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Quantum Theory Quantum Theory A Philosopher’s Overview S C ALVATOR ANNAVO Published by State University of New York Press, Albany © 2009 State University of New York All rights reserved Printed in the United States of America No part of this book may be used or reproduced in any manner whatsoever without written permission. No part of this book may be stored in a retrieval system or transmitted in any form or by any means including electronic, electrostatic, magnetic tape, mechanical, photocopying, recording, or otherwise without the prior permission in writing of the publisher. For information, contact State University of New York Press, Albany, NY www.sunypress.edu Production by Kelli W. LeRoux Marketing by Anne M. Valentine Library of Congress Cataloging-in-Publication Data Cannavo, S. (Salvator) Quantum theory : a philosopher’s overview / Salvator Cannavo. p. cm. Includes bibliographical references and index. ISBN 978-0-7914-9347-2 (hardcover : alk. paper) 1. Quantum theory—Philosophy. I. Title. QC174.13.C36 2009 530.12—dc22 2008027670 10 9 8 7 6 5 4 3 2 1 Contents Preface vii 1. The Quantum and Classical Theories: A Crucial Difference of Theory-Type 1 Quantum Theory 1 Classical Theory 2 The “Unfi nished” Quantum Theory 3 2. Quantum Puzzles: A Clash with the Traditional Realism of Natural Science 7 The Core Formalism 7 The Hypostatization of the Core Formalism 8 The Nondeterministic Part of the Quantum Formalism 9 Wave-Particle Duality in Quantum Experiments 9 Superposition 14 The Measurement Problem 15 The Projection Postulate: Wave Collapse 17 3. More Quantum Puzzles 23 Quantum Uncertainty 23 Virtual Pair Production 29 Phase Entanglement 30 Quantum-Theoretic Description and Completeness 31 Bell’s Inequality: The Unyielding Challenge to Traditional Scientifi c Realism 34 4. Interpretation 39 The Problem of Interpretation: Old and Persistent 39 Objective Realism in Physical Science 39 Hidden Variable Interpretations: Highly Problematic 42 Copenhagenism: No Less Problematic 51 vi Contents 5. Fresh Starts 57 The Many Worlds Interpretation: New and Old Problems 57 The Many Minds Interpretation: More Problems 62 Decoherence Theory: Somewhat Promising 69 GRW Theory 75 Positivism 77 Interpretation in a Fuller Sense: Ontic Interpretation 78 6. Explanatory and Algorithmic Nomologicals: Of Which Kind is Quantum Theory? 81 Nomological Types 81 Scientifi c Explanation 83 Causation and Explanation 84 Quantum Theory; Born Algorithmic 85 Settling for Prediction 87 Dirac Transformation Theory 90 Symmetry in Scientifi c Theorizing 91 Abstract Symmetrizing 95 7. A Modest Proposal 97 Interpretation: A Failed Program 97 Away from Interpretation 100 Hidden Variables Are OK 101 No End to Science 102 8. Quantumization: The Quantum Supplementation of Explanatory Theory 105 The Quantum-Theoretic Context 105 Quantum Electrodynamics 106 Quantum Field Theory 107 String Theory 109 9. Beyond Quantumization 119 A Deeper Incorporation 119 Conclusion 122 Notes 131 Bibliography 161 Index 165 Preface My interest in the foundations and philosophy of quantum theory was fi rst sparked by J. M. Jauch who taught our graduate course in quantum mechanics at Princeton University. But this was only the beginning. The seminars and teas that were occasionally held in Fine Hall and which we graduate students were privileged to attend were the ultimate in stimulation and fascination. The participants were Princeton faculty and members of the Institute for Advanced Studies. And it was an unforgettable experience to see some of the very architects of quantum theory express themselves impromptu on how to understand or “interpret” it. Most remarkably the issues that arose then are the issues of interpretation that persist to this very day. In essence, therefore, the conceptualization of this book began at that time. The actual writing, however, jumpstarted with my own lectures on quantum theory at the City University of New York. My thoughts in this area evolved further with papers in the philosophy of science that I read to the Teilhard de Chardin Conference at Brooklyn College of CCNY, to the Royal Institute of Philosophy at the University of Southern California, to the Long Island Philosophical Society, and to the Academy for the Humanities and the Sciences at the Graduate Center of the City University of New York. This last lecture was a lead paper on “The Reality Problem in Quantum Mechanics,” and it was this reading followed by the long and searching philosophical discussion that followed that helped shape the main themes in this book. Among the features that any scientifi c theory about the physical world is expected to have, two are basic, though not both required. First, the theory must make prediction possible. That is, by means of its mathematical formalism and, on the basis of the initial state of a physical system at some given time, the theory must enable one to compute the state of that system at some future time. Secondly, but not required, a theory may also be expected to provide for explanation. vii viii Preface That is, it may be expected to enable one to say, either in causal terms or in terms of some sort of unifi cation, how the change from one state to another comes about. While all physical theories must predict successfully (this goes into granting them confi rmation and eventual acceptance), not all can (nor must they) explain what they predict. In this general regard, one need hardly note that the notion of “explaining” ranges over a variety of senses, such as that of subsuming under more general principles, explicating, justifying, and more. This, however, need not delay us. Explaining, either in causal terms or in terms of some sort of unifi cation is one of these senses and the one concerning us here. In order for a physical theory to explain. it must, as an addition to its formalism, make the existential or, as we might say, “ontological” claim that there exist physical entities to which some terms of the theory make general reference. The entities must be either capable of interacting dynamically over space and time (e.g., masses, particles, forces, charges, fi elds) or they must be relatable in other essential respects. Moreover, in order that the resulting explanations do what they’re supposed to do—namely, enlighten our grasp or understanding of the “how and why” of things—the posited existential subject matter must itself be coherent and therefore intelligible. This means it must, at least in some respects, be observer independent or objective, existentially stable, uniquely locatable in physical space-time, and preferably susceptible only to proximate or local infl uences rather than to unmediated, instantaneous, and therefore, mysterious ones. To this, one might cautiously add that what an explanatory theory tells us about the physical world must, to some suffi cient extent, be intuitable. Indeed, what we are describing here is what one might more succinctly call a “reality” model, and the coordination of such a model with the formalism of a theory is what we are calling the ontology or interpretation of the theory. After one hundred years of astoundingly successful prediction, quantum theory has yet to fi nd itself such an interpretation in this sense and on which there is general agreement. Paradoxically, therefore, quantum theory—perhaps the most elegantly structured mathematical edifi ce in the history of science—predicts but does not explain what it so accurately predicts. Some might want to say at this point that the idea of framing a physical theory in such a way as to invest it with the sort of content we are describing and therefore with explanatory power is no more than the arbitrary imposition of classical notions and content on an essentially nonclassical theory. We shall argue, however, that any Preface ix such concern would be a misguided one. The power of a theory to explain is not merely a feature limited to classical physics operating in classical contexts but a feature for delivering something essential to an understanding of the physical world—something epistemically basic and quite apart from any distinction between classical and nonclassical modes of description. In fact there are, as will be discussed in the main text, quantum-type theories, for example, quantum electrodynamics, quantum fi eld theory, and string theory that—whatever their present stage of development—are explanatory in a sense that is philosophically satisfying, though requiring a degree of liberalization or “tolerance” in the underlying realism. Though falling short of suffi cient physical content for explanation, quantum theory must nevertheless be tied to observational subject matter (scintillations, clicks, photographic patterns, etc.). If it weren’t, it would be not physics but only a mathematical system for relating abstract symbols. This subject matter, however, does not, by itself, comprise a coherent physical model or interpretation. True, quantum- theoretic terms, are customarily understood to refer to a variety of entities and their attributes (particles, spin, momentum, location, energy, etc.). This “quantum subject matter,” however, immediately tests our understanding with its strangeness. We fi nd ourselves dealing with such physical oddities as entities that have no unique locations, particles that have spins but no dimensions, unsettling discontinuities and much, much more to perplex us. Indeed, the quantum formalism, which, in itself, seriously blocks physical interpretations, is framed in a space of variable dimensions whose abstract constructions cannot be simply coordinated with much more than raw observational results and the parameters of given experiments. Any attempt, for example, to assign concrete existential status to the so-called “matter waves” sometimes associated with the very heart of quantum theory seems hopeless. The dynamical features required of vibrating physical systems simply do not apply to these abstract “waves.” And all other versions of the quantum mechanical formalism are similarly unreceptive to dynamical interpretation. The diffi culties deepen as theorists try to make better sense of the reality that underlies the phenomena that the quantum formalism enables us to predict. What they come up with is a microworld that is causally unruly, situationally and existentially elusive, and clashes head-on both with our most basic intuition as well as with the objective realism that rules not only common sense but, demonstrably, the deepest philosophical attitudes of virtually all natural scientists. Indeed, quantum predictions and some of the basic theorems of the quantum