qxp 1/28/2008 11:33 AM Page i Quantum Physics A Beginner’s Guide www.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. Innovative and affordable, these books are perfect for anyone curious about the way the world works and the big ideas of our time. anarchism democracy mafia & organized ruth kinna david beetham crime james o. finckenauer anti-capitalism energy simon tormey vaclav smil NATO jennifer medcalf artificial intelligence evolution blay whitby burton s.
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rae keith ward leonard weinberg religion cloning hinduism martin forward aaron d. klostermaier the small arms trade criminal psychology life in the universe m. stohl ray bull et al. smith FORTHCOMING: animal behaviour feminist theory medieval philosophy beat generation forensic science modern slavery bioethics french revolution oil british politics galaxies philosophy of religion censorship gender & sexuality political philosophy climate change globalization racism conspiracy theories history of science radical philosophy crimes against humanity human rights renaissance art engineering humanism romanticism ethics immigration socialism existentialism indigenous peoples time extrasolar planets literary theory volcanoes www.qxp 1/28/2008 11:33 AM Page iii Quantum Physics A Beginner’s Guide Alastair I.qxp 1/28/2008 11:33 AM Page iv A Oneworld Book First published by Oneworld Publications 2005 Copyright © Alastair I.
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.com NL08 Learn more about Oneworld. Join our mailing list to find out about our latest titles and special offers at: www.qxp 1/28/2008 11:33 AM Page v To Amelia and Alex www.qxp 1/28/2008 11:33 AM Page vi www.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 www.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 www.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 www.qxp 1/28/2008 11:33 AM Page x x Preface thirty years, for giving me the opportunity to widen and deepen my knowledge of the subject.
Victoria Roddam and others at Oneworld Publications have shown considerable patience, while applying the pressure needed to ensure the manuscript was delivered, if not in time, then not too late. Thanks are also due to Ann and the rest of my family for their patience and toler- ance. Finally, I of course take responsibility for any errors and inaccuracies.qxp 1/28/2008 11:40 AM Page 1 1 Quantum physics is not rocket science ‘Rocket science’ has become a byword in recent times for something really difficult. Rocket scientists require a detailed knowledge of the properties of the materials used in the construction of spacecraft; they have to understand the potential and danger of the fuels used to power the rockets and they need a detailed understanding of how planets and satellites move under the influence of gravity.
Quantum physics has a similar reputation for difficulty, and a detailed understanding of the behaviour of many quantum phenomena certainly presents a considerable challenge – even to many highly trained physicists. The greatest minds in the physics community are probably those working on the unresolved problem of how quantum physics can be applied to the extremely powerful forces of gravity that are believed to exist inside black holes, and which played a vital part in the early evolution of our universe. However, the funda- mental ideas of quantum physics are really not rocket science: their challenge is more to do with their unfamiliarity than their intrinsic difficulty. We have to abandon some of the ideas of how the world works that we have all acquired from our obser- vation and experience, but once we have done so, replacing them with the new concepts required to understand quantum physics is more an exercise for the imagination than the intellect.
Moreover, it is quite possible to understand how the principles of quantum mechanics underlie many everyday phenomena, without using the complex mathematical analysis needed for a full professional treatment.qxp 1/28/2008 11:40 AM Page 2 2 Quantum Physics: A Beginner’s Guide The conceptual basis of quantum physics is strange and unfamiliar, and its interpretation is still controversial. However, we shall postpone most of our discussion of this to the last chapter,1 because the main aim of this book is to understand how quantum physics explains many natural phenomena; these include the behaviour of matter at the very small scale of atoms and the like, but also many of the phenomena we are familiar with in the modern world. We shall develop the basic principles of quantum physics in Chapter 2, where we will find that the fundamental particles of matter are not like everyday objects, such as footballs or grains of sand, but can in some situations behave as if they were waves. We shall find that this ‘wave–particle duality’ plays an essential role in determining the structure and properties of atoms and the ‘subatomic’ world that lies inside them.
Chapter 3 begins our discussion of how the principles of quantum physics underlie important and familiar aspects of modern life. Called ‘Power from the Quantum’, this chapter explains how quantum physics is basic to many of the methods used to generate power for modern society. We shall also find that the ‘greenhouse effect’, which plays an important role in controlling the temperature and therefore the environment of our planet, is fundamentally quantum in nature. Much of our modern technology contributes to the greenhouse effect, leading to the problems of global warming, but quantum physics also plays a part in the physics of some of the ‘green’ technologies being developed to counter it.
In Chapter 4, we shall see how wave–particle duality features in some large-scale phenomena; for example, quantum physics explains why some materials are metals that can conduct electricity, while others are ‘insulators’ that completely obstruct such current flow. Chapter 5 discusses the physics of ‘semicon- ductors’ whose properties lie between those of metals and insulators. We shall find out how quantum physics plays an www.qxp 1/28/2008 11:40 AM Page 3 Quantum physics is not rocket science 3 essential role in these materials, which have been exploited to construct the silicon chip. This device is the basis of modern electronics, which, in turn, underlies the information and communication technology that plays such an important role in the modern world.
In Chapter 6 we shall turn to the phenomenon of ‘super- conductivity’, where quantum properties are manifested in a particularly dramatic manner: the large-scale nature of the quantum phenomena in this case produces materials whose resis- tance to the flow of electric current vanishes completely. Another intrinsically quantum phenomenon relates to recently developed techniques for processing information and we shall discuss some of these in Chapter 7. There we shall find that it is possible to use quantum physics to transmit information in a form that cannot be read by any unauthorized person. We shall also learn how it may one day be possible to build ‘quantum computers’ to perform some calculations many millions of times faster than can any present-day machine.
Chapter 8 returns to the problem of how the strange ideas of quantum physics can be interpreted and understood, and intro- duces some of the controversies that still rage in this field, while Chapter 9 aims to draw everything together and make some guesses about where the subject may be going.