Feynman's Rainbow

  Copyright © 2003 by Leonard Mlodinow

  All rights reserved.

  Warner Books, Inc.,

  Hachette Book Group,

  237 Park Avenue,

  New York, NY 10017

  Visit our Web site at www.HachetteBookGroup.com.

  The “Warner Books” name and logo are trademarks of Hachette Book Group, Inc.

  An AOL Time Warner Company

  First eBook Edition: May 2003

  ISBN: 978-0-7595-2798-0

  Contents

  Acknowledgements

  Preface

  Chapter I

  Chapter II

  Chapter III

  Chapter IV

  Chapter V

  Chapter VI

  Chapter VII

  Chapter VIII

  Chapter IX

  Chapter X

  Chapter XI

  Chapter XII

  Chapter XIII

  Chapter XIV

  Chapter XV

  Chapter XVI

  Chapter XVII

  Chapter XVIII

  Chapter XIX

  Chapter XX

  Chapter XXI

  Chapter XXII

  Chapter XXIII

  Chapter XXIV

  Further Reading

  Feynman’s Rainbow:

  A Search for Beauty in Physics and in Life

  By Leonard Mlodinow, Ph.D.

  A memoir of how an ongoing relationship with Richard Feynman at Caltech inspired the author to a deeper understanding of both his own creative imagination and the nature of humanity itself. The book will include extensive transcripts of Feynman’s conversations with the author.

  FEYNMAN’S RAINBOW tells the story of a young physicist trying to find his place in the world, and of the famous, old, and dying physicist whose wisdom helped him.

  It is also the story of Richard Feynman’s last years, his rivalry with fellow Nobel laureate Murray Gell-Mann, and the beginnings of string theory.

  Also by Leonard Mlodinow

  Euclid’s Window: The Story of Geometry from Parallel Lines to Hyperspace

  To Donna Scott

  ACKNOWLEDGEMENTS

  I am grateful to Jamie Raab at Warner Books for seeing the promise of this book, and to Les Pockell and Colin Fox, my editors at Warner, for their invaluable support and insightful suggestions, not to mention all their hard work; to Susan Ginsburg for her guidance, encouragement, friendship, and—most of all—her faith in me; to Michelle Feynman, Eric Wilson, Mark Hillery, Matt Costello, Erhard Seiler, Fred Rose, Annie Leuenberger and Stephen Morrow for their input, support and friendship; to Donna Scott, for her love and friendship; and to the Five Spot bar in Brooklyn, where I was always kindly tolerated as I lingered over a few beers, pondering the meaning of physics and life.

  So spoke an honest man; the outstanding intuitionist of our age and a prime example of what may lie in store for anyone who dares to follow the beat of a different drum.

  —Nobel Laureate Julian Schwinger,

  in his obituary of Feynman in

  Physics Today,

  February 1989

  PREFACE

  Fewer than eight hundred Americans earn a Ph.D. in physics each year. Worldwide, the number is probably in the thousands. And yet from this small pool comes the discovery and innovation that shapes the way we live and think. From X-rays, lasers, radio waves, transistors, atomic energy—and atomic weapons—to our view of space and time, and the nature of the universe, all this has arisen from this dedicated pool of individuals. To be a physicist is to have an enormous potential to change the world. It is also to share a proud history and tradition.

  To a physicist, the most important years are those of graduate school and immediately after. It is the time you find yourself and build your career. This book is about my time just after graduation in 1981, when I was on the faculty of the California Institute of Technology, one of the world’s top research facilities.

  My experience there was not the usual one. I arrived at Caltech feeling lost and intimidated. I was uncertain of my abilities and unusually unfocused in the vision I had for my future. I was also unusually lucky to have landed an office just down the hall from one of the greatest physicists of the century—Richard Feynman. It was Feynman who, while on the 1986 space shuttle commission, made worldwide headlines demonstrating the solution to the riddle of the failed O-ring by dunking it in ice water and pounding it on the table to show it had become brittle. That was vintage Feynman: a triumph of common sense over computer models, of insight over equations. A year earlier Feynman’s irresistible memoir, “Surely You’re Joking, Mr. Feynman!” had exploded on the bestseller lists. In the popular psyche, Feynman has become, since his death in 1988, the Einstein of modern times. In 1981, Feynman was largely unknown outside the physics world, though within it he had been a legend for decades.

  I had been given my fellowship because my Ph.D. thesis, which was on quantum theory in infinite dimensions, had caught the attention of some notable physicists. Did I really fit in here, with two Nobel Prize winners down the hall, and the best students in the country all around me? Week after week I came to my office and pondered the great open problems of physics. No ideas came to me. I was certain that my earlier work had been a fluke and that I would never again discover anything worthwhile. I suddenly understood why Caltech had one of the highest suicide rates of any college in the country.

  One day I got the courage to knock on the door to Feynman’s office and, to my surprise, found that I was welcome. He had just undergone his second surgery for the cancer that would eventually kill him. Over the next two years we spoke many times, and I had the opportunity to ask him questions, such as: How do I know if I have what it takes? How does a scientist think? What is the nature of creativity? From this famous scientist near the end of his days, I found the answers I sought about the nature of science and the scientist. But more than that, I discovered a new approach to life.

  This book tells the story of my first year on the Caltech faculty, beginning in the winter of 1981. In that sense it is the narrative of a young physicist trying to find his place in the world, and of the famous, old, and dying physicist whose wisdom helped him. But it is also the story of Richard Feynman’s last years, his rivalry with fellow Nobel laureate Murray Gell-Mann, and the beginnings of string theory, today the leading theory on the frontiers of physics and cosmology.

  This book tells a story, but it is not a novel. I took notes on and recorded many of my conversations with Feynman because I was awestruck. The passages in italics are based on these notes and the transcripts of some of these discussions. Everything I describe in this book happened to me. But I have combined and altered events, and, other than the historical figures and those whose specific work I quote—Feynman, Murray Gell-Mann, Helen Tuck, John Schwarz, Mark Hillery, and Nick Papanicolaou—I have altered names and personalities in order to best portray my experience.

  I am grateful to Caltech for being such a lively and exciting place to do research, and for, so long ago, having the confidence that they had in me; and I am especially grateful to the late Richard Feynman, for his many lessons on life.

  I

  IN A GRAY CEMENT building on the olive tree–lined Caltech campus on California Boulevard in Pasadena, a thin man with longish hair steps into his modest office. Some students, on this planet less than one-third as long as the professor has been, stop in the hallway and stare. No one would say a word if he didn’t come to the office this day, but nothing could keep him away, especially not the surgery, the effects of which he would no longer allow to ruin his routine.

  Outside, bright sun bathes the palm trees, but it is no longer the withering sun of the summer. The hills rise, brown now giving
way to green, their vegetation reborn with the coming of the more hospitable winter season. The professor might have wondered how many more cycles of green and brown he would live to witness; he knew he had a disease that would kill him. He loved life, but he believed in natural law, and not in miracles. When his rare form of cancer was first discovered in the summer of 1978, he had searched the literature. Five-year survival rates were generally reported to be less than 10 percent. Virtually no one survived ten years. He was into his fourth.

  Some forty years earlier, when he was almost as young as the students currently around him, he had sent a series of papers to the prestigious journal Physical Review. The papers contained odd little diagrams, which constituted a new way of thinking about quantum mechanics, less formal than the standard mathematical language of physics. Though few seemed convinced of his new approach, he thought how amusing it would be if some day that journal would be full of his diagrams. As it turned out, the method they reflected proved to be not only correct and useful, but revolutionary, and on that day late in 1981, in the Physical Review, his diagrams were ubiquitous. They were about as famous as diagrams get. And he was about as famous, at least in the world of science, as scientists get.

  The professor has been working on a new problem the past couple of years. The method he worked out in his student days had been wildly successful when applied to a theory called quantum electrodynamics. That is the theory of the electromagnetic force that governs, among other things, the behavior of the electrons that orbit the nucleus of the atom. These electrons impart to atoms their chemical properties and their spectral properties (the colors of light they emit and absorb). Hence the study of these particular electrons and their behavior is called atomic physics. But since the professor’s student days physicists had made great progress in a new field called nuclear physics. Nuclear physics looks beyond the electronic structure of atoms to the potentially much more violent interactions of the protons and neutrons within the nucleus. Though protons are subject to the same electromagnetic force that governs the behavior of the atomic electrons, these interactions are dominated by a new force, a force that is far stronger than the electromagnetic force. It is called, fittingly, the “strong force.”

  To describe the strong force a grand new theory had been invented. The new theory had some mathematical similarities to quantum electrodynamics, and it was given a name that reflected these similarities—quantum chromodynamics (despite the root, chromo, it has nothing to do with color as we know it). In principle quantum chromodynamics provided a precise quantitative description of protons, neutrons, and related particles and how they interact—how they might bind to each other, or behave in collisions. But how do we extract descriptions of these processes from the theory? The professor’s approach applied in principle to this new theory but practical complications arose. Though quantum chromodynamics had had certain triumphs, for many situations neither the professor nor anyone else knew how to use his diagrams—or any other method—to extract accurate numerical predictions from the theory. Theorists couldn’t even calculate the mass of the proton—a very basic quantity that had long ago been accurately measured by the experimentalists.

  The professor thinks, perhaps, that with the months or years he has left on earth he’ll play around with the problem of quantum chromodynamics, considered one of the most important of its day. To create the energy and will he needs for his effort, he tells himself that everyone else who had for so many years unsuccessfully attacked this problem lacked certain qualities that he possesses. What they are he, Richard Feynman, isn’t sure: an oddball approach, perhaps. Whatever those qualities are, they had served him well—he had one Nobel Prize, but might arguably have deserved two or three when you considered all the wide-ranging and important breakthroughs he had made in his career.

  Meanwhile, in 1980, several hundred miles north in Berkeley, a much younger man had sent off a couple papers with his own new approach to solving some of the old mysteries of atomic physics. His method offered answers to some difficult problems, but there was a catch. The world he explored in his imagination was one in which space has an infinite number of dimensions. It is a world with not just up/down, right/left, and forward/backward, but also a countless array of other directions. Could you really say anything useful about our three-dimensional existence by studying a universe like that? And could the method be extended to other areas of study, such as the more modern field of nuclear physics? It would turn out that it is promising enough that this student received a beginning faculty appointment at Caltech, and an office down the hall from Feynman.

  The night after receiving that offer of employment, I remembered lying in my bed half my life earlier, wondering what it would be like the next day, my first day in junior high. More than anything else, as I recall, I was worried about gym and showering in front of all those other boys. What I was really worried about was ridicule. I would be exposed, too, at Caltech. In Pasadena there would be no faculty advisor, no mentor, just my own answers to the hardest problems the best physicists could think of. To me, a physicist who didn’t produce brilliant ideas was one of the living dead. At a place like Caltech, he would also be shunned, and soon unemployed.

  Did I have it or didn’t I? Or was I asking the wrong question? I started talking to the thin, dying professor with long hair in an office down the hall. What the old man told me is the subject of this book.

  II

  THE STORY REALLY BEGINS in the winter of 1973. I lived on a kibbutz, a communal farm, in Israel, in the foothills near Jerusalem. My hair was shoulder-length, and my politics pacifist, but I was there because of a war, the Yom Kippur War, named after the day on which it had started. Though it was mostly over by the time I arrived, its vestige was dragging on. The troops were still mobilized. This led to a serious labor shortage. I took leave from college in the midst of my second year to go help out.

  I was twenty and felt grown-up. But I was still a child—guided, taken care of, and protected. The kibbutz experience was my first experience in many areas of life—my first time in a foreign country, my first time working with farm animals, my first time taking refuge in a bomb shelter while shells exploded outside. And it was the first time I ever lived without certain amenities we take for granted—stereos, televisions, telephones . . . indoor bathrooms.

  At night there was little to do except chat with the other volunteers, look at the stars, or visit the small “library” on the kibbutz, which had a few dozen books in English. A number of the books in the library were physics books, apparently donations by a kibbutznik who had attended college in the States. I had a double major at the time—in chemistry and mathematics—and everyone who knew me assumed I’d someday be a chemistry professor at a major university. I’d always been an academic kid, and as long as anyone could remember, my two subjects were chemistry and math. The “advanced” physics course I had in high school had been dry and boring. I didn’t get the big fuss everyone made over Isaac Newton—who could get excited about the speed of a ball rolling down an inclined plane, or the force of a weight you dropped from the second floor? It was no competition to the fireworks and rockets I could throw together in a chemistry lab or the curved space I could dream about in math courses. Still, given the thin set of choices, I eventually looked over the physics books.

  One of them was a paperback called The Character of Physical Law by a fellow I had vaguely heard of—Richard Feynman. The book was the transcript of some lectures he had given in the sixties. I picked it up. It explained, without employing mathematics, the principles of modern physics, especially quantum theory.

  “Quantum theory” is not really a particular theory, but rather a type of theory. A quantum theory is any theory based on the “quantum hypothesis,” revealed to the world by Max Planck in the year 1900, which states that certain quantities such as your energy can take on only certain discrete values. For instance, at any given height above the surface of the earth, you possess something called gr
avitational potential energy. This is the energy with which you’d hit the ground if you fell from that height (in the absence of air resistance). In a quantum theory of gravity, your gravitational potential energy could not have just any value—there would be only a discrete set of energies you could possess. There is even a minimum possible energy that corresponds to being a little above the earth’s surface. This has recently been measured in an experiment on neutrons, for which the minimum energy corresponds to a height of roughly five ten-thousandths of an inch. If your ruler has the accustomed precision, it is a restriction you’d hardly be able to detect. Quantum effects are important, however, when you study objects like neutrons, nuclei, or atoms.

  Theories that do not incorporate Planck’s quantum hypothesis are called classical theories. Obviously, before 1900, all theories in physics were classical theories. For the most part classical theories work just fine unless you are concerned with the nuances of behavior on the atomic scale, or smaller. This proved to be most physicists’ focus for most of the next hundred years.

  Physicists spent the first few decades of the twentieth century working out the consequences of Planck’s quantum hypothesis. One of them is the famous uncertainty principle, which states that in nature there are certain pairs of quantities whose values cannot be simultaneously pinpointed. For instance, if you determine the position of an object with great precision, then you cannot know its velocity very precisely. Again, for the large objects we encounter in everyday life, these limitations are not noticeable, but for the constituents of atoms, they make an enormous difference.

  Another consequence of quantum theory is what physicists call “wave-particle duality,” which means that, under certain circumstances, particles such as electrons exhibit the behavior of waves, and vice versa. For example, if you shoot a series of electrons at a tiny slit in a wall, as they pass through they will spread in a circular pattern like a water wave that passes through a small opening. And if you put two tiny slits in the wall, you will see interference ripples similar to those you see when two water waves collide. An electron as a wave is an electron spread out in space, an electron that acts as if it were an excitation of some pervasive medium rather than a discrete object in itself. On the other hand, wave-particle duality also tells us that there are circumstances in which waves of energy exhibit particlelike behavior. An example of this is light. We have known light through the ages mostly as a wavelike phenomenon. For instance, think of the way it bends as it passes through a lens, or the way it spreads out in a prism. But it can also behave as a particle, a discrete localized object, which we call a photon. This concept of light proved to be the key to understanding the photoelectric effect, in which certain metals eject an electron after being impinged upon by a photon. Einstein, the first to accept the quantum hypothesis as a fundamental physical law, explained certain mysterious properties of the photoelectric effect in these terms in one of his famous papers of 1905. (It was for this work, not his controversial relativity theories, that he received the 1921 Nobel Prize.)