Physics of particles matter and the universe blin stoyle

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EUREKA! Physics of Particles, Matter and the Universe Physics of Particles, Matter and the Universe Roger J Blin-Stoyle, FRS Emeritus Professor of Physics University of Sussex Institute of Physics Publishing Bristol and Philadelphia 0 IOPPublishing Ltd 1997 All rights reserved. No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without the prior permission of the publisher. Multiple copying is permitted in accordance with the terms of licences issued by the Copyright Licensing Agency under the terms of its agreement with the Committee of Vice-Chancellors and Principals. British Library Cataloguing-in-Publication Data A catalogue record for this book is available from the British Library. ISBN 0 7503 0415 4 (hbk) ISBN 0 7503 0416 2 (pbk) Library of Congress Cataloguing-in-Publication Data Blin-Stoyle, R. J. (Roger John) Eureka! : physics of particles, matter and the universe / Roger Blin-Stoyle p. cm. Includes index. ISBN 0-7503-0415-4 (hc : alk. paper) ISBN 0-7503-0416-2 (pbk. 1. Physics. I. Title. : alk. paper) QC21.2.B567 1997 5304~21 97- 19999 CIP Consultant Editor: Frank Close, FRS Published by Institute of Physics Publishing,wholly owned by The Institute of Physics, London Institute of Physics Publishing, Dirac House, Temple Back, Bristol BS16BE. UK US Editorial Office: Institute of Physics Publishing, The Public Ledger Building, Suite 1035, 150 South Independence Mall West, Philadelphia, PA 19106, USA Typeset by Mackreth Media Services, Hemel Hempstead, Herts Printed in the UK by J W Arrowsmith Ltd, Bristol To Helena and Anthony Preface 1 1.1 1.2 1.3 1.4 1.5 1.6 2 2.1 2.2 2.3 2.4 2.5 2.6 2.7 3 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 4 4.1 4.2 4.3 Understanding the World Around Us What is Physics? The Nature of Understanding The Problem of Complexity Conceptual Models in Physical Theory Human Experience of the Physical World Moving Forward Everyday Experience of Motion and Energy Motion and Forces Force, Mass and Acceleration Momentum and Angular Momentum Work and Energy Oscillating Systems Wave Motion Moving Forward The Nature and Behaviour of Matter Atoms and Molecules The Particulate Nature of Gases, Liquids and Solids Internal Energy, Heat and Temperature The Second Law of Thermodynamics Solids and their Behaviour Liquids and their Behaviour Gases and their Behaviour Moving Forward Everyday Experience of Electromagnetism Electric and Magnetic Forces Electric Potential and Electric Current Magnetism and Electromagnetic Induction xi 1 1 2 4 7 8 10 11 11 13 16 19 22 25 30 31 31 34 36 39 41 44 46 47 48 48 50 53 Viii Eureka! Physics of Particles, Matter and the Universe 4.4 Electromagnetic Radiation 4.5 4.6 4.7 Moving Forward The Reflection and Refraction of Light The Interference and Diffraction of Light 5 5.1 5.2 5.3 5.4 5.5 5.6 5.7 6 6.1 6.2 6.3 6.4 6.5 6.6 6.7 Quantum Physics and the Atom Atomic Constituents-Electrons and Nuclei The Rise of Quantum Mechanics Waves and Particles Using Quantum Mechanics Atomic Structure Atomic Radiation Moving Forward Properties of Matter-Some Quantum Explanations The Origins of the Interatomic Force Conductors and Insulators Semiconductors Superconductivity Magnetism in Solids Superfluidity Moving Forward 7 Einstein’s Relativity Theory 7.1 What is Relativity? 7.2 Simultaneity 7.3 Time Dilation 7.4 Length Contraction 7.5 Mass and Energy 7.6 Relativistic Quantum Mechanics 7.7 General Relativity 7.8 Moving Forward 8 The Atomic Nucleus 8.1 Nuclear Constituents 8.2 General Properties of Nuclei 8.3 The Nuclear Force 8.4 Nuclear Models 8.5 Nuclear Reactions 8.6 Radioactivity 56 59 62 64 65 65 68 72 76 79 81 84 85 85 88 91 95 97 100 102 103 103 106 107 109 111 113 117 122 123 123 125 128 133 136 139 Contents ix 8.7 Nuclear Physics-a Few Remarks 8.8 Moving Forward 9 9.1 9.2 9.3 9.4 The Weak Interaction 9.5 9.6 Moving Forward The Fundamental Constituents of Matter The Classification of Elementary Particles Intrinsic Particle Properties and Conservation Laws Understanding the Nature of Hadrons The Electroweak Interaction and Unification 10 Astrophysics and Cosmology 10.1 An Outline of the ‘Visible’ Universe 10.2 Electromagnetic Radiation in the Universe 10.3 The Expanding Universe and the Big Bang 10.4 The Early Stages of the Universe and the Formation 10.5 The Lives of Stars 10.6 Problems and Conjectures 10.7 Moving Forward of Stars 11 11.1 Gathering the Threads Together 11.2 Theories of Everything 11.3 The Anthropic Principle 11.4 Reductionism, Complexity, Determinism and Chaos 11.5 Advancing Physics and Technology 11.6 What about Physicists? Reflections on Physics and Physicists Glossary Mathematical Notation for Large and Small Numbers Units Fundamental Physical Constants Physical Terms 143 144 145 145 148 152 157 161 165 166 166 169 171 175 178 181 184 185 185 188 190 192 195 198 200 200 200 202 203 Index 219 There is a general perception that physics is a difficult science to understand. This arises for two main reasons. First, it is the most quantitative of all the sciences and, inevitably, the detailed description of its underlying theories is mostly couched in very advanced mathematical language. Second, at the most funda- mental level, it deals with processes and phenomena on time and space scales inconceivably smaller or larger than those ex- perienced in our everyday life. In other words it deals with a great deal of alien territory in terms of, for many people, an alien language. Hence the aforementioned ‘difficulty’. This is not to say that what physics has achieved and is trying to achieve cannot be communicated to the lay person. At one extreme this can be done by attempting entirely qualitative descriptions and explanations of physical phenomena. A great many words are used in the process but some idea of what physics is about can be conveyed. A closer approach to the real nature of physics is to deal with physical processes just a little more quanti- tatively, occasionally using the sort of elementary mathematics met with regularly by young secondary- or high-school pupils. This is the approach adopted in this book, which attempts to give a brief, matter-of-fact, account of what the whole of physics is about at all levels of scale-from the ultimate constituents of matter, through nuclei, atoms and molecules, to the behaviour of the different forms of matter and, finally, on to stars, galaxies and the nature of the universe itself. It is a short book requiring no previous detailed knowledge of physics other than a general awareness of everyday physical concepts such as matter, force, energy, speed, space and time. It starts with down-to-earth physical processes including topics that are key parts of the National Curriculum in the UK. Parts of this could, no doubt, be omitted by some readers-but revision of some early learning is not, perhaps, a bad thing! The book then moves into less familiar but more exciting and challenging xii Eureka! Physics of Particles, Matter and the Universe territory. The hope is that it will illuminate the nature of the whole of physics for a wide variety of readers-school pupils, college or university students, teachers at all levels and any lay person who wishes to know about physics and is prepared to countenance the occasional algebraic symbol! A Glossary is provided which, first of all, gives a brief account of the way in which very small and very large numbers are represented and it is suggested that the uninitiated should study this section carefully before embarking on the main text. It then goes on to list the units which are used to measure physical quantities and also gives the values of some of the key physical constants (e.g. the speed of light). Finally, brief definitions are given of physical terms which are used in the text. In concluding this Preface I would like to thank all those with whom I have discussed physics over the last 50 years-school pupils, teachers, undergraduates, research students, fellow researchers and colleagues. All have contributed in their very different ways to whatever understanding I have managed to communicate in this book and to the enjoyment of my career as a physicist. Roger Blin-Stoyle May 1997 CHAPTER 1 Towards a Theory of Everything? 1.1 What is Physics? Physics is that branch of science which seeks to understand the behaviour and properties of matter at all levels of scale. At one extreme it is concerned with the fundamental constituents of matter-the so-called elementary particles-and with atoms and molecules. The latter are the building blocks of everyday matter and it is in terms of them that it interprets the very varied properties of solids, liquids and gases. On the larger terrestial scale it studies the behaviour of the air and ocean masses, climate and the environment. Finally, at the other extreme it concerns itself with the structure of stars and stellar systems and, ultimately, the nature and evolution of the universe itself. Such a description implies that physics encompasses most of science. It is certainly true that physics underlies and underpins most, if not all, scientific understanding; however, as science developed over the centuries, many areas have come to be regarded and organized as separate, although related, sciences. Thus the interactions between and processes involving simple or complex molecular structures are generally classified as chemistry, whilst the study of living matter with all its extreme molecular complexity is classified as biology. However, the dividing lines are extremely fuzzy and are spanned by various ‘bridging’ sciences such as chemical physics, biophysics and biochemistry. Further, physics concerned with larger-scale phenomena is generally referred to by other names. Thus, at the terrestrial level, we have meteorology; at the stellar level we have astronomy and astrophysics; and, at the scale of the whole universe, we have cosmology. [...]... line and it is the central inward force due to the hand and string-known as the centripetal force-which holds it in its ‘orbit’ The heavier the weight, the faster it moves or the further it is away from the centre of rotation the greater the force needed and the greater the angular momentum of the weight In the case of such a rotating weight, the magnitude of its angular momentum is simply defined as the. .. as the product of the pushing force and the distance over which the trolley is pushed (The standard unit of work and energy used in physics, called the joule (see section 3.3), is the product of the unit of force (1N) multiplied by the unit of distance (lm).) Such a definition coincides readily with our perception of doing work -the harder we push and/ or the greater the distance covered, the greater the. .. terms of their motion under the gravitational attraction of the sun The ‘basic idea’ involves the general specification of the way in which bodies of different mass move in space when subject to an external force and the specification of the nature of the force of gravity between two massive bodies, in this case the sun and the planet Such a ‘basic idea’ is called a theory and, in physics, a theory... is on the earth! The effect of exerting a force on a body is to make it move faster in the direction of the force; the body accelerates If this is the only force acting on the body then the acceleration will be steady and the body will move faster and faster The size of this acceleration is proportional to the size of the force and, as should be expected from our discussion of the trolley and the car,... conservation of momentum leads to the mishap that may occur when you jump from an unmoored boat onto dry land: the boat moves away from the land as you jump towards it! 18 Eureka! Physics of Particles, Matter and the Universe There is another type of momentum which is extremely important in many aspects of physics, not least the quantum understanding of atoms and nuclei (see Chapters 5 and S), namely... weighed on the moon will have one-sixth of its weight on the earth simply because the moon is smaller and less massive than the earth and therefore exerts less gravitational attraction Mass, on the other hand, is intrinsic to the body and has the same value 14 Eureka! Physics of Particles, Matter and the Universe wherever the body is; it is essentially just as hard to move a car from rest on the moon... forecasting is notoriously inaccurate The problem is that the evolution of such systems over time is a very complicated process and, further, depends extremely sensitively on the very fine details of the intial state of the system In the case of the weather, the example often quoted that the development of the weather in the USA can be affected significantly by the beating of a butterfly’s wings in South... along and suddenly having the brakes applied Again there are frictional forces at work and, on application of the brakes, there is heating of the tyres and the road surface There is also a screeching noise and the emitted sound carries away energy in the form of oscillations in the atmosphere The effect of friction might be so large that sparks are emitted and then some energy is in the form of light... If we neglect the friction between the balls and the surface (i.e assume no external force) then, after the collision, the sum of their momenta in the direction of the line of impact will be equal to the momentum of the initial ball Alternatively, consider the firing of a gun Initially it is at rest and there is zero momentum After firing it, the forward momentum of the bullet must be compensated for... our rooms and the objects in and on them-are moving at high speed as the earth rotates and moves around the sun Further, at the other extreme, the atoms and molecules from which they are constituted are, as we shall see, in incessant motion It is therefore essential to understand at an early stage the nature of motion and how it can be changed First, to state the virtually obvious, the motion of a body . EUREKA! Physics of Particles, Matter and the Universe Physics of Particles, Matter and the Universe Roger J Blin-Stoyle, FRS Emeritus Professor. on the very fine details of the intial state of the system. In the case of the weather, the example often quoted that the development of the weather