When physics became this baffling, Einstein frequently turned to a new woman, and he had a candidate ready for the role. She was Toni Mendel, a well-to-do widow, Jewish, about his age. She would arrive at his home in her chauffeured limousine to whisk him away from Elsa’s company to a night at the opera. But this time, frustrating as Solvay had been, the story took an unexpected turn. Einstein collapsed on a visit to Switzerland. He was carrying a suitcase up a snowy hill when he fell straight down and lay there beside his host, a German industrialist named Willy Meinhardt. He had insisted on hauling his own bag. Meinhardt was terrified that he had allowed his famous guest to bring on a heart attack. Slowly he got Einstein off the ground and even more slowly the pair made their way to the Meinhardt chalet. There had been no heart attack, but Einstein was plainly exhausted. Perhaps, too, he was worn down. Solvay had been hard and then just a month before his own collapse, on February 4, 1928, Hendrik Lorentz had died.

“I have behind me a good and wonderful life,” Lorentz had told his daughter Geertruide, shortly before he began showing the effects of his final illness. Einstein went to the funeral as the representative of the Prussian Academy. The ceremony itself was an enormous affair with astonishing touches of national honor. The Dutch telegraph system observed three minutes of silence, starting at noon. Government

buildings in Haarlem—the Town Hall, railway station, and cavalry barracks—flew their flags at half-staff. A special train from Leiden brought students and teachers to the funeral. A photograph of the funeral cortege passing through Haarlem’s main market square shows that it was packed with ordinary citizens, the men baring their heads, to pay their respects to the great scientist. At the graveside Ehrenfest, Rutherford, Langevin, and Einstein each spoke about Lorentz. “The noblest man of our times,” Einstein called him. He spoke again the next day at a memorial service held in Leiden.

How deeply the spectacle moved Einstein remains unclear. He once remarked to an assistant as they walked in a funeral procession, “Attending funerals is something one does for the people around us. In itself it is meaningless. It seems to me not unlike the zeal with which we polish our shoes every day just so that no one will say we are wearing dirty shoes.”

A few weeks later he was sprawled in the snow. When he was fit enough, Heinrich Zangger, his old friend from the University of Zürich, came down and oversaw his return to Berlin. Elsa took charge when he arrived. Ten years earlier, she had used her nursing skills to good effect, both for Einstein and herself. At the end of that period Einstein’s health was recovered and he had agreed to divorce Mileva. Now he was back in Berlin, badly in need of steady care.

Elsa was ready. She once told a friend, “God has put so much into him [her husband] that is beautiful, and I find him wonderful, even though life at his side is debilitating and difficult in every respect.” Besides looking after him, Elsa also seized the moment to bring an ally into the house. This was Helen Dukas, a woman whom Elsa personally selected to be Einstein’s new secretary. She was to become a lifelong assistant and, after his death, coexecutor of Einstein’s literary estate. She seems to have been beyond seduction, for there is no evidence that Einstein ever made a move in her direction. With her arrival, Elsa at last had a permanent wall against a long-open flank.

Einstein’s society doctor, Janos Plesch, combined flair with knowledge. John Maynard Keynes pronounced him “something between a genius and a quack.” Plesch ordered Einstein to relax, stay at home, stop sailing his boat, and minimize contacts with people beyond the family. Elsa stood watch by the front door, turning away most of the

would-be visitors. When visitors did come in, she soon chased them out to make sure they did not overtire the invalid. She led him away for a long summer on the Baltic beach where he wrote letters, read Spinoza, and thought about physics. That summer turned out to be the last grand one that Berlin would enjoy for many decades, and Einstein missed most of it.

In May, a national election led to a new coalition government, one that tilted left. In those days, leftist German leaders were the ones who fully accepted the legitimacy of the republic and were neither nostalgic for monarchy nor ambitious for tyranny. Nationalist parties appeared to be in retreat from popularity. Brecht’s proletarian production of The Threepenny Opera was the “show of the season,” suggesting that the city’s bourgeoisie boasted a left sensibility. Seventy plus years later, it is impossible to view Germany in the late 1920s and not see the shadow of coming catastrophe, but the future’s shadow is seldom visible to those on the scene. Count Kessler’s diary for that summer shows the opposite of worry. 14 June 1928: Lunched with [the composer] Richard Strauss … [who] aired his quaint views, about the need for dictatorship, and so on, which nobody takes seriously. Republicans were so confident that summer they could laugh.

Meanwhile, Einstein was sunbathing on the Baltic shores, enjoying a relaxed correspondence with Ehrenfest and Schrödinger. A photograph taken that summer shows him lounging on a beach chair and wearing a robe that was sufficiently eye-catching to be a stage magician’s costume. Women’s bathing suits had changed radically, making the seaside a perfect place for Einstein to enjoy himself while scribbling letters and postcards. He sounded like someone enjoying his convalescence. “Here I am forced to laze about under splendid beech trees,” he told Ehrenfest. “How happy one can be in quietude and solitude. It is also wonderful for contemplation…. I now believe less than ever in the essentially statistical nature of events and have decided to use what little energy is left me in accordance with my own predilection, regardless of the present hustle around me.”

Did Ehrenfest shriek when he read that? When had Einstein ever surrendered his predilections to the hustle around him? Whatever was heroic or petty about him came from his ability to ignore all hustle

and follow his own compass. He must have been truly exhausted if he ever thought he might just go along with the ideas about quantum statistics. Ehrenfest needed help himself just then, precisely because he had lost faith in his compass. He had sided with Bohr and rejected Einstein’s opposition to quantum mechanics, but he was not happy. He feared that physics no longer made sense to him, or at least that he could not use it creatively. This notion seems to have been part of a depressive delusion. The physicist and “father of the H-bomb,” Edward Teller, was a student in those days and recalls, ”Ehrenfest did not invent quantum mechanics, but he had the reputation [among students] of understanding it, or at least of explaining it, better than those who invented it.”

The real inventors of quantum mechanics that summer were distracted by more routine work. Heisenberg had just arrived in Leipzig where his reputation and up-to-date physics had been summoned to restore the university’s program. Bohr was teaching too, although one must never forget that teaching for Bohr was never routine. He had become one of the most persuasive teachers since Plato; it was how he made his mark. In August 1928, as an example, an unknown student named George Gamow turned up at the door of Bohr’s institute and asked for an audience, which, grudgingly, was granted.

What are you up to, Bohr wanted to know.

Gamow reported that he had been studying a kind of radioactivity known as alpha-decay. Rutherford had won his Nobel prize for studying the phenomenon.

What about alpha-radioactivity? Bohr wondered.

Gamow had shown that such radiation was not the result of some mysterious atomic instability, but a logical consequence of quantum mechanics.

Ah. “My secretary tells me you cannot stay more than one day because you have no money,” Bohr said.

Gamow was more like a poet than a physicist and could not even afford to buy food. He had bummed his way to Copenhagen that summer in the same bohemian spirit that had sent William Faulkner exploring Paris.

“If I arrange for you a fellowship,” Bohr wondered, “would you stay for a year?”

“Yes,” Gamow told him and Bohr won another disciple.

Einstein took advantage of the long, enforced calm to think of physics, mathematics, and the laws of nature. He wanted an experiment that would show the incompleteness of quantum mechanics, but there he was like a chess champion looking for a move that had been missed in the heat of surprise and competition. He had plenty of time before the next match and his letters that summer show that he was not looking for an immediately publishable way to recoup against quantum mechanics.

While Einstein recovered, Schrödinger called for a continuation of the revolutionary effort. He wrote Bohr a letter saying that the classical concepts represented in the Heisenberg principle by p and q would eventually have to be replaced by less vague ideas.

No, Bohr said, the old concepts could survive perfectly well in the framework of complementarity. Note, by the way, that in this exchange it is Bohr who is insisting on accustomed principles while Schrödinger is calling for a more radical break with the old ways of thinking. Yet this paradox does not mean Schrödinger was the real revolutionary. Schrödinger and Einstein had both expected a traditional revolution—if we can use that oxymoron. Einstein’s achievement showed what a traditional revolution could accomplish. It had redefined space, time, and gravity (the revolutionary part) but kept it all in a context of natural explanations (the traditional part). Newton would have recognized and sympathized with Einstein’s ambition. Bohr and Max Born, however, had produced a revolution in which the terms kept their old meanings, but they were removed from physically coherent context into one of pure mathematical description. In that sense, it is fair to compare Einstein and Schrödinger with freethinkers during an old regime who had wanted great changes but were horrified when the king himself was sent to the guillotine.

From his seaside beach chair Einstein kept up with the Schrödinger-Bohr letters and he sympathized. “Your claim,” he wrote Schrödinger, “that the concepts p, q will have to be given up if they can only claim such ‘shaky’ meaning seems to me to be fully justified.” (It should be reassuring to nonphysicists who scratch their heads over just what p and q mean to see that trained, creative physicists also muttered in dismay.)

Einstein continued, telling Schrödinger, “The Heisenberg-Bohr tranquilizing philosophy—or religion?—is so delicately contrived that for the time being, it provides a gentle pillow for the true believer from which he cannot very easily be aroused. So let him lie there.”

However, at some point Einstein did find a challenge that he could set before Bohr at their next meeting. When he hit upon his secret retort is uncertain. Whenever he thought of it—the night after Solvay 1927, the night before Solvay 1930, or somewhere in between—he would be ready with his zinger. During the wait it was the search for a single field uniting gravitational and electromagnetic fields that held his thoughts.

He had been struggling with this question throughout the 1920s, but it now seemed a bit of an old-fashioned problem. Between Einstein’s post-Nobel lecture at Göteborg in the summer of 1923 and his convalescence on the Baltic five years later had come the whole of the quantum revolution: matrix mechanics, wave mechanics, Max Born’s probabilistic interpretation, Heisenberg’s principle, and Bohr’s notion of complementarity. The effect of this intervention was to divorce parts of physics in a way that had previously seemed impossible. The reluctant divorcee was Einstein’s physics—general relativity, a set of mathematical laws whose physics was governed by space-time, and from which the present flows continuously from the past. Georges Lemaître had only just then begun developing an idea based on Einstein’s laws that would become known as the “Big Bang” theory of the universe; it is the perfect model of Einstein’s physics. Once, billions of years ago, something happened and since then the universe has been evolving like a wondrous symphony in which each astonishing note flows from its predecessor. This cosmological physics is objective, coherent, and inevitable.

Quantum physics—mathematical, discontinuous, and probabilistic—was the breakaway partner. If the heavens since the Big Bang are the model for macro-physics, the Big Bang itself is the model for quantum physics. On the two sides of it you have two distinct, unrelated states of nature; between them lies the mysterious discontinuity, the incomprehensible verb whose essence is invisible but whose intervention changes everything. By persisting with his search for a unifi-

cation of gravity and electromagnetism in a continuous, inevitable law of nature—a law that did not even include the quantum h—Einstein was defying the very revolution he had once prophesied.

As he convalesced, Einstein suddenly had one of his most famous ideas. As usual, he was testing one of his physics’ most fundamental assumptions. In this case he was reexamining the Riemann geometry that supported his general theory of relativity. Particularly he was challenging its most distinctive feature, its absence of parallel lines in anything but infinitely small spaces. In this search he really had gone back to the starting point, because Riemann’s no-parallelism is what makes everything in the universe appear to curve as it moves through space. No-parallelism was the aspect of Einstein’s theory that guaranteed that the relative time for every moving object is slightly different. If any of the anti-Einsteinians had been up to it, the way to defeat relativity and reduce Einstein to the level of one more overphotographed celebrity was to overthrow its geometric basis. Of course, none of them were up to it, but there was Einstein, picking at it himself.

In June 1928, Max Planck appeared before the Prussian Academy and presented Einstein’s new mathematics of “distant parallelism.” (Einstein was not yet strong enough to read his own paper.) In this geometry, parallel lines were possible, although they would meet in infinitely large spaces. Somehow this doctrine became part of the Einstein legend: He was the smartest man in the world; only 12 people could understand his theory; time is the fourth dimension; and parallel lines meet in infinity. Those details would become what the well-educated schoolchild knows of Einstein.

Distant parallelism was a purely mathematical idea, but Einstein suspected that it could provide the basis for a new physics step that would at last allow him to unite the gravitational and electromagnetic fields. As summer turned to autumn, his confidence of success grew. Elsa told a friend, “He has solved the problem whose solution was the dream of his life.”

It was while Einstein was in that good mood that the New York Times’s Berlin correspondent paid a surprise visit to the Einstein home. He gave no record about why he dropped by, but probably he was just following the routine of a good beat reporter who periodically checks

out his usual suspects. So the newspaperman, Paul Miller, knocked on Einstein’s door and Elsa opened it. Her job as gatekeeper demanded that she shoo off unwanted visitors, but Miller had not become a leading reporter by being shy. He persuaded Elsa to permit an audience with the resident genius.

“He will scream and shriek and rave,” she advised, leading Miller one flight up to Einstein’s study, “but never mind that. When he calms down he may have something to say.”

Elsa opened the study door and found Einstein so absorbed in doing mathematical manipulations on a writing pad that he did not look up. Books were scattered about. Einstein remained lost in his work on unified field theory until Elsa called to him.

As promised, Einstein began to curse the interruption.

Miller immediately called out a question about the proposed new telescope that was eventually built for Mount Palomar, “Professor, do you think the new telescope with a 200-inch lens to be erected in California will be able to disclose visual proof of relativity? You are aware that this telescope will be five times the size of the largest one in the world.”

Perhaps Miller’s editor really had sent him to get Einstein’s comment on the telescope project, but the question was so weak that it sounds like a desperate stab at locking his foot in the door.

Einstein did not think much of the question. The reporter seemed not to know that visual “proof” of relativity had been announced almost exactly 10 years earlier, or that there was already a 100-inch telescope on Mount Wilson, so the new one would double, not quintuple, the current giant. Einstein made a feeble attempt to brush the question aside with a mot, “Not the eye, but the spirit furnishes proof of theories, and that errs most of the time.”

Miller noted the comment, marvelously unintelligible, just the sort of impenetrable wisdom you would expect from the world’s smartest man. “Is it your opinion,” the reporter persisted, “that visual proof of relativity will be disclosed by this or any future telescope?”

Einstein visibly relaxed himself, smoothing his famous hair. The reporter seemed not to realize that bursting in on Einstein while he was in the midst of fruitful thought was like waking somebody from a

deeply satisfying dream and pummeling him with daytime banalities. Einstein got a hold on himself. The quickest way to get rid of such people is to answer their immediate questions and discourage others. “The only means of proving relativity with a telescope,” he explained in plain language, “is by measuring the deflection of light through the field of gravity. This proof has already been furnished and is correct without the slightest doubt. What one may expect from the great telescope of dimensions not yet constructed lies in another territory—namely exploration of the systems of fixed stars.”

Then something happened. Einstein made a mistake. Miller’s report does not make clear exactly how it happened. Einstein wanted to send the reporter away.

Miller wanted to stay.

Einstein had important work to get back to.

Miller wondered what Einstein was working on.

Einstein did not wish to say, but he said something that allowed Miller to close his story with the news, “Dr. Einstein then said he was treading on the edge of a great scientific discovery, one that will startle the world far more than relativity.”

The next day in New York, the paper’s front page carried the headline, “Einstein on Verge of Great Discovery; Resents Intrusion.” Soon many of Berlin’s newshounds were barking after a story. Einstein quickly realized he had erred in talking to the reporter, but there was no turning off the machinery he had jarred into motion. The streets around the Einstein apartment began to fill with the commotion of flashbulb monkeys, to use Einstein’s term for the proto-paparazzi who regularly pestered him.