by Michio Kaku
Meanwhile, amidst the storm unleashed by the atomic and hydrogen bombs, Einstein maintained his peace and sanity by returning stubbornly to his physics. In the 1940s, pioneering work was still being done in the areas he helped to found, including cosmology and the unified field theory. This was to be his last and final attempt to “read the mind of God.”
After the war, Schrödinger and Einstein maintained a lively transatlantic correspondence. Almost alone, these two fathers of the quantum theory resisted the tide of quantum mechanics and focused on the quest for unification. In 1946, Schrödinger confessed to Einstein, “You are after big game. You are on a lion hunt, while I am speaking of rabbits.” Encouraged by Einstein, Schrödinger continued his hot pursuit of a particular type of unified field theory, called “affine field theory.” Soon, Schrödinger completed his own theory, which convinced him that he finally accomplished what Einstein had failed to achieve, the unification of light and gravity. He marveled that his new theory was a “miracle,” a “totally unhoped for gift from God.”
Working in Ireland, Schrödinger had felt isolated from the mainstream of physics, being reduced to a college administrator and a has-been. Now he was convinced that his new theory might win him a second Nobel Prize. Hurriedly, he called a major press conference. Ireland’s prime minister, Eamon De Valera, and others showed up to listen to his presentation. When a reporter asked him how confident he was about his theory, he said, “I believe I am right. I shall look an awful fool if I am wrong.” However, Einstein quickly saw that Schrödinger had pursued a theory that he himself had discarded years earlier. As physicist Freeman Dyson wrote, the trail leading to the unified field theory is littered with the corpses of failed attempts.
Undaunted, Einstein kept working on the unified field theory, largely in isolation from the rest of the physics community. Lacking a guiding physical principle, he would try to find beauty and elegance in his equations. As mathematician G. H. Hardy once said, “Mathematical patterns like those of the painters or the poets must be beautiful. The ideas, like the colors or the words must fit together in a harmonious way. Beauty is the first test. There is no permanent place for ugly mathematics.” But lacking something like an equivalence principle for the unified field theory, Einstein was left without a guiding star. He lamented the fact that other physicists did not see the world as he did, but he never lost any sleep over this. He would write, “I have become a lonely old fellow. A kind of patriarchal figure who is known chiefly because he does not wear socks and is displayed on various occasions as an oddity. But in my work I am more fanatical than ever and I really entertain the hope that I have solved my old problems of the unity of the physical field. It is, however, like being in an airship in which one can cruise around in the clouds but cannot see clearly how one can return to reality, i.e. to earth.”
Einstein realized that by working on his unified field theory rather than the quantum theory, he was isolated from the main avenues of research at the institute. “I must seem like an ostrich who forever buries its head in the relativistic sand in order not to face the evil quanta,” he lamented. Over the years, other physicists would whisper that he was over the hill and behind the times, but this did not bother him. “I am generally regarded as a sort of petrified object, rendered blind and deaf by the years. I find this role not too distasteful, as it corresponds very well with my temperament,” he wrote.
In 1949, on his seventieth birthday, a special celebration was held in Einstein’s honor at the institute. Scores of physicists came to praise the greatest scientist of their time and contribute articles for a book in his honor. However, from the tone of some speakers and interviews with the press, it became apparent that some of them took Einstein to task for his position on the quantum theory. Einstein partisans were not happy with this, but Einstein took it good-naturedly. A family friend, Thomas Bucky, noted that “Oppenheimer made fun of Einstein in a magazine article with such statements as, ‘He’s old. Nobody pays any attention to him anymore.’ We were madder than all hell about it. But Einstein was not mad at all. He just didn’t believe it and later Oppenheimer denied he had said it.”
That was Einstein’s manner, to take his critics with a grain of salt. When the book in his honor came out, he wrote in good humor, “This is not a jubilee book for me, but an impeachment.” He was a seasoned enough scientist to know that new ideas were hard to come by, and that he was not producing ideas like he did in his youth. As he would write, “Anything really new is invented only in one’s youth. Later one becomes more experienced, more famous—and more stupid.”
What kept him going, however, were the clues he saw everywhere that unification was one of the grand schemes of the universe. He would write, “Nature shows us only the tail of the lion. But I do not doubt that the lion belongs to it even though he cannot at once reveal himself because of his enormous size.” Every day, when he woke up, he would ask himself a simple question: If he were God, how would he create the universe? In fact, given all the constraints necessary to create a universe, he asked himself another question: Did God have any choice? As he gazed at the universe, everything he saw told him that unification was the greatest theme in nature, that God could not have created a universe that made gravity, electricity, and magnetism as separate entities. What he lacked, as he knew, was a guiding principle, a physical picture that would light the way to the unified field theory. None came.
With special relativity the picture was a sixteen-year-old youth racing after a light beam. With general relativity, it was a man leaning back in his chair, about to fall, or marbles rolling on curved space. However, with the unified field theory, he had no such guidance. Einstein was famous for his statement, “Subtle is the Lord, but malicious he is not.” After he struggled for so many decades on the problem of unification, he admitted to his assistant Valentine Bargman, “I have second thoughts. Maybe God is malicious.”
Although the quest for a unified field theory was known to be the hardest problem in all of physics, it was also the most glamorous and seduced legions of physicists. It is ironic, for example, that Wolfgang Pauli, one of Einstein’s severest critics of the unified field theory, would eventually catch the bug himself. In the late 1950s, both Heisenberg and Pauli were increasingly interested in a version of the unified field theory that they claimed could solve the problems that stumped Einstein for thirty years. In fact, writes Pais, “From 1954 to the end of his life, Heisenberg (d. 1976) was immersed in attempts at deriving all of particle physics from a fundamental non-linear wave equation.” In 1958, Pauli visited Columbia University and gave a presentation on the Heisenberg-Pauli version of the unified field theory. The audience, needless to say, was skeptical. Niels Bohr, who was in the audience, finally stood up and said, “We in the back are convinced your theory is crazy. But what divides us is whether your theory is crazy enough.”
Physicist Jeremy Bernstein, also in the audience, remarked, “It was an uncanny encounter of two giants of modern physics. I kept wondering what in the world a non-physicist visitor would have made of it.” Eventually, Pauli became disillusioned with the theory, believing it had too many flaws. When his collaborator insisted on plunging ahead with the theory, Pauli wrote to Heisenberg and enclosed a blank sheet of paper, stating that if his theory was really the unified field theory, then this blank sheet of paper was a work by Titian.
Although progress in the unified field theory was slow and painful, there were plenty of other interesting breakthroughs that kept Einstein busy. One of the strangest was time machines.
To Newton, time was like an arrow. Once fired, it unerringly flew in a straight line, never deviating from its path. One second on the earth was one second in outer space. Time was absolute and beat uniformly through the entire universe at the same rate. Events could take place simultaneously throughout the universe. However, Einstein introduced the concept of relative time, so one second on the earth was not one second on the moon. Time was like Old Man River, meandering its way p
ast planets and stars, slowing down as it went by neighboring heavenly bodies. The question that the mathematician Kurt Gödel now raised was, can the river of time have whirlpools and turn back on itself? Or can it fork into two rivers, creating a parallel universe? Einstein was forced to confront this question in 1949 when Gödel, Einstein’s neighbor at the institute and arguably the greatest mathematical logician of the century, showed that Einstein’s equations allowed for time travel. Gödel started with a universe that was filled with a gas and rotating. If one started off in a rocket ship and went around the entire universe, then one might arrive on the earth before one left! In other words, time travel would be a natural phenomenon in Gödel’s universe, where one would routinely travel back in time during a trip around the universe.
This shook Einstein. So far, every time people tried to find solutions to Einstein’s equations, they found solutions that seemed to fit the data. The perihelion of Mercury, the red shift, the bending of starlight, the gravity of a star, and so on, all fit experimental data very nicely. Now, his equations were giving solutions that challenged all our beliefs about time. If time travel were routinely possible, then history could never be written. The past, like shifting sands, could be changed anytime someone entered his or her time machine. Worse, one might destroy the universe itself by creating a time paradox. What if you went back in time and shot your parents before you were born? This was problematic, because how could you be born in the first place if you just killed your parents?
Time machines violated causality, which was a cherished principle of physics. Einstein was not happy with the quantum theory precisely because it replaced causality with probabilities. Now, Gödel was eliminating causality entirely! After much consideration, Einstein finally dismissed Gödel’s solution by pointing out that it did not fit the observational data: the universe was expanding, not rotating, so time travel, at least for the time being, could be dismissed. But this left open the possibility that if the universe rotated instead of expanded, then time travel would be routine. It would, however, take another five decades before the concept of time travel would be revived into a major field of investigation.
The 1940s was also a turbulent time in cosmology. George Gamow, who was Einstein’s liaison with the U.S. Navy during the war, was less interested in designing explosives than asking questions about the biggest explosion of all, the big bang. Gamow would ask himself several questions that would turn cosmology upside down. He took the big bang theory to its logical conclusion. He shrewdly speculated that if the universe was indeed born in a fiery explosion, then it should be possible to detect the leftover heat from the early fireball. There should be an “echo of creation” from the big bang itself. He used the work of Boltzmann and Planck, who showed that the color of a hot object should correlate with its temperature since both are different forms of energy. For example, if an object is red hot, it means that its temperature is approximately 3,000 degrees Celsius. If an object is yellow hot (like our sun), then it is roughly 6,000 degrees Celsius (which is the temperature of the surface of our sun). Similarly, our own bodies are warm, so we can calculate the “color” of our bodies, which correlates to infrared radiation. (Army night-vision goggles are effective because they detect the infrared radiation emitted from our warm bodies.) Arguing that the Big Bang happened billions of years ago, two members of Gamow’s group, Robert Herman and Ralph Alpher, calculated as early as 1948 that the afterglow of the Big Bang should be 5 degrees above absolute zero, which is remarkably close to the correct value. This radiation corresponds to microwave radiation. Therefore, the “color of creation” is microwave radiation. (This microwave radiation, which was eventually found decades later and determined to correspond to 2.7 degrees above absolute zero, would completely revolutionize the field of cosmology.)
Although he was relatively isolated at Princeton, Einstein lived to see the day when his theory of general relativity was spawning rich new avenues of research in cosmology, black holes, gravity waves, and other areas. However, the last years of his life were also filled with sorrows. In 1948, he received word that Mileva, after a long, hard life caring for their mentally ill son, had passed away, apparently of a stroke during a tantrum of Eduard’s. (Later, 85,000 francs in cash was found stuffed in her bed, apparently the last money left from her Zurich apartments. It was used to help pay for Eduard’s long-term care.) In 1951, his dear sister Maja died.
In 1952, Chaim Weizmann, the man who had organized Einstein’s triumphant tour of America in 1921, passed away after being president of Israel. Unexpectedly, Israel’s premier, David Ben-Gurion, then offered Einstein the presidency of Israel. Although it was quite an honor, he had to decline.
In 1955, Einstein received word that Michele Besso, who had helped Einstein refine his ideas on special relativity, had died. In a letter to Besso’s son, Einstein wrote movingly, “What I admired most about Michele was the fact that he was able to live so many years with one woman, not only in peace but also in constant unity, something I have lamentably failed at twice…. So in quitting this strange world he has once again preceded me by a little. That doesn’t mean anything. For those of us who believe in physics, this separation between past, present, and future is only an illusion, however tenacious.”
That year, with his health failing, he said, “It is tasteless to prolong life artificially. I have done my share; it is time to go. I will do it elegantly.” Einstein finally died on April 18, 1955, of a burst aneurysm. After his death, the cartoonist Herblock published in the Washington Post a moving cartoon depicting the earth, as seen from outer space, with a large sign that read, “Albert Einstein lived here.” That night, newspapers around the world flashed over the wire services a photograph of Einstein’s desk. On it was the manuscript for his greatest unfinished theory, the unified field theory.
CHAPTER 9
Einstein’s Prophetic Legacy
Most biographers uniformly ignore the last thirty years of Einstein’s life, considering it almost an embarrassment unworthy of a genius, a stain on his otherwise sterling history. However, scientific developments in the last few decades have given us an entirely new look into Einstein’s legacy. Because his work was so fundamental, reshaping the very foundations of human knowledge, his impact continues to reverberate throughout physics. Many of the seeds planted by Einstein are now germinating in the twenty-first century, mainly because our instruments such as space telescopes, X-ray space observatories, and lasers are now powerful and sensitive enough to verify a variety of his predictions made decades ago.
In fact, crumbs that have tumbled off Einstein’s plate are now winning Nobel Prizes for other scientists. Furthermore, with the rise of superstring theory, Einstein’s concept of unification of all forces, once the subject of derision and derogatory comments, is now assuming center stage in the world of theoretical physics. This chapter discusses new developments in three areas where Einstein’s enduring legacy continues to dominate the world of physics: the quantum theory, general relativity and cosmology, and the unified field theory.
When Einstein first wrote his paper on Bose-Einstein condensation in 1924, he did not believe that this curious phenomenon would be discovered anytime soon. One would have to cool materials down to near absolute zero before all the quantum states could collapse into a giant superatom.
In 1995, Eric A. Cornell from the National Institute of Standards and Technology and Carl E. Weiman of the University of Colorado did just that, producing a pure Bose-Einstein condensate of 2,000 rubidium atoms at twenty-billionths of a degree above absolute zero. In addition, Wolfgang Ketterle of MIT independently produced Bose-Einstein condensates with enough sodium atoms to do important experiments on them, such as proving that these atoms displayed interference patterns consistent with atoms that were coordinated with each other. In other words, they acted like the superatom predicted by Einstein over seventy years earlier.
Since the initial announcement, discoveries in this fast-moving field have come ra
pidly. In 1997, Ketterle and his colleagues at MIT created the world’s first “atom laser” using Bose-Einstein condensates. What gives laser light its marvelous properties is the fact that the photons march in unison and lockstep with each other, while ordinary light is chaotic and incoherent. Since matter also has wavelike properties, physicists speculated that beams of atoms could also be made to “lase” as well, but the lack of Bose-Einstein condensates hindered progress in this direction. These physicists accomplished their feat by first cooling down a collection of atoms until they condensed. Then they hit the condensate with a laser beam, which turned the atoms into a synchronized beam.
In 2001, Cornell, Weiman, and Ketterle were awarded the Nobel Prize in physics. The Nobel Prize committee cited them “for the achievement of Bose-Einstein condensation in dilute gases of alkali atoms, and for early fundamental studies of the properties of the condensates.” The practical applications of Bose-Einstein condensates are just being realized. These beams of atomic lasers could prove valuable in the future when applied to nanotechnology. They may allow the manipulation of individual atoms and the creation of layers of atomic films for semiconductors in computers of the future.
In addition to atomic lasers, some physicists have speculated that quantum computers (computers that compute on individual atoms) could be based on Bose-Einstein condensates, which could eventually replace silicon-based computers. Others have speculated that dark matter, in part, could be composed of Bose-Einstein condensates. If so, then this obscure state of matter could make up most of the universe.
Einstein’s contributions have also forced quantum physicists to rethink their devotion to the original Copenhagen interpretation of the theory. Back in the 1930s and 1940s, when quantum physicists were snickering behind Einstein’s back, it was easy to ignore this giant of physics because so many discoveries in quantum physics were being made almost daily. Who had time to contemplate the foundations of the quantum theory when physicists were scrambling to collect Nobel Prizes like apples picked off a tree? Hundreds of calculations on the properties of metals, semiconductors, liquids, crystals, and other materials could now be performed, each of which might create entire industries. There was simply no time to spare. As a consequence, physicists for decades simply got used to the Copenhagen school, brushing the unanswered deeper philosophical questions under the rug. The Bohr-Einstein debates were forgotten. However, now that many of the “easy” questions about matter have been picked clean, the much more difficult questions raised by Einstein are still unanswered. In particular, scores of international conferences are taking place around the world as physicists re-examine the cat problem mentioned in chapter 7. Now that experimentalists can manipulate individual atoms, the cat problem is no longer just an academic question. In fact, the ultimate fate of computer technology, which accounts for a large fraction of the world’s wealth, may depend on its resolution since computers of the future may use transistors made of individual atoms.
