David Wallace argues that we should take quantum theory seriously as an account of what the world is like--which means accepting the idea that the universe is constantly branching into new universes. He presents an accessible but rigorous account of the 'Everett interpretation', the best way to make coherent sense of quantum physics.

Ed. Daniel Greenberger, 750pp May 1995 164.95.

I give an introduction to the conceptual structure of quantum field theory as it is used in mainstream theoretical physics today, aimed at non-specialists. My main focuses in the article are the common structure of quantum field theory as it is applied in solid-state physics and as it is applied in high-energy physics; the modern theory of renormalisation.

Quantum Theory and the Schism in Physics is one of the three volumes of Karl Popper’s Postscript to the Logic of scientific Discovery . The Postscript is the culmination of Popper’s work in the philosophy of physics and a new famous attack on subjectivist approaches to philosophy of science. Quantum Theory and the Schism in Physics is the third volume of the Postscript . It may be read independently, but it also forms part of Popper’s interconnected (...) argument in the Postscript . It presents Popper’s classic statement on quantum physics and offers important insights into his thinking on problems of method within science and physics as a whole. (shrink)

The basic theme of Popper's philosophy--that something can come from nothing--is related to the present situation in physical theory. Popper carries his investigation right to the center of current debate in quantum physics. He proposes an interpretation of physics--and indeed an entire cosmology--which is realist, conjectural, deductivist and objectivist, anti-positivist, and anti-instrumentalist. He stresses understanding, reminding us that our ignorance grows faster than our conjectural knowledge.

The 1927 Solvay conference was perhaps the most important meeting in the history of quantum theory. Contrary to popular belief, the interpretation of quantum theory was not settled at this conference, and no consensus was reached. Instead, a range of sharply conflicting views were presented and extensively discussed, including de Broglie's pilot-wave theory, Born and Heisenberg's quantum mechanics, and Schrödinger's wave mechanics. Today, there is no longer an established or dominant interpretation of quantum (...) theory, so it is important to re-evaluate the historical sources and keep the interpretation debate open. This book contains a complete translation of the original proceedings, with background essays on the three main interpretations of quantum theory presented at the conference, and an extensive analysis of the lectures and discussions in the light of current research in the foundations of quantum theory. The proceedings contain much unexpected material, including extensive discussions of de Broglie's pilot-wave theory (which de Broglie presented for a many-body system), and a theory of 'quantum mechanics' apparently lacking in wave function collapse or fundamental time evolution. This book will be of interest to graduate students and researchers in physics and in the history and philosophy of quantum theory. (shrink)

Philosophers of quantum mechanics have generally addressed exceedingly simple systems. Laura Ruetsche offers a much-needed study of the interpretation of more complicated systems, and an underexplored family of physical theories, such as quantum field theory and quantum statistical mechanics, showing why they repay philosophical attention. She guides those familiar with the philosophy of ordinary QM into the philosophy of 'QM infinity', by presenting accessible introductions to relevant technical notions and the foundational questions they frame--and then develops (...) and defends answers to some of those questions. Finally, Ruetsche highlights ties between the foundational investigation of QM infinity and philosophy more broadly construed, in particular by using the interpretive problems discussed to motivate new ways to think about the nature of physical possibility and the problem of scientific realism. (shrink)

We show that three fundamental information-theoretic constraints -- the impossibility of superluminal information transfer between two physical systems by performing measurements on one of them, the impossibility of broadcasting the information contained in an unknown physical state, and the impossibility of unconditionally secure bit commitment -- suffice to entail that the observables and state space of a physical theory are quantum-mechanical. We demonstrate the converse derivation in part, and consider the implications of alternative answers to a remaining open (...) question about nonlocality and bit commitment. (shrink)

This book is a critical introduction to the long-standing debate concerning the conceptual foundations of quantum mechanics and the problems it has posed for physicists and philosophers from Einstein to the present. Quantum theory has been a major infulence on postmodernism, and presents significant problems for realists. Keeping his own realist position in check, Christopher Norris subjects a wide range of key opponents and supporters of realism to a high and equal level of scrutiny. With a characteristic (...) combination of rigour and intellectual generosity, he draws out the merits and weaknesses from opposing arguments. In a sequence of closely argued chapters, Norris examines the premises of orthodox quantum theory, as developed most influentially by Bohr and Heisenberg, and its impact on varous philosophical developments. These include the ideas developed by W.V Quine, Thomas Kuhn, Michael Dummett, Bas van Fraassen, and Hilary Puttnam. In each case, Norris argues, these thinkers have been influenced by the orthodox construal of quantum mechanics as requiring drastic revision of principles which had hitherto defined the very nature of scientific method, causal explanati and rational enquiry. Putting the case for a realist approach which adheres to well-tried scientific principles of causal reasoning and inference to the best explanation, Christopher Norris clarifies these debates to a non-specialist readership and scholars of philosophy, science studies and the philosophy of science alike. Quantum Theory and the Flight From Realism suggests that philosophical reflection can contribute to a better understanding of these crucial, current issues. (shrink)

`Quantum theory' is not a single physical theory but a framework in which many different concrete theories fit. As such, a solution to the quantum measurement problem ought to provide a recipe to interpret each such concrete theory, in a mutually consistent way. But with the exception of the Everett interpretation, the mainextant solutions either try to make sense of the abstract framework as if it were concrete, or else interpret one particular quantum (...) class='Hi'>theory under the fiction that it is fundamental and exact. In either case, these approaches are unable to help themselves to the very theory-laden, level-relative ways in which quantum theory makes contact with experiment in mainstream physics, and so are committed to major revisionary projects which have not been carried out even in outline. As such, only the Everett interpretation is currently suited to make sense of quantum physics as we find it. (shrink)

I offer an account of how the quantum theory we have helps us explain so much. The account depends on a pragmatist interpretation of the theory: this takes a quantum state to serve as a source of sound advice to physically situated agents on the content and appropriate degree of belief about matters concerning which they are currently inevitably ignorant. The general account of how to use quantum states and probabilities to explain otherwise puzzling regularities (...) is then illustrated by showing how we can explain single-particle interference phenomena, the stability of matter, and interference of Bose–Einstein condensates. Finally, I note some open problems and relate this account to alternative approaches to explanation that emphasize the importance of causation, of unification, and of structure. 1 Introduction2 Two Requirements on Explanations in Physics3 What We Can use Quantum Theory to Explain4 The Function of Quantum States and Born Probabilities5 How These Functions Contribute to the Explanatory Task6 Example One: Single-Particle Interference7 Example Two: Explanation of the Stability of Matter8 Example Three: Bose Condensation9 Conclusion. (shrink)

A sophisticated and original introduction to the philosophy of quantum mechanics from one of the world’s leading philosophers of physics In this book, Tim Maudlin, one of the world’s leading philosophers of physics, offers a sophisticated, original introduction to the philosophy of quantum mechanics. The briefest, clearest, and most refined account of his influential approach to the subject, the book will be invaluable to all students of philosophy and physics. Quantum mechanics holds a unique place in the (...) history of physics. It has produced the most accurate predictions of any scientific theory, but, more astonishing, there has never been any agreement about what the theory implies about physical reality. Maudlin argues that the very term “quantum theory” is a misnomer. A proper physical theory should clearly describe what is there and what it does—yet standard textbooks present quantum mechanics as a predictive recipe in search of a physical theory. In contrast, Maudlin explores three proper theories that recover the quantum predictions: the indeterministic wavefunction collapse theory of Ghirardi, Rimini, and Weber; the deterministic particle theory of deBroglie and Bohm; and the conceptually challenging Many Worlds theory of Everett. Each offers a radically different proposal for the nature of physical reality, but Maudlin shows that none of them are what they are generally taken to be. (shrink)

Is it possible to approach quantum theory in a 'therapeutic' vein that sees its foundational problems as arising from mistaken conceptual presuppositions? The book explores the prospects for this project and, in doing so, discusses such fascinating issues as the nature of quantum states, explanation in quantum theory, and 'quantum non-locality'.

Quantum cognition research applies abstract, mathematical principles of quantum theory to inquiries in cognitive science. It differs fundamentally from alternative speculations about quantum brain processes. This topic presents new developments within this research program. In the introduction to this topic, we try to answer three questions: Why apply quantum concepts to human cognition? How is quantum cognitive modeling different from traditional cognitive modeling? What cognitive processes have been modeled using a quantum account? In (...) addition, a brief introduction to quantum probability theory and a concrete example is provided to illustrate how a quantum cognitive model can be developed to explain paradoxical empirical findings in psychological literature. (shrink)

We present a discrete model theory similar in structure to ordinary quantum mechanics, but based on a finite field instead of complex amplitudes. The interpretation of this theory involves only the “modal” concepts of possibility and necessity rather than quantitative probability measures. Despite its simplicity, our model theory includes entangled states and has versions of both Bell’s theorem and the no cloning theorem.

Science is always presupposing some basic concepts that are held to be useful. These absolute presuppositions (Collingwood) are rarely debated and form the framework for what has been termed paradigm by Kuhn. Our currently accepted scientific model is predicated on a set of presuppositions that have difficulty accommodating holistic structures and relationships and are not geared towards incorporating non-local correlations. Since the theoretical models we hold also determine what we perceive and take as scientifically viable, it is important to look (...) for an alternative model that can deal with holistic relationships. One approach is to generalise algebraic quantum theory, which is an inherently holistic framework, into a generic model. Relaxing some restrictions and definitions from quantum theory proper yields an axiomatic framework that can be applied to any type of system. Most importantly, it keeps the core of the quantum theoretical formalism. It is capable of handling complementary observables, i.e. descriptors which are non-commuting, incompatible and yet collectively required to fully describe certain situations. It also predicts a generalised form of non-local correlations that in quantum theory are known as entanglement. This generalised version is not quantum entanglement but an analogue form of holistic, non-local connectedness of elements within systems, predicted to occur whenever elements within systems are described by observables which are complementary to the description of the whole system. While a considerable body of circumstantial evidence supports the plausibility of the model, we are not yet in a position to use it for clear cut predictions that could be experimentally falsified. The series of papers offered in this special issue are the beginning of what we hope will become a rich scientific debate. (shrink)

Quantum theory is a tremendously successful physical theory, but nevertheless suffers from two serious problems: the measurement problem and the problem of interpretational underdetermination. The latter, however, is largely overlooked as a genuine problem of its own. Both problems concern the doctrine of realism, but pull, quite curiously, into opposite directions. The measurement problem can be captured such that due to scientific realism about quantum theory common sense anti-realism follows, while theory underdetermination usually counts (...) as an argument against scientific realism. I will also consider the more refined distinctions of ontic and epistemic realism and demonstrate that quantum theory in its most viable interpretations conflicts with at least one of the various realism claims. A way out of the conundrum is to come to the bold conclusion that quantum theory is, possibly, wrong (in the realist sense). (shrink)

This conference was devoted to the 80 years of the Copenhagen Interpretation, and to the question of the relevance of the Copenhagen interpretation for the present understanding of quantum mechanics. It is in this framework that fundamental questions raised by quantum mechanics, especially in information theory, were discussed throughout the conference. As has become customary in our series of conference in Växjö, we were glad to welcome a fruitful assembly of theoretical physicists, experimentalists, mathematicians and even philosophers (...) interested in the foundations of probability and physics. The nature of quantum fluctuations---in the form of Stochastic Electrodynamics or in other approaches to stochastic quantum mechanics---was also a central topic discussed during the conference, especially during debates. We should also mention talks on the completeness or incompleteness of quantum mechanics; on macroscopic quantum systems; on Bell's inequality, entanglement and experiments on quantum nonlocality (and locality); on Bohmian mechanics; on the connection between quantum mechanics and general relativity; on quantum probability; on quantum computing, quantum teleportation and quantum cryptography technologies; and more generally on the mathematical formalism of quantum mechanics and on the philosophical problems raised by its interpretations. (shrink)

This Växjö conference was devoted to the reconsideration of quantum foundations. Due to increasing research in quantum information theory, especially on quantum computing and cryptography, many questions regarding the foundations of quantum mechanics, which have long been considered to be exclusively of philosophical interest, nowadays play an important role in theoretical and experimental quantum physics.

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)

In the present work, quantum theory is founded on the framework of consciousness, in contrast to earlier suggestions that consciousness might be understood starting from quantum theory. The notion of streams of consciousness, usually restricted to conscious beings, is extended to the notion of a Universal/Global stream of conscious flow of ordered events. The streams of conscious events which we experience constitute sub-streams of the Universal stream. Our postulated ontological character of consciousness also consists of an (...) operator which acts on a state of potential consciousness to create or modify the likelihoods for later events to occur and become part of the Universal conscious flow. A generalized process of measurement-perception is introduced, where the operation of consciousness brings into existence, from a state of potentiality, the event in consciousness. This is mathematically represented by (a) an operator acting on the state of potential consciousness before an actual event arises in consciousness and (b) the reflecting of the result of this operation back onto the state of potential consciousness for comparison in order for the event to arise in consciousness. Beginning from our postulated ontology that consciousness is primary and from the most elementary conscious contents, such as perception of periodic change and motion, quantum theory follows naturally as the description of the conscious experience. (shrink)

What would it mean to apply quantum theory, without restriction and without involving any notion of measurement and state reduction, to the whole universe? What would realism about the quantum state then imply? This book brings together an illustrious team of philosophers and physicists to debate these questions. The contributors broadly agree on the need, or aspiration, for a realist theory that unites micro- and macro-worlds. But they disagree on what this implies. Some argue that if (...) unitary quantum evolution has unrestricted application, and if the quantum state is taken to be something physically real, then this universe emerges from the quantum state as one of countless others, constantly branching in time, all of which are real. The result, they argue, is many worlds quantum theory, also known as the Everett interpretation of quantum mechanics. No other realist interpretation of unitary quantum theory has ever been found. Others argue in reply that this picture of many worlds is in no sense inherent to quantum theory, or fails to make physical sense, or is scientifically inadequate. The stuff of these worlds, what they are made of, is never adequately explained, nor are the worlds precisely defined; ordinary ideas about time and identity over time are compromised; no satisfactory role or substitute for probability can be found in many worlds theories; they can't explain experimental data; anyway, there are attractive realist alternatives to many worlds. Twenty original essays, accompanied by commentaries and discussions, examine these claims and counterclaims in depth. They consider questions of ontology - the existence of worlds; probability - whether and how probability can be related to the branching structure of the quantum state; alternatives to many worlds - whether there are one-world realist interpretations of quantum theory that leave quantum dynamics unchanged; and open questions even given many worlds, including the multiverse concept as it has arisen elsewhere in modern cosmology. A comprehensive introduction lays out the main arguments of the book, which provides a state-of-the-art guide to many worlds quantum theory and its problems. (shrink)

In this paper we review the general framework of operational probabilistic theories, along with the six axioms from which quantum theory can be derived. We argue that the OPT framework along with a relaxed version of five of the axioms, define a general information theory. We close the paper with considerations about the role of the observer in an OPT, and the interpretation of the von Neumann postulate and the Schrödinger-cat paradox.

Historically, appearance of the quantum theory led to a prevailing view that Nature is indeterministic. The arguments for the indeterminism and proposals for indeterministic and deterministic approaches are reviewed. These include collapse theories, Bohmian Mechanics and the many-worlds interpretation. It is argued that ontic interpretations of the quantum wave function provide simpler and clearer physical explanation and that the many-worlds interpretation is the most attractive since it provides a deterministic and local theory for our physical Universe (...) explaining the illusion of randomness and nonlocality in the world we experience. (shrink)

The measurement problem of quantum theory is discussed, and the difficulty of trying to solve it within the confines of a local, Lorentz-invariant physics is emphasised. This leads to the obvious suggestion to seek a solution beyond physics, in particular, by introducing the concept of consciousness. The resulting dualistic model, in the natural form suggested by quantum theory, is shown to differ in several respects from the classical model of Descartes, and to suggest solutions to some (...) of the long-standing problems concerning the relation of consciousness to the physical world. (shrink)

A human brain operates as a pattern of switching. An abstract definition of a quantum mechanical switch is given which allows for the continual random fluctuations in the warm wet environment of the brain. Among several switch-like entities in the brain, we choose to focus on the sodium channel proteins. After explaining what these are, we analyse the ways in which our definition of a quantum switch can be satisfied by portions of such proteins. We calculate the perturbing (...) effects of normal variations in temperature and electric field on the quantum state of such a portion. These are shown to be acceptable within the fluctuations allowed for by our definition. Information processing and unpredictability in the brain are discussed. The ultimate goal underlying the paper is an analysis of quantum measurement theory based on an abstract definition of the physical manifestations of consciousness. The paper is written for physicists with no prior knowledge of neurophysiology, but enough introductory material has also been included to allow neurophysiologists with no prior knowledge of quantum mechanics to follow the central arguments. (shrink)

Three recent arguments seek to show that the universal applicability of unitary quantum theory is inconsistent with the assumption that a well-conducted measurement always has a definite physical outcome. In this paper I restate and analyze these arguments. The import of the first two is diminished by their dependence on assumptions about the outcomes of counterfactual measurements. But the third argument establishes its intended conclusion. Even if every well-conducted quantum measurement we ever make will have a definite (...) physical outcome, this argument should make us reconsider the objectivity of that outcome. (shrink)

There is a consistent and simple interpretation of the quantum theory of isolated systems. The interpretation suffers no measurement problem and provides a quantum explanation of state reduction, which is usually postulated. Quantum entanglement plays an essential role in the construction of the interpretation.

In his recent book Bananaworld. Quantum mechanics for primates, Jeff Bub revives and provides a mature version of his influential information-theoretic interpretation of Quantum Theory (QT). In this paper, I test Bub’s conjecture that QT should be interpreted as a theory about information, by examining whether his information-theoretic interpretation has the resources to explain (or explain away) quantum conundrums. The discussion of Bub’s theses will also serve to investigate, more in general, whether other approaches succeed (...) in defending the claim that QT is about quantum information. First of all, I argue that Bub’s interpretation of QT as a principle theory fails to fully explain quantum non-locality. Secondly, I argue that a constructive interpretation, where the quantum state is interpreted ontically as information, also fails at providing a full explanation of quantum correlations. Finally, while epistemic interpretations might succeed in this respect, I argue that such a success comes at the price of rejecting some in between the most basic scientific standards of physical theories. (shrink)

Orthodox Copenhagen quantum theory renounces the quest to understand the reality in which we are imbedded, and settles for practical rules describing connections between our observations. Many physicist have regarded this renunciation of our effort describe nature herself as premature, and John von Neumann reformulated quantum theory as a theory of an evolving objective universe interacting with human consciousness. This interaction is associated both in Copenhagen quantum theory and in von Neumann quantum (...) theory with a sudden change that brings the objective physical state of a system in line with a subjectively felt psychical reality. The objective physical state is thereby converted from a material substrate to an informational and dispositional substrate that carries both the information incorporated into it by the psychical realities, and certain dispositions for the occurrence of future psychical realities. The present work examines and proposes solutions to two problems that have appeared to block the development of this conception of nature. The first problem is how to reconcile this theory with the principles of relativistic quantum field theory; the second problem is to understand whether, strictly within quantum theory, a person's mind can affect the activities of his brain, and if so how. Solving the first problem involves resolving a certain non-locality question. The proposed solution to the second problem is based on a postulated connection between effort, attention, and the quantum Zeno effect. This solution explains on the basic of quantum physics a large amount of heretofore unexplained data amassed by psychologists. (shrink)

This book provides the first unified overview of the burgeoning research area at the interface between Quantum Foundations and Quantum Information. Topics include: operational alternatives to quantum theory, information-theoretic reconstructions of the quantum formalism, mathematical frameworks for operational theories, and device-independent features of the set of quantum correlations. Powered by the injection of fresh ideas from the field of Quantum Information and Computation, the foundations of Quantum Mechanics are in the midst of (...) a renaissance. The last two decades have seen an explosion of new results and research directions, attracting broad interest in the scientific community. The variety and number of different approaches, however, makes it challenging for a newcomer to obtain a big picture of the field and of its high-level goals. Here, fourteen original contributions from leading experts in the field cover some of the most promising research directions that have emerged in the new wave of quantum foundations. The book is directed at researchers in physics, computer science, and mathematics and would be appropriate as the basis of a graduate course in Quantum Foundations. (shrink)

The concepts of complementarity and entanglement are considered with respect to their significance in and beyond physics. A formally generalized, weak version of quantum theory, more general than ordinary quantum theory of physical systems, is outlined and tentatively applied to two examples.

This paper provides a brief introduction to quantum theory and the proceeds to discuss the different ways in which the relationship between quantum theory and mind/consciousness is seen in some of the main alternative interpretations of quantum theory namely by Bohr; von Neumann; Penrose: Everett; and Bohm and Hiley. It briefly considers how qualia might be explained in a quantum framework, and makes a connection to research on quantum biology, quantum cognition (...) and quantum computation. The paper notes that it is widely agreed that conscious experience has dynamical and holistic features. It asks whether these features might in some way be a reflection of the dynamic and holistic quantum physical processes associated with the brain that may underlie (and make possible) the more mechanistic neurophysiological processes that contemporary cognitive neuroscience is measuring. If so, these macroscopic processes would be a kind of shadow, or amplification of the results of quantum processes at a deeper (pre-spatial or "implicate") level where our minds and conscious experience essentially live and unfold. The macroscopic, mechanistic level is of course necessary for communication, cognition and life as we know it, including science; but perhaps the experiencing (consciousness) of that world and the initiation of our actions takes place at a more subtle, non-mechanical level of the physical world, which quantum theory has begun to discover. At the very least a quantum perspective will help a “classical” consciousness theorist to become better aware of some of the hidden assumptions in his or her approach. Given that consciousness is widely thought to be a “hard” problem, its solution may well require us to question and revise some of our assumptions that now seem to us completely obvious. This is what quantum theory is all about – learning, on the basis of scientific experiments, to question the “obvious” truths about the nature of the physical world and to come up with more coherent alternatives. (shrink)

Quantum theory is one of science's most thrilling, challenging and even mysterious areas. Scientists such as Planck, Einstein, Bohr, Heisenberg and Schrödinger uncovered bizarre paradoxes in the early 20th century that seemed to destroy the fundamental assumptions of 'classical physics' - the basic laws we are taught in school. Notoriously difficult, quantum theory is nonetheless an amazing and inspiring intellectual adventure, explained here with patience, wit and clarity.

Empirical adequacy, formal explanation and understanding are distinct goals of science. While no a priori criterion for understanding should be laid down, there may be inherent limitations on the way we are able to understand explanations of physical phenomena. I examine several recent contributions to the exercise of fashioning an explanatory discourse to mold the formal explanation provided by quantum mechanics to our modes of understanding. The question is whether we are capable of truly understanding (or comprehending) quantum (...) phenomena, as opposed to simply accepting the formalism and certain irreducible quantum correlations. The central issue is that of understanding versus merely redefining terms to paper over our ignorance. (shrink)

In a recent paper [e-print quant-ph/0101012], Hardy has given a derivation of “quantum theory from five reasonable axioms.” Here we show that Hardy's first axiom, which identifies probability with limiting frequency in an ensemble, is not necessary for his derivation. By reformulating Hardy's assumptions, and modifying a part of his proof, in terms of Bayesian probabilities, we show that his work can be easily reconciled with a Bayesian interpretation of quantum probability.

In this paper I defend the claim that quantum theory, Specifically quantum field theory (qft), Is incompatible with leibniz's principle of the identity of indiscernibles. This is in response to r. Barnette's criticism ("philosophy of science" 45:466-470) of an argument given by alberto cortes ("philosophy of science" 43:491-505) intended to establish this claim. I show that, Using the qft point of view, Cortes' argument can be restated in a way that leaves it immune to barnette's criticism.

The relation between quantum measurement and thermodynamically irreversible processes is investigated. The reduction of the state vector is fundamentally asymmetric in time and shows an observer-relatedness which may explain the double interpretation of the state vector as a representation of physical states as well as ofinformation about physical states. The concept of relevance being used in all statistical theories of irreversible thermodynamics is demonstrated to be based on the same observer-relatedness. Quantum theories of irreversible processes implicitly use an (...) objectivized process of state vector reduction. The conditions for the reduction are discussed, and it is concluded that the final (subjective) observer system may be carried by a space point. (shrink)

In this contribution I will retrace the main stages of my research on the objectification problem in quantum mechanics by highlighting some personal memories of my supervisor, the theoretical physicist Giovanni Morchio. The central aim of my MSc thesis was to ask whether the hypothesis of objectification, which is currently added to the formalism, is not, at least in one case, deducible from it and in particular from the dynamics of the temporal evolution. The case study we were looking (...) for had to: 1) represent a situation similar to that in which a macroscopic system such as a measurement apparatus, following interaction with a system, assumes a well-defined state (which or for example represents the fact that the result of a measurement is a particular value), i.e becomes objective 2) represent a fact in nature in which it is not clear whether its explanation can be derived from the formalism of quantum mechanics or whether a hypothesis of objectification is necessary for its explanation. Proving that such a fact can be deduced from the time evolution of quantum mechanics allowed us to conclude that there are cases in which the hypothesis of objectification is superfluous or, in other words, obtainable from the formalism. (shrink)

From the beginning, the implications of quantum theory for our most general understanding of the world have been a matter of intense debate. Einstein argues that the theory had to be regarded as fundamentally incomplete. Its inability, for example, to predict the exact time of decay of a single radioactive atom had to be due to a failure of the theory and not due to a permanent inability on our part or a fundamental indeterminism in nature (...) itself. In 1964, John Bell derived a theorem which showed that any deterministic theory which preserved locality would have certain consequences for measurements performed at a distance from one another. An experimental check seems to show that these consequences are not, in fact, realized. The correlation between the sets of events is much stronger than any local deterministic theory could allow. What is more, this stronger correlation is precisely that which is predicted by quantum theory. The astonishing result is that local deterministic theories of the classical sort seem to be permanently excluded. Not only can the individual decay not be predicted, but no future theory can ever predict it. The contributors in this volume wrestle with this conclusion. Some welcome it; others leave open a return to at lease some kind of deterministic world, one which must however allow something like action-at-a distance. How much lit it? And how can one avoid violating relativity theory, which excludes action-at-a-distance? How can a clash between the two fundamental theories of modern physics, relativity and quantum theory, be avoided? What are the consequences for the traditional philosophic issue of causality explanation and objectivity? One thing is certain; we can never return to the comfortable Newtonian world where everything that happened was, in principle, predictable and where what happened at one measurement site could not affect another set of measurements being performed light-years away, at a distance that a light-signal could not bridge. Contributors: James T. Cushing, Abner Shimony, N. David Mermin, Jon P. Jarrett, Linda Wessels, Bas C. van Fraassen, Jeremy Butterfield, Michael L. G. Redhead, Henry P. Stapp, Arthur Fine, R. I. G. Hughes, Paul Teller, Don Howard, Henry J. Folse, and Ernan McMullin. (shrink)

This book explains, in simple but accurate terms, how orthodox quantum mechanics works. The author, a distinguished theoretical physicist, shows how this theory, realistically interpreted, assigns an important role to our conscious free choices. Stapp claims that mainstream biology and neuroscience, despite nearly a century of quantum physics, still stick essentially to failed classical precepts in which mental intentions have no effect upon our bodily actions. He shows how quantum mechanics provides a rational basis for a (...) better understanding of this connection, even allowing an explanation of certain phenomena currently held to be "paranormal". These ideas have major implications for our understanding of ourselves and our mental processes, and thus also for the meaningfulness of our lives. (shrink)

The mathematical formalism of quantum theory has been known for almost a century, but its physical foundation has remained elusive. In recent decades, many physicists have noted connections between quantum theory and information theory. In this study, we present a physical account of the derivation of quantum theory's mathematical formalism based on information considerations in physical systems. We postulate that quantum systems are physical systems with only one independent adjustable variable. Using this (...) physical postulate along with the conservation of the total probability, we derive the standard Hilbert space formalism of quantum theory, including the Born probability rule. Our complete derivation of quantum theory provides a clear and concise physical foundation for the mathematical formalism of quantum mechanics. (shrink)

I offer an account of how the quantum theory we have helps us explain the enormous variety of phenomena it is generally taken to explain. The account depends on what I have elsewhere called a pragmatist interpretation of the theory. This rejects views according to which a quantum state describes or represents a physical system, holding instead that it functions as a source of sound advice to physically situated agents like us on the content and appropriate (...) degree of belief about matters concerning which they are currently inevitably ignorant. So while the account given here is incompatible with some views of structural explanation in quantum theory it is nevertheless able to incorporate what I take to be their valuable insights. (shrink)