by Michio Kaku
Einstein’s Cosmos
PUBLISHED TITLES IN THE GREAT DISCOVERIES SERIES
David Foster Wallace: Everything and More: A Compact History of
Sherwin B. Nuland: The Doctors’ Plague: Germs, Childbed Fever, and the Strange Story of Ignác Semmelweis
Michio Kaku: Einstein’s Cosmos: How Albert Einstein’s Vision Transformed Our Understanding of Space and Time
Barbara Goldsmith: Obsessive Genius: The Inner World of Marie Curie
Rebecca Goldstein: Incompleteness: The Proof and Paradox of Kurt Godel
FORTHCOMING TITLES
George Johnson on Hubble and the Measurement of the Universe
Daniel Mendelsohn on Archimedes and the Science of the Ancient Greeks
Richard Reeves on Rutherford and the Atom
Madison Smartt Bell on Lavoisier and Modern Chemistry
David Leavitt on Alan Turing and the Computer
William T. Vollman on Copernicus and the Copernican Revolution
David Quammen on Darwin and Evolution
GENERAL EDITORS: EDWIN BARBER AND JESSE COHEN
BY MICHIO KAKU
Beyond Einstein
Hyperspace
Visions
Einstein’s Cosmos
Parallel Worlds
MICHIO KAKU
Einstein’s Cosmos
How Albert Einstein’s Vision Transformed Our Understanding of Space and Time
W. W. NORTON & COMPANY
NEW YORK • LONDON
Copyright © 2004 by Michio Kaku
All rights reserved
For information about permission to reproduce selections from this book, write to Permissions, W. W. Norton & Company, Inc., 500 Fifth Avenue, New York, NY 10110
Library of Congress Cataloging-in-Publication Data
Kaku, Michio.
Einstein's cosmos : how Albert Einstein's vision transformed our understanding of space and time / Michio Kaku.—1st ed.
p. cm.—(Great discoveries)
Includes bibliographical references.
1. Space and time. 2. Relativity (Physics) 3. Einstein, Albert, 1879–1955.
I. Title. II. Series.
QC173.59.S65 K356 2004
530.11—dc22
2003025580
ISBN: 978-0-393-07783-4
Atlas Books, LLC, 65 E. 55th Street, New York, N.Y. 10022
W. W. Norton & Company, Inc., 500 Fifth Avenue, New York, N.Y. 10110 www.wwnorton.com
W. W. Norton & Company Ltd., Castle House, 75/76 Wells Street, London W1T 3QT
This book is dedicated to Michelle and Alyson.
Contents
Preface: A New Look at the Legacy of Albert Einstein
Acknowledgments
Part I. First Picture:
Racing a Light Beam
CHAPTER 1 Physics before Einstein
CHAPTER 2 The Early Years
CHAPTER 3 Special Relativity and the “Miracle Year”
Part II. Second Picture:
Warped Space-Time
CHAPTER 4 General Relativity and “the Happiest Thought of My Life”
CHAPTER 5 The New Copernicus
CHAPTER 6 The Big Bang and Black Holes
Part III. The Unfinished Picture:
The Unified Field Theory
CHAPTER 7 Unification and the Quantum Challenge
CHAPTER 8 War, Peace, and E = mc2
CHAPTER 9 Einstein’s Prophetic Legacy
Notes
Bibliography
PREFACE
A New Look at the Legacy of Albert Einstein
Genius. Absent-minded professor. The father of relativity. The mythical figure of Albert Einstein—hair flaming in the wind, sockless, wearing an oversized sweatshirt, puffing on his pipe, oblivious to his surroundings—is etched indelibly on our minds. “A pop icon on a par with Elvis Presley and Marilyn Monroe, he stares enigmatically from postcards, magazine covers, T-shirts, and larger-than-life posters. A Beverly Hills agent markets his image for television commercials. He would have hated it all,” writes biographer Denis Brian.
Einstein is among the greatest scientists of all time, a towering figure who ranks alongside Isaac Newton for his contributions. Not surprisingly, Time magazine voted him the Person of the Century. Many historians have placed him among the hundred most influential people of the last thousand years.
Given his place in history, there are several reasons for trying to make a fresh new effort to re-examine his life. First, his theories are so deep and profound that the predictions he made decades ago are still dominating the headlines, so it is vital that we try to understand the roots of these theories. As a new generation of instruments that were inconceivable in the 1920s (e.g., satellites, lasers, supercomputers, nanotechnology, gravity wave detectors) probe the outer reaches of the cosmos and the interior of the atom, Einstein’s predictions are winning Nobel Prizes for other scientists. Even the crumbs off Einstein’s table are opening up new vistas for science. The 1993 Nobel Prize, for example, went to two physicists who indirectly confirmed the existence of gravity waves, predicted by Einstein in 1916, by analyzing the motion of double neutron stars in the heavens. Also, the 2001 Nobel Prize went to three physicists who confirmed the existence of Bose-Einstein condensates, a new state of matter existing near absolute zero that Einstein predicted in 1924.
Other predictions are now being verified. Black holes, once considered a bizarre aspect of Einstein’s theory, have now been identified by the Hubble Space Telescope and the Very Large Array Radio Telescope. Einstein rings and Einstein lenses not only have been confirmed but also are key tools astronomers use to measure invisible objects in outer space.
Even Einstein’s “mistakes” are being recognized as profound contributions to our knowledge of the universe. In 2001, astronomers found convincing evidence that the “cosmological constant,” thought to be Einstein’s greatest blunder, actually contains the largest concentration of energy in the universe and will determine the ultimate fate of the cosmos itself. So experimentally, there has been a “renaissance” in Einstein’s legacy as more evidence piles up verifying his predictions.
Second, physicists are re-evaluating his legacy and especially his thinking process. While recent biographies have minutely examined his private life for clues to the origins of his theories, physicists are becoming increasingly aware that Einstein’s theories are based not so much on arcane mathematics (let alone his love life!) but simple and elegant physical pictures. Einstein would often comment that if a new theory was not based on a physical image simple enough for a child to understand, it was probably worthless.
In this book, therefore, these pictures, these products of Einstein’s scientific imagination, become a formal organizing principle around which his thinking process and his greatest achievements are described.
Part I uses the picture that Einstein first thought of when he was sixteen years old: what a light beam would look like if he could race alongside it. This picture, in turn, was probably inspired by a children’s book that he read. By visualizing what happens if he were to race a light beam, Einstein isolated the key contradiction between the two great theories of the time, Newton’s theory of forces and Maxwell’s theory of fields and light. In the process of resolving this paradox, he knew that one of these two great theories—Newton’s, as it turns out—must fall. In some sense, all of special relativity (which would eventually unlock the secret of the stars and nuclear energy) is contained in this picture.
In Part II, we are introduced to another picture: Einstein imagined planets as marbles rolling around a curved surface centered at the sun, as an illustration of the idea that gravity originates from the bending of space and time. By replacing the forces of Newton with the curvature of
a smooth surface, Einstein gave an entirely fresh, revolutionary picture of gravity. In this new framework, the “forces” of Newton were an illusion caused by the bending of space itself. The consequences of this simple picture would eventually give us black holes, the big bang, and the ultimate fate of the universe itself.
Part III doesn’t have a picture—this section is more about the failure to come up with an image guiding his “unified field theory,” one that would have given Einstein a way to formulate the crowning achievement of two thousand years of investigation into the laws of matter and energy. Einstein’s intuition began to falter, as almost nothing was known in his time about the forces that governed the nucleus and subatomic particles.
This unfinished unified field theory and his thirty-year search for a “theory of everything” was by no means a failure—although this has been recognized only recently. His contemporaries saw it as a fool’s chase. The physicist and Einstein biographer Abraham Pais lamented, “In the remaining 30 years of his life he remained active in research but his fame would be undiminished, if not enhanced, had he gone fishing instead.” In other words, his legacy might have been even greater if he had left physics in 1925 rather than 1955.
In the last decade, however, with the coming of a new theory called “superstring theory” or “M-theory,” physicists have been re-evaluating Einstein’s later work and his legacy, as the search for the unified field theory has assumed center stage in the world of physics. The race to attain the theory of everything has become the ultimate goal of a whole generation of young, ambitious scientists. Unification, once thought to be the final burial ground for the careers of aging physicists, is now the dominant theme in theoretical physics.
In this book, I hope to give a new, refreshing look at the pioneering work of Einstein, perhaps even a more accurate portrayal of his enduring legacy as seen from the vantage point of simple physical pictures. His insights, in turn, have fueled the current generation of revolutionary new experiments being conducted in outer space and in advanced physics laboratories and are driving the intense search to fulfill his most cherished dream, a theory of everything. This is the approach to his life and his work that I think he would have liked the best.
Acknowledgments
I would like to thank the hospitality of the staff at Princeton University Library, where some of the research for this book was carried out. The library contains copies of all of Einstein’s manuscripts and original materials. I would also like to thank Professors V. P. Nair and Daniel Greenberger of City College of New York for reading the manuscript and making helpful and critical comments. In addition, conversations with Fred Jerome, who obtained Einstein’s voluminous FBI file, were very useful. I am also grateful to Edwin Barber for his support and encouragement, and to Jesse Cohen for making invaluable editorial comments and changes that have greatly strengthened the manuscript and given it focus. I am also deeply indebted to Stuart Krichevsky, who has represented many of my books on science for all these years.
PART I
FIRST PICTURE
Racing a Light Beam
CHAPTER 1
Physics before Einstein
A journalist once asked Albert Einstein, the greatest scientific genius since Isaac Newton, to explain his formula for success. The great thinker thought for a second and then replied, “If A is success, I should say the formula is A = X + Y + Z, X being work and Y being play.”
And what is Z, asked the journalist?
“Keeping your mouth shut,” he replied.
What physicists, kings and queens, and the public found endearing was his humanity, his generosity, and his wit, whether he was championing the cause of world peace or probing the mysteries of the universe.
Even children would flock to see the grand old man of physics walk the streets of Princeton, and he would return the favor by wiggling his ears back at them. Einstein liked to chat with a particular five-year-old boy who would accompany the great thinker on his walks to the Institute for Advanced Study. One day while they were strolling, Einstein suddenly burst out in laughter. When the boy’s mother asked him what they talked about, her son replied, “I asked Einstein if he had gone to the bathroom today.” The mother was horrified, but then Einstein replied, “I’m glad to have someone ask me a question I can answer.”
As physicist Jeremy Bernstein once said, “Everyone who had real contact with Einstein came away with an overwhelming sense of the nobility of the man. The phrase that recurs again and again is his ‘humanity,’…the simple, lovable quality of his character.”
Einstein, who was equally gracious to beggars, children, and royalty alike, was also generous to his predecessors in the illustrious pantheon of science. Although scientists, like all creative individuals, can be notoriously jealous of their rivals and engage in petty squabbles, Einstein went out of his way to trace the origins of the ideas he pioneered back to the giants of physics, including Isaac Newton and James Clerk Maxwell, pictures of whom were prominently displayed on his desk and walls. In fact, the work of Newton on mechanics and gravity and of Maxwell on light formed the two pillars of science at the turn of the twentieth century. Remarkably, almost the sum total of all physical knowledge at that time was embodied in the achievements of these two physicists.
It’s easy to forget that before Newton, the motion of objects on Earth and in the heavens was almost totally unexplained, with many believing that our fates were determined by the malevolent designs of spirits and demons. Witchcraft, sorcery, and superstition were heatedly debated even at the most learned centers of learning in Europe. Science as we know it did not exist.
Greek philosophers and Christian theologians, in particular, wrote that objects moved because they acted out of human-like desires and emotions. To the followers of Aristotle, objects in motion eventually slowed down because they got “tired.” Objects fell to the floor because they “longed” to be united with the earth, they wrote.
The man who would introduce order into this chaotic world of spirits was in a sense the opposite of Einstein in temperament and personality. While Einstein was always generous with his time and quick with a one-liner to delight the press, Newton was notoriously reclusive, with a tendency toward paranoia. Deeply suspicious of others, he had bitter, long-standing feuds with other scientists over priority. His reticence was legendary: when he was a member of the British Parliament during the 1689–90 session, the only recorded incident of his speaking before the august body was when he felt a draft and asked an usher to close the window. According to biographer Richard S. Westfall, Newton was a “tortured man, an extremely neurotic personality who teetered always, at least through middle age, on the verge of breakdown.”
But in matters of science, Newton and Einstein were true masters, sharing many key characteristics. Both could obsessively spend weeks and months in intense concentration to the point of physical exhaustion and collapse. And both had the ability to visualize in a simple picture the secrets of the universe.
In 1666, when Newton was twenty-three years old, he banished the spirits that haunted the Aristotelian world by introducing a new mechanics based on forces. Newton proposed three laws of motion in which objects moved because they were being pushed or pulled by forces that could be accurately measured and expressed by simple equations. Instead of speculating on the desires of objects as they moved, Newton could compute the trajectory of everything from falling leaves, soaring rockets, cannonballs, and clouds by adding up the forces acting on them. This was not merely an academic question, because it helped to lay the foundation for the Industrial Revolution, where the power of steam engines driving huge locomotives and ships created new empires. Bridges, dams, and towering skyscrapers could now be built with great confidence, since the stresses on every brick or beam could be computed. So great was the victory of Newton’s theory of forces that he was justly lionized during his lifetime, prompting Alexander Pope to acclaim:
Nature and Nature’s laws lay hid in night,
<
br /> God said, Let Newton be! and all was light.
Newton applied his theory of forces to the universe itself by proposing a new theory of gravity. He liked to tell the story of how he returned to the family estate in Woolsthorpe in Lincolnshire after the black plague forced the closing of Cambridge University. One day, as he saw an apple fall off a tree on his estate, he asked himself the fateful question: if an apple falls, then does the moon also fall? Can the gravitational force acting on an apple on Earth be the same force that guides the motion of heavenly bodies? This was heresy, since the planets were supposed to lie on fixed spheres that obeyed perfect, celestial laws, in contrast to the laws of sin and redemption that governed the wicked ways of humanity.
In a flash of insight, Newton realized he could unify both earthly and heavenly physics into one picture. The force that pulled an apple to the ground must be the same force that reached out to the moon and guided its path. He stumbled upon a new vision of gravity. He imagined himself sitting on a mountaintop throwing a rock. By throwing the rock faster and faster, he realized that he could throw it farther and farther. But then he made the fateful leap: what happens if you throw the rock so fast that it never returns? He realized that a rock, falling continually under gravity, would not hit the earth but would circle around it, eventually returning to its owner and hitting him on the back of his head. In this new view, he replaced the rock with the moon, which was constantly falling but never hit the ground because, like the rock, it moved completely around the earth in a circular orbit. The moon was not resting on a celestial sphere, as the church thought, but was continually in free fall like a rock or apple, guided by the force of gravity. This was the first explanation of the motion of the solar system.
