probability and non-locality in several current interpretations of quantum theory, with a good deal of detailed analysis, both reporting other people's and Dickson's own results, and developing his own ideas|which are often heterodox, but always well-defended and thought-provoking. The treatment is often concise, especially when reporting standard material or others' results. There are also frequent changes of gear; both (...) because the issues are complexly related to each other, and because Dickson sensibly does not aim for a de nitive treatment of issues that are at present so controversial|accordingly, he weaves about, not forcing his material into some single line of argument. So this is a monograph, not a textbook for teaching or a treatise summing up a conquered eld. But the style is clear and vigourous; the book is packed with information (sometimes about ancillary issues); and as we shall see, Dickson does have some provocative main claims, if not an overarching single line of argument. In this short space, I can only praise the book's general virtues and state some of the main claims. (shrink)

I compare deterministic and stochastic hidden variable models of the Bell experiment, exphasising philosophical distinctions between the various ways of combining conditionals and probabilities. I make four main claims. (1) Under natural assumptions, locality as it occurs in these models is equivalent to causal independence, as analysed (in the spirit of Lewis) in terms of probabilities and conditionals. (2) Stochastic models are indeed more general than deterministic ones. (3) For factorizable stochastic models, relativity's lack of superluminal causation does not favour (...) locality over completeness. (4) If we prohibit all superluminal causation, then the violation of the Bell inequality teaches us a lesson, besides quantum mechanics' familiar ones that quantities can lack precise values and that pairs of quantities can lack joint probabilities: namely, some pairs of events are not screened off by their common past. (shrink)

I apply some of the lessons from quantum theory, in particular from Bell’s theorem, to a debate on the foundations of decision theory and causation. By tracing a formal analogy between the basic assumptions of causal decision theory (CDT)—which was developed partly in response to Newcomb’s problem— and those of a local hidden variable theory in the context of quantum mechanics, I show that an agent who acts according to CDT and gives any nonzero credence to some possible causal interpretations (...) underlying quantum phenomena should bet against quantum mechanics in some feasible game scenarios involving entangled systems, no matter what evidence they acquire. As a consequence, either the most accepted version of decision theory is wrong, or it provides a practical distinction, in terms of the prescribed behaviour of rational agents, between some metaphysical hypotheses regarding the causal structure underlying quantum mechanics. (shrink)

give a proof of the existence of nonlocal influences acting on correlated spin-1/2 particles in the singlet state which does not require any particular interpretation of quantum mechanics (QM). (Except Stapp holds that the proof fails under a many-worlds interpretation of QM—a claim we analyse in 1.2.) Recently, in responding to Redhead's ([1987], pp. 90-6) criticism that the Stapp 1 proof fails under an indeterministic interpretation of QM, Stapp [1989] (henceforth Stapp 2), has revised the logical structure of his proof (...) including its crucial locality assumption. Our main aim is to show that this revision is a step in the wrong direction because it faces two difficulties which undermine the resulting proof's significance (3.1) and validity (3. 2). We also clarify and extend the Stapp 1 proof (1. 1) with the aid of Lewis' analysis of counterfactuals (1. 2) and causal dependence (2. 2 and 2. 3). In so doing, we are able to identify two new defects in the Stapp 1 proof (1. 3 and 2. 1) in addition to corroborating Redhead's criticism (2. 2). Also, the additional assumptions which save the Stapp 1 proof's validity are detailed (2. 3) and some new difficulties for the determinist are pointed out by exploiting a slightly extended version of the proof (2. 4). In providing this full analysis of the Stapp 1 proof, we also construct the necessary framework within which to provide a critique of Stapp 2's proof (3). *Portions of this paper were presented by R. K. Clifton to the 1988 British Society for the Philosophy of Science Conference at the University of Southampton. R. K. Clifton wishes to thank the Natural Sciences and Engineering Research Council of Canada, the Royal Commission for the Exhibition of 1851, and the Governing Body of Peterhouse at Cambridge University for support during this work. (shrink)

Einstein's "spookiness" is now called nonlocality, the mysterious ability of Nature to enforce correlations between separated but entangled parts of a quantum system that are out of speed-of-light contact, to reach faster-than-light across vast spatial distances or even across time itself to ensure that the parts of a quantum system are made to match. This column is about nonlocality, and how, through Bell's theorem, the nonlocality implicit in nature has been demonstrated in the laboratory.

This book examines in detail two of the fundamental questions raised by quantum mechanics. First, is the world indeterministic? Second, are there connections between spatially separated objects? In the first part, the author examines several interpretations, focusing on how each proposes to solve the measurement problem and on how each treats probability. In the second part, the relationship between probability (specifically determinism and indeterminism) and non-locality is examined, and it is argued that there is a non-trivial relationship between probability and (...) non-locality. The author then re-examines some of the interpretations of part one of the book in the light of this argument, and considers how they fare with regard to locality and Lorentz invariance. The book will appeal to anyone with an interest in the interpretation of quantum mechanics, including researchers in the philosophy of physics and theoretical physics, as well as graduate students in those fields. (shrink)

A violation of Bell’s inequalities is generally considered to be the Holy Grail of experimental proof that a specific natural phenomenon cannot be explained in a classical framework and is based on a non-boolean structure of predications. Generalized quantum theory allows for such non-boolean predications. We formulate temporal Bell’s inequalities for cognitive two-state systems and indicate how these inequalities can be tested. This will introduce the notion of temporally non-local measurements. The Necker-Zeno model for bistable perception predicts a violation of (...) these temporal Bell’s inequalities. (shrink)

This paper constructs two classes of models for the quantum correlation experiments used to test the Bell-type inequalities, synchronization models and prism models. Both classes employ deterministic hidden variables, satisfy the causal requirements of physical locality, and yield precisely the quantum mechanical statistics. In the synchronization models, the joint probabilities, for each emission, do not factor in the manner of stochastic independence, showing that such factorizability is not required for locality. In the prism models the observables are not random variables (...) over a common space; hence these models throw into question the entire random variables idiom of the literature. Both classes of models appear to be testable. (shrink)

Some recent work in the philosophy of quantum mechanics has suggested that quantum systems can be thought of as non-separable and therefore non-individual, in some sense, in Bell and E.P.R. type situations. This suggestion is set in the context of previous work regarding the individuality of quantal particles and it is argued that such entities can be considered as individuals if their non-classical statistical correlations are understood in terms of non-supervenient relations holding between them. We conclude that such relations (...) are strongly non-supervenient in Cleland's sense and note a possible connection between this idea and the realist quantum logic programme. (shrink)

Mathematics equivalent to Bell's derivation of the inequalities, also allows a local hidden variables explanation for the correlation between distant measurements.

A class of probability functions is studied. This class contains the probability functions of half-spin particles and spinning classical objects. A notion of realisability for these functions is defined. In terms of this notion two versions of Bell's theorem and their inverses are stated and proved.

We will formulate two Bell arguments. Together they show that if the probabilities given by quantum mechanics are approximately correct, then the properties exhibited by certain physical systems must be nontrivially dependent on thetypes of measurements performedand eithernonlocally connected orholistically related to distant events. Although a number of related arguments have appeared since John Bell's original paper (1964), they tend to be either highly technical or to lack full generality. The following arguments depend on the weakest of premises, and the (...) structure of the arguments is simpler than most (without any loss of rigor or generality). The technical simplicity is due in part to a novel version of the generalized Bell inequality. The arguments are self contained and presuppose no knowledge of quantum mechanics. We will also offer a Dutch Book argument for measurement type dependence. (shrink)

Standard proofs of generalized Bell theorems, aiming to restrict stochastic, local hidden-variable theories for quantum correlation phenomena, employ as a locality condition the requirement of conditional stochastic independence. The connection between this and the no-superluminary-action requirement of the special theory of relativity has been a topic of controversy. In this paper, we introduce an alternative locality condition for stochastic theories, framed in terms of the models of such a theory (§2). It is a natural generalization of a light-cone determination condition (...) that is essentially equivalent to mathematical conditions that have been used to derive Bell inequalities in the deterministic case. Further, it is roughly equivalent to a condition proposed by Bell that, in one investigation, needed to be supplemented with a much stronger assumption in order to yield an inequality violated by some quantum mechanical predictions. It is shown here that this reflects a very general situation: from the proposed locality condition, even adding the strict anticorrelation condition and the auxiliary hypotheses needed to derive experimentally useful (and theoretically telling) inequalities, no Bell-type inequality is derivable. (These independence claims are the burden of §4.) A certain limitation on the scope of the proposed stochastic locality condition is exposed (§5), but it is found to be rather minor. The conclusion is thus supported that conditional stochastic independence, however reasonable on other grounds, is essentially stronger than what is required by the special theory.Our results stand in apparent contradiction with a class of derivations purporting to obtain generalized Bell inequalities from locality alone. It is shown in Appendix (B) that such proofs do not achieve their goal. This fits with our conclusion that generalized Bell theorems are not straightforward generalizations of theorems restricting deterministic hidden-variable theories, and that, in fact, such generalizations do not exist. This leaves open the possibility that a satisfactory, non-deterministic account of the quantum correlation phenomena can be given within the framework of the special theory. (shrink)

It is a well known fact that a common common causal explanation of the EPR scenario which consists in providing a local, non-conspiratorial common common cause system for a set of EPR correlations is excluded by various Bell inequalities. But what if we replace the assumption of a common common cause system by the requirement that each correlation of the set has a local, non-conspiratorial separate common cause system? In the paper we show that this move does not yield a (...) solution by providing a general recipe how to derive any Bell(δ) inequality---that is an inequality differing from some Bell inequality in a term of order of δ---from the assumption that an appropriate set of almost perfect anticorrelations has a separate common causal explanation. (shrink)

Since the validity of Bell's inequalities implies the existence of joint probabilities for non-commuting observables, there is no universal consensus as to what the violation of these inequalities signifies. While the majority view is that the violation teaches us an important lesson about the possibility of explanations, if not about metaphysical issues, there is also a minimalist position claiming that the violation is to be expected from simple facts about probability theory. This minimalist position is backed by theorems due to (...) A. Fine and I. Pitowsky.Our paper shows that the minimalist position cannot be sustained. To this end,we give a formally rigorous interpretation of joint probabilities in thecombined modal and spatiotemporal framework of `stochastic outcomes inbranching space-time' (SOBST) (Kowalski and Placek, 1999; Placek, 2000). We show in this framework that the claim that there can be no joint probabilities fornon-commuting observables is incorrect. The lesson from Fine's theorem is notthat Bell's inequalities will be violated anyhow, but that an adequate modelfor the Bell/Aspect experiment must not define global joint probabilities. Thus we investigate the class of stochastic hidden variable models, whichprima facie do not define such joint probabilities. The reasonwhy these models fail supports the majority view: Bell's inequalities are notjust a mathematical artifact. (shrink)

The hidden-variables model constructed by Karl Hess and Walter Philipp is claimed by its authors to exploit a "loophole" in Bell's theorem; according to Hess and Philipp, the parameters employed in their model extend beyond those considered by Bell. Furthermore, they claim that their model satisfies Einstein locality and is free of any "suspicion of spooky action at a distance." Both of these claims are false; the Hess-Philipp model achieves agreement with the quantum-mechanical predictions, not by circumventing Bell's theorem, but (...) via Parameter Dependence. (shrink)

Its interpretation, however, is as unsettled now as in the heroic days of Einstein and Bohr.This book focuses on quantum non-locality, the curious quantum ...

The paper extends the framework of outcomes in branching space-time (Kowalski and Placek [1999]) by assigning probabilities to outcomes of events, where these probabilities are interpreted either epistemically or as weighted possibilities. In resulting models I define the notion of common cause of correlated outcomes of a single event, and investigate which setups allow for the introduction of common causes. It turns out that a deterministic common cause can always be introduced, but (surprisingly) only special setups permit the introduction of (...) truly stochastic common causes. I analyse next the Bell-Aspect experiment and derive the Bell-CH inequalities. I observe that we postulate there not a common cause for outcomes of a single event but rather a common common cause that accounts for outcomes of many events, where 'events' mean 'measurements with (different) directions of polarization'. Since the inequalities are violated, I claim that no causal story can be told about the Bell correlations, where causality is subliminal and restricted by screening-off condition. Similarly, given certain intuitive principles, no deterministic story can be told about these correlations. (shrink)

The paper develops models of statistical experiments that combine propensities with frequencies, the underlying theory being the branching space-times (BST) of Belnap (1992). The models are then applied to analyze Bell's theorem. We prove the so-called Bell-CH inequality via the assumptions of a BST version of Outcome Independence and of (non-probabilistic) No Conspiracy. Notably, neither the condition of probabilistic No Conspiracy nor the condition of Parameter Independence is needed in the proof. As the Bell-CH inequality is most likely experimentally falsified, (...) the choice is this: contrary to the appearances, experimenters cannot choose some measurement settings, or some transitions, with spacelike related initial events, are correlated; or both. (shrink)

A number of writers have been attracted to the idea that some of the peculiarities of quantum theory might be manifestations of 'backward' or 'retro' causality, underlying the quantum description. This idea has been explored in the literature in two main ways: firstly in a variety of explicit models of quantum systems, and secondly at a conceptual level. This note introduces a third approach, intended to complement the other two. It describes a simple toy model, which, under a natural interpretation, (...) shows how retrocausality can emerge from simple global constraints. The model is also useful in permitting a clear distinction between the kind of retrocausality likely to be of interest in QM, and a different kind of reverse causality, with which it is liable to be confused. The model is proposed in the hope that future elaborations might throw light on the potential of retrocausality to account for quantum phenomena. (shrink)

Forthcoming in Studies in History and Philosophy of Modern Physics, 39(2008).

Bell’s theorem requires the assumption that hidden variables are independent of future measurement settings. This independence assumption rests on surprisingly shaky ground. In particular, it is puzzlingly time-asymmetric. The paper begins with a summary of the case for considering hidden variable models which, in abandoning this independence assumption, allow a degree of ‘backward causation’. The remainder of the paper clarifies the physical significance of such models, in relation to the issue as to whether quantum mechanics provides a complete description of (...) physical reality. (shrink)

"Indeed I have very little idea of what this means. I do not understand in what sense the word `mechanical' is used, in characterizing the disturbances that Bohr does not contemplate, as distinct from those he does. I do not know what the italicized passage means--- `an influence on the very conditions...' . Could it mean just that different experiments on the first system give different kinds of information about the second? But this was one of the main points of (...) EPR, who observed that one could learn *either* the position *or* the momentum of the second system..... Is Bohr just rejecting the premise--- `no action at a distance'---rather than refuting the argument?". (shrink)

In 1935, Einstein, Podolsky, and Rosen (EPR) published an important paper in which they claimed that the whole formalism of quantum mechanics together with what they called a “Reality Criterion” imply that quantum mechanics cannot be complete. That is, there must exist some elements of reality that are not described by quantum mechanics. They concluded that there must be a more complete description of physical reality involving some hidden variables that can characterize the state of affairs in the world in (...) more detail than the quantum mechanical state. This conclusion leads to paradoxical results. -/- As Bell proved in 1964, under some further but quite plausible assumptions, this conclusion that there are hidden variables implies that, in some spin-correlation experiments, the measured quantum mechanical probabilities should satisfy particular inequalities (Bell-type inequalities). The paradox consists in the fact that quantum probabilities do not satisfy these inequalities. And this paradoxical fact has been confirmed by several laboratory experiments since the 1970s. -/- Some researchers have interpreted this result as showing that quantum mechanics is telling us nature is non-local, that is, that particles can affect each other across great distances in a time too brief for the effect to have been due to ordinary causal interaction. Others object to this interpretation, and the problem is still open and hotly debated among both physicists and philosophers. It has motivated a wide range of research from the most fundamental quantum mechanical experiments through foundations of probability theory to the theory of stochastic causality as well as the metaphysics of free will. (shrink)

A realist separable hidden variables theory in conformity with Einstein's principle of causality is developed in this paper to explain the Einstein-Podolsky-Rosen paradox, and the experimental results (including those in Aspect's four polarizers experiment) obtained so far with a view to test the non-separability of quantum mechanics.

This book uses the formal semantics of counterfactual conditionals to analyze the problem of non-locality in quantum mechanics. Counterfactual conditionals enter the analysis of quantum entangled systems in that they enable us to precisely formulate the locality condition that purports to exclude the existence of causal interactions between spatially separated parts of a system. They also make it possible to speak consistently about alternative measuring settings, and to explicate what is meant by quantum property attributions. The book develops the possible-world (...) semantics of quantum counterfactuals using David Lewis's famous approach as a starting point but modifying it significantly in order to achieve compatibility with the demands of the special theory of relativity as well as quantum mechanics. There have been several attempts to use counterfactuals semantics to strengthen Bell's theorem and its cognates such as the GHZ and Hardy theorems. These are critically evaluated in the book. Finally, a counterfactual reconstruction of the EPR argument and Bell's theorem is proposed that sheds a new light on their philosophical consequences regarding the relations between realism and local causation. (shrink)

In this paper I do a bit of theoretical work in neo-Bohrian interpretation quantum mechanics, making explicit and clarifying a concept that does important work in Bohr's own discussions of quantum theory and complementarity, and has been discussed by certain of Bohr's contemporary interpreters. It is not an attempt at Bohr exegesis, but an attempt to make a contribution to foundations of physics that begins from Bohr's suggestive and insightful, though sometimes murky, ideas.

This is an excellent book, by one of the philosophy of quantum theory's brightest stars. It combines a clear presentation of determinism, probability and non-locality in several current interpretations of quantum theory, with a good deal of detailed analysis, both reporting other people's and Dickson's own results, and developing his own ideas|which are often heterodox, but always well-defended and thought-provoking. The treatment is often concise, especially when reporting standard material or others' results. There are also frequent changes of gear; both (...) because the issues are complexly related to each other, and because Dickson sensibly does not aim for a de nitive treatment of issues that are at present so controversial|accordingly, he weaves about, not forcing his material into some single line of argument. So this is a monograph, not a textbook for teaching or a treatise summing up a conquered eld. But the style is clear and vigourous; the book is packed with information (sometimes about ancillary issues); and as we shall see, Dickson does have some provocative main claims, if not an overarching single line of argument. In this short space, I can only praise the book's general virtues and state some of the main claims. (shrink)

We argue against the common view that it is impossible to give a causal account of the distant correlations that are revealed in EPR-type experiments. We take a realistic attitude about quantum mechanics which implies a willingness to modify our familiar concepts according to its teachings. We object to the argument that the violation of factorizability in EPR rules out causal accounts, since such an argument is at best based on the desire to retain a classical description of nature that (...) consists of processes that are continuous in space and time. We also do not think special relativity prohibits the superluminal propagation of causes in EPR, for the phenomenon of quantum measurement may very well fall outside the domain of application of special relativity. It is possible to give causal accounts of EPR as long as we are willing to take quantum mechanics seriously, and we offer two such accounts. (shrink)

As part of the creation-discovery interpretation of quantum mechanics Diederik Aerts presented a setting with macroscopical coincidence experiments designed to exhibit significant conceptual analogies between portions of stuff and quantum compound entities in a singlet state in Einstein—Podolsky—Rosen/Bell-experiments (EPR-experiments). One important claim of the creation-discovery view is that the singlet state describes an entity that does not have a definite position in space and thus does not exist in space. Free Process Theory is a recent proposal by Johanna Seibt of (...) an integrated ontology, i.e., of an ontology suitable for the interpretation of theories of the macrophysical and microphysical domain (quantum field theory). The framework of free process theory allows us to show systematically the relevant analogies and disanalogies between Aerts' experiment and EPR-experiments. From free process ontology it also follows quite naturally that the quantum compound entity described by the singlet state does not exist in space. (shrink)

Last June I was an invited speaker at the symposium “Frontiers of Time: Reverse Causation—Experiment and Theory,” part of a meeting of the American Association for the Advancement of Science (AAAS) held on the beautiful campus of the University of San Diego. (Here, reverse causation means a violation of that most mysterious law of physics, the Principle of Causality, which requires that any cause must precede its effects in all reference frames.) I had originally intended to just talk about my (...) work on the transactional interpretation of quantum mechanics and its somewhat retrocausal aspects (i.e., back-in-time handshakes of quantum waves, etc.). However, a new idea involving signaling with nonlocal quantum processes had come my way, and I decided to present it as a retrocausal quantum paradox at the symposium. It made a big splash there, but none of the experts present could identify any problem with the proposed thought experiment or resolve the paradox. In this column I want to tell you about this causality-violating communications scheme and its possible consequences. (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)

This book examines in detail two of the fundamental questions raised by quantum mechanics. First, is the world indeterministic? Second, are there connections between spatially separated objects? In the first part, the author examines several interpretations, focusing on how each proposes to solve the measurement problem and on how each treats probability. In the second part, the relationship between probability (specifically determinism and indeterminism) and non-locality is examined, and it is argued that there is a non-trivial relationship between probability and (...) non-locality. The author then re-examines some of the interpretations of part one of the book in the light of this argument, and considers how they fare with regard to locality and Lorentz invariance. The book will appeal to anyone with an interest in the interpretation of quantum mechanics, including researchers in the philosophy of physics and theoretical physics, as well as graduate students in those fields. (shrink)

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)

D. H. Sharp has recently argued that Einstein, Podolsky, and Rosen failed to make good their claim that elementary quantum theory provides only an incomplete description of physical reality. Sharp expounds in detail three criticisms (a fourth is mentioned) which focus largely on formal features of the quantum theory. I argue, on grounds centered largely in our search for an adequate physical understanding of the micro domain, that each of these criticisms must be rejected. The original criticism of quantum theory (...) reemerges as a still-important baseline in our search for an adequate understanding of quantum theory. (shrink)

A new constructivist approach to modeling in economics and theory of consciousness is proposed. The state of elementary object is defined as a set of its measurable consumer properties. A proprietor's refusal or consent for the offered transaction is considered as a result of elementary economic measurement. Elementary (indivisible) technology, in which the object's consumer values are variable, in this case can be formalized as a generalized economic measurement. The algebra of such measurements has been constructed. It has been shown (...) that in the general case the quantummechanical formalism of the theory of selective measurements is required for description of such conditions. The economic analogs of the elementary slit experiments in physics have been created. The proposed approach can be also used for consciousness modeling. (shrink)

More specifically, one notices that X1  X2, P1  P2  0 where X1, X2 are the position operators for the first and second particles respectively, and P1, P2 their momenta operators. This means that, in principle, one can prepare the pair of particles with simultaneously known values of X1  X2 and P1  P2. Then the knowledge of the value of P2 allows to infer the value of P1.(However, performing the experiment with these continuous variables is technically (...) impossible and it remains a thought experiment.). (shrink)

Its interpretation, however, is as unsettled now as in the heroic days of Einstein and Bohr.This book focuses on quantum non-locality, the curious quantum ...

It is argued that formal reconstructions of the EPR-argument do not only show semantical incompleteness, but also incorrectness of quantum mechanics together with the projection postulate. The latter has to be rejected because it contradicts Schrödinger's equation. A logical analogon to the problem is given.

This paper discusses the Einstein-Podolsky-Rosen paradox from a new point of view. In section II, the arguments by which Einstein, Podolsky and Rosen reach their paradoxical conclusions are presented. They are found to rest on two critical assumptions: (a) that before a measurement is made on a system consisting of two non-interacting but correlated sub-systems, the state of the entire system is exactly represented by: ψ a (r̄ 1 ,r̄ 2 )=∑ η a η τ η (r̄ 1 ,r̄ 2 (...) )=∑ i,k α ik ψ i (r̄ 1 )σ k (r̄ 2 ) (b) that the exact measurement of an observable A in one of the sub-systems is possible. In section III it is shown that assumption (b) is incorrect. Thus we conclude, as did Bohr, that the results of Einstein, Podolsky and Rosen are not valid. The arguments of section III are quite distinct from Bohr's, and therefore in Section IV this work is related to that of Bohr. (shrink)

b>: Replacing faulty nineteenth century physics by its orthodox quantum successor converts the earlier materialist conception of nature to a structure that does not enforce the principle of the causal closure of the physical. The quantum laws possess causal gaps, and these gaps are filled in actual scientific practice by inputs from our streams of consciousness. The form of the quantum laws permits and suggests the existence of an underlying reality that is built not on substances, but on psychophysical events, (...) and on objective tendencies for these events to occur. These events constitute intrinsic mind-brain connections. They are fundamental links between brain processes described in physical terms and events in our streams of consciousness. This quantum ontology confers upon our conscious intentions the causal efficacy assigned to them in actual scientific practice, and creates a substance- free interactive dualism. This putative quantum ontology has previously been shown to have impressive explanatory power in both psychology and neuroscience. Here it is used to reconcile the existence of physically efficacious conscious free will with causal anomalies of both the Libet and Einstein-Rosen-Podolsky types. (shrink)

In 1935, Einstein, Podolsky, and Rosen (EPR) published an important paper in which they claimed that the whole formalism of quantum mechanics together with what they called a “Reality Criterion” imply that quantum mechanics cannot be complete. That is, there must exist some elements of reality that are not described by quantum mechanics. They concluded that there must be a more complete description of physical reality involving some hidden variables that can characterize the state of affairs in the world in (...) more detail than the quantum mechanical state. This conclusion leads to paradoxical results. -/- As Bell proved in 1964, under some further but quite plausible assumptions, this conclusion that there are hidden variables implies that, in some spin-correlation experiments, the measured quantum mechanical probabilities should satisfy particular inequalities (Bell-type inequalities). The paradox consists in the fact that quantum probabilities do not satisfy these inequalities. And this paradoxical fact has been confirmed by several laboratory experiments since the 1970s. -/- Some researchers have interpreted this result as showing that quantum mechanics is telling us nature is non-local, that is, that particles can affect each other across great distances in a time too brief for the effect to have been due to ordinary causal interaction. Others object to this interpretation, and the problem is still open and hotly debated among both physicists and philosophers. It has motivated a wide range of research from the most fundamental quantum mechanical experiments through foundations of probability theory to the theory of stochastic causality as well as the metaphysics of free will. (shrink)

The violation of Bell inequalities by quantum physical experiments disproves all relativistic micro causal, classically real models, short Local Realistic Models (LRM). Non-locality, the infamous “spooky interaction at a distance” (A. Einstein), is already sufficiently ‘unreal’ to motivate modifying the “realistic” in “local realistic”. This has led to many worlds and finally many minds interpretations. We introduce a simple many world model that resolves the Einstein Podolsky Rosen paradox. The model starts out as a classical LRM, thus clarifying that the (...) many worlds concept alone does not imply quantum physics. Some of the desired ‘non-locality’, e.g. anti-correlation at equal measurement angles, is already present, but Bell’s inequality can of course not be violated. A single and natural step turns this LRM into a quantum model predicting the correct probabilities. Intriguingly, the crucial step does obviously not modify locality but instead reality: What before could have still been a direct realism turns into modal realism. This supports the trend away from the focus on non-locality in quantum mechanics towards a mature structural realism that preserves micro causality. (shrink)

My aim in this paper is a modest one. I do not have any particular thesis to advance about the nature of entanglement, nor can I claim novelty for any of the material I shall discuss. My aim is simply to raise some questions about entanglement that spring naturally from certain developments in quantum information theory and are, I believe, worthy of serious consideration by philosophers of science. The main topics I discuss are different manifestations of quantum nonlocality, entanglement-assisted communication, (...) and entanglement thermodynamics. (shrink)

We will formulate two Bell arguments. Together they show that if the probabilities given by quantum mechanics are approximately correct, then the properties exhibited by certain physical systems must be nontrivially dependent on thetypes of measurements performedand eithernonlocally connected orholistically related to distant events. Although a number of related arguments have appeared since John Bell's original paper (1964), they tend to be either highly technical or to lack full generality. The following arguments depend on the weakest of premises, and the (...) structure of the arguments is simpler than most (without any loss of rigor or generality). The technical simplicity is due in part to a novel version of the generalized Bell inequality. The arguments are self contained and presuppose no knowledge of quantum mechanics. We will also offer a Dutch Book argument for measurement type dependence. (shrink)

It has sometimes been suggested that quantum phenomena exhibit a characteristic holism or nonseparability, and that this distinguishes quantum from classical physics. One puzzling quantum phenomenon arises when one performs measurements of spin or polarization on certain separated quantum systems. The results of these measurements exhibit patterns of statistical correlation that resist traditional causal explanation. Some have held that it is possible to understand these patterns as instances or consequences of quantum holism or nonseparability. Just what holism and nonseparability are (...) supposed to be has not always been made clear, though, and each of these notions has been understood in different ways. Moreover, while some have taken holism and nonseparability to come to the same thing, others have thought it important to distinguish the two. Any evaluation of the significance of quantum holism and/or nonseparability must rest on a careful analysis of these notions. (shrink)

(STARS Conference, Cancún, January 2007).

Its interpretation, however, is as unsettled now as in the heroic days of Einstein and Bohr.This book focuses on quantum non-locality, the curious quantum ...

Entangled quantum systems can be harnessed to transmit, store, and manipulate information in a more efficient and secure way than possible in the realm of classical physics. Given this resource character of entanglement, it is an important problem to characterize ways to manipulate it and meaningful approaches to its quantification. This is the objective of entanglement theory.

How much of philosophical, scientific, and political thought is caught up with the idea of continuity? What if it were otherwise? This paper experiments with the disruption of continuity. The reader is invited to participate in a performance of spacetime (re)configurings that are more akin to how electrons experience the world than any journey narrated though rhetorical forms that presume actors move along trajectories across a stage of spacetime (often called history). The electron is here invoked as our host, an (...) interesting body to inhabit (not in order to inspire contemplation of flat-footed analogies between ‘macro’ and ‘micro’ worlds, concepts that already presume a given spatial scale), but a way of thinking with and through dis/continuity – a dis/orienting experience of the dis/jointedness of time and space, entanglements of here and there, now and then, that is, a ghostly sense of dis/continuity, a quantum dis/continuity. There is no overarching sense of temporality, of continuity, in place. Each scene diffracts various temporalities within and across the field of spacetimemattering. Scenes never rest, but are reconfigured within, dispersed across, and threaded through one another. The hope is that what comes across in this dis/jointed movement is a felt sense of différance, of intra-activity, of agential separability – differentiatings that cut together/apart – that is the hauntological nature of quantum entanglements. (shrink)

According to D. Bohm’s interpretation of quantum mechanics, a particle always has a well-defined spatial trajectory. A change in boundary conditions can nonlocally change that trajectory. In this note we point out a striking instance of this phenomenon that is easy to understand qualitatively.