Einstein and the Quantum

EINSTEIN AND THE QUANTUM

EINSTEIN
AND THE
QUANTUM

THE QUEST OF THE VALIANT SWABIAN

A. DOUGLAS STONE

PRINCETON UNIVERSITY PRESS

PRINCETON AND OXFORD

Copyright © 2013 by Princeton University Press
Published by Princeton University Press, 41 William Street, Princeton, New Jersey 08540
In the United Kingdom: Princeton University Press, 6 Oxford Street, Woodstock, Oxfordshire OX20 1TW

press.princeton.edu

Jacket photograph: Albert Einstein reading. Courtesy of The Hebrew University of Jerusalem / Corbis Historical Images. Personality rights of ALBERT EINSTEIN are used with permission of The Hebrew University of Jerusalem. Represented exclusively by GreenLight.

All Rights Reserved

Library of Congress Cataloging-in-Publication Data

Stone, A. Douglas, 1954–

Einstein and the quantum : the quest of the valiant Swabian / A. Douglas Stone.

   pages      cm

Includes bibliographical references and index.

ISBN 978-0-691-13968-5 (hardback)

1. Einstein, Albert, 1879–1955. 2. Physicists—Biography. 3. Quantum theory. 4. Science—History. I. Title.

QC
16.
E
5
S
76   2013

530.12—dc23      2013013162

British Library Cataloging-in-Publication Data is available

This book has been composed in Verdigris MVB

Printed on acid-free paper. ∞

Printed in the United States of America

10 9 8 7 6 5 4 3 2 1

This book is dedicated to my father, Alan, who has been my intellectual inspiration, and to my wife, Mary, who has been my emotional inspiration.

Science as something already in existence
, already completed, is the most objective, most impersonal thing that we humans know. Science as something coming into being, as a goal, however, is just as subjectively, psychologically conditioned, as all other human endeavors.

—ALBERT EINSTEIN, 1932

CONTENTS

Acknowledgments
ix

INTRODUCTION
A Hundred Times More Than Relativity Theory 1

CHAPTER
1
     “An Act of Desperation” 5

CHAPTER
2
     The Impudent Swabian 15

CHAPTER
3
     The Gypsy Life 21

CHAPTER
4
     Two Pillars of Wisdom 26

CHAPTER
5
     The Perfect Instruments of the Creator 36

CHAPTER
6
     More Heat Than Light 44

CHAPTER
7
     Difficult Counting 51

CHAPTER
8
     Those Fabulous Molecules 62

CHAPTER
9
     Tripping the Light Heuristic 70

CHAPTER
10
   Entertaining the Contradiction 80

CHAPTER
11
   Stalking the Planck 86

CHAPTER
12
   Calamity Jeans 94

CHAPTER
13
   Frozen Vibrations 103

CHAPTER
14
   Planck's Nobel Nightmare 111

CHAPTER
15
   Joining the Union 122

CHAPTER
16
   Creative Fusion 129

CHAPTER
17
   The Importance of Being Nernst 141

CHAPTER
18
   Lamenting the Ruins 149

CHAPTER
19
   A Cosmic Interlude 160

CHAPTER
20
   Bohr's Atomic Sonata 168

CHAPTER
21
   Relying on Chance 181

CHAPTER
22
   Chaotic Ghosts 193

CHAPTER
23
   Fifteen Million Minutes of Fame 204

CHAPTER
24
   The Indian Comet 215

CHAPTER
25
   Quantum Dice 228

CHAPTER
26
   The Royal Marriage:
E
=
mc
²
=
hν
241

CHAPTER
27
   The Viennese Polymath 254

CHAPTER
28
   Confusion and Then Uncertainty 268

CHAPTER
29
   
Nicht diese Töne
279

Appendix 1: The Physicists
287

Appendix 2: The Three Thermal Radiation Laws
291

Notes
295

References
319

Index
325

ACKNOWLEDGMENTS

This project began after I gave several public lectures at Aspen and at Yale on Einstein, Planck, and the beginning of quantum theory, when it became clear that most of this story was completely unknown both to the interested layman and to most working physicists. While several eminent historians of science, T. S. Kuhn, Martin Klein, Abraham Pais, and John Stachel for example, have written excellent but relatively technical works analyzing various facets of Einstein's work on quantum theory, no book for the general reader had attempted to synthesize all this into a complete picture. I have tried to fill that void with this book, while making it a fun read along the way. The book is based on the Collected Papers of Albert Einstein and the large body of outstanding historiography that has been produced on the history of quantum theory, blended with material from a number of biographies of Einstein, with a particular debt to the recent ones by Albrecht Folsing and Walter Isaacson. While I chose not to footnote quotations in the text, all their sources are identified in extensive notes at the back of the book.

I want to thank the late Martin Klein for his encouragement at the very early stages of this project, and Walter Isaacson for his generous advice and assistance, which was so important to a first-time author. I am very grateful to my editor, Ingrid Gnerlich, for her critical reading of the manuscript and useful guidance, and to Deborah Chasman, who made key suggestions for improving my initial draft. I also want to thank Samantha Hasey and Eric Henney at Princeton University Press, who helped with the final stages of preparation for publication. Barbara Wollf at the Albert Einstein Archive of the Hebrew University in Jerusalem was very generous with her advice and experience relating to the copyright permissions I was seeking, and Andy Shimp helped
me navigate the library systems at Yale and retrieve difficult-to-find items. Both my father, Alan Stone, and my wife, Mary Schwab Stone, read the work with a keen eye and helped me immeasurably, not the least in keeping up my enthusiasm for the project. My son, Will Stone, found time between his journalistic pursuits to work as my editorial assistant in assembling the final version of the manuscript.

EINSTEIN AND THE QUANTUM

INTRODUCTION

A HUNDRED TIMES MORE THAN RELATIVITY THEORY

“Let's see if Einstein can solve our problem.” This was not an idea I had ever entertained, much less verbalized, during my previous twenty-six years doing research in quantum physics. Physicists don't read the works of the great masters of earlier generations. We learn physics from weighty textbooks in which the ideas are stated with cold-blooded logical inevitability, and the history that
is
mentioned is sanitized to eliminate the passions, egos, and human frailties of the great “natural philosophers.” After all, since physical science (we believe) is a cumulative discipline, why shouldn't we downplay or even censor the missteps and misunderstandings of our predecessors? It is daunting enough to attempt to master and then extend the most complex concepts produced by the human mind, such as the bizarre description of the atomic world provided by quantum theory. Wouldn't telling the real human history of discovery just confuse people?

Thus, while I had studied history and philosophy of science avidly as an undergraduate, I had not read a single word written by Einstein during my actual career as a research physicist. I was of course aware that Einstein had contributed to the subject of quantum physics. Even freshman physics students learn that Einstein explained the photoelectric effect and said something fundamental about the quantized nature of light. And both atomic and solid-state physics (my specialty) have specific equations of quantum theory named for Einstein. So clearly the guy did
something
important in the subject. But the most familiar fact about Einstein and quantum mechanics is that
he just didn't
like it
. He refused to use the theory in its final form. And troubled by the fundamental indeterminism of quantum mechanics, he famously dismissed its worldview with the phrase “God does not play dice.”

Despite its esoteric-sounding name, quantum mechanics represents arguably the greatest achievement of human understanding of nature. By the end of the nineteenth century progress in physical science was stymied by the most basic problem: what are the fundamental constituents of matter, and how do they work? The existence of atoms was fairly well established, but they were clearly much too small to be observed in any direct manner. Hints were emerging from indirect probes that the microscopic world did not obey the settled laws of macroscopic Newtonian physics; but would scientists ever be able to understand and predict the properties of objects and forces so far from our everyday experience? For decades the answer was in doubt, until a theory emerged, a theory that has now withstood almost a century of tests and extensions. That theory has wrung human knowledge from the deep interior of the atomic nucleus and from the vacuum of intergalactic space. It is the theory that most physicists use every day in their work. This is the theory that Einstein rejected. Thus most physicists think of Einstein as playing a significant but still secondary role in this intellectual triumph.

I might have continued with this conventional view of Einstein and quantum physics for my entire career, if not for a coincidental intersection of my own research with that of the great man. I am interested in quantum systems, which if they were not microscopic but were scaled up in size to everyday proportions, would behave “chaotically.” In physics this is a technical term; it means that very small differences in the initial state of a system lead to large differences in the final state, similar to the way a pencil, momentarily balanced on its point, will fall to the left or right when nudged by the smallest puff of air. I was searching (with one of my PhD students) for a good explanation of the difficulty that arises when mixing this sort of unstable situation with quantum theory. I recalled hearing that Einstein had written something related to this in 1917 and, almost as a lark, I suggested that we see if this work were relevant to our task.

Well the joke was on us. When we finally got our hands on the paper, we quickly realized that Einstein had put his finger on the essence of the problem and had delineated when it has a solution,
before
the invention of the modern quantum theory. Moreover, Einstein wrote with great lucidity about the subject, so that it seemed as if he were speaking directly to us, a century later. There was nothing dated or quaint about the analysis. For the first time in a long while, I found myself thinking, “Wow, this man really was a genius.”

This experience piqued my interest in the actual history of Einstein and quantum theory, and as I delved into the subject I came to a stunning realization. It was Einstein who had introduced almost all the revolutionary ideas underlying quantum theory, and who saw first what these ideas meant. His ultimate rejection of quantum theory was akin to Dr. Frankenstein's shunning of the monster he had originally created for the betterment of mankind. Had Einstein not done so, in all likelihood
he
would be seen as the father of the modern theory.

This is not a view that one could extract from any of the popular biographies of Einstein, where the focus is always on his development of relativity theory. Nonetheless, I discovered to my surprise that, for much of Einstein's scientifically productive career, he was obsessed with solving the problems of quantum theory, not relativity theory. He commented to his friend the Nobel laureate Otto Stern, “
I have thought a hundred times
as much about the quantum problems as I have about Relativity Theory.”

It is crucial to understand that while relativity theory is an important part of modern physics, for most of us quantum mechanics
is
the theory of everything. Quantum mechanics explains the periodic table of the elements, the nuclear reactions that power the sun, and the greenhouse effect that leads to global warming. The quantum theory of radiation and electrical conduction underlies all of modern information technology. Moreover, quantum mechanics has already subsumed part of relativity theory (the “special theory”). The goal of modern string theorists and their well-publicized “theory of everything” is to have quantum mechanics gobble up all of general relativity as well. Since quantum mechanics is the big kahuna, it behooves us to
appreciate the role of Einstein in the “other” revolution of twentieth-century physics, the quantum one.