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  QUANTUM GENERATIONS

  QUANTUM GENERATIONS

  A HISTORY OF PHYSICS IN THE

  TWENTIETH CENTURY

  HELGE KRAGH

  PRINCETON UNIVERSITY PRESS

  PRINCETON, NEW JERSEY

  Copyright © 1999 by Princeton University Press

  Published by Princeton University Press, 41 William Street,

  Princeton, New Jersey 08540

  In the United Kingdom: Princeton University Press, 3 Market Place,

  Woodstock, Oxfordshire OX20 1SY

  All Rights Reserved

  Fifth printing, and first paperback printing, 2002

  Paperback ISBN 0 691 09552 3

  The Library of Congress has cataloged the cloth edition of this book as follows

  Kragh, Helge, 1944

  Quantum generations : a history of physics in the twentieth

  century / Helge Kragh.

  p. cm.

  Includes bibliographical references and index.

  ISBN 0 691 01206 7 (cloth : alk. paper)

  1. Physics History 20th century. I. Title.

  QC7.K7 1999

  530'.09'04 dc21 99 17903

  British Library Cataloging in Publication Data is available

  www.pup.princeton.edu

  ISBN-13: 978-0-691-09552-3 (pbk.)

  eISBN: 978-0-691-21419-1

  R0

  CONTENTS

  PREFACE xi

  PART ONE: FROM CONSOLIDATION TO REVOLUTION 1

  CHAPTER ONE

  Fin-de-Siècle Physics: A World Picture in Flux 3

  CHAPTER TWO

  The World of Physics 13

  Personnel and Resources 13

  Physics Journals 19

  A Japanese Look at European Physics 22

  CHAPTER THREE

  Discharges in Gases and What Followed 27

  A New Kind of Rays 28

  From Becquerel Rays to Radioactivity 30

  Spurious Rays, More or Less 34

  The Electron before Thomson 38

  The First Elementary Particle 40

  CHAPTER FOUR

  Atomic Architecture 44

  The Thomson Atom 44

  Other Early Atomic Models 48

  Rutherford’s Nuclear Atom 51

  A Quantum Theory of Atomic Structure 53

  CHAPTER FIVE

  The Slow Rise of Quantum Theory 58

  The Law of Blackbody Radiation 58

  Early Discussions of the Quantum Hypothesis 63

  Einstein and the Photon 66

  Specific Heats and the Status of Quantum Theory by 1913 68

  CHAPTER SIX

  Physics at Low Temperatures 74

  The Race Toward Zero 74

  Kammerlingh Onnes and the Leiden Laboratory 76

  Superconductivity 80

  CHAPTER SEVEN

  Einstein’s Relativity, and Others’ 87

  The Lorentz Transformations 87

  Einsteinian Relativity 90

  From Special to General Relativity 93

  Reception 98

  CHAPTER EIGHT

  A Revolution that Failed 105

  The Concept of Electromagnetic Mass 105

  Electron Theory as a Worldview 108

  Mass Variation Experiments 111

  Decline of a Worldview 114

  Unified Field Theories 116

  CHAPTER NINE

  Physics in Industry and War 120

  Industrial Physics 120

  Electrons at Work, I: Long-Distance Telephony 123

  Electrons at Work, II: Vacuum Tubes 126

  Physics in the Chemists’ War 130

  PART TWO: FROM REVOLUTION TO CONSOLIDATION 137

  CHAPTER TEN

  Science and Politics in the Weimar Republic 139

  Science Policy and Financial Support 139

  International Relations 143

  The Physics Community 148

  Zeitgeist and the Physical Worldview 151

  CHAPTER ELEVEN

  Quantum Jumps 155

  Quantum Anomalies 155

  Heisenberg’s Quantum Mechanics 161

  Schrödinger’s Equation 163

  Dissemination and Receptions 168

  CHAPTER TWELVE

  The Rise of Nuclear Physics 174

  The Electron-Proton Model 174

  Quantum Mechanics and the Nucleus 177

  Astrophysical Applications 182

  1932, Annus Mirabilis 184

  CHAPTER THIRTEEN

  From Two to Many Particles 190

  Antiparticles 190

  Surprises from the Cosmic Radiation 193

  Crisis in Quantum Theory 196

  Yukawa’s Heavy Quantum 201

  CHAPTER FOURTEEN

  Philosophical Implications of Quantum Mechanics 206

  Uncertainty and Complementarity 206

  Against the Copenhagen Interpretation 212

  Is Quantum Mechanics Complete? 215

  CHAPTER FIFTEEN

  Eddington’s Dream and Other Heterodoxies 218

  Eddington’s Fundamentalism 218

  Cosmonumerology and Other Speculations 221

  Milne and Cosmophysics 223

  The Modern Aristotelians 226

  CHAPTER SIXTEEN

  Physics and the New Dictatorships 230

  In the Shadow of the Swastika 230

  Aryan Physics 236

  Physics in Mussolini’s Italy 238

  Physics, Dialectical Materialism, and Stalinism 240

  CHAPTER SEVENTEEN

  Brain Drain and Brain Gain 245

  American Physics in the 1930s 245

  Intellectual Migrations 249

  CHAPTER EIGHTEEN

  From Uranium Puzzle to Hiroshima 257

  The Road to Fission 257

  More than Moonshine 261

  Toward the Bomb 265

  The Death of Two Cities 269

  PART THREE: PROGRESS AND PROBLEMS 277

  CHAPTER NINETEEN

  Nuclear Themes 279

  Physics of Atomic Nuclei 279

  Modern Alchemy 283

  Hopes and Perils of Nuclear Energy 285

  Controlled Fusion Energy 290

  CHAPTER TWENTY

  Militarization and Megatrends 295

  Physics A Branch of the Military? 295

  Big Machines 302

  A European Big Science Adventure 308

  CHAPTER TWENTY ONE

  Particle Discoveries 312

  Mainly Mesons 312

  Weak Interactions 317

  Quarks 321

  The Growth of Particle Physics 325

  CHAPTER TWENTY TWO

  Fundamental Theories 332

  QED 332

  The Ups and Downs of Field Theory 336

  Gauge Fields and Electroweak Unification 339

  Quantum Chromodynamics 344

  CHAPTER TWENTY THREE

  Cosmology and the Renaissance of Relativity 349

  Toward the Big Bang Universe 349

  The Steady State Challenge 354

  Cosmology after 1960 357

  The Renaissance of General Relativity 361

  CHAPTER TWENTY FOUR

  Elements of Solid State Physics 366

  The Solid State Before 1940 366

  Semiconductors and the Rise of the Solid State Community 370

  Breakthroughs in Superconductivity 375

  CHAPTER TWENTY FIVE

  Engineering Physics and Quantum Electronics 382

  It Started with the Transistor 382

  Microwaves, the Laser, and Quantum Optics 386

  Optical Fibers 391

  CHAPTER TWENTY SIX

  Science under Attack Physics in Crisis? 394

  Signs of Crisis 394


  A Revolt against Science 401

  The End of Physics? 405

  CHAPTER TWENTY SEVEN

  Unifications and Speculations 409

  The Problem of Unity 409

  Grand Unified Theories 411

  Superstring Theory 415

  Quantum Cosmology 419

  PART FOUR: A LOOK BACK 425

  CHAPTER TWENTY EIGHT

  Nobel Physics 427

  CHAPTER TWENTY NINE

  A Century of Physics in Retrospect 440

  Growth and Progress 440

  Physics and the Other Sciences 444

  Conservative Revolutions 447

  APPENDIX

  Further Reading 453

  BIBLIOGRAPHY 461

  INDEX 481

  PREFACE

  THIS WORK WAS written between 1996 and 1998, at the suggestion of Princeton University Press. Originally, when I accepted the invitation to write a book about the development of physics during the twentieth century, I thought it would be a relatively easy matter. I soon became wiser. I should have known that it is simply not possible to write a balanced and reasonably comprehensive one-volume account of twentieth-century physics. What follows is a substitute, a fairly brief and much condensed and selective account of what I believe have been the most significant developments in a century of physical thought and experiment that can well be called the most important century of physics.

  The book is structured in three largely chronological parts. The first part covers developments from the 1890s to about 1918, the end of World War I. The second part concentrates on developments between the two world wars, roughly 1918 1945, and the third part takes up developments in the remainder of the century. The chosen periodization should be uncontroversial, and so should the decision to start in the mid-1890s rather than in 1900. It is generally accepted that “modern physics” started with the great discoveries of the 1890s and not with Planck’s introduction of the quantum discontinuity in 1900.

  I have endeavored to write an account that goes all the way up to the present and so includes parts of very recent developments that normally would be considered to be “not yet historical.” There are problems with writing historically about recent developments, but these are practical problems and not rooted in contemporary science being beyond historical analysis. The book is of a type and size that preclude any ambitions of comprehensiveness, not to mention completeness. At any rate, a “complete” history of twentieth-century physics would probably be as pointless as it would be impossible to write from a practical point of view. Like most historical works, this one is selective and limited in scope and content. The selections can undoubtedly be criticized. The material I have included has been chosen for a variety of reasons, one of them being the availability of historical writings and analyses. The book’s goal is to give an account of the development of physics during a one-hundred-year period that is digestible, informative, and fairly representative. There are, unavoidably, many interesting topics and subdisciplines that I do not include, in part because of lack of space and in part because of lack of secondary sources. Among the topics that I originally contemplated to include, but in the end had to leave out, are optics, materials science, chemical physics, geophysics, medical physics, physics in third-world countries, and the post-1950 discussion concerning the interpretation of quantum mechanics. Yet I believe that what is included does not, in spite of the more or less arbitrary selection criteria, misrepresent to any serious extent the general trends in the development of modern physics.

  The problem of a balanced account is a difficult one, not only with regard to subdisciplines and dimensions, but also with regard to nations. Physics is and has always been international, but of course, some nations have contributed more to scientific progress than others. My account is essentially a history of physics in Europe and North America, with some mention also of contributions from Japan. This is simply a reflection of how the important contributions to physics have been distributed among nations and geographical regions. Whether one likes it or not, most of the world’s nations have played almost no role at all in the development of modern physics. One of the significant trends of the postwar period has been the dominance of American physicists in a science that was originally European. Because of this dominance, and because of the strong position that American scholars have in the history of science, the historical knowledge of modern American physics is much richer than it is in the case of Europe and other regions, including the former Soviet Union. It is quite possible that the relative predominance of writings about American physics has caused my account to focus too much on the American scene, but under the circumstances, there was little I could do about it.

  Taken together, the twenty-nine chapters cover a broad spectrum of physics, not only with respect to topics and disciplines, but also with respect to the dimensions of physics. We should always keep in mind that physics (or the physical sciences) is a rich and multifaceted area that has implications far beyond the purely scientific aspects related to fundamental physics. I have wanted to write a broad book, although not so broad that it loses its focus on what is distinctly the world of physics. The present work is not devoted solely to the scientific or intellectual aspects of physics, but neither does it concentrate on social and institutional history. It tries to integrate the various approaches or, at least, to include them in a reasonably balanced way. I have also paid more attention to applied or engineering physics than is usually done. To ignore the physics-technology interface, and concentrate on so-called fundamental physics alone, would surely give a distorted picture of how physics has developed in this century. Not only are many of the world’s physicists occupied with applied aspects of their science, and have been so during most of the century, but it is also largely through the technological applications that physics has become a major force of societal change.

  The intended audience of the book is not primarily physicists or specialists in the history of science. It is my hope that it will appeal to a much broader readership and that it may serve as a textbook in courses of an interdisciplinary nature or in introductory courses in physics and history. With a few exceptions I have avoided equations, and although the book presupposes some knowledge of physics, it is written mainly on an elementary level. My decision to avoid the note apparatus that is often seen as a hallmark of so-called academic books is an attempt to make the book more easily accessible to readers not acquainted with the (sometimes rather artificial) note system of more scholarly works. In almost all cases of citations, I have included references in the text to sources where they can be readily found. Rather than referring to the original source, I have in most cases referred to a later, secondary source, quite often the place where I happened to pick up the quotation. In a book of this type, there is no point in numerous references to old papers in Annalen der Physik or Philosophical Magazine; the reader who might want to dig up the original source can do so via the source I have quoted. The entire book is, to a large extent, based on secondary sources, especially the many fine books and articles written by historians of the physical sciences. I have also drawn freely and extensively on some of my earlier works dealing with the history of modern physics, chemistry, technology, and cosmology.

  The source problem is quite different with regard to physics in the last third or quarter of the century. Whereas there is an abundance of secondary sources dealing with older developments in physics, written by either historians or participants, there are only few historical analyses of post-1960 physics (high-energy physics is an exception). Within this part of the chronology, I have had to base my account on useful material that happens to exist, on physicists’ more or less historically informed recollections, and on a not-very-systematic survey of what I could find in scientific articles and reviews. Physics Today has been a helpful source; references to this journal in Part Three are abbreviated PT. The bibliography and the appendix on “further reading” list a good deal of the literature that th
e reader may wish to consult in order to go more deeply into the subjects covered by this book.

  The working title of the book was originally Revolution through Tradition. With this title I wanted to refer to the dialectics between existing theories and revolutionary changes that has been characteristic of physics during the twentieth century. There have indeed been revolutions in the theoretical frameworks of physics, but these have not been wholesale rejections of the classical traditions; on the contrary, they have been solidly connected with essential parts of the physics of Newton, Maxwell, and Helmholtz. Relativity theory and quantum mechanics, undoubtedly the two major revolutions in twentieth-century physical thought, were carefully constructed to correspond with existing theories in the classical limits.

  The respect for traditions has likewise been a characteristic theme in all the major theoretical changes that occurred after the completion of quantum mechanics. To the extent that these may be termed revolutionary, they have been conservative revolutions. Changes have been much less important on the methodological level than on the cognitive level. There have been some changes, but not of a fundamental nature. Basically, the accepted methods of science of the 1990s are the same methods that were accepted in the 1890s. If we are looking for really radical changes during the last three-quarters of the century, we should not look toward the methods, the conceptual structure, or the cognitive content of physics, but rather toward the basic fabric of the world, the ontology of physics; or we should look toward the social, economic, and political dimensions. In terms of manpower, organization, money, instruments, and political (and military) value, physics experienced a marked shift in the years following 1945. The sociopolitical changes made physics in 1960 a very different science than it had been a century earlier, but they did not cause a corresponding shift in the methodological and cognitive standards. In any event, this is not the place to discuss these broader issues at any length. In the book that follows, I have described, rather than analyzed, important parts of the development of physics between 1895 and 1995. The reader who is interested to draw the big picture say, to evaluate the revolutionary changes and make comparisons over the course of a century should be better equipped with the material and information that are presented here.

  I would like to express my thanks to my colleague Ole Knudsen, who read the manuscript and suggested various improvements.