Physics Meets Philosophy at the Planck Scale: Contemporary Theories in Quantum Gravity - Edited by Craig Callender and Nick Huggett Frontmatter More Information

Cambridge University Press 052166280X - Physics Meets Philosophy at the Planck Scale: Contemporary Theories in Quantum Gravity - Edited by Craig Callender and Nick Huggett Frontmatter More information

Physics meets philosophy at the Planck scale The greatest challenge in fundamental physics is how quantum mechanics and general relativity can be reconciled in a theory of ‘quantum gravity’. The project suggests a profound revision of our notions of space, time, and matter, and so has become a key topic of debate and collaboration between physicists and philosophers. This timely volume collects classic and original contributions from leading experts in both ﬁelds for a provocative discussion of all the issues. This volume contains accessible introductions to the main and less well known approaches to quantum gravity. It includes exciting topics such as the fate of spacetime in various theories, the so-called ‘problem of time’ in canonical quantum gravity, black hole thermodynamics, and the relationship between the interpretation of quantum theory and quantum gravity. This book will be essential reading for anyone interested in the profound implications of trying to marry the two most important theories in physics.

Craig Callender is an Assistant Professor of Philosophy at the University of California at San Diego. Formerly a Senior Lecturer in Logic, Philosophy and Scientiﬁc Method at the London School of Economics, he has worked as Deputy Editor of the British Journal for the Philosophy of Science and as Associate Editor of Mind. His research interests include the philosophical foundations of modern physics, the problem of the direction of time, and the metaphysics of science. He has published in physics, law and philosophy journals.

Nick Huggett is an Assistant Professer of Philosophy at the University of Illinois at Chicago, who earned his Ph.D. in Philosophy from Rutgers University. He has published and lectured extensively on topics concerning the philosophical foundations of quantum mechanics, quantum ﬁeld theory, and spacetime theories. He is the author of the book Space from Zeno to Einstein: Classic Readings with a Contemporary Commentary.

© Cambridge University Press www.cambridge.org Cambridge University Press 052166280X - Physics Meets Philosophy at the Planck Scale: Contemporary Theories in Quantum Gravity - Edited by Craig Callender and Nick Huggett Frontmatter More information

Physics meets philosophy at the Planck scale Contemporary theories in quantum gravity

edited by Craig Callender

University of California at San Diego

Nick Huggett

University of Illinois at Chicago

published by the press syndicate of the university of cambridge The Pitt Building, Trumpington Street, Cambridge, United Kingdom

cambridge university press The Edinburgh Building, Cambridge CB2 2RU, UK 40 West 20th Street, NewYork, NY 10011-4211, USA 10 Stamford Road, Oakleigh, VIC 3166, Australia Ruiz de Alarcon´ 13, 28014 Madrid, Spain Dock House, The Waterfront, Cape Town 8001, South Africa

http://www.cambridge.org

This book is in copyright. Subject to statutory exception and to the provision of relevant collective licensing agreements, no reproduction of any part may take place without the written permission of Cambridge University Press.

First published 2001

Printed in the United States of America

Typeface Minion 10½/12½ pt System LaTeX2e [KW]

A catalogue record for this book is available from the British Library

Library of Congress Cataloging-in-Publication Data

ISBN 0 521 66280 X hardback ISBN 0 521 66445 4 paperback

For Joanna and Lisa

Contents

Preface ix

1 Introduction 1 Craig Callender and Nick Huggett

Part I Theories of Quantum Gravity and their Philosophical Dimensions

2 Spacetime and the philosophical challenge of quantum gravity 33 Jeremy Butterﬁeld and Christopher Isham

3 Naive quantum gravity 90 Steven Weinstein

4 Quantum spacetime: What do we know? 101 Carlo Rovelli

Part II Strings

5 Reﬂections on the fate of spacetime 125 Edward Witten

6 A philosopher looks at string theory 138 Robert Weingard

7 Black holes, dumb holes, and entropy 152 William G. Unruh

Part III Topological Quantum Field Theory

8 Higher-dimensional algebra and Planck scale physics 177 John C. Baez

vii

Contents

Part IV Quantum Gravity and the Interpretation of General Relativity

9 On general covariance and best matching 199 Julian B. Barbour

10 Pre-Socratic quantum gravity 213 Gordon Belot and John Earman

11 The origin of the spacetime metric: Bell’s ‘Lorentzian pedagogy’ and its signiﬁcance in general relativity 256 Harvey R. Brown and Oliver Pooley

Part V Quantum Gravity and the Interpretation of Quantum Mechanics

12 Quantum spacetime without observers: Ontological clarity and the conceptual foundations of quantum gravity 275 Sheldon Goldstein and Stefan Teufel

13 On gravity’s role in quantum state reduction 290 Roger Penrose

14 Why the quantum must yield to gravity 305 Joy Christian

References 339

Notes on contributors 357

Index 361

viii

Preface

Both philosophy and quantum gravity are concerned with fundamental questions regarding the nature of space, time, and matter, so it is not surprising that they have a great deal to say to each other. Yet the methods and skills that philosophers and physicists bring to bear on these problems are often very different. However, and especially in recent years, there is an increasing recognition that these two groups are indeed tackling the same issues, and moreover, that these different methods and skills may all be of use in answering these fundamental questions. Our aim in this volume is thus to introduce and explore the philosophical foundations of quantum gravity and the philosophical issues within this field. We believe that some insight will be gained into the many deep questions raised by quantum gravity by examining these issues from a variety of perspectives. Toward this end, we collected together ten original and three previously published contributions on this topic from eminent philosophers of science, mathematicians, and physicists. Though the papers assume that the reader is scientifically literate, the majority are written with the non-specialist in philosophy or quantum gravity in mind. The brief that we gave the contributors was to write pieces that would introduce the key elements of the physics and philosophy, whilst making original contributions to the debates. The book should therefore be of interest to (and appro- priate for) anyone challenged and fascinated by the deep questions facing the cutting edge of fundamental theoretical physics. We also feel that these essays will lay the foundation for a wider consideration of quantum gravity in the philosophical com- munity, and hopefully a fruitful dialogue between physicists and philosophers. After all, many of the greatest advances in physics were inseparable from philosophical reflection on foundational questions. We could not have completed this volume without a great deal of support and assistance, and we owe thanks to many people: to all our contributors for their efforts; to Carlo Rovelli and John Baez especially, for their encouragement and advice in the

Preface

early stages; to Jeeva Anandan, Jossi Berkovitz, Jeremy Butterﬁeld, Joy Christian, Carl Hoefer, Jeffrey Ketland, Tom Imbo, and Steve Savitt for help and comments on a number of issues; to Adam Black and Ellen Carlin, our editors, and Alan Hunt of Keyword Publishing Services Ltd. for their enthusiasm, help, and (most of all) patience. We are also grateful to Andrew Hanson for letting us use his wonderful 4-D projection of Calabi-Yau space on the cover. We also thank Damian Steer for his efforts with the bibliography and Jason Wellner for his help preparing the reprinted articles. Nick thanks the Centre for Philosophy of Natural and Social Sciences at the London School of Economics for support during a residence, and the Center for the Humanities and the Ofﬁce of the Vice Chancellor for Research at the University of Illinois at Chicago for a faculty fellowship and Grants-in-Aid support. Finally, we thank Robert Weingard who taught us that these ideas existed, and of course our families, Joanna and Lisa, Ewan and Lily, without whom none of this would be worthwhile.

Craig Callender Nick Huggett