Walter Isaacson - Einstein - His Life and Universe

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 thought-experiments assaulting quantum mechanics. 15In any event, it was soon abandoned as well.

Einstein’s final strategy, which he pursued for the final decade of his life, was a resurrection of one he had tried during the 1920s. It used a Riemannian metric that was not assumed to be symmetric, which opened the way for sixteen quantities. Ten combinations of them were used for gravity, and the remaining ones for electromagnetism.

Einstein sent early versions of this work to his old comrade Schrödinger. “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. “The attempt depends on an idea that at first seems antiquated and unprofitable, the introduction of a non-symmetrical tensor ... Pauli stuck his tongue out at me when I told him about it.” 16

Schrödinger spent three days poring over Einstein’s work and wrote back to say how impressed he was. “You are after big game,” he said.

Einstein was thrilled with such support. “This correspondence gives me great joy,” he replied, “because you are my closest brother and your brain runs so similarly to mine.” But he 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.” 17

And yet he soldiered on, churning out papers and producing the occasional headline. 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 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.” 18

But Einstein soon realized that it still wasn’t right. During the six weeks between when he submitted the chapter and when it went to the printers, he had second thoughts and revised it yet again.

In fact, he continued to revise the theory repeatedly, but to no avail. His growing pessimism was visible in the lamentations he sent to his old friend from the Olympia Academy days, Maurice Solovine, then Einstein’s publisher in Paris. “I shall never ever solve it,” he wrote in 1948. “It will be forgotten and must later be rediscovered again.”Then, the following year: “I am uncertain as to whether I was even on the right track. The current generation sees in me both a heretic and a reactionary who has, so to speak, outlived himself.” And, with some resignation, in 1951: “The unified field theory has been put into retirement. It is so difficult to employ mathematically that I have not been able to verify it. This state of affairs will last for many more years, mainly because physicists have no understanding of logical and philosophical arguments.” 19

Einstein’s quest for a unified theory was destined to produce no tangible results that added to the framework of physics. He was able to come up with no great insights or thought experiments, no intuitions about underlying principles, to help him visualize his goal. “No pictures came to our aid,” his collaborator Hoffmann lamented. “It is intensely mathematical, and over the years, with helpers and alone, Einstein surmounted difficulty after difficulty, only to find new ones awaiting him.” 20

Perhaps the search was futile. And if it turns out a century from now that there is indeed no unified theory to be found, it 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, for he might thus sacrifice a promising career. So, Einstein said, it was his duty to do it. 21

Einstein’s repeated failures in seeking a unified theory did not soften his skepticism about quantum mechanics. Niels Bohr, his frequent sparring partner, came to the Institute for a stay in 1948 and spent part of his time writing an essay on their debates at the Solvay Conferences before the war. 22Struggling with the article in his office one floor above Einstein’s, he developed writer’s block and called in Abraham Pais to help him. As Bohr paced furiously around an oblong table, Pais coaxed him and took notes.

When he got frustrated, Bohr sometimes would simply sputter the same word over and over. Soon he was doing so with Einstein’s name. He walked to the window and kept muttering, over and over, “Einstein . . . Einstein . . .”

At one such moment, Einstein softly opened the door, tiptoed in, and signaled to Pais not to say anything. He had come to steal a bit of tobacco, which his doctor had ordered him not to buy. Bohr kept muttering, finally spurting out one last loud “Einstein” and then turning around to find himself staring at the cause of his anxieties. “It is an understatement to say that for a moment Bohr was speechless,” Pais recalled. Then, after an instant, they all burst into laughter. 23

Another colleague who tried and failed to convert Einstein was John Wheeler, Princeton University’s renowned theoretical physicist. One afternoon he came by Mercer Street to explain a new approach to quantum theory (known as the sum-over-histories approach) that he was developing with his graduate student, Richard Feynman. “I had gone to Einstein with the hope to persuade him of the naturalness of the quantum theory when seen in this new light,” Wheeler recalled. Einstein listened patiently for twenty minutes, but when it was over repeated his very familiar refrain: “I still cannot believe that the good Lord plays dice.”