Authors: Walter Isaacson
Einstein pushed his realist approach in a textbook on the history of physics that he coauthored in 1938,
The Evolution of Physics.
Belief in an “objective reality,” the book argued, had led to great scientific advances throughout the ages, thus proving that it was a useful concept even if not provable. “Without the belief that it is possible to grasp reality with our theoretical constructions, without the belief in the inner harmony of our world, there could be no science,” the book declared. “This belief is and always will remain the fundamental motive for all scientific creation.”
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In addition, Einstein used the text to defend the utility of field theories amid the advances of quantum mechanics. The best way to do that was to view particles not as independent objects but as a special manifestation of the field itself:
There is no sense in regarding matter and field as two qualities quite different from each other ... Could we not reject the concept of matter and build a pure field physics? We could regard matter as the regions in
space where the field is extremely strong. A thrown stone is, from this point of view, a changing field in which the states of the greatest field intensity travel through space with the velocity of the stone.
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There was a third reason that Einstein helped to write this textbook, a more personal one. He wanted to help Leopold Infeld, a Jew who had fled Poland, collaborated briefly in Cambridge with Max Born, and then moved to Princeton.
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Infeld began working on relativity with Banesh Hoffmann, and he proposed that they offer themselves to Einstein. “Let’s see if he’d like us to work with him,” Infeld suggested.
Einstein was delighted. “We did all the dirty work of calculating the equations and so on,” Hoffmann recalled. “We reported the results to Einstein and then it was like having a headquarters conference. Sometimes his ideas seemed to come from left field, to be quite extraordinary.”
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Working with Infeld and Hoffmann, Einstein in 1937 came up with elegant ways to explain more simply the motion of planets and other massive objects that produced their own curvatures of space.
But their work on unified field theory never quite gelled. At times, the situation seemed so hopeless that Infeld and Hoffmann became despondent. “But Einstein’s courage never faltered, nor did his inventiveness fail him,” Hoffmann recalled. “When excited discussion failed to break the deadlock, Einstein would quietly say in his quaint English, ‘I will a little tink.’ ” The room would become silent, and Einstein would pace slowly up and down or walk around in circles, twirling a lock of his hair around his forefinger. “There was a dreamy, far-away, yet inward look on his face. No sign of stress. No outward indication of intense concentration.” After a few minutes, he would suddenly return to the world, “a smile on his face and an answer to the problem on his lips.”
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Einstein was so pleased with Infeld’s help that he tried to get Flexner to give him a post at the Institute. But Flexner, who was annoyed that the Institute had already been forced to hire Walther Mayer, balked. Einstein even went to a fellows meeting in person, which he rarely did, to argue for a mere $600 stipend for Infeld, but to no avail.
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So Infeld came up with a plan to write a history of physics with Einstein, which was sure to be successful, and split the royalties. When he went to Einstein to pitch the idea, Infeld became incredibly tongue-tied, but he was finally able to stammer out his proposal. “This is not at all a stupid idea,” Einstein said. “Not stupid at all. We shall do it.”
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In April 1937, Richard Simon and Max Schuster, founders of the house that published this biography, drove out to Einstein’s home in Princeton to secure the rights. The gregarious Schuster tried to win Einstein over with jokes. He had discovered something faster than the speed of light, he said: “The speed with which a woman arriving in Paris goes shopping.”
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Einstein was amused, or at least so Schuster recalled. In any event, the trip was successful, and the
Evolution of Physics,
which is in its forty-fourth printing, not only propagandized for the role of field theories and a faith in objective reality, it also made Infeld (and Einstein) more secure financially.
No one could accuse Infeld of being ungrateful. He later called Einstein “perhaps the greatest scientist and kindest man who ever lived.” He also wrote a flattering biography of Einstein, while his mentor was still alive, that praised him for his willingness to defy conventional thinking in his quest for a unified theory. “His tenacity in sticking to a problem for years, in returning to the problem again and again—this is the characteristic feature of Einstein’s genius,” he wrote.
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Was Infeld right? Was tenacity the characteristic feature of Einstein’s genius? To some extent he had always been blessed by this trait, especially in his long and lonely quest to generalize relativity. There was also ingrained in him, since his school days, a willingness to sail against the current and defy the reigning authorities. All of this was evident in his quest for a unified theory.
But even though he liked to claim that an analysis of empirical data had played a minimal role in the construction of his great theories, he had generally been graced with an intuitive feel for the insights and
principles that could be wrested from nature based on current experiments and observations. This trait was now becoming less evident.
By the late 1930s, he was becoming increasingly detached from new experimental discoveries. Instead of the unification of gravity and electromagnetism, there was greater disunity as two new forces, the weak and the strong nuclear forces, were found. “Einstein chose to ignore those new forces, although they were not any less fundamental than the two which have been known about longer,” his friend Abraham Pais recalled. “He continued the old search for a unification of gravitation and electromagnetism.”
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In addition, a menagerie of new fundamental particles were discovered beginning in the 1930s. Currently there are dozens of them, ranging from bosons such as photons and gluons to fermions such as electrons, positrons, up quarks, and down quarks. This did not seem to bode well for Einstein’s quest to unify everything. His friend Wolfgang Pauli, who joined him at the Institute in 1940, quipped about the futility of this quest. “What God has put asunder,” he said, “let no man join together.”
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Einstein found the new discoveries to be vaguely disconcerting, but he felt comfortable not putting much emphasis on them. “I can derive only small pleasure from the great discoveries, because for the time being they do not seem to facilitate for me an understanding of the foundations,” he wrote Max von Laue. “I feel like a kid who cannot get the hang of the ABCs, even though, strangely enough, I do not abandon hope. After all, one is dealing here with a sphinx, not with a willing streetwalker.”
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So Einstein beat on against the current, borne back ceaselessly into the past. He realized that he had the luxury to pursue his lonely course, something that would be too risky for younger physicists still trying to make their reputations.
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But as it turned out, there were usually at least two or three younger physicists, attracted by Einstein’s aura, willing to collaborate with him, even if the vast majority of the physics priest-hood considered his search for a unified field theory to be quixotic.
One of these young assistants, Ernst Straus, remembers working on an approach that Einstein pursued for almost two years. One evening, Straus found, to his dismay, that their equations led to some conclusions
that clearly could not be true. The next day, he and Einstein explored the issue from all angles, but they could not avoid the disappointing result. So they went home early. Straus was dejected, and he assumed that Einstein would be even more so. To his surprise, Einstein was as eager and excited as ever the next day, and he proposed yet another approach they could take. “This was the start of an entirely new theory, also relegated to the trash heap after a half-year’s work and mourned no longer than its predecessor,” Straus recalls.
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Einstein’s quest was driven by his intuition that mathematical simplicity, an attribute he never fully defined though he felt he knew it when he saw it, was a feature of nature’s handiwork.
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Every now and then, when a particularly elegant formulation cropped up, he would exult to Straus, “This is so simple God could not have passed it up.”
Enthusiastic letters to friends continued to pour forth from Princeton about the progress of his crusade against the quantum theorists who seemed wedded to probabilities and averse to believing in an underlying reality. “I am working with my young people on an extremely interesting theory with which I hope to defeat modern proponents of mysticism and probability and their aversion to the notion of reality in the domain of physics,” he wrote Maurice Solovine in 1938.
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Likewise, headlines continued to emanate from Princeton on purported breakthroughs. “Soaring over a hitherto unscaled mathematical mountain-top, Dr. Albert Einstein, climber of cosmic Alps, reports having sighted a new pattern in the structure of space and matter,” the distinguished
New York Times
science reporter William Laurence reported in a page 1 article in 1935. The same writer and the same paper reported on page 1 in 1939, “Albert Einstein revealed today that after twenty years of unremitting search for a law that would explain the mechanism of the cosmos in its entirety, reaching out from the stars and galaxies in the vastness of infinite space down to the mysteries within the heart of the infinitesimal atom, he has at last arrived within sight of what he hopes may be the ‘Promised Land of Knowledge,’ holding what may be the master key to the riddle of creation.”
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The triumphs in his salad days had come partly from having an instinct that could sniff out underlying physical realities. He could intuitively sense the implications of the relativity of all motion, the
constancy of the speed of light, and the equivalence of gravitational and inertial mass. From that he could build theories based on a feel for the physics. But he later became more reliant on a mathematical formalism, because it had guided him in his final sprint to complete the field equations of general relativity.
Now, in his quest for a unified theory, there seemed to be a lot of mathematical formalism but very few fundamental physical insights guiding him. “In his earlier search for the general theory, Einstein had been guided by his principle of equivalence linking gravitation with acceleration,” said Banesh Hoffmann, a Princeton collaborator. “Where were the comparable guiding principles that could lead to the construction of a unified field theory? No one knew. Not even Einstein. Thus the search was not so much a search as a groping in the gloom of a mathematical jungle inadequately lit by physical intuition.” Jeremy Bernstein later called it “like an all but random shuffling of mathematical formulas with no physics in view.”
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After a while, the optimistic headlines and letters stopped emanating from Princeton, and Einstein publicly admitted that he was, at least for the time being, stymied. “I am not as optimistic,” he told the
New York Times.
For years the paper had regularly headlined each of Einstein’s purported breakthroughs toward a unified theory, but now its headline read, “Einstein Baffled by Cosmos Riddle.”
Nonetheless, Einstein insisted that he still could not “accept the view that events in nature are analogous to a game of chance.” And so he pledged to continue his quest. Even if he failed, he felt that the effort would be meaningful. “It is open to every man to choose the direction of his striving,” he explained, “and every man may take comfort from the fine saying that the search for truth is more precious than its possession.”
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Around the time of Einstein’s sixtieth birthday, early in the spring of 1939, Niels Bohr came to Princeton for a two-month visit. Einstein remained somewhat aloof toward his old friend and sparring partner. They met at a few receptions, exchanged some small talk, but did not reengage in their old game of volleying thought experiments about quantum weirdness.
Einstein gave only one lecture during that period, which Bohr attended. It dealt with his latest attempts to find a unified field theory. At the end, Einstein fixed his eyes on Bohr and noted that he had long tried to explain quantum mechanics in such a fashion. But he made clear that he would prefer not to discuss the issue further. “Bohr was profoundly unhappy with this,” his assistant recalled.
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Bohr had arrived in Princeton with a piece of scientific news that was related to Einstein’s discovery of the link between energy and mass,
E=mc
2
. In Berlin, Otto Hahn and Fritz Strassman had gotten some interesting experimental results by bombarding heavy uranium with neutrons. These had been sent to their former colleague, Lise Meitner, who had just been forced to flee to Sweden because she was half Jewish. She in turn shared them with her nephew Otto Frisch, and they concluded that the atom had been split, two lighter nuclei created, and a small amount of lost mass turned into energy.
After they substantiated the results, which they dubbed
fission,
Frisch informed his colleague Bohr, who was about to leave for America. Upon his arrival in late January 1939, Bohr described the new discovery to colleagues, and it was discussed at a weekly gathering of physicists in Princeton known as the Monday Evening Club. Within days the results had been replicated, and researchers began churning out papers on the process, including one that Bohr wrote with a young untenured physics professor, John Archibald Wheeler.