Light and Life in the Universe. Selected Lectures in Physics, Biology and the Origin of Life PDF
Preview Light and Life in the Universe. Selected Lectures in Physics, Biology and the Origin of Life
This book is sold subject to the con-r dition that it shall not, by way of trade, be lent, resold, hired out, or otherwise disposed of without the publisher's consent, in any form of binding or cover other than that in which it is published. LIGHT AND LIFE IN THE UNIVERSE Selected Lectures in Physics, Biology and the Origin of Life EDITED BY S. T. BUTLER M.SC., PH.D., D.SC. Professor of Theoretical Physics AND H. MESSEL B.A., B.SC, PH.D. Head of the School of Physics UNIVERSITY OF SYDNEY PERGAMON PRESS OXFORD · LONDON · EDINBURGH · NEW YORK PARIS · FRANKFURT Pergamon Press Ltd., Headington Hill Hall, Oxford 4 & 5 Fitzroy Square, London W.l Pergamon Press (Scotland) Ltd., 2 & 3 Teviot Place, Edinburgh 1 Pergamon Press Inc., 122 East 55th Street, New York 22, N.Y. Pergamon Press GmbH, Kaiserstrasse 75, Frankfurt-am-Main Federal Publications Ltd., Times House, River Valley Rd., Singapore Samcax Book Services Ltd., Queensway, P.O. Box 2720, Nairobi, Kenya A course of lectures contributed to the Nuclear Research Foundation Summer Science School for Fourth-year High School students at the University of Sydney, January 6-17, 1964 For Copyright reasons this Edition is not for sale in Australasia Copyright © 1965 Pergamon Press Ltd. Library of Congress Catalog No. 65-18522 First published in THE COMMONWEALTH AND INTERNATIONAL LIBRARY 1965 Printed in Great Britain by Taylor Garnett Evans & Co. Lid Watford, Herts THE SPONSORS The Nuclear Research Foundation within the University of Sydney gratefully acknowledges the generous financial assistance given by the following group of individual philanthropists and companies, without whose help the 1964 Summer Science School for Fourth-year High School students and the production of this book would not have been possible. Ampol Petroleum Limited Australian Factors Group Ducon Industries Limited H. G. Palmer, Esq. INTRODUCTION The lectures of the 1964 Nuclear Research Foundation Sum- mer Science School for High School Students, contained in the chapters of this book, will be concerned primarily with various aspects of life—life here on earth and life in the universe generally. The main lectures of this Summer School, by Professors J. D. Watson and M. Yeas, are concerned basically with the following topics: • The "units" of living matter. • How life may have started on earth. • The possibility of life on other planets. It may seem to you that these topics can have very little to do with ordinary physics and chemistry. Yet it is the purpose of the first six chapters of this book to develop for you some of the basic physics and chemistry which is necessary for appreciation of the later biology lectures. You will find in these later lectures how certain large molecules are characteristic of life forms—mole- cules which themselves have amazing properties and which are able to reproduce replicas of themselves. The question of how life may have originated on earth is thus intimately connected with how these large molecules may have been formed to start with. Similarly, the question of life elsewhere in the universe is vitally concerned with a number of other planets which may exist and which may have properties that can support life. But do you really know what a molecule is? Do you know how electro-magnetic radiation can be responsible for the building up of large molecules? Do you know what electro-magnetic radia- tion is? Do you know the theories of what the earth was like thousands of millions of years ago when life originated on it? Are you aware of the scientific thoughts regarding the origin of our solar system, and which are essential to any estimates of the possible number of other planets with life? These are all topics in physics and chemistry which go hand in hand with our Summer School's main lectures on the subject of life. In order that you be able to appreciate fully these later lectures we devote much of the book's first six chapters to dis- cussing the above-mentioned subjects. Because all lectures have been specifically prepared, written and edited for fourth-year High School students, we feel that they will be of interest to the widest section of the public. We feel that the material as presented will be appreciated not only by the increas- ingly science-conscious layman in this scientific age but also, in fields other than his own, by the specialised scientist. The 1964 Nuclear Research Foundation Summer Science School and, indeed, this book are intended to stimulate and develop science-consciousness in Australia generally, and in particular in the 150 outstanding fourth-year High School students of 1963 who won scholarships to attend the School. The Foundation wishes to applaud and reward their ability and diligence. Finally, we accept complete responsibility for the contents of this book and apologise for any errors which may have crept into the texts. Sydney, January, 1964. S. T. BUTLER and H. MESSEL CONTRIBUTORS OF LECTURES R. N. BRACEWELL Professor of Electrical Engineering, Stanford University, Stanford, California, S. T. BUTLER Professor of Theoretical Physics, University of Sydney. H. MESSEL Professor of Physics and Head of the School of Physics, University of Sydney. J. D. WATSON Professor of Biology, Harvard University, Cambridge, Massachusetts. M. YCAS Associate Professor of Microbiology, State University of New York, New York. CHAPTER 1 Atoms, Molecules and Nuclei All matter, whether in life forms or in inanimate objects, is made up of elementary particles called atoms. In many substances, atoms are joined together into larger units called molecules. In this chapter we describe, briefly, some of the properties of atoms and how they join up to form molecules, for it is this very process that has built up characteristic molecules of living beings. At the same time we shall outline some of the properties of the central core of each atom—the by now famous nucleus—because, as you will see in Chapter 4, a certain amount of nuclear physics enters into any discussion as to the origin of the sun and its solar system, (a) Matter consisting of atoms or molecules. As you know, most substances can exist in any one of three states—the solid state, liquid state or gaseous state. In the solid state the atoms or molecules are closely bound together by forces between them, and are arranged in a regular geometrical pattern called a "solid lattice." In this case the atoms or molecules possess rather little freedom of motion ; their main motion is a small to-and-fro movement around their proper positions in the lattice. The distance between particles in such a lattice is about the same as the size of the particles themselves. In the liquid state the atoms or molecules are also fairly closely bound together by forces between them, but they are no longer arranged in a regular pattern, and it is possible for individual atoms and molecules to wander all over the liquid. The atoms or molecules slide over one another with great freedom, allowing the liquid to assume any shape. But since the elementary particles are still quite tightly packed and held together by strong forces, the liquid resists any attempt to change its volume. In the gaseous state the molecules are on the average widely separ- ated from each other and exert but little attraction upon each other. 9 10 LIGHT AND LIFE IN THE UNIVERSE The molecules of a gas move freely from place to place, the spaces between them being much larger than their size. It is on the basis of this picture of matter that we are able to understand such properties as the pressure in gases and liquids, heat content and temperature of bodies of matter, and sound pro- pagation through a medium. Indeed all properties of matter are determined by the charged and uncharged atoms and molecules of which everything consists. As we shall see later the properties of electricity and magnetism are a direct consequence of the structure within an atom. To understand light, electricity and magnetism we must make use of the fact that each atom consists of a central positively charged core called the nucleus, around which revolve negatively charged particles called electrons. It will be our purpose in the present work to discuss in some detail the relationship of all these phenomena based upon the above picture of atoms. For the remainder of this chapter we shall present the general picture, as it is now known, of atoms and molecules. (b) Fundamental Particles Atoms and molecules themselves are made up from three funda- mental building blocks—neutrons, protons and electrons. Their properties are as follows: ma S S = 9 Π x 28 3 0 Electron i * 10" g (approx. 2 X 10 lb> 10 (charge (negative) = 4-8 x 10~ esu m a S S = 1#672 X 10 24 g Pr ton i ~ -10 {charge (positive) = 4-8 x 10 esu 24 XT , (mass = 1-675 x 10" g Neutron { . 4 . , , (zero electrical charge. If we designate the mass of the electron by me, that of the proton by mv and of the neutron by mn it has been accurately measured that mv = 1836 me mn = 1846 me. Thus protons and neutrons have very nearly equal masses and each is very much more massive than an electron. The proton has a positive charge, usually designated by +e, which is exactly equal in magnitude to the negative charge of the ATOMS, MOLECULES AND NUCLEI 11 electron — e. The neutron, however, has no charge whatsoever and this made it much more difficult to discover. All three of these 13 fundamental particles are extremely small in size being 10' cm or less in diameter. Setting aside the question of the way in which these particles were discovered and their properties determined, let us accept the fact that they exist and see how they are built up into atoms and molecules and thus into matter as we know it. (c) Atoms Matter which is made up purely of atoms of one kind is called an element. There are 92 different types of atoms which occur naturally, and there are thus 92 natural elements (although other unstable elements can now be created artificially). Each atom con- sists of a very dense and small central core known as the nucleus, around which electrons move in satellite or planetary orbits. The nucleus itself contains no electrons but consists of protons and neu- trons. The number of protons in a nucleus is usually designated by Z, the so-called atomic number, and the number of neutrons in a nucleus is designated by N. The total number of protons and neutrons in a nucleus is known as the mass number A — N -\- Z. Atoms are electrically neutral, and this means that there is a number Z of planetary electrons moving around a nucleus. These electrons which move in planetary orbits around nuclei do so because of their electrostatic attraction to the protons in the nucleus. If an atom or molecule loses an electron—we say it is ionized—it becomes a singly charged positive ion. If it loses two electrons, it becomes a doubly charged posi- tive ion, and so forth. On the other hand, if a neutral atom or molecule gains an electron, it becomes a singly charged negative ion. If a nucleus has atomic number Z it contains Z protons each of charge +e. An electron of charge — e is therefore attracted towards such a nucleus; if the electron is a distance r away, the magnitude of the Coulomb attraction is 2 Ze Attractive force on electron = — . 2 r It is to be noted that this is an inverse square force, exactly analogous to the force of gravitation. (Indeed there is also a gravita
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