NOBEL LECTURES IN PHYSICS 1991-1995 NOBEL LECTURES I NCLUDING P RESENTATION S PEECHES AND LAUREATES' BIOGRAPHIES PHYSICS CHEMISTRY PHYSIOLOGY OR MEDICINE LITERATURE PEACE ECONOMIC SCIENCES NOBEL LECTURES I NCLUDING P RESENTATION S PEECHES AND LAUREATES' BIOGRAPHIES PHYSICS 1991-1995 EDITOR Gösta Ekspong Department of Physics University of Stockholm Published for the Nobel Foundation in 1997 by World Scientific Publishing Co. Pte. Ltd. PO Box 128, Farrer Road, Singapore 912805 USA office: Suite lB, 1060 Main Street, River Edge, NJ 07661 UK office: 57 Shelton Street, Covent Garden, London WC2H 9HE NOBEL LECTURES IN PHYSICS (1991-1995) All rights reserved. ISBN 981-02-2677-2 ISBN 981-02-2678-0 (pbk) Printed in Singapore by Uto-Print FOREWORD Since 1901 the Nobel Foundation has published annually “Les Prix Nobel” with reports from the Nobel award ceremonies in Stockholm and Oslo as well as the biographies and Nobel lectures of the laureates. In order to make the lectures available for people with special interests in the different prize fields the Foundation gave Elsevier Publishing Company the right to publish in English the lectures for 1901-1970, which were published in 1964-1972 through the following volumes: Physics 1901-l 970 4 vols. Chemistry 1901-1970 4 vols. Physiology or Medicine 1901-1970 4 vols. Literature 1901-1967 1 vol. Peace 1901-1970 3 vols. Thereafter, and onwards the Nobel Foundation has given World Scientific Publishing Company the right to bring the series up to date and also publish the Prize lectures in Economics from the year 1969. The Nobel Foundation is very pleased that the intellectual and spiritual message to the world laid down in the laureates’ lectures, thanks to the efforts of World Scientific, will reach new readers all over the world. Bengt Samuelsson Michael Sohlman Chairman of the Board Executive Director Stockholm, October 1996 vii PREFACE The lectures in physics by the Nobel laureates in 1991-1995 are collected in this volume. These lectures have been given at the Royal Swedish Academy of Sciences in Stockholm in the Nobel week of the year and originally published in a yearly volume Les prix Nobel. The present volume also contains the presentation speeches held by a member of the Nobel Committee for physics during the prize-awarding ceremony on December 10 of each year. Included also are the short speeches by one of the physics laureates at the banquets on the evening of the same day. Very interesting reading can be found in the autobiographies of each prizewinner. Some have started life without any thought of becoming a physicist and others have had a determined will to enter the research world of international physics. What influences are guiding a child or a youth turn out to be so diverse, that one can hardly write a recipe of how to develop into a physicist - let alone how to become a Nobel prizewinner. The discoveries or inventions honoured by prizes during the five years covered here range from the smallest subatomic particles to one of the most extraordinary star systems in the sky. In 1991 the prize to Pierre-Gilles de Gennes focused on his investigations of liquid crystals and polymers, materials of great practical importance and scientific interest. The 1992 prize to Georges Charpak was given for his inventions and developments of charged particle detectors, in particular for his multiwire proportional counters, used in many high energy experiments the world over and more recently also applied to medicine. In 1993 astrophysics came into focus by awarding the prize in physics to Russell Hulse and Joseph Taylor for their discovery of a close system of two stars, one of which is a fast rotating pulsar, which acts as an extraordinary accurate clock. The discovery story is a most fascinating one. The ultimate result turned out to be the best test of Einstein’s theory of gravitation. Pioneering contributions to neutron scattering techniqueswas the motivation for the physics prize in 1994 to Bertram Brockhouse and Clifford Shull. Neutrons, discovered in 1932, became available in large numbers after the war and were then tamed to serve science and technology. The methods worked out by the two prizewinners have been widely used and have become indispensible tools for the study and investigation of solid matter and liquids. In 1995 the Academy focused on the smallest units of matter by honouring two achievements; the detection of the tiny neutrino was cited as motivation for the prize to Fredrick Reines and the discovery of the small but heavy tau-lepton for the prize to Martin Perl. Both particles are somewhat esoteric and remote from our everyday world, but both particles are believed to be of great importance for the life and development of the universe at large. Gösta Ekspong CONTENTS Foreword V Preface vii 1991 PIERRE-GILLES de GENNES Presentation by Ingvar Lindgren 3 Biography of Pierre-Gilles de Gennes 7 Soft Matter 8 1992 GEORGES CHARPAK Presentation by Carl Nordling 17 Biography of Georges Charpak 21 Electronic Imaging of Ionizing Radiation with Limited Avalanches in Gases 23 1993 RUSSELL A. HULSE and JOSEPH H. TAYLOR, JR. Presentation by Carl Nordling 39 Biography of Russell A. Hulse 43 The Discovery of the Binary Pulsar 48 Biography of Joseph H. Taylor, Jr. 71 Binary Pulsars and Relativistic Gravity 73 1994 BERTRAM N. BROCKHOUSE and CLIFFORD G. SHULL Presentation by Carl Nordling 95 Biography of Bertram N. Brockhouse 99 Slow Neutron Spectroscopy and the Grand Atlas of the Physical World 107 Biography of Clifford G. Shull 141 Early Development of Neutron Scattering 145 1995 MARTIN L. PERL and FREDERICK REINES Presentation by Carl Nordling 157 Biography of Martin L. Per1 161 Rejections on the Discovery of the Tau Lepton 168 Biography of Frederick Reines 197 The Neutrino: From Poltergeist to Particle 202 Physics 1991 PIERRE-GILLES de GENNES for discovering that methods developed for studying order phenomena in simple systems can be generalized to more complex forms of matter, in particular to liquid crystals and polymers 3 THE NOBEL PRIZE IN PHYSICS Speech by Professor Ingvar Lindgren of the Royal Swedish Academy of Sciences. Translation from the Swedish text. Your Majesties, Your Royal Highnesses, Ladies and Gentlemen. This year’s Nobel Prize in Physics has been awarded to Pierre-Gilles de Gennes, College de France, Paris, for his investigations of liquid crystals and polymers. De Gennes has shown that mathematical models, developed for studying simpler systems, are applicable also to such complicated systems. De Gennes has discovered relations between different, seemingly quite unrelated, fields of physics - connections which noboby has seen before. Liquid crystals and polymers can be regarded as intermediate states between order and disorder. A simple crystal, such as ordinary salt, is an example of almost perfect order - its atoms or ions are located in exact positions relative to each other. An ordinary liquid is an example of the opposite, complete disorder, its atoms or ions seem to move in completely irregular fashion. These examples represent two extremes of the concept order-disorder. In nature, there are more subtle forms of order and a liquid crystal is an example of that. It can be well ordered in one dimension but completely disordered in another. De Gennes has generalized the descrip- tion of order for media of this type and been able to see analogies with, e.g. magnetic and superconducting materials. The discovery of the remarkable substances we now call liquid crystals was made by the Austrian botanist Friedrich Reinitzer slightly more than a hundred years ago. In studying plants, he found that a substance related to the cholesterol had two distinct melting points. At the lower temperature, the substance became liquid but opaque and at the higher temperature com- pletely transparent. Earlier, similar properties had been found in stearin. The German physicist Otto Lehmann found that the material was completely uniform between these temperatures with properties characteristic of a liquid as well as a crystal. Therefore, he named it “liquid crystal”. All of us have seen liquid crystals in the display of digital watches and pocket calculators. Most likely, we shall shortly see them also on the screen of our TV sets. Applications of this kind depend upon the unique optical properties of the liquid crystals and the fact that these can easily be changed, e.g. by an electric field. It has been known for a long time that liquid crystals scatter light in an exceptional way, but all early explanations of this phenomenon failed. De Gennes found the explanation in the special way the molecules of a liquid crystal are ordered. One of the phases of a liquid crystal, called nemutic, can be compared with a ferromagnet, where the atoms, which are themselves 4 Physics 1991 tiny magnets, are ordered so that they point in essentially the same direction - with slight variations. These variations follow a strict mathematical rule, which near the so-called critical temperature, where the magnet ceases to be magnetic, attains a very special form. In the liquid crystal the molecules are ordered in a similar way at every temperature, which explains its remarkable optical properties. Another large field, where de Gennes has been very active, is that of polymer physics. A polymer consists of a large number of molecular frag- ments, monomers, which are linked together to form long chains or other structures. These molecules can be formed in a countless number of ways, giving the polymer materials a great variety of chemical and physical proper- ties. We are quite familiar with some of the applications, which range from plastic bags to parts of automobiles and aircraft. Also in these materials, de Gennes has found analogies with critical phenomena appearing in magnetic and superconducting materials.