Schrodingers rabbits the many worlds of quantum

Colin Bruce Joseph Henry Press Washington, DC Joseph Henry Press • 500 Fifth Street, N.W • Washington, D.C 20001 The Joseph Henry Press, an imprint of the National Academies Press, was created with the goal of making books on science, technology, and health more widely available to professionals and the public Joseph Henry was one of the founders of the National Academy of Sciences and a leader in early American science Library of Congress Cataloging-in-Publication Data Bruce, Colin Schrödinger’s rabbits : the many worlds of quantum / Colin Bruce p cm ISBN 0-309-09051-2 (case) Quantum theory—Popular works I Title QC174.12.B78 2004 530.12—dc22 2004021021 Any opinions, findings, conclusions, or recommendations expressed in this volume are those of the author and not necessarily reflect the views of the National Academy of Sciences or its affiliated institutions Cover design by Michele de la Menardiere Copyright 2004 by Colin Bruce All rights reserved Hand-drawn illustrations by Laura Dawes from sketches by Colin Bruce Printed in the United States of America Dedicated to Paul Dirac physicist extraordinary who believed we must seek visualizable processes and Jim Cushing philosopher of science who believed we must find local stories PREFACE D oes the weirdness of quantum indicate that there is a deep problem with the theory? Some of the greatest minds in physics, including Einstein, have felt that it does Others prefer to believe that any conceptual difficulties can be ignored or finessed away I would put the choice differently The flip side of a problem is an opportunity, and the problems with the old interpretations of quantum present us with valuable opportunities First, there is the hope of finding ways to think more clearly about the subject I have several times seen highly respected scientists— physicists whose ability to work with the math of quantum mechanics is certainly better than my own—make appalling freshman howlers in describing what the result of an experiment would be, because their qualitative thinking about such matters as quantum collapse was as fuzzy as everyone else’s Better conceptual tools are badly needed— and now they are becoming available Second, there is the possibility that a clearer view of quantum will cause us to see the universe in a fundamentally different way, with implications both practical and philosophical Then, as has happened so many times in physics, the resolution of a seemingly arcane problem will open our eyes to great new wonders To ignore such an opportunity would be sheer cowardice The past few years have seen a sudden explosion of light in the vii viii / Preface murkier corners of quantum The old stories, involving such quaint characters as dead-alive cats and conscious observers with the power to “collapse” the whole universe, or even split it in two, are passé There are new stories to choose from, one of them particularly promising It restores us to a classical universe where things behave predictably rather than randomly and where interactions between things are local rather than long range But it comes at a price We must accept that the universe we inhabit is much vaster than we thought, in an unexpected way Although the many-worlds view was invented in the United States, it is in Europe, and especially in Oxford, that it has developed to maturity That is my good luck, for I have had the privilege of seeing the process at first hand Here I describe the remarkable new picture that has recently emerged, which I dub the Oxford Interpretation My warmest thanks go to my editor Jeff Robbins at Joseph Henry Press for his vision and determination in ensuring that this book came to be Also to many physicists and philosophers at Oxford and elsewhere for valuable advice and discussion, including in particular Harvey Brown, David Deutsch, Roger Penrose, Simon Saunders, David Wallace and Anton Zeilinger Special thanks to Lev Vaidman, Jacob Foster, and Heather Bradshaw, who read the manuscript at an advanced stage and made many useful comments Responsibility for any mistakes that remain, and any controversial opinions expressed herein, is of course entirely my own Colin Bruce Oxford, 2004 CONTENTS 10 11 12 13 14 15 16 A Magical Universe Clinging to the Classical Collapse by Inference A Horror Story Writ Large The Old Testament Let’s All Move into Hilbert Space Pick Your Own Universe A Desirable Locality Introducing Many-Worlds Harnessing Many-Worlds 1: Impossible Measurements Harnessing Many-Worlds 2: Impossible Computers Many-Worlds Heroes and Dragons The Terror of Many-Worlds The Classical Warrior: Roger Penrose The New Age Warrior: Anton Zeilinger Proving and Improving Many-Worlds 13 27 40 57 74 92 106 126 140 155 169 185 198 211 228 Appendix 251 Notes 253 Index 261 ix ... Harnessing Many- Worlds 1: Impossible Measurements Harnessing Many- Worlds 2: Impossible Computers Many- Worlds Heroes and Dragons The Terror of Many- Worlds The Classical Warrior: Roger Penrose The New... the choice differently The flip side of a problem is an opportunity, and the problems with the old interpretations of quantum present us with valuable opportunities First, there is the hope of. .. one of the founders of the National Academy of Sciences and a leader in early American science Library of Congress Cataloging-in-Publication Data Bruce, Colin Schrödinger’s rabbits : the many worlds