Einstein: His Life and Universe

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.⁶⁵

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.⁶⁶ 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 1938.⁶⁷

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.”⁶⁸

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.”⁶⁹

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.”⁷⁰

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.⁷¹

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=mc². 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.

Einstein had long been skeptical about the possibility of harnessing atomic energy or unleashing the power implied by E=mc². On a visit to Pittsburgh in 1934, he had been asked the question and replied that “splitting the atom by bombardment is something akin to shooting birds in the dark in a place where there are only a few birds.” That produced a banner headline across the front page of the Post-Gazette:“Atom Energy Hope Is Spiked by Einstein / Efforts at Loosing Vast Force Is Called Fruitless / Savant Talked Here.”⁷²

With the news in early 1939 that it was, apparently, very possible to bombard and split an atomic nucleus, Einstein faced the question again. In an interview for his sixtieth birthday that March, he was asked whether mankind would find some use for the process. “Our results so far concerning the splitting of the atom do not justify the assumption of a practical utilization of the energies released,” he replied. This time he was cautious, however, and went on to hedge his answer slightly. “There is no physicist with soul so poor who would allow this to affect his interest in this highly important subject.”⁷³

Over the next four months, his interest would indeed grow rapidly.

CHAPTER TWENTY-ONE

THE BOMB

1939–1945

With Leo Szilard reenacting (in 1946) their 1939 meeting

The Letter

Leo Szilard, a charming and slightly eccentric Hungarian physicist, was an old friend of Einstein’s. While