Institute. A brilliant, chain-smoking theoretical physicist, he proved charismatic and competent enough to be an inspiring leader for the scientists who built the atomic bomb. With his charm and biting wit, he tended to produce either acolytes or enemies, but Einstein fell into neither category. He and Oppenheimer viewed each other with a mixture of amusement and respect, which allowed them to develop a cordial though not close relationship.3
When Oppenheimer first visited the Institute in 1935, he called it a “madhouse” with “solipsistic luminaries shining in separate and hapless desolation.” As for the greatest of these luminaries, Oppenheimer declared, “Einstein is completely cuckoo,” though he seemed to mean it in an affectionate way.4
Once they became colleagues, Oppenheimer became more adroit at dealing with his luminous charges and his jabs became more subtle. Einstein, he declared, was “a landmark but not a beacon,” meaning he was admired for his great triumphs but attracted few apostles in his current endeavors, which was true. Years later, he provided another telling description of Einstein: “There was always in him a powerful purity at once childlike and profoundly stubborn.”5
Einstein became a closer friend, and a walking partner, of another iconic figure at the Institute, the intensely introverted Kurt Godel, a German-speaking mathematical logician from Brno and Vienna. Godel was famous for his “incompleteness theory,” a pair of logical proofs that purport to show that any useful mathematical system will have some propositions that cannot be proven true or false based on the postulates of that system.
Out of the supercharged German-speaking intellectual world, in which physics and mathematics and philosophy intertwined, three jarring theories of the twentieth century emerged: Einstein’s relativity, Heisenberg’s uncertainty, and Godel’s incompleteness. The surface similarity of the three words, all of which conjure up a cosmos that is tentative and subjective, oversimplifies the theories and the connections between them. Nevertheless, they all seemed to have philosophical resonance, and this became the topic of discussion when Godel and Einstein walked to work together.6
They were very different personalities. Einstein was filled with good humor and sagacity, both qualities lacking in Godel, whose intense logic sometimes overwhelmed common sense. This was on glorious display when Godel decided to become a U.S. citizen in 1947. He took his preparation for the exam very seriously, studied the Constitution carefully, and (as might be expected by the formulator of the incompleteness theory) found what he believed was a logical flaw. There was an internal inconsistency, he insisted, that could allow the entire government to degenerate into tyranny.
Concerned, Einstein decided to accompany—or chaperone—Godel on his visit to Trenton to take the citizenship test, which was to be administered by the same judge who had done so for Einstein. On the drive, he and a third friend tried to distract Godel and dissuade him from mentioning this perceived flaw, but to no avail. When the judge asked him about the Constitution, Godel launched into his proof that its internal inconsistency made a dictatorship possible. Fortunately, the judge, who by now cherished his connection to Einstein, cut Godel off. “You needn’t go into all that,” he said, and Godel’s citizenship was saved.7
During their walks, Godel explored some of the implications of relativity theory, and he came up with an analysis that called into question whether time, rather than merely being relative, could be said to exist at all. Einstein’s equations, he figured, could describe a universe that was rotating rather than (or in addition to) expanding. In such a case, the relationship between space and time could become, mathematically, mixed up. “The existence of an objective lapse of time,” he wrote, “means that reality consists of an infinity of layers of ‘now’ which come into existence successively. But if simultaneity is something relative, each observer has his own set of ‘nows,’ and none of these various layers can claim the prerogative of representing the objective lapse of time.”8
As a result, Godel argued, time travel would be possible. “By making a round trip on a rocket ship in a sufficiently wide curve, it is possible in these worlds to travel into any region of the past, present and future, and back again.” That would be absurd, he noted, because then we could go back and chat with a younger version of ourselves (or, even more discomforting, our older version could come back and chat with us). “Godel had achieved an amazing demonstration that time travel, strictly understood, was consistent with the theory of relativity,” writes Boston University philosophy professor Palle Yourgrau in his book on Godel’s relationship with Einstein,
Einstein responded to Godel’s essay along with a variety of others that had been collected in a book, and he seemed to be mildly impressed but also not totally engaged by the argument. In his brief assessment, Einstein called Godel’s “an important contribution” but noted that he had thought of the issue long ago and “the problem here involved disturbed me already.” He implied that although time travel may be true as a mathematical conceivability, it might not be possible in reality.“It will be interesting to weigh whether these are not to be excluded on physical grounds,” Einstein concluded.10
For his part, Einstein remained focused on his own white whale, which he pursued not with the demonic drive of Ahab but the dutiful serenity of Ishmael. In his quest for a unified field theory, he still had no compelling physical insight—such as the equivalence of gravity and acceleration, or the relativity of simultaneity—to guide his way, so his endeavors remained a groping through clouds of abstract mathematical equations with no ground lights to orient him. “It’s 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., earth,” he lamented to a friend.11
His goal, as it had been for decades, was to come up with a theory that encompassed both the electromagnetic and the gravitational fields, but he had no compelling reason to believe that they in fact
Likewise, he was still hoping to explain the existence of particles in terms of a field theory by finding permissible pointlike solutions to his field equations. “He argued that if one believed wholeheartedly in the basic idea of a field theory, matter should enter not as an interloper but as an honest part of the field itself,” recalled one of his Princeton collaborators, Banesh Hoffmann. “Indeed, one might say that he wanted to build matter out of nothing but convolutions of spacetime.” In the process he used all sorts of mathematical devices, but constantly searched for others. “I need more mathematics,” he lamented at one point to Hoffmann.12
Why did he persist? Deep inside, such disjunctures and dualities—different field theories for gravity and electromagnetism, distinctions between particles and fields—had always discomforted him. Simplicity and unity, he intuitively believed, were hallmarks of the Old One’s handiwork. “A theory is more impressive the greater the simplicity of its premises, the more different things it relates, and the more expanded its area of applicability,” he wrote.13
In the early 1940s, Einstein returned for a while to the five-dimensional mathematical approach that he had adopted from Theodor Kaluza two decades earlier. He even worked on it with Wolfgang Pauli, the quantum mechanics pioneer, who had spent some of the war years in Princeton. But he could not get his equations to describe particles.14
So he moved on to a strategy dubbed “bivector fields.” Einstein seemed to be getting a little desperate. This new approach, he admitted, might require surrendering the principle of locality that he had sanctified in some of his
