# Einstein's Final Quest

In the later years of his life, after he had fled Nazi Germany at age fifty-four and moved to Princeton, New Jersey, Albert Einstein focused his scientific energies on what would turn out to be a futile quest: the search for a unified field theory. Such a theory would tie together the forces of gravity and electromagnetism with the subatomic forces described by quantum theory. He had befriended a fellow refugee physicist, Leopold Infeld, who occasionally tried to help in that effort. Most of Einstein’s colleagues were bemused by his stubbornness, but Infeld admired what he saw as yet another example of the determination that, over the decades, had made Einstein so great. “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 said.

Was Infeld right? Was tenacity — grit — one of the characteristic features of Einstein’s genius? Yes. He had been blessed with that trait since youth. When he was six, his father had given him a compass. Einstein spent days and nights twisting and turning it, marveling at how the needle would twitch and point north even though nothing seemed to be touching it. Most of us remember getting a compass when we were kids and being fascinated by it for a while, at least until we find something else intriguing — oh, look, a dead bird! — and promptly quit puzzling about the compass. Unlike most of us, Einstein remained fascinated by the mystery and magic of force fields, and how to relate electromagnetic fields to gravitational fields, for the rest of his life. Even on his deathbed, he was scribbling field equations that he hoped would lead to a unified theory.

This tenacity was most notably on display during his long quest, which culminated in 1915, to come up with a general theory of relativity. Perhaps the most elegant theory in the history of science, it was the product of a decade of solitary persistence during which Einstein wove together the laws of space, time, and motion based on a simple yet amazing insight: that gravity and acceleration produced equivalent effects.

In his quest for a unified field theory, Einstein was not aided by a physical insight such as the equivalence of gravity and acceleration. Instead, he was driven by his discomfort at how quantum theory, which primarily focuses on activities in the subatomic realm, had evolved into a new view of mechanics in which things could happen by chance, in which probabilities governed events, and in which there was an inherent uncertainty in nature — rather than a fixed reality — that made it impossible to know both the position and the momentum of a particle at the same instant.

To Einstein, this simply did not smell true. The ultimate goal of physics, he repeatedly said, was to discover the laws that strictly determined causes and effects. He could not believe that things happened by chance, by probability, like some cosmic game of dice. This led to one of his most famous quotes. “Quantum mechanics is certainly imposing,” he said. “But an inner voice tells me that it is not yet the real thing. The theory says a lot, but it does not really bring us any closer to the secrets of the Old One. I, at any rate, am convinced that He does not play dice.” He repeated this declaration that “God would not play dice with the universe” so often that at one conference his colleague Niels Bohr was moved to exclaim, with mock exasperation, “Einstein, please quit telling God what to do.”

Einstein hoped that a unified field theory would unite the various forces of nature in a way that would explain what seemed like the uncertainties and probabilities of quantum mechanics. Even though the vast majority of the physics priesthood considered this quest quixotic, there were usually one or two younger physicists in Princeton willing to assist him. One of them, Ernst Straus, remembers working on an approach that Einstein pursued with astonishing grit and determination for almost two years. Then one evening Straus found 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.

Einstein’s quest was driven by his belief that mathematical simplicity was a feature of nature’s handiwork. 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 poured 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 to a longtime colleague in 1938.

Occasionally Einstein’s pursuit made headlines. “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-one article in 1935. And again, the same writer and the same paper reported on page one 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.”

The triumphs in Einstein’s 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, or the constancy of the speed of light, or the equivalence of gravitational and inertial mass. In his quest for a unified theory, there seemed to be a lot of mathematical equations 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.”

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.”

So why did Einstein persevere? The disjunctures and dualities that other physicists had learned to accept — different field theories for gravity and electromagnetism, distinctions between particles and fields — deeply discomforted him. Simplicity and unity, he intuitively believed, were hallmarks of the Old One’s handiwork. He simply could not “accept the view that events in nature are analogous to a game of chance.”

And so he continued his quest. Even if he failed to find a unified theory, 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.”

He continued throughout the 1940s to try one mathematical approach after another, stubbornly plowing ahead with new formulas every time an old one had to be discarded. Like modern string theorists are doing today, he conjured up the possibility of a universe that had five, six, or even more dimensions. Another strategy involved “bivector fields,” which led him to abandon temporarily the idea that particles existed in only one location in space and time. A third strategy, which he pursued for an entire decade until his death, involved a tensor calculus that produced a metric with sixteen quantities that he hoped — to no avail — might supply what was needed to describe both gravity and electromagnetism in one field theory.

Einstein sent early versions of this work to his longtime colleague Erwin Schrödinger, who appreciated his quest more than quantum theorists such as Wolfgang Pauli did. “I am sending them to nobody else, because you are the only person known to me who is not wearing blinders in regard to the fundamental questions in our science,” Einstein wrote. “Pauli stuck his tongue out at me when I told him about it.”

“You are after big game,” Schrödinger replied. But Einstein soon began to realize that the gossamer theories he was spinning were mathematically elegant but never seemed to relate to anything physical. “Inwardly I am not so certain as I previously asserted,” he confessed to Schrödinger a few months later. “We have squandered a lot of time on this, and the result looks like a gift from the devil’s grandmother.”

Yet still he soldiered on. When a new edition of his book *The Meaning of Relativity* was being prepared in 1949, he added the latest version of the paper he had shown Schrödinger, “Generalization of Gravitation Theory,” as an appendix. The *New York Times* reprinted an entire page of complex equations from the manuscript along with a front-page story headlined “New Einstein Theory Gives A Master Key to Universe; Scientist, After 30 Years’ Work, Evolves Concept That Promises to Bridge Gap Between the Star and the Atom.”

Unfortunately, Einstein soon realized that it still wasn’t right. During the six weeks between when he submitted the chapter and it went to the printer, he had second thoughts and revised it yet again. In fact, he continued to revise the theory repeatedly, year after year, remaining determined despite each setback.

On one level it is fair to say that his search was futile, that all his grit and determination amounted to naught. And if it turns out a century from now that there is indeed no unified theory to be found, the quest will also look misconceived. But Einstein never regretted his dedication to it. When a colleague asked him one day why he was spending — perhaps squandering — his time in this lonely endeavor, he replied that even if the chance of finding a unified theory was small, the attempt was worthy. He had already made his name, he noted. His position was secure, and he could afford to take the risk and expend the time. A younger theorist, however, could not take such a risk, since he might thus sacrifice a promising career. So it was, Einstein said, his duty to do it.

Even during the final year of his life, Einstein continued to amble to his office in Princeton to wrestle with his equations and try to push them a little closer toward the receding horizon of a unified field theory. He would come in with his new ideas, often clutching equations he had scribbled the night before on scraps of paper, and go over them with his assistant that final year, Bruria Kaufman, a female physicist from Israel.

She would write the new equations on a blackboard and point out problems. Einstein would then try to counter them. Even when they were defeated by the obstacles to a new approach, as they invariably were, Einstein remained optimistic. “Well, we’ve learned something,” he would say as the clock ticked down.

In writing to colleagues who questioned why he pursued so tenaciously what seemed to them like a hopeless quest, Einstein began to apologize for his stubbornness. Nevertheless, he proudly refused to abandon it. “I must seem like an ostrich who forever buries its head in the relativistic sand in order not to face the evil quanta,” he wrote Louis de Broglie, another of his colleagues in the long struggle against the uncertainties found in quantum mechanics. He refused to let go of his underlying principle that there must be some unified theory that would dispel such uncertainties. He had discovered general relativity by trusting an underlying principle, and that made him a “fanatic believer” that comparable methods would eventually lead to a unified field theory. “This should explain the ostrich policy,” he wryly told de Broglie.

Einstein’s belief in the certainty of nature’s laws became not just a principle but an article of faith as he grew older. And that faith was, for him, religious in nature. As he responded in a letter to a young girl who asked him whether he believed in God: “Everyone who is seriously involved in the pursuit of science becomes convinced that a spirit is manifest in the laws of the Universe — a spirit vastly superior to that of man, and one in the face of which we with our modest powers must feel humble. In this way the pursuit of science leads to a religious feeling of a special sort.”

One day in April 1955, when he was working at his office on yet another set of unified field equations, Einstein began to feel a great pain in his stomach. He had long been plagued by an aneurism in his abdominal aorta, and it had started to rupture. A group of doctors convened at his home the next day, and they recommended a surgeon who might be able, though it was thought unlikely, to repair the aorta. Einstein refused. “It is tasteless to prolong life artificially,” he told his assistant Helen Dukas. “I have done my share, it is time to go. I will do it elegantly.”

He was taken to the Princeton hospital, where one of his final requests was for some notepaper and pencils so he could continue to work on his elusive unified field theory. He died shortly after one a.m. on April 18, 1955. By his bed were twelve pages of tightly written equations, littered with cross-outs and corrections. To the very end, he struggled to read the mind of the creator of the cosmos. And the final thing he wrote, before he went to sleep for the last time, was one more line of symbols and numbers that he hoped might get him, and the rest of us, just a little step closer to the spirit manifest in the laws of the universe.