BOSTON STUDIES IN THE PHILOSOPHY OF SCIENCE
VOLUME XXI
SELECTED PAPERS OF
LEON ROSENFELD SYNTHESE LIBRARY
STUDIES IN EPISTEMOLOGY,
LOGIC, METHODOLOGY, AND PHILOSOPHY OF SCIENCE
Managing Editor:
JAAKKO HINTIKKA, Academy of Finland and Stanford University
Editors:
ROBER T S. COHEN, Boston University
DONALD DAVIDSON, University of Chicago
GABRIEL NUCHELMANS, University of Leyden
WESLEY C. SALMON, University of Arizona
VOLUME 100 LEON ROSENFELD (1904·1974) BOSTON STUDIES IN THE PHILOSOPHY OF SCIENCE
EDITED BY ROBERT S. COHEN AND MARX W. WARTOFSKY
VOLUME XXI
SELECTED PAPERS OF
LEON ROSENFELD
Edited by
ROBERT S. COHEN AND JOHN J. ST ACHEL
D. REIDEL PUBLISHING COMPANY
DORDRECHT: HOLLAND I BOSTON: U.S.A. LONDON:ENGLAND Library of Congress Cataloging in Publication Data
Rosenfeld, Leon, 1904--1974. Selected papers of Leon Rosenfeld.
(Boston studies in the philosophy of science; v. 21) (Synthese library; v. 1(0) 'Bibliography of the writings of Leon Rosenfeld': p. Includes index. I. Physics-History-Collected works. 2. Physics-Philosophy• Collected works. 3. Physics-Collected works. 4. Science-History• Collected works. I. Cohen, Robert Sonne. II. Stachel,J.J. III. Title. IV. Series. Q174.B67 vol. 21 [QC7] 50lS [5301.09] 77-17620 ISBN-13: 978-90-277-0652-2 e-ISBN-13: 978-94-009-9349-5 DOl: 10.1007/978-94-009-9349-5
The translation of Article 1 in Part 11 was prepared by Prof Aage Petersen and edited by RSC and JJS. The translations of Articles 3. 7. 11. 15. 16. 17. and 20 of Part 1.5. 15 and 18 ~l Part II. 1. 2, and 3 ~l Part Ill. and 1 ~l Part IV were prepared by the AAA Linguistic Service ( Boston). Betty Krikorian and Jean Rel'ol and edited by RSC and JJS.
Published by D. Reidel Publishing Company, P.O. Box 17, Dordrecht, Holland
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All Rights Reserved Copyright © 1979 by D. Reidel Publishing Company, Dordrecht, Holland and copyrightholders as specified on appropriate pages within Softcover reprint of the hardcover I st edition 1979 No part of the material protected by this copyright notice may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording or by any informational storage and retrieval system, without written permission from the copyright owner EDITORIAL PREFACE
The decision to undertake this volume was made in 1971 at Lake Como during the Varenna summer school ofthe Italian Physical Society, where Professor Leon Rosenfeld was lecturing on the history of quantum theory. We had long been struck by the unique blend of epistemological, histori• cal and social concerns in his work on the foundations and development of physics, and decided to approach him there with the idea of publishing a collection of his papers. He responded enthusiastically, and agreed to help us select the papers; furthermore, he also agreed to write a lengthy introduction and to comment separately on those papers that he felt needed critical re-evaluation in the light of his current views. For he was still vigorously engaged in both theoretical investigations of, and critical reflections on the foundations of theoretical physics. We certainly did not conceive of the volume as a memorial to a 'living saint', but rather more practically, as a useful tool to place in the hands of fellow workers and students engaged in wrestling with these difficult problems. All too sadly, fate has added a memorial aspect to our labors. We agreed that in order to make this book most useful for the con• temporary community of physicists and philosophers, we should trans• late all non-English items into English. Selection of the items for inclusion proceeded by correspondence and at the time of Professor Rosenfeld's visit to Boston University in 1973 had reached a stage that enabled us to draw up a nearly final list with him; that list is the basis for this volume. Unfortunately, he had not set to work on the introduction and critical notes at the time of his death. Professor Stefan Rozental, his close friend and co-worker, has kindly supplied us with an introductory tribute; but he joins us in the sense of loss to the volume due to the absence of Rosen• feld's own editorial contributions. VIII EDITORIAL PREFACE
II Naturally, we cannot dream of filling that gap in these prefatory com• ments. We should just like to include a few words on some unique features of Professor Rosenfeld's work, which we feel will be of significance to physicists and philosophers, and especially to students. At the time when Professor Rosenfeld started his scientific career, the number of physicists who concerned themselves with social issues, let alone those who saw any organic relationship between their creative acti• vity and their social concerns, was small. Today, of course, under the impact of the great leap forward in the industrialization of science, and of so many scientific and technological developments upon all aspects of social life - and indeed of possible social death - this number has grown considerably. But often this concern, even among some scientists, takes the form of a rejection of science, or at any rate a rejection of any claim that science gives us a truthful picture of the world. How to reconcile an understanding of the social role of science, and likewise of the role of social forces in the development of science, with a concept of objective scientific truth has become an issue of concern to a growing number of scientists, young and old. Rosenfeld's lifelong example of just such an attempt can serve as an inspiration and example.
III Professor Rosenfeld was a Marxist. He made no bones about this, as may be seen from the many references to Marx and Engels in this volume, as well as the integral spirit in which he approached such problems as the origins of thermodynamics or the history of electromagnetic theory, to give but two examples. His Marxism was of an undogmatic variety, how• ever, at a time when dogmatism reigned supreme in the dominant currents of several 'official' Marxisms. His work thus provides a valuable example of the attempt by a critical intellect to utilize the categories of Marxist thought in discussing not only the social and historical aspects of the development of physics, but also conceptual evolution within various branches of physics themselves. Indeed, it is precisely in his early refusal to see a sharp separation between these 'external' and 'internal' moments in the evolution of the sciences that we may see a distinctive feature of EDITORIAL PREFACE IX
Rosenfeld's approach, which he owes to the Marxist tradition, a tradition which his own specific, detailed studies have materially developed and enriched. This by no means implies that only the committed Marxist can benefit from the reading of those papers most directly concerned with social and historical matters. For while he approaches the issues in each case from his own viewpoint, Rosenfeld does not come armed with a bag of pre• conceived answers: rather, he displays a fine sense for the uniqueness of the historical event, the role of individual traits and how they blend with, or rub against. the grain of the historical development. We believe readers will time and again find themselves charmed by the concise characteriza• tions of persons and situations, as well as informed about the way they fit into a larger picture of scientific and social development through the clash of individual viewpoints. The Marxist scholar will in addition find num• erous models for the tactful and sympathetic application of his method to concrete situations. He will also find some tart comments on what Rosenfeld found to be dogmatic or vulgar Marxist misapplications, notably in the review of Bernal.
IV Rosenfeld is probably best known to the public of physics for his work on the foundations of quantum theory, especially for his critical development and defense of Bohr's viewpoint. Without going into any discussion ofthe issues (on which Rosenfeld speaks for himself eloquently enough through• out this volume), it may be helpful to recall that this viewpoint has been, and to some extent still is, under attack by some orthodox Marxists and others as an idealist, or positivist distortion; while at the same time it has been 'defended', under the umbrella labelled the 'Copenhagen' inter• pretation, by a wide variety of champions who clearly were in fact philo• sophical idealists. Rosenfeld engaged in a running battle on both fronts. First, he tries to show that Bohr's viewpoint was basically materialist, and that these attacks from the 'left' were being launched from the standpoint of a dogmatically simple or mechanical 'materialism' - which is no true materialism. Second, he argued that views expressed by such 'defenders' of Copenhagen as Heisenberg were really attempts to saddle quantum mechanics with a Platonic ideology. Obviously the debates about the x EDITORIAL PREFACE philosophical significance of quantum theory are not over; but those who want to understand some of the genuine issues in these debates must reckon with Rosenfeld's views.
v Rosenfeld was not, and did not claim to be a philosopher, nor was he a historian. However, he undertook investigations into the philosophical and historical aspects of physics because of two deep motivations. First, he was convinced that a rigorous understanding of the development of ideas would profoundly clarify his own understanding of physics, and that of his contemporaries. He never went so far as to claim that such historical and philosophical studies would solve current problems - only clarify, which was precious enough in view of the perplexing obscurity of the crises in 20th-century physics. Second, Rosenfeld's appreciation of the wider social position of scien• tists, and of their labors, was a component of his general outlook upon society and its history. Hence it was the most natural thing for him to seek understanding of the relationship between scientific ideas and social forces, social problems, social opportunities. It was equally natural for him to apply his mind to contemporary social questions (especially where physics was relevant) as well as to the historical interactions of society and science in classical and post-renaissance times. These interests in the social or 'external' history of physics did not occupy him more than episodically, in no way as extensive a pre-occupation as for some other creative scientists of this century who had similar social sympathies, such as Haldane, Bernal, Needham, and others. Nevertheless, while his research and writing on these social factors of physics was modest, his public efforts to stimulate such interests and concerns among several generations of students and colleagues were far-reaching indeed. Rosenfeld's work in the history of physics was akin to that combina• tion of historical investigation and logical-conceptual analysis known to us from such giants of the history and logic of physics as Mach and Duhem. Unhappily he produced no treatise in the history of modern physics, and he did not follow through after his dozen superb pioneering papers in the history of physics. Among these we may particularly note: EDITORIAL PREFACE Xl
(1) The Genesis of the Laws of Thermodynamics (1941) (2) The Velocity of Light and the Evolution of Electro• dynamics (1956) (3) The Evolution of Oersted's Scientific Concepts (1970) (4) The First Phase in the Evolution of the Quantum Theory (1936) (5) Max Planck and the Statistical Definition of Entropy (1959)
In addition Rosenfeld continued throughout his scientific life to record and interpret his own historical ambiance, which meant, of course, the history of Niels Bohr, in paper after paper of sometimes repetitive but always thoughtful and provocative writing. So much for history. As a philosopher of science, Rosenfeld especially was concerned with the classical issues of epistemology. Of first impor• tance perhaps were his joint papers with Bohr on measurement, including the classic paper of 1933. But he went on to explore the central notions, particularly those in quantum physics, and here we would select a note• worthy group: (1) The Evolution of the Idea of Causality (1942) (2) Strife about Complementarity (1953) (3) The Measuring Process in Quantum Mechanics (1965) (4) On the Foundations of Statistical Thermodynamics (1955) (5) Questions of Irreversibility and Ergodicity (1960) (6) Some Reflections on Knowledge (1971) His last research, in collaboration with IIya Prigogine and his group, was devoted to elucidating the significance of quantum mechanics for understanding some epistemological features of quantum theory. At no point was Rosenfeld singled out for intensive study by profes• sional philosophers, nor even by philosophers of science; and the same can be said for his reception by the historians of science. He was seen by both groups mainly as a profound physicist rather than a colleague in their own fields, and to some extent as a profound dilettante. We are not sure he would have minded this description, but we feel sure that his work in the history and philosophy of physics, incomplete though it was, was XII EDITORIAL PREFACE of first-rate quality. If he had been working with a critical group of logi• cians and philosophers of science, he might have been stimulated to go further, but it would also be quite difficult to name many other scientists or philosophers who were competent to match him in these matters. The notable exception is Piaget, whose modes of thought and critical exchange were acknowledged by Rosenfeld. At any rate, we believe that Rosen• feld's selected papers in this volume, show a neglected major philosophical historian of modem physics.
VI In conclusion, we express our hope that the reader will share with us that sense of high spirits which pervaded Rosenfeld's discussion of even the most abstruse topics; one sensed in conversations with him, as in so many of his written works, that he knew that the highest form of human engage• ment in serious issues must go with a joyfulness of spirit, a good humor in the deepest meaning of these words. It is in this way that we shall re• member him.
Boston University Center for the History ROBERT S. COHEN and Philosophy of Science JOHN J. STACHEL October 1977
NOTES
We should like gratefully to acknowledge the help of Mrs. Yvonne Rosenfeld in the prepara• tion of this volume, of Professor S. Rozental in contributing the Introduction, of Professor I. Prigogine for permission to use certain of his papers, and of our good friend G. E. Brown for allowing us to adapt the bibliography of Rosenfeld's writings which he had prepared for Nuclear Physics, and some paragraphs from his thoughtful obituary of Rosenfeld. We are especially pleased that this book contains the classic paper of 1933 on measure• ment written by Bohr and Rosenfeld (in an accurate translation by Aage Petersen with some emendations by us). ACKNOWLEDG MENTS
The editors and the publisher are grateful to the following persons and institutions for permission to reprint papers included in this volume:
'On the Method of History of Science', from Archives Intern. d'Histoire des Sciences 1 (1947) 1--6, by permission of Academie Internationale d'Histoire des Sciences. 'J. D. Bernal, Science in History' (book review), from Centaurus 4 (1956) 285-296, by permission of the Board of Editors of Centaurus. 'Le probleme logique de la definition des nombres irrationnels', from Isis 9 (1927) 345-358, by permission of Dr. Robert P. Multhauf, Editor, Isis. 'Rationalism in Antiquity', from Bull. Brit. Soc. Hist. Sc. 1 (1954) 255-257, by permission of The British Journal for the History of Science. 'Atombegrebets forvandlinger gennem tiderne', from Fysisk Tidsskrift 67, nos. 2-3 (1969) 78-91, by permission of N.O. Lassen, Editor, Fysisk Tidsskrift. 'Flicker in the Darkness' (book review of Nicole Oresme and the Medieval Geometry of Qualities and Motions, ed. M. Clagett), from Nature 222 (1969) 197, by permission of Nature. 'Marcus Marcis Untersuchungen tiber das Prisma und ihr Verhaltnis zu Newtons Farbentheorie', from Isis 17 (1932) 325-330, by permission of Dr. Robert P. Multhauf, Editor, Isis. 'Descartes i Uppsala, Striderna om "nya filosofien" 1663-1689, Rolf Lindborg', from Isis 58 (1967) 136, by permission of Dr. Robert P. Multhauf, Editor, Isis. 'Newton and the Law of Gravitation', from Arch. Hist. Exact Sci. 2 (1965) 365-386, by permission of Prof. C. Truesdell and of Springer• Verlag, Heidelberg. 'Newton's Views on Aether and Gravitation', from Arch. Hist. Exact Sci. 6 (1969) 29-37, by permission of Prof. C. Truesdell and of Springer• Verlag, Heidelberg. 'La genese des principes de la thermodynamique', from Bull. Soc. Roy. XIV ACKNOWLEDGMENTS
Sc. Liege 10 (1941) 199-212, by permission of the Societe Royale des Sciences de Liege. 'Joule's Scientific Outlook', from Bull. Brit. Soc. Hist. Sc. 1 (1952) 169-176, by permission of The British Journal for the History of Science. 'An Analysis of Joule's Experiments on the Expansion of Air', from Centaurus 4 (1956) 311-318, by permission of the Board of Editors of Centaurus. 'The Velocity of Light and the Evolution of Electrodynamics', from Suppl. Nuovo Cim. 4 (1956) 1630-1669, by permission of the Societa Italiana di Fisica. 'L'evolution des conceptions scientifiques d'0rsted', from Overs. Dan. Vid. Selsk. (1970-71) 1-17, by permission of The Royal Danish Acade• my of Sciences and Letters. 'La premiere phase de l'evolution de la theorie des quanta', from Osiris 2 (1936) 149-196, by permission of Uitgeverij 'De Tempel'. 'Max Planck et la definition statistique de l'entropie', from Max-Planck• Festschr~ft 1958 (1959) 203-211, by permission of Deutscher Verlag der Wissenschaften. 'Matter and Force after Fifty Years of Quantum Theory', from Physics in the Sixties, S.K. Runcom, Editor, (1963), pp. 1-22, by permission of Oliver and Boyd. 'Men and Ideas in the History of Atomic Theory', from Arch. Hist. Exact Sci. 7 (1971) 69-90, by permission of Prof. C. Truesdell and of Springer• Verlag, Heidelberg. 'Quantum Theory in 1929: Recollections from the First Copenhagen Conference', from Rhodos (1971), by permission of Niels Blaedel, Rhodos (Copenhagen). Niels Bohr, An Essay Dedicated to Him on His Sixtieth Birthday 1945 (1945; 2nd. 1961), by permission of North-Holland Publishing Com• pany. 'The Conception of the Meson Field: Some Reminiscences and Episte• mological Comments', from Suppl. Progr. Theor. Phys. 41 (1968) pp. CI-C7, 257-267, by permission of Prof. Hideki Yukawa, Editor, Progress of Theoretical Physics. 'Nuclear Reminiscences', from Cosmology, Fusion and Other Matters: George Gamow Memorial Volume, Frederick Reines, Editor, (1972), pp. 289-299, by permission of the Colorado Associated Universities ACKNOWLEDGMENTS xv
Press. 'Celestial and Terrestrial Physics in Historical Perspective', from The Application of Modern Physics to the Earth and Planetary Interiors, S.K. Runcom, Editor, (1969), pp. 1-6, by permission of John Wiley & Sons Ltd. 'Zur Frage der Messbarkeit der elektromagnetischen Feldgrossen', from Mat.-fys. Medd. Dan. Vid. Selsk. 12, no. 8 (1933), by permission of the Royal Danish Academy of Sciences and Letters. 'Field and Charge Measurements in Quantum Electrodynamics', from Phys. Rev. 78 (1950) 794-798, by permission of The American Physical Society. 'On Quantum Electrodynamics', from Niels Bohr and the Development of Physics (1955), pp. 70-95, by permission of Pergamon Press Ltd. 'On Quantization of Fields', from Nucl. Phys. 40 (1963) 353-356, by permission of the North-Holland Publishing Company. 'L'evolution de l'idee de causalite', from Mem. Soc. Roy. Sc. Liege 6 (1942) 59-87, by permission of the Societe Royale des Sciences de Liege. 'Strife about Complementarity', from Science Progress 163 (1953) 393- 410, by permission of Blackwell Scientific Publications Ltd. 'Complementarity and Statistics, I-II', from Det Kgl. Norske Vid. Selsk. Fohr. 31, nos. 9-10 (1958), by permission of The Norwegian Academy of Science and Letters. 'Misunderstandings about the Foundations of Quantum Theory', from Observation and Interpretation, Colston Paper No.9, S. Komer, Editor, (1957), pp. 41-61, by permission of Butterworths, London. 'Foundations of Quantum Theory and Complementarity', from Nature 190 (1961) 384-388, by permission of Nature. 'Le conflit epistemologique entre Einstein et Bohr', from Revue de meta• physique et de morale 67 (1962) 147-151, by permission of Paul Ricoeur, Editor, and Revue de metaphysique et de morale. 'The Epistemological Conflict between Einstein and Bohr', from Zeit. for Physik 171 (1963) 242-245, by permission of Zeitschriftfor Physik, Max-Planck Institut ffir Kemphysik. 'Niels Bohr's Contribution to Epistemology' from Physics Today 16 (October 1963), © American Institute of Physics. 'The Measuring Process in Quantum Mechanics', from Suppl. Prog. Theor. Phys., Commemoration Issue for the 30th Anniversary of the XVI ACKNOWLEDGMENTS
Meson Theory by Dr. H. Yukawa (1965) 222-231, by permission of Prof. Hideki Yukawa, Editor, Progress of Theoretical Physics. 'Statistical Causality in Atomic Theory', from History of the Interaction Between Science and Philosophy, Yehuda Elkana, Editor, (The Van Leer Jerusalem Series, Humanities Press, N.Y., 1974), by permission of The Van Leer Jerusalem Foundation. 'General Introduction to Irreversibility', from Irreversibility in the Many• Body Problem, J. Biel and J. Rae, Editors, (1972), by permission of Plenum Publishing Corporation. 'The Macroscopic Level of Quantum Mechanics', from Nature 240 (1972) 25-27, by permission of Nature and Prof. I. Prigogine. 'Quantentheorie und Gravitation', from Entstehung, Entwicklung und Perspektiven der Einsteinschen Gravitationstheorie (Akademie-Verlag, Berlin, 1966), by permission of Prof.-Dr. Hans-Jiirgen Treder, Aka• demie der Wissenschaften der DDR. 'Questions of Method in the Consistency Problem of Quantum Mecha• nics', from Nuc!. Phys. AI08 (1968) 241-244, by permission of the North-Holland Publishing Company. 'The Method of Physics', a report prepared for UNESCO and repro• duced with its permission. © UNESCO 1968. 'Quelques reflections sur la connaissance', from Mem. Soc. Roy. Sc. Liege, 6me serie, tome I, fasc. 2 (Volume Jubilaire Louis d'Or) (1971), pp. 187-190, by permission of the Societe Royale des Sciences de Liege. 'Erkendelsesteori pa naturvidenskabeligt grundlag', from Physica Nor• vegica 5 (1971) 319-326, by permission of The Norwegian Academy of Science and Letters. 'Condillac's Influence on French Scientific Thought', from The Triumph of Culture: 18th Century Perspectives, P. Fritz and D. Williams, Editors, (1972), pp. 157-168, by permission of A. M. Hakkert Ltd. 'Unphilosophical Considerations on Causality in Physics', reprinted from Perspectives in Quantwn Theory: Essays in Honor of Alfred Lande, edited by Wolfgang Yourgrau and van der Merwe (1971, pp. 219-235), by permission of the MIT Press, Cambridge, Mass. 'Berkeley redivivus' (book review of Natural Law and the Structure of Matter by W. Heisenberg), from Nature 228 (1970) 479, by permission of Nature. 'Sur Ie tenseur d'impulsion-energie', from Mem. A cad. Roy. de Belgique ACKNOWLEDGMENTS XVII
18 no. 6 (1940) 1-30, by permission of the Academie Royale des Sciences, des Lettres et des Beaux-Arts de Belgique. 'Sur la definition du spin d'un champ de rayonnement', from Bull. Acad. Roy. de Belgique 28 (1942) 562-568, by permission of the Academie Royale des Sciences, des Lettres et des Beaux-Arts de Belgique. 'Sur Ie comportement d'un ensemble canonique lor d'une transforma• tion adiabatique', from Proc. Nederl. Akad. van Wetenschappen 45 (1942) 970-972, by permission of Koninklijke Nederlandse Akademie van Wetenschappen. 'On the Isolated and Adiabatic Susceptibilities', from Physica 27 (1961) 67-78, by permission of the North-Holland Publishing Company. 'On the Foundations of Statistical Thermodynamics', from Acta Physica Polonica 14 (1955) 3-39, by permission of the Institute of Physics, Polish Academy of Science. 'Questions of Irreversibility and Ergodicity', from Ergodic Theories, P. Caldirola, Editor, (Rendiconti della Scuola Intern. d. Fisica "Enrico Fermi", corso 14, Varenna 1960) (Zanichelli, 1962), pp. 1-20, by permission of the Societa Italiana di Fisica. 'Dynamical Theory of Nuclear Resonances' and 'Coupling between Compound and Single-Particle Resonances', from Spectroscopic and Group Theoretical Methods in Physics, Racah memorial volume (1968), pp. 203-230, by permission of the North-Holland Publishing Com• pany. 'The Structure of Quantum Theory', from Revue de Synthese 3, nos. 49-52 (1968), by permission of Madame Suzanne Delorme, Centre International de Synthese. 'Aspects techniques et sociaux du developpement des organismes europeens de recherche scientifique', from Le Monde Scientifique 14 (1970) 13-15, by permission of the World Federation of Scientific Workers. 'Sociale og individuelle aspelter af naturvidenskabens udvikling', from Fysisk Tidsskrift 69, nos. 4-5 (1971) 97-106, by permission of N. O. Lassen, Editor, Fysisk Tidsskr(ft. Special Note: The illustration which appears in 'Irreversibility - A lay Sermon', entitled 'Cast with Proposed Restoration of Three-Sided Relief', a large marble sculpture, from ca. 470-460 B.C. (original piece), H. L. Pierce Fund, 08.205, was reproduced by courtesy of the Museum of Fine Arts, Boston. PUBLISHER'S NOTE
The reader should note that due to the fact that the articles by Professor Leon Rosenfeld came from various publishers and sources with different styles in denoting symbols, especially with regard to the differential symbol 'd' and to symbols representing vectors, we had to make a choice in order to be consistent throughout the present volume.
For this reason we have used the following notation: the differential symbol 'd' appears in roman upright type; those symbols representing vectors and indicated by letters with arrows over them in some of the papers from which we set, have been substituted by bold roman or italic type. T ABLE OF CONTENTS
EDITORIAL PREFACE VII
ACKNOWLEDGMENTS XIII
PUBLISHER'S NOTE XVIII
INTRODUCTION/Stefan Rozental XXIII
MY INITIATION (l945)/Uon Rosenfeld XXXI
PART I / HISTORY OF SCIENCE
1. On the Method of History of Science (1947) 3 2. Science in History (Review of J. D. Bernal's Science in History) (1956) 7 3. The Logical Problem of the Definition of Irrational Numbers (1927) 16 4. Rationalism in Antiquity (1954) 29 5. The Transformations of the Atomic Concept through the Ages (1969) 32 6. Flicker in the Darkness (Review of Nicole Oresme and the Medieval Geometry of Qualities and Motions, ed. M. Clagett) (1969) 45 7. Marcus Marci's Investigations of the Prism and Their Relation to Newton's Theory of Color (1932) 49 8. Descartes at Uppsala (Review of R. Lindborg's Descartes i Uppsala) (1967) 55 9. Newton and the Law of Gravitation (1965) 58 10. Newton's Views on Aether and Gravitation (1969) 88 11. The Genesis of the Laws of Thermodynamics (1941) 99 12. Joule's Scientific Outlook (1952) 112 13. An Analysis of Joule's Experiments on the Expansion of Air (with A. P. Hatton) (1956) 123 xx T ABLE OF CONTENTS
14. The Velocity of Light and the Evolution of Electrodynamics (1956) 134 15. The Evolution of Oersted's Scientific Concepts (1970) 178 16. The First Phase in the Evolution of the Quantum Theory (1936) 193 17. Max Planck and the Statistical Definition of Entropy (1959) 235 18. Matter and Force after Fifty Years of Quantum Theory (1963) 247 19. Men and Ideas in the History of Atomic Theory (1971) 266 20. Jacques Solomon (1959) 297 21. Quantum Theory in 1929: Recollections from the First Copen- hagen Conference (1971) 302 22. Niels Bohr: An Essay Dedicated to Him on the Occasion of his Sixtieth Birthday, October 7,1945 (1945; 2nd edition 1961) 313 23. The Conception ofthe Meson Field: Some Reminiscences and Epistemological Comments (1968) 327 24. Nuclear Reminiscences (1972) 335 25. Celestial and Terrestrial Physics in Historical Perspective (1969) 346
PART II / EPISTEMOLOGY
1. On the Question of the Measurability of Electromagnetic Field Quantities (with Niels Bohr) (1933) 357 2. Field and Charge Measurements in Quantum Electrodynamics (with Niels Bohr) (1950) 401 3. On Quantum Electrodynamics (Among Essays Dedicated to Niels Bohr on the Occasion of his 70th Birthday) (1955) 413 4. On Quantization of Fields (1963) 442 5. The Evolution of the Idea of Causality (1942) 446 6. Strife about Complementarity (1953) 465 7. Complementarity and Statistics, I and II (1958) 484 8. Misunderstandings about the Foundations of Quantum Theory (1957) 495 9. Foundations of Quantum Theory and Complementarity (1961) 503 10. The Epistemological Conflict between Einstein and Bohr (Dedicated to Max Born on his 80th Birthday) (1963) 517 11. Niels Bohr's Contribution to Epistemology (1963) 522 T ABLE OF CONTENTS XXI
12. The Measuring Process in Quantum Mechanics (On the 30th Anniversary of the Meson Theory by Dr. H. Yukawa, 1965) (1965) 536 13. Statistical Causality in Atomic Theory: A General Introduc- tion to Irreversibility (1972 and 1974) 547 14. The Macroscopic Level of Quantum Mechanics (with C. George and I. Prigogine) (1972) 571 15. Quantum Theory and Gravitation (1966) 599 16. Questions of Method in the Consistency Problem of Quantum Mechanics (1968) 609 17. The Method of Physics (1968) 614 18. Some Reflections on Knowledge (1971) 637 19. Epistemology on a Scientific Basis (1971) 643 20. Condillac's Influence on French Scientific Thought (1972) 655 21. Unphilosophical Considerations on Causality in Physics (1971) 666 22. Irreversibility - a Lay Sermon (On the Occasion of Professor K. Bleuler's Sixtieth Birthday) (1977) 681 23. Berkeley Redivivus (Review of W. Heisenberg's Natural Law and the Structure of Matter) (1970) 686 24. The Wave-Particle Dilemma (1973) 688 25. A Voyage to Laplacia (1955) 704
PART III / THEORETICAL PHYSICS
1. On the Energy-Momentum Tensor (1940) 711 2. On the Definition of Spin for a Radiation Field (1942) 736 3. On the Behavior of a Canonical Ensemble during an Adiabatic Transformation (1942) 742 4. On the Isolated and Adiabatic Susceptibilities (1961) 747 5. On the Foundations of Statistical Thermodynamics (1955) 762 6. Questions of Irreversibility and Ergodicity (1962) 808 7a. Dynamical Theory of Nuclear Resonances (1968) 830 7b. Coupling between Compound and Single-Particle Resonances (1968) 861 8. The Structure of Quantum Theory (1968) 866 XXII T ABLE OF CONTENTS
PART IV / SOCIAL RELATIONS OF SCIENCE
1. The Organization of Scientific Research (1948) 881 2. The Atomic Researcher: The Atomic Physicist's Tasks, Goals and Methods (1968) 892 3. Technical and Social Aspects of the Development ofthe Euro- pean Scientific Research Organizations (1970) 897 4. Social and Individual Aspects of the Development of Science (1971) 902
BIBLIOGRAPHY OF THE WRITINGS OF LEON ROSENFELD 911
INDEX OF NAMES 922 INTRODUCTION
The decision to publish this volume was taken nearly two years ago. Rosenfeld himself took part in the preparations, and he planned to write an introduction which would of course have given an authoritative analysis of the articles and their interconnections. The papers he chose for this volume form only a small part of Rosenfeld's rich and varied scientific production, but the choice he made can yield an insight into his way of thinking by showing what he regarded to be really important and representative of his views. His extensive training in the humanities enabled Rosenfeld to survey many sides of human life and to trace interconnections between various fields of knowledge. Having mastered a number of languages, he could follow developments in many countries. In this respect his ramified international relations also played an important role. As a student Rosenfeld had already published several articles on mathematical and physical topics in a students' journal in Liege, but his scientific activity began in earnest in the late twenties. It was an exciting time, this 'heroic period' of physics when the newly developed methods of quantum physics, were being tested to their limits. Nearly every issue of the main physical journals - especially the German Zeitschrift fur Physik - brought theoretical contributions dealing with properties of atomic structure and proving the power of the novel theoretical tools. The rapid progress also gave a beautiful example of international co• operation on a broad scale, and Rosenfeld, at that time on studies abroad, in Gottingen and in Zurich, took a lively part in it. While some of his papers from that time deal with important problems, none of them are included into Part III (Theoretical Physics) where they could have served as examples of his participation in the early stages of the establishment of a consistent system of quantum physics. Perhaps he regarded these contributions rather as an introduction to what he felt to be most important in his life work: the study of the very foundations of the new field of physics. But even his later work on physical problems is repre- XXIV INTRODUCTION sented only to a small extent. As a matter offact, Rosenfeld had, through the years, made important contributions to nearly every field of modern physics. This can be seen from the full list of publications [See Bibliog• raphy, p. 911 - Ed.]. Here mainly such papers are included which touch upon foundations of physics. In particular, Rosenfeld's special interest in statistical physics and thermodynamics is connected with the role which statistical considerations play in quantum theory. It was at the end of the twenties that Rosenfeld became attached to the circle around Niels Bohr in Copenhagen. Bohr had just formulated his idea of complementarity, and problems of the epistemological implica• tions of quantum theory were then very much in the foreground of in• terest. Even when he held permanent positions in Belgium, the Nether• lands, and Great Britain, and visiting professorships in other countries, Rosenfeld continued to keep up his close connection with the Copenhagen group, until in 1958 he moved to Copenhagen to take a position at Nordita where he was active until his death in March 1974. The papers presented in Part II (Epistemology) occupy a most central position in Rosenfeld's scientific work. When Rosenfeld arrived in Copenhagen for the first time the discussion on the foundations of quantum theory, a discussion initiated by Bohr, had just started. Rosen• feld became fascinated by the perspectives opened by the new approach. He was interested in many aspects of physical theory, but here he was confronted with a way of presenting problems which appealed to his searching mind. Complementarity made it possible to penetrate much deeper into the fundamental problems of physical knowledge and threw light on the general situation in which a scientist finds himself when trying to bring experimental evidence into a consistent logical scheme. As is well known, the starting point of this development was due to the discovery of the quantum of action which specifies a lower limit to all interactions between physical objects. The apparent contradiction ex• hibited by the necessity to describe microscopic objects in some cases as particles and in other cases as waves finds its resolution in the fact that the experimental arrangements used in the one case are mutually ex• clusive, or, in Bohr's terminology, complementary, to those used in the other case. This complementary relationship between those situations for which space-time coordination, characteristic of the particle picture, is envisaged and those situations where we aim at establishing an energy• momentum balance, is essential for Bohr's reasoning. INTRODUCTION xxv
As a consequence of this analysis one has to replace the deterministic laws, typically used in classical physics, by statistical laws. This forced departure from a way of description of physical phenomena followed by scientists for many centuries gave rise to many, at times violent dis• cussions among physicists, echoes of which still can be heard. Rosenfeld took a leading part in these discussions. They are to be observed in many papers from his hand, some of them reprinted in Part II. It is charac• teristic of Rosenfeld that the chronologically most early paper on physical problems in the present volume (the still earlier articles 1.3 and 1.7, from 1927 and 1932 respectively; deal with the history of mathe• matics and classical optics) is placed as the first one in Section II. It is the classical paper on the measurement of electric and magnetic fields, written together with Bohr in 1933, one of the most fundamental con• tributions to the discussions of those years. Most of the other articles in this section contain more general presen• tations of their subject. Great effort is made and much skill displayed to explain the situation from many angles in order to convince those still reluctant that complementarity is only a logical consequence of experi• mental experiences obtained in atomic physics. In the first years, some physicists could not get out of "the metaphysical jungle which obscures the view". They could not reconcile themselves with the prospect of abandoning the accustomed idea of causality and replacing it by the more general method of statistical causality. In this connection the analysis of thought experiments (Gedankenexperimente), often sophisticated and ingeniously conceived, played an important role. The most famous exam• ple is the discussion between Bohr and Einstein which lasted for a quarter of a century (cf. 11.10 and 11.11). As can be seen from the articles, but perhaps even more from his correspondence with authors of papers sent to him, Rosenfeld took painstaking care in trying to disclose and discuss in detail basic mistakes and misunderstandings in the attempts by various authors to find contradictions in complementarity. His criticism could be slashing and expressed in an extremely sharp way if the author's reasoning was based on some vague philosophical ideas. However, if the manuscript - especially when written by a young scientist - con• tained a fair presentation and original ideas, Rosenfeld could go far in expressing his appreciation and encouragement and in assisting in the publication of the paper. XXVI INTRODUCTION
It was Bohr who on many occasions pointed to the far-reaching validity of complementarity, extending beyond the domain of quantum theory. Rosenfeld followed this thought in several directions. Thus, in later years he revived his active interest in thermodynamics. He took the view that in this field, although it belongs to classical physics, a statis• tical approach is unavoidable and that a kind of complementary rela• tionship can be established. This point was taken up in a work in collabo• ration with I. Prigogine (II.14). Also disciplines which seem to lie far away from physics came under the searchlight. An experiment is - to use Bohr's expression - something by which we can tell others what we have done and what we have learned. This emphasizes of course the question of the technical side of the experi• ment but also the importance of language as a tool for communication both on daily life level and in exchange of scientific information (see e.g. 11.18). Therefore, a study of the function of language is essential. Going further in the same direction we are presented with the problem of how the human mind works and this is again highly dependent on how it develops from its very beginning in infancy. It was no accident that Rosenfeld became so passionately interested in the work of Piaget whose research into the evolution of children's thinking through the various periods of their growth led to a reliable picture of changes in coordina• tion of impressions from the outside world. Piaget's work filled a gap, confirming what Helmholtz and Mach anticipated. Shortly before his last illness, Rosenfeld gave an inspiring course of lectures on Piaget's results. The importance he ascribed to Piaget's work can be seen from the fact that when he was entrusted with the organization of a symposium to commemorate the 50th anniversary of the Niels Bohr Institute in Copen• hagen he chose as its subject 'Statistical Causality'. In the introduction to the program of the symposium he emphasized that "in order to obtain an all-round survey of the position of statistical causality, it was necessary to include a consideration of the psychological side of the problem". A substantial part of the time was devoted to reports by Piaget and other psychologists working on similar lines, and a fruitful and animated discussion developed. Rosenfeld's immediate acceptance of the idea of complementarity was no doubt mainly due to his strict and logical way of thinking. Besides, he had for many years a close relation with Niels Bohr and in the day- INTRODUCTION XXVII to-day working together and discussing, Rosenfeld could not but find stimulus for his own lines of thinking. Now, Bohr had a peculiar method of writing papers. Every attempt to formulate sentences, every dis• cussion in order to find the right word or expression, was used to clarify his own ideas. No criticism, even the most superficial, was disregarded; on the contrary it gave Bohr a welcome opportunity to improve the argumentation. This procedure, even if it often became rather time• consuming, must have appealed very much to Rosenfeld's analytical mind. His own manuscripts were always the result of a prolonged and determined work at the improvement of the text. The way in which the idea of complementarity developed from the recent advances in physics was also in harmony with Rosenfeld's con• ception of the structure of science. In many of his articles he advocates the materialist view of the development of science. He is materialist in the sense that he regards experience and experiment as the only source of knowledge. All theories based on 'self-evident axioms' or a priori ideas are of no use and only apt to obscure things, to "put physics upside down". What matters is only and solely what we can learn from nature by asking it the right questions. All the time we have to be prepared for the possibility that new empirical evidence can force us to revise and even to abandon accustomed ideas. In the dialectical approach which is the leitmotifof the papers presented here, the development of science can, in short, be described as follows. When a certain amount of empirical information is collected, scientists try to create a conceptual framework which allows us to comprehend the known phenomena and predict the results of further investigations. The usefulness of the theory depends entirely on agreement of its predictions with experimental findings. Classical mechanics is an example of such a beautiful and consistent theory. The concepts developed for a certain domain can still be useful when our knowledge grows, perhaps supplemented by some new concepts. But it can also happen that in this development we are brought to the limit of the applicability of the old concepts. For the field lying outside this limit a new conceptual frame has to be conceived which is an antithesis of the old one. What one is aiming at is to create a synthesis, a broader, more general theory in which the old theory will be a special case for a limited domain of application. Examples of such a situation can, in our century, be found in the relativity XXVIII INTRODUCTION theory and in quantum physics. In the latter, description by means of deterministic laws had to be replaced by the more general notion of statistical causality. The deterministic description can however still be used in the limit where the quantum of action can be neglected, that is generally in macroscopic physics. There is nothing extraordinary or alarming in such a step. It has however given rise to so many discussions because determinism has been regarded by generations of scientists as a firm and a priori inherent basis of all scientific thinking. Rosenfeld's view was, as we have briefly sketched, diametrically opposite. The application of any method in science is justified only as long as it is adapted to the empirical situation. A detailed account of the whole problem is to be found for instance in 11.6. A major part of the present volume, Part I, is devoted to the history of science. One might think that occupation with this subject was for Rosenfeld a kind of a hobby. In the light of what was said earlier it be• comes clear however that it is not so. Historical research was for him a serious matter, a necessary consequence of his interest in epistemological problems. It is from the lesson derived from studies of the past that the present can better be understood. When Rosenfeld, a few years ago, gave an extensive course of lectures in Copenhagen on the foundations of physics it turned out to be a harmonious synthesis of a thorough analysis of the present situation in physics and a broad outlook upon various periods in the history of science and philosophy. The lectures were recorded and the transcript was intended to be used as outline materials for a major publication. It is most deplorable that Rosenfeld, who was one of the very few people with the necessary broad knowledge, was not given the time to write the planned book. Obviously, the borderline between Parts I and II cannot be very sharp. In II one finds extensive use of historical evidence, while in I many of the articles are more or less connected with the problems discussed in II. One important point should especially be noticed. As a natural con• sequence of his materialist view. Rosenfeld stresses the connection be• tween scientific progress and social conditions (cf. I.l and 2). He is aware of the fact that the studies in this field are only in their beginnings, but he did his best to encourage them. Actually, to underline the importance of the problem, Part IV, albeit rather short, is introduced as a separate heading: 'Social relations of science'. International co- INTRODUCTION XXIX operation in science should also be mentioned in this context. Rosenfeld not only expressed theoretical views of the paramount importance of such co-operation, but he also tried, in many ways, to implement his views in practice. He served as member of a number of international scientific bodies. He was the founder and editor of a journal which under his guidance became one of the leading journals in its field and brought contributions from all over the world. He also took part in meetings whose purpose was to bridge over difficulties in relations between people from countries with different cultural and political backgrounds, and he never gave up even when the difficulties seemed to be insurmountable. In the eyes of many people, a materialistic conception of history is unavoidably connected with a certain political attitude and above all with an uniformity of thought which does not allow for divergent opinions. Nothing could be more alien to Rosenfeld. In science, he was devoted to a complete openness to new experience and new ideas, and in general human relations he fought against prejudice and dogmatism. His ma• terialist conception has - as already stressed - to be understood as the belief that a scientific theory can only be based on what we learn from experience. He attacks severely the adherents of the politically coloured 'dialectical materialism' (his quotation marks) which he calls a meta• physical system (1.2, p. 12). It is hardly possible to state his position in sharper terms than he does himself in speaking of a dogmatic attitude, a "contemporary scholasticism which makes its adherents blind to the progress of scientific thought and misleads them into sterile opposition to it" (1.2, p. 13). Complementarity allowed Rosenfeld to realize that mutually excluding approaches to cope with a given situation may both be necessary to ensure a complete description (cf. 1.23, p. 329) where he says: "Philosophers will endlessly dispute whether this (duality of mat• ter and force) is a victory for materialism or for idealism. I am afraid I can only say, in the spirit of complementarity, that is neither the one nor the other". The same point is made in a witty travesty of Mark Twain's lines introducing the article on method on physics (11.17). Niels Bohr used to quote as an example the complementary relation• ship between seriousness and humour. The more stress is put on the one of them, the more the other disappears, but both are necessary to provide a proper balance in human life. Rosenfeld lived up to this balanced attitude and made many contributions to the humourous pic- xxx INTRODUCTION ture of physics. He did not refrain - as can be seen in several articles in this volume - from putting witty remarks into a serious scientific text. He also took active part in the organization of joking entertainment in connection with conferences and congresses. They always had some scientific point with a crazy twist. One of the last contributions from his side was the amusing sketch played after the closing dinner at a relativity conference in Copenhagen. It was also meant to celebrate J. A. Wheeler's 60th birthday and contained subtle digs at a number of participants. Rosenfeld disliked,to say the least, those philosophers who created theories at their writing desks with no regard to the information gained by the study of nature (cf. the quotation in 11.7 from Morgenstern, a German writer of grotesque poetry, very popular in the 1930's among the physicists in Copenhagen). Their products, he says, are more metaphysics than science. But if real philosophy is defined as an attempt to find common features and laws in the wide variety of human knowledge, without prejudices and above all without preconceived opinions, then Rosenfeld may rightly be called a philosopher par excellence. It would therefore seem appropriate to end this introductory note with a quotation from one of Rosenfeld's articles (See Bibliography [1953eJ) :
(It) is a vital requirement for fruitful scientific enquiry that the truth can only impose itself by its own strength and that the greatest disservice which can be done to it is to try to force evidence into any rigid system. STEFAN ROZENTAL Niels Bohr Institute University of Copenhagen 1974 MY INITIATION*
[1945f]
The first message I got from Bohr was a telegram, announcing that the Easter Conferencet was to be postponed two days. I was then - in 1929- in Gottingen and, together with Heitler, had expressed the wish to attend that famous Conference; we had both received from Klein a favourable answer. to which the aforementioned telegram brought the master's eleventh-hour correction. When we arrived in Copenhagen, Bohr in• formed us of the reason for the postponement: he had to complete ('with Klein's help') a Danish translation of some of his recent papers to be published as a Festskrift of Copenhagen University; he told us all about this venerable Festskrift tradition and added: 'It would have been a cata• strophe if that work had not been ready in time!' This struck me as a hyperbolic way of stating the matter. How little I imagined at that moment the tragedy hidden behind this seemingly innocuous procedure of putting the finishing touch to a paper! How little I knew that it was my destiny to playa part in a whole lot of such tragedies! My sole excuse for the failure to grasp the earnestness of this paper• writing subject is that I was by no means an exception in that respect. In fact. as experience taught me since, people are on the whole distressingly unimaginative on that point. Take, for instance, the case of the Faraday Lecture. Bohr arrived in London for the Faraday celebration with a manuscript of his lecture, which he described as 'practically finished.' There were just a few pages lacking. The plan was to seek the required isolation in the romantic environment of some old English inn, and in a week's time, 'with Rosenfeld's kind help' (he explained to Mr Carr, the secretary of the Chemical Society), the thing would be definitively dis• posed of. Mr Carr was delighted. After a week's hard labour in a rather crowded and thoroughly unromantic hotel, in which we had to wage a regular war of nerves against an irascible schoolmistress for the posses• sion of the parlour, the ten odd lacking pages had actually been written. We had furthermore gained the insight that a great improvement could be obtained by the mere addition of some twenty more pages. Bohr quite XXXII LEON ROSENFELD warmed up at this idea, which (he persuaded me) brought us really a good deal nearer to the end. I was accordingly dispatched to Mr Carr to report on the new development. Well, Mr Carr did not at all cheer the prospect; he was just annoyed; he even made no effort to conceal his annoyance. When I alluded to our having worked the whole week without respite, I am sorry to say he looked decidedly incredulous. I was quite downhearted when I left him. Fortunately, I had just then an appointment with Del• briick, whom I found in company of one of his innumerable lady-friends. He was a man of feeling and understanding; he comforted me like the true friend he was. But to return to the scene on the platform in Copenhagen station. What impressed me most about Bohr at this first meeting, was the benevolence radiating from his whole being. There was a paternal air about him, which was enhanced by the presence of some of his sons. These sons of Bohr's were a great matter of speculation to me. When I again saw Bohr at the Institute the next morning, there were also a few sons around him. Different ones, I thought; he must have a host of them. On the afternoon of the same day, however, I was bewildered at the sight of still another son at his side. He seemed to stamp them from the ground or draw them forth from his sleeve, like a conjurer. At length, however, I learned to distinguish the sons from one another and I found out that there was only a finite number of them after all. I don't know how the Athenian delegates for oracle consultation felt on their return from Delos. But I imagine their feelings must have been akin to mine after I had listened to Bohr's introductory lecture at the Conference. He had begun with a few general considerations calculated, no doubt, to convey to the audience that peculiar sensation of having the ground suddenly removed from under their feet, which is so effective in promoting receptiveness for complementary thinking. This preliminary result being readily achieved, he had eagerly hastened to his main subject and stunned us all (except Pauli) with the non-observability of the elec• tron spin. I spent the afternoon with Heitler pondering on the scanty fragments of the hidden wisdom which we had been able to jot down in our note books. Towards the evening we felt the need for some fortifica• tion and proceeded to the Str0g. The following evening we spent at the cinema, together with some others. Picture theatres have always been institutions of high educational MY INITIATION XXXIII value to young theoretical physicists. So it turned out this time too. There it was that Casimir started his important calculation of the magnetic field exerted by an atomic Dirac electron on the nucleus of the atom. He had to work under very trying circumstances. For as soon as any part of the show started, the lights went out, and poor Casimir had to wait until the lovers had safely got over their troubles and married and all before he could resume his calculations. He did not lose a second either: every time the lights went up, they invariably disclosed our friend bent over odd bits of paper and feverishly filling them with intricate formulae. The way in which he made the best of a desperate situation was truly admirable. It was inspiring to watch him. On the last day of the Conference I experienced the climax of my Copenhagen initiation. It came about rather unexpectedly in the follow• ing way. At the meeting that morning one of the most distinguished guests had developed some views about the vexed question of the 'cut' between system and observer, which seemed to me rather erroneous. Bohr, how• ever, had only opposed them feebly (as I thought); in his rather confused speech, the phrase 'very interesting' recurred insistently; and finally, turning to the speaker, he had concluded by expressing the conviction that 'we agree much more than you think.' I was much worried by this extraordinary attitude, the more so as the highbrow bench seemed to find it all right. I therefore ventured to explain my doubts straight away to Bohr. I began cautiously to state that the speaker's argument did not seem to me quite justified. 'Oh,' said Bohr quickly, 'it is pure nonsense!' So J knew J had been led astray by a mere matter of terminology. But now the unexpected happened. Bohr summoned me to a little room, in the middle of which stood a rather long table. He manoeuvred me towards that table and as soon as I stood leaning against it, he began to describe around it, at a rather lively pace, a Keplerian ellipse of large eccentricity, of which the place where I was standing was a focus. All the time, he was talking in a soft low voice, explaining to me the broad out• lines of his philosophy. He walked with bent head and knit brows; from time to time, he looked up at me and underlined some important point by a sober gesture. As he spoke, the words and sentences which I had read before in his papers suddenly took life and became loaded with meaning. It was one of the few solemn moments that count in an existence, the revelation of a world of dazzling thought, truly an initiation. XXXIV LEON ROSENFELD
It is generally recognized that no initiation can be properly accom• plished without being combined with a painful experience of some sort. In that particular also my initiation left nothing to be desired. For since I had to strain my hearing to the utmost to catch the master's words, I was compelled to execute a continuous rotation at the same rate as that of his orbital motion. The true purpose ofthe ceremony, however, did not occur to me until Bohr ended by emphasizing that you can't even catch a glimpse of complementarity if you don't feel completely dizzy. When I heard that, I realized everything and I could only pay him a silent homage of thankfulness and admiration for such touching solicitude.
NOTE
* [This text was condensed from (1945f) for A Random Walk in Science, compiled by R. L. Weber and edited by E. Mendoza (The Institute of Physics, London and Bristol, and Crane, Russak & Co., New York, 1973) - Ed.] t [For a detailed account by Rosenfeld of the first Copenhagen Conference in 1929 see [197Ic] reprinted in this volume on p. 302 - Ed.]