The QuanTum RevoluTion Titles in Greenwood Guides to Great Ideas in Science Brian Baigrie, Series Editor Electricity and Magnetism: A Historical Perspective Brian Baigrie Evolution: A Historical Perspective Bryson Brown The Chemical Element: A Historical Perspective Andrew Ede The Gene: A Historical Perspective Ted Everson The Cosmos: A Historical Perspective Craig G. Fraser Planetary Motions: A Historical Perspective Norriss S. Hetherington Heat and Thermodynamics: A Historical Perspective Christopher J. T. Lewis The Quantum Revolution: A Historical Perspective Kent A. Peacock Forces in Physics: A Historical Perspective Steven Shore The QuanTum RevoluTion a historical Perspective Kent A. Peacock Greenwood Guides to Great Ideas in Science Brian Baigrie, Series Editor GREENWOOD PRESS Westport, Connecticut • London Library of Congress Cataloging-in-Publication Data Peacock, Kent A., 1952– The quantum revolution : a historical perspective / Kent A. Peacock. p. cm. — (Greenwood guides to great ideas in science, ISSN 1559–5374) Includes bibliographical references and index. ISBN-13: 978–0–313–33448–1 (alk. paper). 1. Quantum theory— History—Popular works. I. Title. QC173.98.P43 2008 530.1209—dc22 2007039786 British Library Cataloguing in Publication Data is available. Copyright © 2008 by Kent A. Peacock All rights reserved. No portion of this book may be reproduced, by any process or technique, without the express written consent of the publisher. Library of Congress Catalog Card Number: 2007039786 ISBN-13: 978–0–313–33448–1 ISSN: 1559–5374 First published in 2008 Greenwood Press, 88 Post Road West, Westport, CT 06881 An imprint of Greenwood Publishing Group, Inc. www.greenwood.com Printed in the United States of America The paper used in this book complies with the Permanent Paper Standard issued by the National Information Standards Organization (Z39.48–1984). 10 9 8 7 6 5 4 3 2 1 ConTenTs List of Illustrations vii Series Foreword ix Preface xi Acknowledgments xiii Introduction: Why Learn the History of Quantum Mechanics? xv 1 The Twilight of Certainty 1 2 Einstein and Light 15 3 The Bohr Atom and Old Quantum Theory 29 4 Uncertain Synthesis 45 5 Dualities 63 6 Elements of Physical Reality 79 7 Creation and Annihilation 93 8 Quantum Mechanics Goes to Work 107 9 Symmetries and Resonances 119 10 “The Most Profound Discovery of Science” 133 11 Bits, Qubits, and the Ultimate Computer 149 12 Unfinished Business 161 Timeline 175 Glossary 185 Further Reading 195 References 211 Index 213 lisT of illusTRaTions 1.1 Max Planck. 2 1.2 Light Waves. 4 1.3 The Electromagnetic Spectrum. 5 1.4 Planck’s Law. 14 2.1 Fluctuations and Brownian Motion. 17 2.2 Spacetime According to Minkowski. 20 3.1 Spectral Lines. 30 3.2 Niels Bohr. 36 3.3 Energy Levels in the Bohr Atom. 38 4.1 Werner Heisenberg. 51 4.2 Erwin Schrödinger. 54 4.3 Typical Electron Orbitals. 56 4.4 Heisenberg’s Microscope. 60 5.1 Paul Dirac. 66 5.2 The Dirac Sea. 68 5.3 The Double Slit Experiment. 74 6.1 Niels Bohr and Albert Einstein. 80 6.2 Schrödinger’s Cat. 82 6.3 The EPR Apparatus. 89 7.1 Feynman Diagrams. 101 7.2 There Is Only One Electron in the Universe! 102 7.3 Richard P. Feynman. 103 8.1 Barrier Penetration. 108 8.2 Lise Meitner. 110 8.3 The Laser. 115 viii list of illustrations 9.1 Typical Bubble Chamber Tracks. 121 9.2 Table of “Elementary” Particles in the Standard Model. 126 10.1 David Bohm. 134 10.2 John S. Bell. 138 10.3 The Aspect Experiment. 140 10.4 Bob Phones Alice on the Bell Telephone. 144 11.1 Classical Turing Machine. 150 11.2 Quantum Turing Machine. 151 11.3 Quantum Teleportation. 158 12.1 The Hawking Effect. 169 12.2 The Unruh Effect. 169 12.3 Stephen Hawking. 170 seRies foRewoRd The volumes in this series are devoted to concepts that are fundamental to different branches of the natural sciences—the gene, the quantum, geologi- cal cycles, planetary motion, evolution, the cosmos, and forces in nature, to name just a few. Although these volumes focus on the historical development of scientific ideas, the underlying hope of this series is that the reader will gain a deeper understanding of the process and spirit of scientific practice. In particular, in an age in which students and the public have been caught up in debates about controversial scientific ideas, it is hoped that readers of these volumes will better appreciate the provisional character of scientific truths by discovering the manner in which these truths were established. The history of science as a distinctive field of inquiry can be traced to the early seventeenth century when scientists began to compose histories of their own fields. As early as 1601, the astronomer and mathematician Johannes Kepler composed a rich account of the use of hypotheses in astronomy. During the ensuing three centuries, these histories were increasingly integrated into elementary textbooks, the chief purpose of which was to pinpoint the dates of discoveries as a way of stamping out all too frequent propriety disputes, and to highlight the errors of predecessors and contemporaries. Indeed, histori- cal introductions in scientific textbooks continued to be common well into the twentieth century. Scientists also increasingly wrote histories of their disci- plines—separate from those that appeared in textbooks—to explain to a broad popular audience the basic concepts of their science. The history of science remained under the auspices of scientists until the establishment of the field as a distinct professional activity in the middle of the twentieth century. As academic historians assumed control of history of science writing, they expended enormous energies in the attempt to forge a distinct and autonomous discipline. The result of this struggle to position the history of science as an intellectual endeavor that was valuable in its own right, series foreword and not merely in consequence of its ties to science, was that historical studies of the natural sciences were no longer composed with an eye toward educat- ing a wide audience that included nonscientists, but instead were composed with the aim of being consumed by other professional historians of science. And as historical breadth was sacrificed for technical detail, the literature be- came increasingly daunting in its technical detail. While this scholarly work increased our understanding of the nature of science, the technical demands imposed on the reader had the unfortunate consequence of leaving behind the general reader. As Series Editor, my ambition for these volumes is that they will combine the best of these two types of writing about the history of science. In step with the general introductions that we associate with historical writing by scien- tists, the purpose of these volumes is educational—they have been authored with the aim of making these concepts accessible to students—high school, college, and university—and to the general public. However, the scholars who have written these volumes are not only able to impart genuine enthusiasm for the science discussed in the volumes of this series, they can use the research and analytic skills that are the staples of any professional historian and phi- losopher of science to trace the development of these fundamental concepts. My hope is that a reader of these volumes will share some of the excitement of these scholars—for both science, and its history. Brian Baigrie University of Toronto Series Editor PRefaCe This book is a short version of the story of quantum mechanics. It is meant for anyone who wants to know more about this strange and fascinating theory that continues to transform our view of the physical world. To set forth quantum physics in all its glorious detail takes a lot of mathematics, some of it quite complicated and abstract, but it is possible to get a pretty accurate feeling for the subject from a story well told in words and pictures. There are almost no mathematical formulas in this book, and what few there are can be skimmed without seriously taking away from the storyline. If you would like to learn more about quantum mechanics, the books and Web pages I describe in “Fur- ther Reading” can lead you as far into the depths of the subject as you wish to go. One thing this book does not do is to present a systematic account of all of the interpretations that have been offered of quantum mechanics. That would take another book at least as long. However, certain influential interpretations of quantum theory (such as the Copenhagen Interpretation, the causal inter- pretation, and the many-world theory) are sketched because of their historical importance. Quantum mechanics is often said to be the most successful physical theory of all time, and there is much justification for this claim. But, as we shall see, it remains beset with deep mysteries and apparent contradictions. Despite its tremendous success, it remains a piece of unfinished business. It is the young people of today who will have to solve the profound puzzles that still remain, and this little work is dedicated to them and their spirit of inquiry. aCknowledgmenTs My own research in foundations of quantum mechanics has been supported by the Social Sciences and Humanities Research Council of Canada, the Uni- versity of Lethbridge and the University of Western Ontario. For valuable dis- cussions, suggestions, guidance, and support in various ways I thank Brian Baigrie, Bryson Brown, James Robert Brown, Jed Buchwald, Kevin deLaplante, Kevin Downing, Brian Hepburn, Jordan Maclay, Ralph Pollock, and (espe- cially) Sharon Simmers. inTRoduCTion: why leaRn The hisToRy of QuanTum meChaniCs? This book tells the story of quantum mechanics. But what is quantum mechan- ics? There are very precise and technical answers to this question, but they are not very helpful to the beginner.