Giải thích Lý thuyết Lượng tử: Một Tiếp cận Trị liệu của Simon Friederich

New Directions in the Philosophy of Science Series Editor: Steven French, Professor of Philosophy of Science, University of Leeds, UK The philosophy of science is going through exciting times. New and productive rela- tionships are being sought with the history of science. Illuminating and innovative comparisons are being developed between the philosophy of science and the philoso- phy of art. The role of mathematics in science is being opened up to renewed scrutiny in the light of original case studies.

The philosophies of particular sciences are both drawing on and feeding into new work in metaphysics, and the relationships between science, metaphysics, and the philosophy of science in general are being re-examined and reconfigured. The intention behind this new series from Palgrave Macmillan is to offer a new, dedi- cated publishing forum for the kind of exciting new work in the philosophy of science that embraces novel directions and fresh perspectives. To this end, our aim is to publish books that address issues in the philosophy of science in the light of these new developments, including those that attempt to initiate a dialogue between various perspectives, offer constructive and insightful critiques, or bring new areas of science under philosophical scrutiny. Titles include: THE APPLICABILITY OF MATHEMATICS IN SCIENCE Indispensability and Ontology Sorin Bangu THE PHILOSOPHY OF EPIDEMIOLOGY Alex Broadbent PHILOSOPHY OF STEM CELL BIOLOGY Knowledge in Flesh and Blood Melinda Fagan INTERPRETING QUANTUM THEORY A Therapeutic Approach Simon Friederich SCIENTIFIC ENQUIRY AND NATURAL KINDS From Planets to Mallards P.

Magnus COMBINING SCIENCE AND METAPHYSICS Contemporary Physics, Conceptual Revision and Common Sense Matteo Morganti COUNTERFACTUALS AND SCIENTIFIC REALISM Michael J. Shaffer ARE SPECIES REAL? An Essay on the Metaphysics of Species Matthew Slater www.com MODELS AS MAKE-BELIEVE Imagination, Fiction and Scientific Representation Adam Toon Forthcoming titles include: SCIENTIFIC MODELS AND REPRESENTATION Gabriele Contessa New Directions of the Philosophy of Science Series Standing Order ISBN 978–0–230–20210–8 (hardcover) (outside North America only) You can receive future titles in this series as they are published by placing a standing order. Please contact your bookseller or, in case of difficulty, write to us at the address below with your name and address, the title of the series and the ISBN quoted above. Customer Services Department, Macmillan Distribution Ltd, Houndmills, Basingstoke, Hampshire RG21 6XS, England www.com Interpreting Quantum Theory A Therapeutic Approach Simon Friederich www.com © Simon Friederich 2015 All rights reserved.

No reproduction, copy or transmission of this publication may be made without written permission. No portion of this publication may be reproduced, copied or transmitted save with written permission or in accordance with the provisions of the Copyright, Designs and Patents Act 1988, or under the terms of any licence permitting limited copying issued by the Copyright Licensing Agency, Saffron House, 6–10 Kirby Street, London EC1N 8TS. Any person who does any unauthorised act in relation to this publication may be liable to criminal prosecution and civil claims for damages. The author has asserted his right to be identified as the author of this work in accordance with the Copyright, Designs and Patents Act 1988.

First published 2015 by PALGRAVE MACMILLAN Palgrave Macmillan in the UK is an imprint of Macmillan Publishers Limited, registered in England, company number 785998, of Houndmills, Basingstoke, Hampshire RG21 6XS. Palgrave Macmillan in the US is a division of St Martin’s Press LLC, 175 Fifth Avenue, New York, NY 10010. Palgrave Macmillan is the global academic imprint of the above companies and has companies and representatives throughout the world. Palgrave® and Macmillan® are registered trademarks in the United States, the United Kingdom, Europe and other countries.

ISBN: 978–1–137–44714–2 This book is printed on paper suitable for recycling and made from fully managed and sustained forest sources. Logging, pulping and manufacturing processes are expected to conform to the environmental regulations of the country of origin. A catalogue record for this book is available from the British Library. A catalog record for this book is available from the Library of Congress.com To Sibylla, Alma, and Lydia www.com Contents Series Editor’s Foreword x Preface xii Part I Introduction and Background 1 Introduction 3 1.2 The idea of a therapeutic approach 6 1.3 Outline of this work 8 2 Sketch of the Formalism 13 2.1 The Hilbert space formalism 13 2.2 Measurement and collapse 18 2.3 Many-component systems and entanglement 21 3 Interpretations as Solutions to the Measurement Problem 26 3.1 Exposition of the problem 26 3.1 Pilot wave theory 31 3.2 Alternatives: modal interpretations 37 3.3 Schrödinger time-evolution not universal? 38 3.1 From Wigner to Penrose 39 3.2 The GRW model 40 3.4 No determinate outcomes 41 3.2 How do probabilities fit into the picture? 44 Part II The Rule Perspective 4 Motivating a Therapeutic Approach 49 4.1 Absence of the foundational problems in practice 49 4.2 Philosophy as therapy 50 4.3 Quantum states as non-descriptive 53 4.1 Dissolving the measurement problem 54 vii www.com viii Contents 4.2 Collapse as update 55 4.3 Types of epistemic accounts 56 4.4 Space-time structure and collapse 58 5 In Search of a Viable Epistemic Account 61 5.1 Knowledge of probabilities versus probabilities as degrees of belief 61 5.1 Probabilities as subjective 62 5.2 Values of observables as subjective? 64 5.3 Objectivity of observables measured in an epistemic account of states 68 5.4 Constitutive rules 71 6 Quantum Probabilities: What Are They? 75 6.1 Probabilities of what? 75 6.2 Probabilities of what kind? 79 6.3 Objective probabilities as constraints on rational credences 84 6.3 Objections to this interpretation of probabilities 85 6.1 The means/ends objection 85 6.2 The quantum Bayesian Moore’s paradox 87 Part III Objections 7 Copenhagen Reloaded? 95 7.1 Bohr and ‘classical language’ 96 7.2 Heisenberg and the epistemic conception of quantum states 99 7.1 Heisenberg on pure versus mixed states 99 7.2 Heisenberg on quantum probabilities as ‘objective tendencies’ 102 8 The Charge of Anthropocentrism 105 8.2 Anthropocentric notions and value determinateness 108 9 Reduction and Explanation 113 9.1 The micro/macro divide 113 9.2 Explanation without ontic quantum states 115 www.com Contents ix Part IV Non-locality, Quantum Field Theory, and Reality 10 Non-locality Reconsidered 125 10.1 Quantum theory and special relativity – again 125 10.2 Formulating local causality 127 10.1 Causation and counterfactuals 129 10.2 Local causality probabilistically 132 10.3 The Principal Principle and admissible evidence 136 10.4 Intuitive probabilistic local causality in the language of the Principal Principle 139 10.5 Quantum theory, local causality, and the Principal Principle 141 10.6 But how does nature perform the trick? 143 11 A Look at Quantum Field Theory 146 11.1 Lagrangian versus algebraic quantum field theory 146 11.2 Basics of the algebraic approach 147 11.4 The Rule Perspective and unpristine interpretations 150 11.5 The case for an unpristine interpretation 152 12 Quantum Theory and ‘Reality’ 157 12.2 Sharp values for all observables? 161 12.3 Conclusion 166 Appendices Appendix A Sketch of Bell’s Theorem 168 Appendix B The Kochen–Specker Theorem in a Nutshell 172 Appendix C The Pusey–Barrett–Rudolph (PBR) Theorem – A Short Introduction 175 Notes 178 Bibliography 187 Index 197 www.com Series Editor’s Foreword The motivation behind our series is to create a dedicated publishing forum for the kind of exciting new work in the philosophy of sci- ence that embraces novel directions and fresh perspectives.

To this end, our aim is to publish books that address issues in the philosophy of science in the light of these new developments, including those that attempt to bring new areas of science under philosophical scrutiny, ini- tiate a dialogue between competing perspectives, or explore and develop distinctive new approaches. Simon Friederich has written an exciting and provocative book that tackles the so-called measurement problem in quantum physics in a new and thought-provoking way. His overall philosophical stance is ‘thera- peutic’, in a Wittgensteinian sense, whereby foundational problems are effectively dissolved by pointing out that they arise from certain con- ceptual confusions. In this particular case, Friederich argues that the confusion surrounds the notion of ‘state’ in quantum mechanics.

Stan- dardly, this term is taken to represent an objective feature of quantum systems, thus generating the problem of how to account for what we observe at the ‘everyday’ level given the ‘entangled’ states presented by quantum mechanics. If we drop this standard understanding and regard such states as reflecting our epistemic condition, so that the distinc- tion between the quantum level and the everyday can be seen as a shift in our epistemic situation, then, Friederich insists, the problem simply dissolves. Crucial to this approach is Searle’s notion of a ‘constitutive rule’, in the sense of a rule that constitutes a particular activity (as in the case of the game of chess, for example). According to Friederich, to assign a state to a physical system in accordance with the rules of quantum mechanics is simply what it means to perform such a state assignment correctly, so that this assignment is logically dependent on those rules.

This ‘Rule Perspective’ offers an entirely novel stance on the foun- dations of quantum physics and Friederich sets it in the context of a carefully articulated review of both the relevant formalism and the most well-known interpretations of the theory, including the currently much-discussed ‘Many Worlds View’. He also contrasts it with ‘quantum Bayesianism’, which is found to be wanting insofar as it cannot account x www.com Series Editor’s Foreword xi for our knowledge of observables. A detailed account of how probabil- ities should be understood in quantum mechanics is then developed from the standpoint offered by the ‘Rule Perspective’. Friederich also carefully considers a range of possible objections to his approach.

One is that it is just the infamous Copenhagen interpretation re-heated, but he notes the differences, as well as similarities, with the views of Bohr and Heisenberg. Another has to do with accommodating the extensive empirical success of quantum theory and Friederich shows how this can also be accounted for within his epistemic view. Finally, he tackles Bell’s charge that such views amount to a form of anthro- pocentrism by articulating which uses of anthropocentric notions are legitimate in this context. The book concludes by examining the implications of this approach for three further issues: non-locality, the foundations of quantum field theory, and scientific realism.

In his final words, Friederich insists that it is not only what we learn from quantum theory about reality that is intriguing and fascinating but also how we do so. Friederich’s book represents a bold new approach to an old and much- discussed problem. It offers clearly articulated and powerful arguments for the dissolution of this problem and a re-orientation of our view of quantum physics in general. In this way it takes the field in a new and exciting direction.

It is precisely the sort of work that the editorial board and I aim to support through the New Directions series and we are sure that it will have a major impact on both philosophers of science and philosophically reflective physicists. Steven French Professor of Philosophy of Science University of Leeds www.com Preface This book develops and explores what I call a ‘therapeutic’ approach to the foundational problems of quantum theory. It considers and devel- ops the idea that quantum states do not represent any objective features of the quantum systems they are assigned to without denying that there are objective standards of correctness that govern the application of quantum theory to the world. All the essential ingredients of my work on quantum theory in the past few years are combined (and further developed) in this work.

Try- ing to formulate an account in the ‘therapeutic’ spirit just mentioned I have profited greatly from enormously helpful suggestions by many col- leagues and friends. In particular, I would like to thank Andreas Bartels, who supervised my work on a thesis that eventually turned into this book.