THE OSKAR KLEIN MEMORIAL LECTURES

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1 THE OSKAR KLEIN MEMORIAL LECTURES

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3 THE OSKAR KLEIN MEMORIAL LECTURES Vol. 1: Lectures by C.N. Yang and S. Weinberg with translated reprints by 0. Klein Editor: Qosta Ekspong Fysikum, University of Sweden Stockholm World Scientific Singapore * New Jersey * London Hong Kong

4 Published by World Scientific Publishing Co. Pte. Ltd. P O Box 128, Fairer Road, Singapore 9128 USA office: 687 HartweU Street, Teaneck, NJ UK office: 73 Lynton Mead, Totteridge, London N20 8DH Library of Congress Cataloging-in-Publication data is available. THE OSKAR KLEIN MEMORIAL LECTURES Vol. 1: Lectures by C. N. Yang and S. Weinberg with translated reprints by O. Klein. Copyright 1991 by World Scientific Publishing Co. Pte. Ltd. All rights reserved. This book, or parts thereof, may not be reproduced in any form or by any means, electronic or mechanical, including photocopying, recording or any information storage and retrieval system now known or to be invented, without written permission from the Publisher. ISBN (pbk)

5 FOREWORD The present volume contains the first and second Oskar Klein Memorial Lectures, given in 1988 and 1989 at the Department of Physics at the University of Stockholm. This series of lectures, held once a year by a world renowned physicist, has been made possible through a grant from the Nobel Committee for Physics at the Royal Swedish Academy of Sciences. In 1988, Chen Ning Yang, professor at the State University of New York at Stony Brook, USA, and Nobel prize winner in Physics 1957, gave the first lectures. The lectures of the second year, 1989, were given by Steven Weinberg, professor at the University of Texas, Austin, USA, Nobel prize winner in Physics The main lecture every year is aimed towards an audience of gifted students and their teachers, whereas the second lecture contains material of a somewhat more advanced nature. Thanks to an initiative from World Scientific in Singapore it is now possible to present these highly stimulating and enjoyable lectures to a wider audience. Oskar Klein was 23 years old when he, in 1918, came to Niels Bohr in Copenhagen. He stayed there with some interruptions until 1931, at which time he became professor at Stockholm University, devoting himself to theoretical physics. Before his arrival in Copenhagen, Klein had published a-few scientific papers, the first at the age of 18. When he was 16, his father, the chief rabbi in Stockholm, arranged for him to work in the chemistry laboratory of Svante Arrhenius, famous for his dissociation theory of electrolytes and his Nobel prize in chemistry in Klein's professorship lasted until his retirement in A biography was written after his death in 1977 jointly by two scientists who knew Klein well. The authors were Professor Inga Fischer- Hjalmars, a specialist in molecular theory who had been a student of V

6 vi Foreword Klein and who later became his successor, and Professor Bertel Laurent, also a student of Klein, specializing in general relativity and field theory. Their article, first published in the yearbook of the Swedish Physical Society, Kosmos, is here presented in an English translation. The biography clearly shows Klein's broad interest in various fields of physics. This is also evident from the list of his scientific publications, included at the end of this volume. Klein's attempt to unify general relativity and electromagnetism dates back to the 1920s. One of his key papers, originally published in German, introduces five-dimensional space-time. It is here reproduced for the first time in an English translation. Klein has told the story of how he struggled for years with his attempt to reach a deeper understanding. He was ready in 1926, only to be told by Wolfgang Pauli that Th. Kaluza had done similar work already in Typical of Klein was that he never hesitated to give Kaluza the honour. He did that in his short paper in Nature in 1926, in which he proposed that the fifth dimension was rolled up, i.e. compactified. As a service to present day "compactifiers" this paper is also included here. Klein was ready for Schrodinger's wave mechanics when it appeared in He had already for several years considered matter wave propagation as a natural way to introduce whole numbers through interference. When Dirac's paper on the quantization of the radiation field appeared, Klein immediately sat down to generalize it; a work he published jointly with Jordan. Dirac's paper on the electron led Niels Bohr to send Oskar Klein to Cambridge to learn more. Soon after Klein and Nishina did their joint work on the Compton effect. The third scientific paper by Klein included here was originally inspired by Yukawa's theory of mesons, which led Klein to apply his fivedimensional ideas to the problem of forces between the neutron-proton pair and the electron-neutrino pair through intermediary charged fields. The complete Lagrangian would entail couplings between the heavy and light fermions, i.e. beta-decay processes. This famous paper was pub-

7 Foreword vii lished in French in connection with a conference in Warsaw in It is included here in a new English translation done by Dr. Lars Bergstrom, Stockholm, who also helped the editor to correct some misprints in the original of this as well as of the German paper. Both Yang and Weinberg refer in interesting ways to Klein's contributions to physics in their main lectures. The changed role of symmetry in modern physics is emphasized by Professor Yang in his main lecture. The earlier passive role is now an active one, so that symmetry dictates interaction. This will certainly remain as a lasting contribution to science from the second half of this century. Along this road the Yang-Mills gauge theory paper from 1954 represents a milestone. In his second lecture Yang asks a question regarding the Yang- Baxter equation, namely, why is this equation involved in so many different areas of physics and mathematics? His own answer lies in his proof of its deep relation to the permutation group, being a generalization of its structure. Professor Weinberg's seminal work on the unification of weak and electromagnetic forces was based on symmetry considerations. From this grew the successful standard model of elementary particle theory. In his first lecture Professor Weinberg brings the reader to the forefront of research in this field as well as in that of cosmology. He is convinced that there must be something new beyond. The unanswered questions are addressed by Weinberg who emphasizes that one must not be satisfied with what the standard models offer. To quote him: "we understand that we know less than we thought we did." Quantum mechanics is a linear theory. Weinberg deals in his second lecture with the question of how precisely the absence of nonlinearities is known. His recent proposal to test this by experiment has led to impressive and successful results. This paper would in all likelihood have appealed to Oskar Klein who, in the pre-schrodinger days, worried about possible nonlinearities. The volume begins with the biography of Klein and ends with his

8 viii Foreword autobiography in the form of a lecture once held at the International Centre for Theoretical Physics at Trieste, Italy. It makes interesting reading for those who want to know more about the roots of modern physics. Klein's kindness, as experienced by those who met him in person, can also be noticed in his writings. Finally, I wish to thank my colleagues in the Organizing Committee for the Oskar Klein Memorial Lectures, Professor Tor Ragnar Gerholm, Professor Cecilia Jarlskog and Professor Bertel Laurent. To Dr Lars Bergstrom I owe special thanks for his expert help with the translations from French and from German of two of Klein's papers. Holmsveden, Sweden, August 1990 Gosta Ekspong

9 CONTENTS Foreword Gosta Ekspong v Oskar Klein (translated from the Swedish) 1 Inga Fischer-Hjalmars and Bertel Laurent Symmetry and Physics 11 Chen Ning Yang From the Bethe-Hulthen Hypothesis to the Yang-Baxter Equation 35 Chen Ning Yang Beyond the Standard Models 45 Steven Weinberg Precision Tests of Quantum Mechanics 59 Steven Weinberg Quantum Theory and Five-Dimensional Relativity Theory (translated from the German) 67 Oskar Klein The Atomicity of Electricity as a Quantum Theory Law 81 Oskar Klein On the Field Theory of Charged Particles (translated from the French) 85 Oskar Klein ix

10 x Contents From My Life of Physics 103 Oskar Klein Scientific Bibliography of Oskar Klein 119