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  Quantum Legacies

  QUANTUM LEGACIES

  Dispatches from an Uncertain World

  DAVID KAISER

  With a Foreword by Alan Lightman

  The University of Chicago Press

  Chicago and London

  The University of Chicago Press, Chicago 60637

  The University of Chicago Press, Ltd., London

  © 2020 by The University of Chicago

  All rights reserved. No part of this book may be used or reproduced in any manner whatsoever without written permission, except in the case of brief quotations in critical articles and reviews. For more information, contact the University of Chicago Press, 1427 E. 60th St., Chicago, IL 60637.

  Published 2020

  Printed in the United States of America

  29 28 27 26 25 24 23 22 21 20 1 2 3 4 5

  ISBN-13: 978-0-226-69805-2 (cloth)

  ISBN-13: 978-0-226-69819-9 (e-book)

  DOI: https://doi.org/10.7208/chicago/9780226698199.001.0001

  Library of Congress Cataloging-in-Publication Data

  Names: Kaiser, David, author.

  Title: Quantum legacies : dispatches from an uncertain world / David Kaiser ; with a foreword by Alan Lightman.

  Description: Chicago : University of Chicago Press, 2020. | Includes bibliographical references and index.

  Identifiers: LCCN 2019037201 | ISBN 9780226698052 (cloth) | ISBN 9780226698199 (ebook)

  Subjects: LCSH: Quantum theory. | Physics—History.

  Classification: LCC QC173.98.K358 2020 | DDC 530.12—dc23

  LC record available at https://lccn.loc.gov/2019037201

  This paper meets the requirements of ANSI/NISO Z39.48–1992 (Permanence of Paper).

  For Ellery and Toby: quantum wondertwins

  CONTENTS

  Foreword

  Alan Lightman

  Introduction

  QUANTA

  1 All Quantum, No Solace

  2 Life-and-Death: When Nature Refuses to Select

  3 Operation: Neutrino

  4 Quantum Theory by Starlight

  CALCULATING

  5 From Blackboards to Bombs

  6 Boiling Electrons

  7 Lies, Damn Lies, and Statistics

  8 Training Quantum Mechanics

  9 Zen and the Art of Textbook Publishing

  MATTER

  10 Pipe Dreams

  11 Something for Nothing

  12 Higgs Hunting

  13 When Fields Collide

  COSMOS

  14 Guess Who’s Coming to Dinner

  15 Gaga for Gravitation

  16 The Other Evolution Wars

  17 No More Lonely Hearts

  18 Learning from Gravitational Waves

  19 A Farewell to Stephen Hawking

  Acknowledgments

  Abbreviations

  Notes

  Index

  FOREWORD

  : : Alan Lightman

  Physics has always attracted those thinkers who might have been philosophers, or musicians. Newton. Einstein. Heisenberg.

  Autumn. There’s a smell of fall leaves through an open window. We sit at a long table. A baker’s dozen of us, I would guess. An associate provost of the institution, a couple of theater directors, a couple of playwrights, a financial person or two, an actress constantly changing her face as if putting on makeup in the dressing room, and a few physicists. David Kaiser at one end of the table, always razor sharp in dress and attentiveness. Another physicist enters the room and apologizes for being late. We are discussing the sponsorship of new plays about science, some not even yet written, to be performed at a theater nearby. It is a happy collision between science and art, between the icy equations of Newton and Einstein and the heart-wrenching dramas of Chekhov and Wilde. The deliberate joined with the spontaneous. The rational with the intuitive. The quantitative with that which cannot be quantified. Several times a year, we gather here to enter and bless this world between worlds.

  It isn’t surprising that Professor Kaiser perches at one end of the table. Trained as both a physicist and a historian of science, over the years he has developed into a first-rate storyteller, with his articles and books tracing not only scientific ideas but also the personal lives of the scientists and the institutional and cultural forces shaping the landscape. All revealed in the delightful essays in this book. But still. Why so many physicists at the table?

  Physics attempts to reduce the world to a small number of fundamental particles and forces—the bare minimum to explain everything in the physical cosmos. I would argue that such a project reflects a deep human desire to make order out of the world, both the animate and the inanimate, and thus far transcends the mathematical runes of Newton and Einstein. The Gestalt psychologists say that we humans unavoidably try to reduce the world into meaningful patterns. Perhaps that act is what holds off insanity. The constellations, for example. If we see a random collection of dots, we parse it into some kind of figure against a background. If we see a broken circle, we mentally fill in the missing pieces. Henry Adams tried to understand the historical rise and fall of human civilizations in terms of energy and the second law of thermodynamics. Plato claimed that God made the world out of just four fundamental elements: fire, earth, air, and water. Ancient India used only three: fire was associated with bone and speech, water with blood and urine, earth with flesh and mind. We are pattern seekers and pattern makers. Physics is the ultimate distillation of that need. Art as well. Perhaps that is why there are so many physicists at this table.

  Although these various human needs work together within our psyche, modern science owes much of its success to envisioning a disembodied, dispassionate universe out there, to walling itself off from the personal, and particularly the emotional. The scientists who planned the first human landing on the moon in 1969 calculated trajectories and rocket thrusts so that the spacecraft and the moon would be at the same place at the same time. Those calculations did not include the mood of the astronauts or anything about their personal lives.

  A closely related issue: science does not normally concern itself with the narrative of its own (human) history of discovery. In this sense, as well as in others, science distinguishes itself from the humanities. The body of knowledge in the humanities might be called “horizontal”—the seminal works of all eras are considered equally relevant and enriching. The works of no era are considered superior to those of any other era. When we study philosophy, for example, we might begin with Confucius and Plato and Aristotle and move toward Nietzsche and Bertrand Russell. Or with literature, we might begin with the Iliad and the Odyssey and slowly advance to The Great Gatsby. There is no sense in which The Great Gatsby is considered more “correct” or wiser than the Iliad. By contrast, science is a vertical endeavor. The theories, data, and knowledge of each century are thought to improve and replace the understanding of previous centuries. In predicting the orbits of planets and other gravitational phenomena, Einstein’s theory of gravity is simply more accurate than Newton’s theory of gravity. Period. A graduate student in science studies the most up-to-date results of her field before launching into research at the “frontiers” of the field. There is no time, and often little interest, in the history of the subject, which now lies in the dusty stacks of libraries alongside candles for lighting and slide rules for calculating. My college textbook on heat, titled Thermal Physics, is full of equations describing the modern understanding of heat as the random motion of atoms and molecules. There isn’t a single word about the earlier theory of heat as a material fluid, called phlogiston. Or about the colorful story of Benjamin Tho
mpson (1753–1814), who began life as a schoolteacher in New Hampshire and later fled to England after the fall of Boston in the Revolutionary War and became head of the Bavarian army. It was Thompson who discovered that heat was motion, not substance, by way of his job superintending the boring of cannon in the military arsenal at Munich. In his essay read before the Royal Society of London in 1798, Thompson wrote, “It frequently happens that in the ordinary affairs and occupations of life, opportunities present themselves of contemplating some of the most curious operations of Nature. . . . I was struck with the very considerable degree of Heat which a brass gun acquires, in a short time, in being bored . . . in the Friction of two metallic surfaces.”

  In contrast to the usual view of science as a disembodied enterprise, the essays in this book are full of the human drama and historical context that accompany scientific discovery and knowledge.

  The smell of the leaves and their symphony of color remind me that our human senses, as rich as they are, provide a misleading picture of the world—a picture that has been radically revised by modern physics. We’ve learned that, contrary to appearances, the Earth spins on its axis and races through space. We’ve learned that, contrary to appearances, zillions of x-rays and radio waves and gamma rays stream by us each second, invisible to the eye. We’ve learned that in the tiny world of the atom, particles behave as if they could be in several places at once and, further, seem to have instantaneous effects on each other, violating the usual notions of cause and effect. These last discoveries are the subject matter of quantum physics, a central theme of Kaiser’s new book. If we must question the validity of our sense perceptions, if we must give up our intuitive understanding of “reality,” if we must accept a new narrative of the physical world, let us at least do so with the charming human stories in this book.

  Introduction

  “Don’t laugh,” physicist Paul Ehrenfest had scribbled on a tiny scrap of paper. He was attending a scientific meeting in Brussels with about two dozen leading physicists, late in October 1927. While his colleagues spoke, one after the other, of their struggles to make sense of the new quantum theory, Ehrenfest, like a giddy schoolboy, had passed the note to his friend Albert Einstein. A bit lower on the page, Einstein had scrawled his response. “I laugh only at the naiveté,” he wrote back in his curvy, looping handwriting. “Who knows who will be laughing in the coming years.”1

  I still remember the jolt I felt when I came across the handwritten notes in the early 1990s. I had made a trip to the rare books library at Princeton University, my first foray into archival research. Princeton’s library has an official duplicate set of Einstein’s unpublished papers and correspondence, the originals of which are housed at Hebrew University in Jerusalem. The Einstein collection at Princeton consists of nearly one hundred boxes, stuffed with faded photocopies and microfilms, and I had begun poking around in a tiny corner of the vast archive. I was hardly the first person to notice the playful notes between Ehrenfest and Einstein—other historians had already quoted the exchange—but I was transfixed all the same.2

  Holding the page in my hand, I tried to imagine the scene. Huddled in a conference room within a nondescript academic building next to the leafy Parc Léopold, Einstein, Ehrenfest, and their colleagues had scrambled to lash together a new framework with which to describe the behavior of matter at its most fundamental. In the years leading up to the meeting in Brussels, much of what previous generations of physicists had thought they knew about light and atoms seemed to unravel. Young guns at the conference, like Werner Heisenberg and Wolfgang Pauli—still in their twenties—insisted upon new ideas. Theirs was a vision of the world that was at root probabilistic, riven by inevitable trade-offs between what physicists could ever hope to know, as Heisenberg had boldly suggested just a few months earlier when he introduced his now-famous uncertainty principle. Ehrenfest and Einstein, each in their late forties, appreciated the cleverness of the new ideas but wrestled with doubts. Einstein, in particular, would soon emerge as one of the most trenchant critics of the new quantum mechanics, concerned that the theory harbored too many weaknesses to support the broad edifice of theoretical physics.3

  Figure 0.1. Paul Ehrenfest (left), his son Paul Ehrenfest Jr., and Albert Einstein, relaxing in the Ehrenfest home in Leiden, June 1920. (Source: Wikimedia Commons.)

  Even so, as the heady debates spilled past the prepared remarks in the conference room and animated the physicists’ dinners at a nearby hotel, Einstein and Ehrenfest responded to the uncertainties with humor, even humility. What a grand intellectual adventure they seemed to be enjoying, as they passed their notes back and forth, kidding their colleagues, oblivious to the darkness they would each soon face. A few years after the Brussels meeting, Hitler assumed power in Germany, forcing Einstein to flee and resettle in Princeton. The impact was even harsher for Ehrenfest, whose ebullience with friends and students had masked a creeping depression. The swirling uncertainties of worldly events exacerbated his growing unease with the rapid-fire changes in physics. “I have completely lost contact with theoretical physics,” he confided at one point to a colleague. “I cannot read anything any more and feel myself incompetent to have even the most modest grasp about what makes sense in the flood of articles and books.” He worried, too, about his younger son, Wassik, who suffered from Down syndrome. His letters to friends became more desperate. Five years after the Brussels meeting, Ehrenfest drafted a new note for Einstein. He wrote of his efforts, “ever more enervated and torn,” to make sense of the new physics. But it all seemed too much; the collected uncertainties made him “completely ‘weary of life.’” He never mailed the letter. Drafts were found late in September 1933, after Ehrenfest shot his young son, Wassik, in the waiting room of his son’s physician, before turning the pistol on himself.4

  : : :

  Long past the earnest and spirited debates at the 1927 Brussels meeting, quantum mechanics remains a centerpiece of physicists’ description of nature. Even after all those years, physicists have yet to find a single instance in which predictions from the theory have failed to match experimental tests. And it has certainly not been for lack of trying.

  A quarter century after stumbling upon Einstein’s and Ehrenfest’s notes, I was lucky to engage in a quantum-mechanical adventure of my own. Early in the morning of 6 January 2018, squinting in the bright sunshine, I walked across the tarmac at the airport of La Palma, a tiny member of the Canary Islands off the western coast of Morocco. At sea level, La Palma looks every bit the tropical paradise, palm trees swaying in a gentle breeze with all the postcard loveliness of Hawaii. Bleary-eyed and sleepy from my overnight flights—New York to Madrid, then several more hours to La Palma—I managed to catch up to my colleague Anton Zeilinger, a renowned physicist who has built a career designing ever more clever experiments to test the strangest properties of quantum theory. Despite his own travels that morning, Anton looked as cheery as ever. (In my experience, Anton is unfailingly cheerful, on any continent and in any time zone.)

  Anton picked up the keys to a rental car, and we drove up the mountain to the Roque de los Muchachos Observatory. Before long, the palm trees gave way to stunted brush, as we wound our way up the narrow road to an elevation of nearly eight thousand feet. As we drove up to the modest headquarters of the observatory, the picture-perfect blue sky that had greeted us at the airport had changed to a driving, freezing hailstorm.

  Figure 0.2. On the distant hillside sits the metallic dome of the Nordic Optical Telescope, part of the Roque de los Muchachos Observatory on the Canary Island of La Palma. Visible to the left of the telescope dome is a rectangular shipping container, which served as a makeshift laboratory during our Cosmic Bell experiment in January 2018. During our brief observing time, we had to contend with freezing rain and occasional hailstorms. (Source: Photograph by Calvin Leung.)

  At the observatory we met up with about a dozen members of our team, most of them young graduate students and postdocs from Anton’s resear
ch group, based in Vienna. Several had been at the observatory for weeks, installing equipment and performing calibration tests. We were there to conduct a new experimental test of quantum entanglement, a phenomenon that Einstein himself had helped to identify in the years following the famous meeting in Brussels. For our new test, we were going to use two of the enormous telescopes at the observatory to collect random bits of information from the sky, gathering light from some of the furthest known quasars, all while shooting pairs of entangled particles between those telescopes from a special laser that Anton and his group had shipped over from Vienna.

  After a few nail-biting nights of poor weather, the skies over La Palma finally cleared, and we were able to conduct our new experiment. Within hours we had preliminary results in hand. After a few more weeks of careful calculation, we could confirm that our latest experiment, like all previous ones, showed results perfectly in line with the quantum-mechanical predictions—and thereby in conflict with the sort of results that Einstein had thought such experiments should yield. Our experiment on the mountaintop relied upon instruments that Einstein himself never lived to see: thirteen-foot telescope mirrors polished to perfection, a high-powered laser, single-photon avalanche diode detectors, and timing circuits for our electronics disciplined to nanosecond accuracy with atomic clocks.5 We had marshaled all these modern tools to test ideas that dated back nearly to the 1927 Brussels meeting. I couldn’t help but wonder what the grand masters of quantum theory, who had gathered all those years ago for their discussions and debates, would have made of our latest efforts.

  : : :

  Ever since my first excursion into Einstein’s papers in the Princeton library, I have been riveted by a kind of doubleness of scientific research. In Einstein’s day as in our own, researchers’ ambition has often been to transcend the vagaries of here and now, to contribute lasting insights into how the world works that might reach beyond a given researcher’s limited view. Yet each of us—today’s scientists no less than Einstein and his peers—remains unavoidably embedded in a certain time and place. Scientists are immersed in the particulars of the world, moment by moment, even as many dream of superseding these accidents of history.