Michael Eckert Statement and Readings Five decades of quantum physics: How Sommerfeld faced the quantum (r)evolution in the first half of the 20th century—a biographical perspective Michael Eckert Deutsches Museum, Munich, Germany Abstract Sommerfeld's attitude towards foundational questions—in particular with regard to the quantum—will be described with respect to the changing context and content of his research at significant stages from the 1910s to the 1940s. In the early period (before 1913) Sommerfeld focused on his so-called "h-hypothesis" as a general scheme to account for processes like the photoelectric effect, the emission of x-ray bremsstrahlung and other non-periodic elementary processes. In the subsequent period of the "Bohr–Sommerfeld model" he perceived foundational questions from the vantage point of atomic spectra. With the advent of quantum mechanics and new discoveries like the Compton effect and electron diffraction in the 1920s Sommerfeld made wave mechanics the basis from which he perceived quantum riddles. This became a major effort during the 1930s when he transformed the Wavemechanical Supplementary Volume of Atomic Structure and Spectral Lines from 1929 into a new edition in 1939. Sommerfeld kept a vivid interest in the progress of quantum research until his death in 1951. I hope that this biographical approach illustrates how foundational questions in physics depend on time and on the broader context. Although I reach only a little beyond the formative period of quantum mechanics I hope the lessons drawn from this example are more generally of interest. Michael Eckert translated by Tom Artin Arnold Sommerfeld Science, Life and Turbulent Times 1868–1951 Michael Eckert Deutsches Museum Munich , Germany Translation of Arnold Sommerfeld: Atomphysiker und Kulturbote 1868–1951, originally published in German by Wallstein Verlag, Göttingen ISBN ---- ISBN ---- (eBook) DOI ./---- Springer New York Heidelberg Dordrecht London Library of Congress Control Number: © Springer Science+Business Media New York Th is work is subject to copyright. All rights are reserved by the Publisher, whether the whole or part of the material is concerned, specifi cally the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfi lms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. 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While the advice and information in this book are believed to be true and accurate at the date of publication, neither the authors nor the editors nor the publisher can accept any legal responsibility for any errors or omissions that may be made. Th e publisher makes no warranty, express or implied, with respect to the material contained herein. Printed on acid-free paper Springer is part of Springer Science+Business Media (www.springer.com) Acknowledgment In the case of such a source-dependent work, fi rst thanks are due Sommerfeld’s heirs for access to the private papers and for permission to make full use of their content. Sommerfeld’s granddaughter, Monika Baier, deserves particular thanks for ordering her grandfather’s private papers and for providing valuable information on the family background. Th e archivists of the various public institutions in which Sommerfeld correspondence resides, too, are gratefully acknowledged for their readiness to help. Th e bibliography reveals how much support the project has thereby received. Cited passages from letters and texts from other source materials have been adapted to modern notation for the sake of legibility. Numerous letters cited here only in excerpts are printed in full in editions of correspondence. In these cases, references are given indicating the respective volume of the published corre- spondence (e.g., ASWB I and ASWB II as abbreviations for the two volumes of Arnold Sommerfeld – Wissenschaftlicher Briefwechsel, Band I und II : since in those volumes the letters are printed in chronological order, there is no need to specify page or letter numbers). Th us the reader can study the respective letters in full and in the context of the other correspondence reproduced there. Since Sommerfeld’s private letters are not publicly accessible, they are identifi ed only by date, and no source is given. It is conventional for the published work of a scientist to take precedence over unpublished papers at the beginning of a biographical endeavor. Th is approach refl ects his life’s work as a scientist as it has been perceived by his contemporaries. Usually this kind of biographical work begins with the mile-stone birthdays mark- ing decades of a scientist’s life. 1 Th us, festschrifts were assembled to celebrate Sommerfeld’s 60th, 70th, and 80th birthdays. In 1968, on the occasion of his 100th birthday, the physicists of the University of Munich, organized an “Arnold Sommerfeld Centennial Memorial Meeting,” and an “International Symposium on the Physics of the One- and Two-Electron Atoms.” On this occasion, his succes- sor at the Institute for Th eoretical Physics (Fritz Bopp) was commissioned by the Bavarian Academy of Sciences to arrange for Sommerfeld’s most important scien- tifi c papers to be published in the form of a four-volume edition. 2 Th e biographer is gratefully obliged to all those involved in this preliminary work. Th e editors of the scientifi c correspondence (the author and Karl Märker) had the support of the Munich Physics Department (especially Harald Fritzsch and Herbert Wagner), and the Bavarian Academy of Sciences (in the person of Past President Arnulf Schlüter). Special thanks are also due the Dean of the Faculty of Physics (Axel Schenzle) of Munich University for the fi nancial support that has enabled the translation of the German original of this biography into English. 1 See chapter 14. 2 Sauter, Sommerfeld , 1969. v acknowledgment Th e biographer owes thanks and acknowledgment also to his colleagues in the history of science who have concerned themselves from a historical perspective with Sommerfeld and his fi elds of research. Atop the list are John L. Heilbron, and Paul Forman, who as participants in the SHQP project actually fi rst set Sommerfeld research in motion. Subsequently, above all Armin Hermann, Ulrich Walter Benz, and Karl von Meyenn have helped cause this spark to jump over to Germany. In recent years, a new project on the history of quantum physics 3 at the Max Planck Institute for History of Science in Berlin brought further impetus to analyze Sommerfeld’s work within the network of modern atomic and quantum theory. For this biography, it was a piece of good fortune to participate in this project. It would lead too far afi eld to list all the names of colleagues and friends who in this and in previous decades have researched the history of quantum physics—and thus also important aspects of the fi eld of Sommerfeld biography. Even if, in retrospect, quantum physics be deemed Sommerfeld’s most signifi - cant area of research, the less spectacular mathematical, physical, and technical work to which he devoted himself in the course of his long scientifi c career deserves inclusion in his biography. Th e gratitude of the historian of science and biographer is therefore directed to all those who have devoted their scholarly attention to these aspects of Sommerfeld’s work, and thus in diverse ways have advanced the work of this biography. Th eir names and contributions are to be found in the bibliography. Special thanks to our colleagues at the Research Institute of the Deutsches Museum, which constitutes a particularly sympathetic setting for the work of history of sci- ence. Last but not least, thanks to the German Research Foundation, without whose fi nancial support this project would not have been possible. 3 http://quantum-history.mpiwg-berlin.mpg.de/main/ (28 January 2013) vi Contents Prologue. xi Königsberg Roots . . Childhood. . School Years . . University Study. . A Competition . . Th e Dissertation. . A Mechanical Basis of Electrodynamics . Setting the Course. . Missed Opportunities . . Military Service . . Mineralogical Interlude . . Stick It Out, or Resign? . . Approach to Felix Klein . . Physics or Mathematics?. Klein’s Assistant . . Physical Mathematics . . Th en I’ll Grow into the Lectureship . . Reading Room and Model Collection . . Habilitation . . Lecturer . . Th e Engagement. Clausthal . . An Off er from America . . Th e Appointment at the Clausthal School of Mining . . Th e School of Mining . . Th e Wedding . . Gyroscope Matters and Electrodynamic Problems. . Encyclopedia Travels. . Gyroscope + Encyclopedia = Aachen-Recommendation . vii contents Aachen . . Backgrounds of an Appointment . . Rapprochement with Engineering. . Technological Expert . . Family Life . . Duties and Inclinations . . Th e “Super-Mechanics” of Electrons. . “In Truth I Am No Engineering Professor; I Am a Physicist” . Munich . . Academic Traditions. . Quarrel over Electron Th eory . . Th e Origins of the Sommerfeld School . . Th e Mathematical Attack . . Th e “h-Discovery” . . Th e First Solvay Congress . . X-Rays and Crystals . Physics in War and Peace . . “For Me, the Political Future Lies in Utter Darkness” .