Prelims.qxp 1/28/2008 11:33 AM Page i Quantum Physics A Beginner’s Guide Prelims.qxp 1/28/2008 11:33 AM Page ii Where today’s news only scratches the surface, ONEWORLD BEGINNER’S GUIDES combine a truly engaging approach with expert analysis of the most challenging issues facing modern society. 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M. Rae Prelims.qxp 1/28/2008 11:33 AM Page iv A Oneworld Book First published by Oneworld Publications 2005 Copyright © Alastair I. M. Rae 2005 Reprinted 2006, 2007, 2008 All rights reserved Copyright under Berne Convention A CIP record for this title is available from the British Library ISBN 978–1–85168–369–7 Typeset by Jayvee, Trivandrum, India Cover design by Two Associates Printed and bound in Great Britain by TJ International, Padstow, Cornwall Oneworld Publications 185 Banbury Road Oxford OX2 7AR England www.oneworld-publications.com NL08 Learn more about Oneworld. Join our mailing list to find out about our latest titles and special offers at: www.oneworld-publications.com Prelims.qxp 1/28/2008 11:33 AM Page v To Amelia and Alex Prelims.qxp 1/28/2008 11:33 AM Page vi Prelims.qxp 1/28/2008 11:33 AM Page vii Contents Preface viii 1 Quantum physics is not rocket science 1 2 Waves and particles 27 3 Power from the quantum 68 4 Metals and insulators 91 5 Semiconductors and computer chips 113 6 Superconductivity 134 7 Spin doctoring 157 8 What does it all mean? 176 9 Conclusions 201 Glossary 207 Index 219 Prelims.qxp 1/28/2008 11:33 AM Page viii Preface The year 2005 is the ‘World Year of Physics’. It marks the centenary of the publication of three papers by Albert Einstein during a few months in 1905. The most famous of these is probably the third, which set out the theory of relativity, while the second paper provided definitive evidence for the (then controversial) idea that matter was composed of atoms. Both had a profound effect on the development of physics during the rest of the twentieth century and beyond, but it is Einstein’s first paper that led to quantum physics. In this paper, Einstein showed how some recent experiments demonstrated that the energy in a beam of light travelled in packets known as ‘quanta’ (singular: ‘quantum’), despite the fact that in many situations light is known to behave as a wave. This apparent contradiction was to lead to the idea of ‘wave–particle duality’ and eventually to the puzzle of Schrödinger’s famous (or notorious) cat. This book aims to introduce the reader to a selection of the successes and triumphs of quantum physics; some of these lie in explanations of the behaviour of matter on the atomic and smaller scales, but the main focus is on the manifestation of quantum physics in everyday phenomena. It is not always realized that much of our modern technology has an explicitly quantum basis. This applies not only to the inner workings of the silicon chips that power our computers, but also to the fact that electricity can be conducted along metal wires and not through insulators. For many years now, there has been considerable concern about the effect of our technology on the Prelims.qxp 1/28/2008 11:33 AM Page ix Preface ix environment and, in particular, how emission of carbon dioxide into the Earth’s atmosphere is leading to global warming; this ‘greenhouse effect’ is also a manifestation of quantum physics, as are some of the green technologies being developed to counter- act it. These phenomena are discussed here, as are the applica- tion of quantum physics to what is known as ‘superconductivity’ and to information technology. We address some of the more philosophical aspects of the subject towards the end of the book. Quantum physics has acquired a reputation as a subject of great complexity and difficulty; it is thought to require consid- erable intellectual effort and, in particular, a mastery of higher mathematics. However, quantum physics need not be ‘rocket science’. It is possible to use the idea of wave–particle duality to understand many important quantum phenomena without much, or any, mathematics. Accordingly, the main text contains practically no mathematics, although it is complemented by ‘mathematical boxes’ that flesh out some of the arguments. These employ only the basic mathematics many readers will have met at school, and the reader can choose to omit them without missing the main strands of the argument. On the other hand, the aim of this book is to lead readers to an understanding of quantum physics, rather than simply impressing them with its sometimes dramatic results. To this end, considerable use is made of diagrams and the reader would be well advised to study these carefully along with the text. Inevitably, technical terms are introduced from time to time and a glossary of these will be found towards the end of the volume. Some readers may already have some expertise in physics and will no doubt notice various simplifications of the arguments they have been used to. Such simplifications are inevitable in a treatment at this level, but I hope and believe that they have not led to the use of any incor- rect models or arguments. I should like to thank my former students and colleagues at the University of Birmingham, where I taught physics for over