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Heart

"What further hurts me deeply is that as an adult man, I have to look on without being able to do anything. I am nothing but a burden to my family... It would be better off if I were not alive at all. Only the thought that I have always done what lay in my modest powers, and that I do not permit myself a single pleasure or distraction save for what my studies offer me, sustains me and sometimes protects me from despair."

“To dwell on the things that depress or anger us does not help in overcoming them. One must knock them down alone.”

As Christmas 1913 neared, Einstein’s struggle to generalize relativity had the added benefit of being a way to avoid family emotions. The effort produced yet another eloquent restatement of how science could rescue him from the merely personal. “The love of science thrives under these circumstances,” he told Elsa, “for it lifts me impersonally from the vale of tears into peaceful spheres.”

“One of the strongest motives that leads men to art and science is escape from everyday life with its painful crudity and hopeless dreariness,” Einstein said. “Such men make this cosmos and its construction the pivot of their emotional life, in order to find the peace and security which they cannot find in the narrow whirlpool of personal experience.”

In early 1917, it was Einstein’s turn to fall ill. He came down with stomach pains that he initially thought were caused by cancer. Now that his mission was complete, death did not frighten him. He told the astronomer Freundlich that he was not worried about dying because now he had completed his theory of relativity.

As long as someone put no strong demands or emotional burdens on him, Einstein could readily forge friendships and even affections.

[...] “My passionate sense of social justice and social responsibility has always contrasted oddly with my pronounced lack of need for direct contact with other human beings and communities,” he reflected. “I am truly a ‘lone traveler’ and have never belonged to my country, my home, my friends, or even my immediate family, with my whole heart; in the face of all these ties, I have never lost a sense of distance and a need for solitude.”

“I do not know anyone as lonely and detached as Einstein,” said his collaborator Leopold Infeld. “His heart never bleeds, and he moves through life with mild enjoyment and emotional indifference. His extreme kindness and decency are thoroughly impersonal and seem to come from another planet.”

It is easier to be a nonconformist and rebel, both in science and in a militaristic culture like Germany’s, when you can detach yourself easily from others. “The detachment enabled him to walk through life immersed in thought,” Pais said. It also allowed him—or compelled him—to pursue his theories in both a “single-minded and single-handed” manner.

Einstein understood the conflicting forces in his own soul, and he seemed to think it was true for all people. “Man is, at one and the same time, a solitary being and a social being,” he said. His own desire for detachment conflicted with his desire for companionship, mirroring the struggle between his attraction and his aversion to fame.

He was not always merely cold, for there were times, especially when it came to Mileva Mari, that the forces of both attraction and repulsion raged inside him with a fiery heat. His problem, especially with his family, was that he was resistant to such strong feelings in others. “He had no gift for empathy,” writes historian Thomas Levenson, “no ability to imagine himself into the emotional life of anyone else.” When confronted with the emotional needs of others, Einstein tended to retreat into the objectivity of his science.

Why didn’t he leave Berlin? [...] His inertia is hard to explain, but it is indicative of a change that became evident in both his personal life and his scientific work during the 1920s. He had once been a restless rebel who hopped from job to job, insight to insight, resisting anything that smacked of restraint. He had been repelled by conventional respectability. But now he personified it. From being a romantic youth who fancied himself a footloose bohemian he had settled, with but a few stabs at ironic detachment, into a bourgeois life with a doting hausfrau and a richly wallpapered home filled with heavy Biedermeier furniture. He was no longer restless. He was comfortable.

When a ferocious storm, far greater than any he had ever witnessed, seized his ship, he recorded his thoughts in his travel diary. “One feels the insignificance of the individual,” he wrote, “and it makes one happy.”

“American youth has the good fortune not to have its outlook troubled by outworn traditions,” he noted.

The usual pictures of Faraday and Maxwell were tacked on the walls. There was also, of course, one of Newton, although after a while it fell off its hook. To that mix was added a fourth: Mahatma Gandhi, Einstein’s new hero now that his passions were as much political as they were scientific. As a small joke, the only award displayed was a framed certificate of Einstein’s membership in the Bern Scientific Society.

He admitted to Hans Albert that focusing was difficult, but the attempt provided him the means to escape the painfully personal. “As long as I am able to work, I must not and will not complain, because work is the only thing that gives substance to life.”

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.

“But our equations are much more important to me,” Einstein added. “Politics is for the present, while our equations are for eternity.”

Both Maja and Margot preferred living with him to living with their own husbands as they got older. He had been a difficult husband and father because he did not take well to any constricting bonds, but he could also be intense and passionate, both with family and friends, when he found himself engaged rather than confined.

He had lifelong friends who were devoted to him, and he had family members who doted on him, but there were also those few—Mileva and Eduard foremost among them—whom he simply walled out when the relationship became too painful.

“I am generally regarded as sort of a petrified object,” he noted to Max Born, then a professor in Edinburgh, one of those friends whose affection had lasted so long. “I find this role not too distasteful, as it corresponds very well with my temperament... I simply enjoy giving more than receiving in every respect, do not take myself nor the doings of the masses seriously, am not ashamed of my weaknesses and vices, and naturally take things as they come with equanimity and humor.”

The Fall

“Anything truly novel is invented only during one’s youth,” Einstein lamented to a friend after finishing his work on general relativity and cosmology. “Later one becomes more experienced, more famous—and more blockheaded.”

But now, just as he had traded his youthful bohemian attitudes for the comforts of a bourgeois home, he had become wedded to the faith that field theories could preserve the certainties and determinism of classical science. His stubbornness henceforth would work to his disadvantage.

It was a fate that he had begun fearing years before, not long after he finished his famous flurry of 1905 papers. “Soon I will reach the age of stagnation and sterility when one laments the revolutionary spirit of the young,” he had worried to his colleague from the Olympia Academy, Maurice Solovine.

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.”

As for the greatest of these luminaries, Oppenheimer declared, “Einstein is completely cuckoo,” though he seemed to mean it in an affectionate way.

[...] Einstein, he declared, was “a landmark but not a beacon”.

“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.”

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.”

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.

Seventy years earlier, his awe at contemplating a compass caused him to marvel at the concept of fields, and they had guided his theories ever since. But what would happen, he worried to Besso, if field theory turned out to be unable to account for particles and quantum mechanics? “In that case nothing remains of my entire castle in the air, gravitation theory included.”

The End

Einstein likewise had repeatedly bounced back from bouts of anemia and stomach ailments. But he knew that the aneurysm on his abdominal aorta should soon prove fatal, and he began to display a peaceful sense of his own mortality. When he stood at the graveside and eulogized the physicist Rudolf Ladenberg, who had been his colleague in Berlin and then Princeton, the words seemed to be ones he felt personally. “Brief is this existence, as a fleeting visit in a strange house,” he said. “The path to be pursued is poorly lit by a flickering consciousness.”

“The strange thing about growing old is that the intimate identification with the here and now is slowly lost,” he wrote his friend the queen mother of Belgium. “One feels transposed into infinity, more or less alone.”

As if he knew that he had only a few more weeks, Einstein ruminated on the nature of death and time in the condolence letter he wrote to Besso’s family. “He has departed from this strange world a little ahead of me. That means nothing. For us believing physicists, the distinction between past, present and future is only a stubborn illusion.”

A group of doctors convened at his home the next day, and after some consultation 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 Dukas. “I have done my share, it is time to go. I will do it elegantly.”

He did ask, however, whether he would suffer “a horrible death.” The answer, the doctors said, was unclear. The pain of an internal hemorrhage could be excruciating. But it may take only a minute, or maybe an hour. To Dukas, who became overwrought, he smiled and said, “You’re really hysterical—I have to pass on sometime, and it doesn’t really matter when.”

Epilogue

Curiosity, in Einstein’s case, came not just from a desire to question the mysterious. More important, it came from a childlike sense of marvel that propelled him to question the familiar, those concepts that, as he once said, “the ordinary adult never bothers his head about.”

Ever since Newton, for example, scientists had known that inertial mass was equivalent to gravitational mass. But Einstein saw that this meant that there was an equivalence between gravity and acceleration that would unlock an explanation of the universe.

“Behind a formula he immediately saw the physical content, while for us it only remained an abstract formula,” said one of his first students. Planck came up with the concept of the quanta, which he viewed as mainly a mathematical contrivance, but it took Einstein to understand their physical reality. Lorentz came up with mathematical transformations that described bodies in motion, but it took Einstein to create a new theory of relativity based on them.

Perhaps the most important aspect of his personality was his willingness to be a nonconformist. It was an attitude that he celebrated in a foreword he wrote near the end of his life to a new edition of Galileo. “The theme that I recognize in Galileo’s work,” he said, “is the passionate fight against any kind of dogma based on authority.”

Einstein’s fundamental creed was that freedom was the lifeblood of creativity. “The development of science and of the creative activities of the spirit,” he said, “requires a freedom that consists in the independence of thought from the restrictions of authoritarian and social prejudice.” Nurturing that should be the fundamental role of government, he felt, and the mission of education.

There was a simple set of formulas that defined Einstein’s outlook. Creativity required being willing not to conform. That required nurturing free minds and free spirits, which in turn required “a spirit of tolerance.” And the underpinning of tolerance was humility—the belief that no one had the right to impose ideas and beliefs on others.

For some people, miracles serve as evidence of God’s existence. For Einstein it was the absence of miracles that reflected divine providence. The fact that the cosmos is comprehensible, that it follows laws, is worthy of awe. This is the defining quality of a “God who reveals himself in the harmony of all that exists.”

Einstein considered this feeling of reverence, this cosmic religion, to be the wellspring of all true art and science. It was what guided him.

Living

“Life is very short,” he told the mayor, “while the authorities work slowly. My birthday is already past, and I decline the gift.” The headline the next day in the Berliner Tageblatt newspaper read, “Public Disgrace Complete / Einstein Declines.”

By this point, the Einsteins had fallen in love with the plot of land in Caputh, negotiated its purchase, and had a design for a house to build upon it. So they went ahead and bought it with their own money. “We have spent most of our savings,” Elsa complained, “but we have our land.”

[...] “I like living in the new little wooden house enormously, even though I am broke as a result,” he wrote his sister shortly after moving in. “The sailboat, the sweeping view, the solitary fall walks, the relative quiet—it is a paradise.”

There he sailed the new twenty-three-foot boat his friends had given him for his birthday, the Tümmler, or Dolphin, which was built fat and solid to his specifications. He liked to go out on the water alone, even though he didn’t swim. “He was absurdly happy as soon as he reached the water,” recalled a visitor. For hours he would let the boat drift and glide aimlessly as he gently toyed with the rudder.

At one point a friend gave him an expensive outboard motor for emergency use. Einstein declined. He had a childlike delight about taking small risks—he still never took a life jacket even though he could not swim—and escaping to where he could be by himself.

“The professor does not drive,” Elsa often said. “It’s too complicated for him.” Instead, he loved to walk, or, more precisely, shuffle, up Mercer Street each morning to his office at the Institute. People often snapped their heads when he passed, but the sight of him walking lost in thought was soon one of the well-known attractions of the town.

At one dinner where Einstein was being honored, for example, he got so distracted that he pulled out his notepad and began scribbling equations. When he was introduced, the crowd burst into a standing ovation, but he was still lost in thought. Dukas caught his attention and told him to get up. He did, but noticing the crowd standing and applauding, he assumed it was for someone else and heartily joined in. Dukas had to come over and inform him that the ovation was for him.

Philosophy

But how did he come up with the starting blocks for his theoretical thinking—the principles and postulates that would launch his logical deductions? As we’ve seen, he did not usually start with a set of experimental data that needed some explanation. “No collection of empirical facts, however comprehensive, can ever lead to the formulation of such complicated equations,” he said in describing how he had come up with the general theory of relativity. In many of his famous papers, he made a point of insisting that he had not relied much on any specific experimental data—on Brownian motion, or attempts to detect the ether, or the photoelectric effect—to induce his new theories.

Instead, he generally began with postulates that he had abstracted from his understanding of the physical world, such as the equivalence of gravity and acceleration. That equivalence was not something he came up with by studying empirical data. Einstein’s great strength as a theorist was that he had a keener ability than other scientists to come up with what he called “the general postulates and principles which serve as the starting point.”

“The development of the general theory of relativity introduced Einstein to the power of abstract mathematical formalisms, notably that of tensor calculus,” writes the astrophysicist John Barrow. “A deep physical insight orchestrated the mathematics of general relativity, but in the years that followed the balance tipped the other way. Einstein’s search for a unified theory was characterized by a fascination with the abstract formalisms themselves.”

The fact that this method paid off in general relativity, he said, “justifies us in believing that nature is the realization of the simplest conceivable mathematical ideas.”

[...] “I am convinced that we can discover by means of purely mathematical constructions the concepts and the laws connecting them with each other,” he claimed.

[...] “I have been guided not by the pressure from behind of experimental facts, but by the attraction in front from mathematical simplicity,” he said. “It can only be hoped that experiments will follow the mathematical flag.”

“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. He had found his gravitational theories 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.

Religion

“Try and penetrate with our limited means the secrets of nature and you will find that, behind all the discernible laws and connections, there remains something subtle, intangible and inexplicable. Veneration for this force beyond anything that we can comprehend is my religion. To that extent I am, in fact, religious.”

You accept the historical existence of Jesus? “Unquestionably! No one can read the Gospels without feeling the actual presence of Jesus. His personality pulsates in every word. No myth is filled with such life.”

Do you believe in God? “I’m not an atheist. The problem involved is too vast for our limited minds. We are in the position of a little child entering a huge library filled with books in many languages. The child knows someone must have written those books. It does not know how. It does not understand the languages in which they are written. The child dimly suspects a mysterious order in the arrangement of the books but doesn’t know what it is. That, it seems to me, is the attitude of even the most intelligent human being toward God. We see the universe marvelously arranged and obeying certain laws but only dimly understand these laws.”

Is this a Jewish concept of God? “I am a determinist. I do not believe in free will. Jews believe in free will. They believe that man shapes his own life. I reject that doctrine. In that respect I am not a Jew.”

Is this Spinoza’s God? “I am fascinated by Spinoza’s pantheism, but I admire even more his contribution to modern thought because he is the first philosopher to deal with the soul and body as one, and not two separate things.”

How did he get his ideas? “I’m enough of an artist to draw freely on my imagination. Imagination is more important than knowledge. Knowledge is limited. Imagination encircles the world.”

Do you believe in immortality? “No. And one life is enough for me.”

The most beautiful emotion we can experience is the mysterious. It is the fundamental emotion that stands at the cradle of all true art and science. He to whom this emotion is a stranger, who can no longer wonder and stand rapt in awe, is as good as dead, a snuffed-out candle. To sense that behind anything that can be experienced there is something that our minds cannot grasp, whose beauty and sublimity reaches us only indirectly: this is religiousness. In this sense, and in this sense only, I am a devoutly religious man.

“I cannot conceive of a personal God who would directly influence the actions of individuals or would sit in judgment on creatures of his own creation,” Einstein scribbled on the letter. “My religiosity consists of a humble admiration of the infinitely superior spirit that reveals itself in the little that we can comprehend about the knowable world. That deeply emotional conviction of the presence of a superior reasoning power, which is revealed in the incomprehensible universe, forms my idea of God.”

“I believe in Spinoza’s God, who reveals himself in the lawful harmony of all that exists, but not in a God who concerns himself with the fate and the doings of mankind.”

“What separates me from most so-called atheists is a feeling of utter humility toward the unattainable secrets of the harmony of the cosmos,” he explained.

“The fanatical atheists,” he explained in a letter, “are like slaves who are still feeling the weight of their chains which they have thrown off after hard struggle. They are creatures who—in their grudge against traditional religion as the ‘opium of the masses’—cannot hear the music of the spheres.”

[...] “You may call me an agnostic, but I do not share the crusading spirit of the professional atheist whose fervor is mostly due to a painful act of liberation from the fetters of religious indoctrination received in youth,” he explained. “I prefer the attitude of humility corresponding to the weakness of our intellectual understanding of nature and of our own being.”

“The cosmic religious feeling,” he said, “is the strongest and noblest motive for scientific research.”

[...] “Science can be created only by those who are thoroughly imbued with the aspiration toward truth and understanding,” he said. “This source of feeling, however, springs from the sphere of religion.”

Scientists aim to uncover the immutable laws that govern reality, and in doing so they must reject the notion that divine will, or for that matter human will, plays a role that would violate this cosmic causality.

To Einstein, this belief in the existence of an underlying reality had a religious aura to it. That dismayed Solovine, who wrote to say that he had an “aversion” to such language. Einstein disagreed. “I have no better expression than ‘religious’ for this confidence in the rational nature of reality and in its being accessible, to some degree, to human reason. When this feeling is missing, science degenerates into mindless empiricism.”

“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.

Einstein told Pauli that he still objected to the fundamental tenet in quantum mechanics that a system can be defined only by specifying the experimental method of observing it. There was a reality, he insisted, that was independent of how we observed it. “Einstein has the philosophical prejudice that a state, termed ‘real,’ can be defined objectively under any circumstances, that is, without specification of the experimental arrangement used to examine the system,” Pauli marveled in a letter to Max Born.

Morality

This belief in causal determinism, which was inherent in Einstein’s scientific outlook, conflicted not only with the concept of a personal God. It was also, at least in Einstein’s mind, incompatible with human free will. Although he was a deeply moral man, his belief in strict determinism made it difficult for him to accept the idea of moral choice and individual responsibility that is at the heart of most ethical systems.

[...] Einstein, on the other hand, believed, as did Spinoza, that a person’s actions were just as determined as that of a billiard ball, planet, or star. “Human beings in their thinking, feeling and acting are not free but are as causally bound as the stars in their motions,” Einstein declared in a statement to a Spinoza Society in 1932.

[...] I do not at all believe in free will in the philosophical sense. Everybody acts not only under external compulsion but also in accordance with inner necessity. Schopenhauer’s saying, “A man can do as he wills, but not will as he wills,” has been a real inspiration to me since my youth; it has been a continual consolation in the face of life’s hardships, my own and others’, and an unfailing wellspring of tolerance.

Do you believe, Einstein was once asked, that humans are free agents? “No, I am a determinist,” he replied. “Everything is determined, the beginning as well as the end, by forces over which we have no control. It is determined for the insect as well as for the star. Human beings, vegetables, or cosmic dust, we all dance to a mysterious tune, intoned in the distance by an invisible player.”

This attitude appalled some friends, such as Max Born, who thought it completely undermined the foundations of human morality. “I cannot understand how you can combine an entirely mechanistic universe with the freedom of the ethical individual,” he wrote Einstein. “To me a deterministic world is quite abhorrent. Maybe you are right, and the world is that way, as you say. But at the moment it does not really look like it in physics—and even less so in the rest of the world.”

For Born, quantum uncertainty provided an escape from this dilemma. Like some philosophers of the time, he latched on to the indeterminacy that was inherent in quantum mechanics to resolve “the discrepancy between ethical freedom and strict natural laws.” Einstein conceded that quantum mechanics called into question strict determinism, but he told Born he still believed in it, both in the realm of personal actions and physics.

In Einstein’s philosophy, the way to resolve this issue was to look upon free will as something that was useful, indeed necessary, for a civilized society, because it caused people to take responsibility for their own actions. Acting as if people were responsible for their actions would, psychologically and practically, prompt them to act in a more responsible manner. “I am compelled to act as if free will existed,” he explained, “because if I wish to live in a civilized society I must act responsibly.” He could even hold people responsible for their good or evil, since that was both a pragmatic and sensible approach to life, while still believing intellectually that everyone’s actions were predetermined. “I know that philosophically a murderer is not responsible for his crime,” he said, “but I prefer not to take tea with him.”

“The most important human endeavor is the striving for morality in our actions,” he wrote a Brooklyn minister. “Our inner balance and even our existence depend on it. Only morality in our actions can give beauty and dignity to life.”

[...] The foundation of that morality, he believed, was rising above the “merely personal” to live in a way that benefited humanity.

[...] he had flaws. Yet more than most people, he dedicated himself honestly and sometimes courageously to actions that he felt transcended selfish desires in order to encourage human progress and the preservation of individual freedoms. He was generally kind, good-natured, gentle, and unpretentious.

Special Relativity

"the constancy of the velocity of light is not consistent with the law of the addition of velocities. The result was that I had to spend almost one year in fruitless thoughts."

Events that are simultaneous with reference to the embankment are not simultaneous with respect to the train,” said Einstein. The principle of relativity says that there is no way to decree that the embankment is “at rest” and the train “in motion.” We can say only that they are in motion relative to each other. So there is no “real” or “right” answer. There is no way to say that any two events are “absolutely” or “really” simultaneous.

The obvious yet still astonishing conclusion: with no such thing as absolute simultaneity, there is no such thing as “real” or absolute time.

Quantum Mechanics

Einstein, in his talk to the [Solvay] conference [in 1911], sorrowfully demurred: “These discontinuities, which we find so distasteful in Planck’s theory, seem really to exist in nature.”

[...] during the more than four decades in which he would express his discomfort with quantum theory, he increasingly sounded like a scientific realist, someone who believed that an underlying reality existed in nature that was independent of our ability to observe or measure it.

Einstein agreed, perhaps too readily, that “the quantum hypothesis is provisional” and that it “does not seem compatible with the experimentally verified conclusions of the wave theory.” Somehow it was necessary, he told his questioners, to accommodate both wave and particle approaches to the understanding of light. “In addition to Maxwell’s electrodynamics, which is essential to us, we must also admit a hypothesis such as that of quanta.”

Einstein was both impressed and a little jealous when he heard of Bohr’s theory. As one scientist reported to Rutherford, “He told me that he had once similar ideas but he did not dare to publish them.” Einstein later declared of Bohr’s discovery, “This is the highest form of musicality in the sphere of thought.”

Einstein argued that the presence of this cloud of photons made it even more likely that a photon of the same wavelength and direction as the other photons in the cloud would be emitted. This process of stimulated emission would, almost forty years later, be the basis for the invention of the laser, an acronym for “light amplification by the stimulated emission of radiation.”

There was one part of Einstein’s quantum theory of radiation that had strange ramifications. “It can be demonstrated convincingly,” he told Besso, “that the elementary processes of emission and absorption are directed processes.”

[...] But here was the rub: there was no way to determine which direction an emitted photon might go. In addition, there was no way to determine when it would happen.

[...] It undermined the certainty of classical physics and the faith that if you knew all the positions and velocities in a system you could determine its future.

[...] “The thing about causality plagues me very much,” he wrote Max Born in 1920. “Is the quantum-like absorption and emission of light ever conceivable in terms of complete causality?”

[...] “I find the idea quite intolerable that an electron exposed to radiation should choose of its own free will not only its moment to jump off but also its direction,” he despaired to Born a few years later. “In that case, I would rather be a cobbler, or even an employee of a gaming house, than a physicist.”

Bohr was bolder about going into that misty realm. Abandoning strict causality, he countered to Einstein, was “the only way open” given the evidence.

“I could probably have arrived at something like this myself,” Einstein lamented, “but if all this is true then it means the end of physics.”

Their dispute went to the fundamental heart of the design of the cosmos: Was there an objective reality that existed whether or not we could ever observe it? Were there laws that restored strict causality to phenomena that seemed inherently random? Was everything in the universe predetermined?

[...] On one of the many occasions when Einstein declared that God would not play dice, it was Bohr who countered with the famous rejoinder: Einstein, stop telling God what to do!

[...] unlike a gas of classical particles, which will remain a gas unless the particles attract one another, a gas of quantum particles can condense into some kind of liquid even without a force of attraction between them.

This phenomenon, now called Bose-Einstein condensation, was a brilliant and important discovery in quantum mechanics, and Einstein deserves most of the credit for it. Bose had not quite realized that the statistical mathematics he used represented a fundamentally new approach. As with the case of Planck’s constant, Einstein recognized the physical reality, and the significance, of a contrivance that someone else had devised.

Einstein admitted that he found this “mutual influence” of particles to be “quite mysterious,” for they seemed as if they should behave independently. [...] In a postscript he admitted that it all worked well mathematically, but “the physical nature remains veiled.”

[...] a principle that Einstein would nevertheless try to cling to in the future: the principle of separability, which as serts that particles with different locations in space have separate, independent realities. One aim of general relativity’s theory of gravity had been to avoid any “spooky action at a distance,” as Einstein famously called it later, in which something happening to one body could instantly affect another distant body.

[...] And once again, younger colleagues would embrace his ideas more readily than he would—just as he had once embraced the implications of the ideas of Planck, Poincaré, and Lorentz more readily than they had.

An electron could not, in reality, be waving thus, Einstein thought. So what, in the real world, did the wave equation really represent?

[...] Born proposed that the wave did not describe the behavior of the particle. Instead, he said that it described the probability of its location at any moment.

[...] the wavelengths of the spectral lines of the radiation from these electrons as they lost energy. The result was so complex that Heisenberg gave his paper to Born and left on a camping trip with fellow members of his youth group, hoping that his mentor could figure it out. Born did. The math involved what are known as matrices, and Born sorted it all out and got the paper published. In collaboration with Born and others in Göttingen, Heisenberg went on to perfect a matrix mechanics that was later shown to be equivalent to Schrödinger’s wave mechanics.

The very act of observing something—of allowing photons or electrons or any other particles or waves of energy to strike the object—affects the observation. But Heisenberg’s theory went beyond that. An electron does not have a definite position or path until we observe it. This is a feature of our universe, he said, not merely some defect in our observing or measuring abilities.

When Einstein wrote him a note objecting to these features, Heisenberg replied bluntly, “I believe that indeterminism, that is, the nonvalidity of rigorous causality, is necessary.”

“We cannot observe electron orbits inside the atom,” Heisenberg said. “A good theory must be based on directly observable magnitudes.”

“But you don’t seriously believe,” Einstein protested, “that none but observable magnitudes must go into a physical theory?”

“Isn’t that precisely what you have done with relativity?” Heisenberg asked with some surprise.

“Possibly I did use this kind of reasoning,” Einstein admitted, “but it is nonsense all the same.”

“It is wrong to think that the task of physics is to find out how nature is,” Bohr declared. “Physics concerns what we can say about nature.”

As this revolution climaxed in the spring of 1927, Einstein used the 200th anniversary of Newton’s death to defend the classical system of mechanics based on causality and certainty. Two decades earlier, Einstein had, with youthful insouciance, toppled many of the pillars of Newton’s universe, including absolute space and time. But now he was a defender of the established order, and of Newton.

[...] “But the last word has not been said,” Einstein argued. “May the spirit of Newton’s method give us the power to restore union between physical reality and the profoundest characteristic of Newton’s teaching—strict causality.”

Einstein never fully came around, even as experiments repeatedly showed quantum mechanics to be valid. He remained a realist, one who made it his creed to believe in an objective reality, rooted in certainty, that existed whether or not we could observe it.

[...] The belief in an external world independent of the person observing it, he repeatedly said, was the basis of all science.

“We should not insult Mach’s poor horse,” Besso replied. “Didn’t it make possible the tortuous journey through the relativities? And who knows, in the case of the nasty quanta, it may also carry Don Quixote de la Einsteina through it all!”

“You know what I think about Mach’s little horse,” Einstein wrote Besso in return. “It cannot give birth to anything living. It can only exterminate harmful vermin.”

[...] the success of his general theory convinced him that Mach’s skepticism, even though it might be useful for weeding out superfluous concepts, did not provide much help in constructing new theories.

When he posed that question, there was one possibility that he simply could not believe: that the good Lord would have created beautiful and subtle rules that determined most of what happened in the universe, while leaving a few things completely to chance. It felt wrong. “If the Lord had wanted to do that, he would have done it thoroughly, and not kept to a pattern... He would have gone the whole hog. In that case, we wouldn’t have to look for laws at all.”

“Quantum mechanics is certainly imposing,” Einstein 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.”

“One can’t make a theory out of a lot of ‘maybes,’” Pauli recalls Einstein arguing. “Deep down it is wrong, even if it is empirically and logically right.”

“By dinner-time we could usually prove that his thought experiments did not contradict uncertainty relations,” Heisenberg recalled, and Einstein would concede defeat. “But next morning he would bring along to breakfast a new thought experiment, generally more complicated than the previous one.” By dinnertime that would be disproved as well.

“And so it went for several days,” said Heisenberg. “In the end, we—that is, Bohr, Pauli, and I—knew that we could now be sure of our ground.”

“Einstein, I’m ashamed of you,” Ehrenfest scolded. He was upset that Einstein was displaying the same stubbornness toward quantum mechanics that conservative physicists had once shown toward relativity. “He now behaves toward Bohr exactly as the champions of absolute simultaneity had behaved toward him.”

Einstein told de Broglie that all scientific theories, leaving aside their mathematical expressions, ought to lend themselves to so simple a description “that even a child could understand them.” And what could be less simple, Einstein continued, than the purely statistical interpretation of wave mechanics! “Carry on,” he told de Broglie as they parted at the station. “You are on the right track!”

But he wasn’t. By 1928, a consensus had formed that quantum mechanics was correct, and de Broglie relented and adopted that view. “Einstein, however, stuck to his guns and continued to insist that the purely statistical interpretation of wave mechanics could not possibly be complete,” de Broglie recalled, with some reverence, years later.

“I admire to the highest degree the achievements of the younger generation of physicists that goes by the name quantum mechanics, and I believe in the deep level of truth of that theory,” he said in 1929 when accepting the Planck medal from Planck himself. “But”—and there was always a but in any statement of support Einstein gave to quantum theory—“I believe that the restriction to statistical laws will be a passing one.”

[...] the principle says that a similar uncertainty is inherent in measuring the energy involved in a process and the time duration of that process.

Einstein’s thought experiment involved a box with a shutter that could open and shut so rapidly that it would allow only one photon to escape at a time. The shutter is controlled by a precise clock. The box is weighed exactly. Then, at a certain specified moment, the shutter opens and a photon escapes. The box is now weighed again. The relationship between energy and mass (remember, E=mc2) permitted a precise determination of the energy of the particle. And we know, from the clock, its exact time of departing the system. So there!

[...] It was one of the great ironies of scientific debate that, after a sleepless night, Bohr was able to hoist Einstein by his own petard. The thought experiment had not taken into account Einstein’s own beautiful discovery, the theory of relativity. According to that theory, clocks in stronger gravitational fields run more slowly than those in weaker gravity. Einstein forgot this, but Bohr remembered. During the release of the photon, the mass of the box decreases. Because the box is on a spring scale (in order to be weighed), the box will rise a small amount in the earth’s gravity. That small amount is precisely the amount needed to restore the energy-time uncertainty relation.

[...] But Einstein was never fully convinced. Even a year later, he was still churning out variations of such thought experiments.

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.”

[...] “Of course, I may be wrong,” he said in a slow and humorous cadence. Pause. “But perhaps I have earned the right to make my mistakes.” Einstein later confided to a woman friend, “I don’t think I’ll live to find out who is correct.”

Near the end of his life, Einstein regaled a small group of Wheeler’s students. When the talk turned to quantum mechanics, he once again tried to poke holes in the idea that our observations can affect and determine realities. “When a mouse observes,” Einstein asked them, “does that change the state of the universe?”

Quantum Entanglement

The resulting four-page paper, published in May 1935 and known by the initials of its authors as the EPR paper, was the most important paper Einstein would write after moving to America. “Can the Quantum-Mechanical Description of Physical Reality Be Regarded as Complete?” they asked in their title.

[...] “It did not come out as well as I had originally wanted,” Einstein complained to Schrödinger right after it was published. “Rather, the essential thing was, so to speak, smothered by the formalism.”

[...] Einstein, of course, had occasionally succumbed to giving interviews about upcoming articles, but this time he declared himself dismayed by the practice. “It is my invariable practice to discuss scientific matters only in the appropriate forum,” he wrote in a statement to the Times, “and I deprecate advance publication of any announcement in regard to such matters in the secular press.”

“If without in any way disturbing a system we can predict with certainty the value of a physical quantity, then there exists an element of physical reality corresponding to this physical quantity.”

The paper went on to expand Einstein’s thought experiment about two particles that have collided (or have flown off in opposite directions from the disintegration of an atom) and therefore have properties that are correlated. We can take measurements of the first particle, the authors asserted, and from that gain knowledge about the second particle “without in any way disturbing the second particle.” By measuring the position of the first particle, we can determine precisely the position of the second particle. And we can do the same for the momentum. “In accordance with our criterion for reality, in the first case we must consider the quantity P as being an element of reality, in the second case the quantity Q is an element of reality.”

[...] The only alternative, the authors argued, would be to claim that the process of measuring the first particle affects the reality of the position and momentum of the second particle. “No reasonable definition of reality could be expected to permit this,” they concluded.

Wolfgang Pauli wrote Heisenberg a long and angry letter.“Einstein has once again expressed himself publicly on quantum mechanics (together with Podolsky and Rosen—no good company, by the way),” he fumed. “As is well known, every time that happens it is a catastrophe.”

“Everything else was abandoned,” Bohr’s colleague recalled. “We had to clear up such a misunderstanding at once.”Even with such intensity, it took Bohr more than six weeks of fretting, writing, revising, dictating, and talking aloud before he finally sent off his response to EPR.

Until then, the disturbance caused by a measurement had been part of Bohr’s physical explanation of quantum uncertainty.

However, using his concept of complementarity, Bohr added a significant caveat. He pointed out that the two particles were part of one whole phenomenon. Because they have interacted, the two particles are therefore “entangled.” They are part of one whole phenomenon or one whole system that has one quantum function.

In addition, the EPR paper did not, as Bohr noted, truly dispel the uncertainty principle, which says that it is not possible to know both the precise position and momentum of a particle at the same moment.

That's it? Einstein didn't read the literature carefully enough?

“Entanglement of predictions arises from the fact that the two bodies at some earlier time formed in a true sense one system, that is were interacting, and have left behind traces on each other,” Schrödinger wrote. “If two separated bodies enter a situation in which they influence each other, and separate again, then there occurs what I have just called entanglement of our knowledge of the two bodies.”

I describe a state of affairs as follows: the probability is ½ that the ball is in the first box. Is that a complete description? [1] no: A complete statement is: the ball is (or is not) in the first box. That is how the characterization of the state of affairs must appear in a complete description. [2] yes: Before I open them, the ball is by no means in one of the two boxes. Being in a definite box comes about only when I lift the covers.

Einstein’s argument is based on what appears to be common sense. However, sometimes what seems to make sense turns out not to be a good description of nature. Einstein realized this when he developed his relativity theory; he defied the accepted common sense of the time and forced us to change the way we think about nature. Quantum mechanics does something similar. It asserts that particles do not have a definite state except when observed, and two particles can be in an entangled state so that the observation of one determines a property of the other instantly. As soon as any observation is made, the system goes into a fixed state.

he proposed another thought experiment to Schrödinger a few weeks later, in early August 1935. It involved a situation in which quantum mechanics would assign only probabilities, even though common sense tells us that there is obviously an underlying reality that exists with certainty. Imagine a pile of gunpowder that, due to the instability of some particle, will combust at some point, Einstein said. The quantum mechanical equation for this situation “describes a sort of blend of not-yet and already-exploded systems.” But this is not “a real state of affairs,” Einstein said, “for in reality there is just no intermediary between exploded and not-exploded.”

[...] but there is no clear rule for what constitutes such an observation. Can the cat be an observer? A flea? A computer? A mechanical recording device? There’s no set answer. However, we do know that quantum effects generally are not observed in our everyday visible world, which includes cats and even fleas. So most adherents of quantum mechanics would not argue that Schrödinger’s cat is sitting in that box somehow being both dead and alive until the lid is opened.

So, when quantum events have not been observed, we have superposition (a blend of dead and alive); but when we're at a macro level where quantum events cannot be observed, this weirdness no longer exists, and we're back to the intuitive world?

But when the experiments were undertaken in the 1980s by the French physicist Alain Aspect and others, they provided evidence that locality was not a feature of the quantum world. “Spooky action at a distance,” or, more precisely, the potential entanglement of distant particles, was.

But no information is transmitted, no signal sent, and there is no traditional cause-and-effect relationship. One can show by thought experiments that quantum entanglement cannot be used to send information instantaneously.

General Relativity

Until then, Einstein’s scientific success had been based on his special talent for sniffing out the underlying physical principles of nature. He had left to others the task, which to him seemed less exalted, of finding the best mathematical expressions of those principles, as his Zurich colleague Minkowski had done for special relativity.

There was another clue that a new form of geometry might be needed. It became apparent to Einstein when he considered the case of a rotating disk. As a disk whirled around, its circumference would be contracted in the direction of its motion when observed from the reference frame of a person not rotating with it. The diameter of the circle, however, would not undergo any contraction. Thus, the ratio of the disk’s circumference to its diameter would no longer be given by pi. Euclidean geometry wouldn’t apply to such cases.

“The central idea of general relativity is that gravity arises from the curvature of spacetime,” says physicist James Hartle. “Gravity is geometry.”

Riemann (1826–1866) was a child prodigy who invented a perpetual calendar at age 14 as a gift for his parents and went on to study in the great math center of Göttingen, Germany, under Carl Friedrich Gauss, who had been pioneering the geometry of curved surfaces. This was the topic Gauss assigned to Riemann for a thesis, and the result would transform not only geometry but physics.

Gauss and others had developed different types of geometry that could describe the surface of spheres and other curved surfaces. Riemann took things even further: he developed a way to describe a surface no matter how its geometry changed, even if it varied from spherical to flat to hyperbolic from one point to the next. He also went beyond dealing with the curvature of just two-dimensional surfaces and, building on the work of Gauss, explored the various ways that math could describe the curvature of three-dimensional and even four-dimensional space.

His head-snapping insight was that gravity could be defined as the curvature of spacetime, and thus it could be represented by a metric tensor. For more than three years he would fitfully search for the right equations to accomplish his mission. [...]

At Grossmann’s suggestion, he had begun using a tensor developed by Riemann and then a more suitable one developed by Ricci. Finally, by the end of 1912, he had devised [in his Zurich Notebook] a field equation using a tensor that was, it turned out, pretty close to the one that he would eventually use in his triumphant formulation of late November 1915. [...]

But then he rejected it, and it would stagnate in his discard pile for more than two years. Why? Among other considerations, he thought (somewhat mistakenly) that this solution did not reduce, in a weak and static field, to Newton’s laws. When he tried it a different way, it did not meet the requirement of the conservation of energy and momentum. [...]

As a result, Einstein reduced his reliance on the mathematical strategy. It was a decision that he would later regret. Indeed, after he finally returned to the mathematical strategy and it proved spectacularly successful, he would from then on proclaim the virtues—both scientific and philosophical—of mathematical formalism.

In all likelihood, Besso had already warned him that this might be the case. In a memo that he apparently wrote in August 1913, Besso suggested that a “rotation metric” was not in fact a solution permitted by the field equations in the Entwurf.

But Einstein dismissed these doubts, in letters to Besso as well as to Mach and others, at least for the time being. If experiments upheld the theory, “your brilliant investigations on the foundations of mechanics will have received a splendid confirmation,” Einstein wrote to Mach days after the Entwurf was published. “For it shows that inertia has its origin in some kind of interaction of the bodies, exactly in accordance with your argument about Newton’s bucket experiment.”

In part he did so through a thought experiment, which became known as the “hole argument”, that seemed to suggest that the holy grail of making the gravitational field equations generally covariant was impossible to reach, or at least physically uninteresting. “The fact that the gravitational equations are not generally covariant, something that quite disturbed me for a while, is unavoidable,” he wrote a friend. “It can easily be shown that a theory with generally covariant equations cannot exist if the demand is made that the field is mathematically completely determined by matter.”

[...] He also got into an exhausting debate with the Italian mathematician Tullio Levi-Civita, who pointed out problems with his handling of the tensor calculus.

Yet the termination of the eclipse mission had a silver lining. Einstein’s Entwurf equations were not correct. The degree to which gravity would deflect light, according to Einstein’s theory at the time, was the same as that predicted by Newton’s emission theory of light. But, as Einstein would discover a year later, the correct prediction would end up being twice that. If Freundlich had succeeded in 1914, Einstein might have been publicly proven wrong.

[...] He had previously figured that the bending of light by the gravitational field next to the sun would be approximately 0.83 arc-second, which corresponded to what would be predicted by Newton’s theory when light was treated as if a particle. But now, using his newly revised theory, Einstein calculated that the bending of light by gravity would be twice as great, because of the effect produced by the curvature of spacetime. Therefore, the sun’s gravity would bend a beam by about 1.7 arc-seconds, he now predicted. It was a prediction that would have to wait for the next suitable eclipse, more than three years away, to be tested.

Einstein was confident enough in his theory to show it off at a weeklong series of two-hour lectures, starting at the end of June 1915, at the University of Göttingen, which had become the preeminent center for the mathematical side of theoretical physics. [...]

Hilbert was likewise enchanted with Einstein and his theory. So much so that he soon set out to see if he could beat Einstein to the goal of getting the field equations right. Within three months of his Göttingen lectures, Einstein was confronted with two distressing discoveries: that his Entwurf theory was indeed flawed, and that Hilbert was racing feverishly to come up with the correct formulations on his own.

[...] two major blows in early October 1915.

The Entwurf equations were not, as he had believed, covariant under a transformation that uniformly rotated the coordinate axes. Besso had warned him in a memo in 1913 that this seemed to be a problem. But Einstein had ignored him. Now, upon redoing his calculations, he was dismayed to see this pillar knocked away. “This is a blatant contradiction,” he lamented to the astronomer Freundlich.

He assumed that the same mistake also accounted for his theory’s inability to account fully for the shift in Mercury’s orbit. And he despaired that he would not be able to find the problem. “I do not believe I am able to find the mistake myself, for in this matter my mind is too set in a deep rut.”

In addition, he realized that he had made a mistake in what was called his “uniqueness” argument: that the sets of conditions required by energy-momentum conservation and other physical restrictions uniquely led to the field equations in the Entwurf.

And now, as this edifice was crumbling, he could hear what seemed to be Hilbert’s footsteps gaining on him from Göttingen. [...]

When he finally decided his Entwurf approach was untenable, he was willing to abandon it abruptly. That is what he did in October 1915.

[...] “Once every last bit of confidence in the earlier theories had given way,” he told a friend, “I saw clearly that it was only through general covariance theory, i.e., with Riemann’s covariant, that a satisfactory solution could be found.”

Worried about being scooped, he wrote Hilbert a letter saying that he himself had discovered the flaws four weeks earlier, and he sent along a copy of his November 4 lecture. “I am curious whether you will take kindly to this new solution,” Einstein asked with a touch of defensiveness.

The reply that Hilbert sent the next day must have unnerved Einstein. He said he was about ready to oblige with “an axiomatic solution to your great problem.” He had planned to hold off discussing it until he explored the physical ramifications further. “But since you are so interested, I would like to lay out my theory in very complete detail this coming Tuesday,” which was November 16.

[...] Finally, he replied to Hilbert and declined his invitation to visit Göttingen the next day. His letter did not hide his anxiety: “Your analysis interests me tremendously... The hints you gave in your messages awaken the greatest of expectations. Nevertheless, I must refrain from traveling to Göttingen for the moment... I am tired out and plagued by stomach pains... If possible, please send me a correction proof of your study to mitigate my impatience.”

[...] That very morning, November 18, Einstein received Hilbert’s new paper, the one that he had been invited to Göttingen to hear presented. Einstein was surprised, and somewhat dismayed, to see how similar it was to his own work. His response to Hilbert was terse, a bit cold, and clearly designed to assert the priority of his own work:

The system you furnish agrees—as far as I can see—exactly with what I found in the last few weeks and have presented to the Academy. The difficulty was not in finding generally covariant equations ...for this is easily achieved with Riemann’s tensor . . . Three years ago with my friend Grossmann I had already taken into consideration the only covariant equations, which have now been shown to be the correct ones. We had distanced ourselves from it, reluctantly, because it seemed to me that the physical discussion yielded an incongruity with Newton’s law. Today I am presenting to the Academy a paper in which I derive quantitatively out of general relativity, without any guiding hypothesis, the perihelion motion of Mercury. No gravitational theory has achieved this until now.

Hilbert responded kindly and quite generously the following day, claiming no priority for himself. “Cordial congratulations on conquering perihelion motion,” he wrote. “If I could calculate as rapidly as you, in my equations the electron would have to capitulate and the hydrogen atom would have to produce its note of apology about why it does not radiate.”

Yet the day after, on November 20, Hilbert sent in a paper to a Göttingen science journal proclaiming his own version of the equations for general relativity. The title he picked for his piece was not a modest one. “The Foundations of Physics,” he called it.

It is not clear how carefully Einstein read the paper that Hilbert sent him or what in it, if anything, affected his thinking as he busily prepared his climactic fourth lecture at the Prussian Academy. Whatever the case, the calculations he had done the week earlier, on Mercury and on light deflection, helped him realize that he could avoid the constraints and coordinate conditions he had been imposing on his gravitational field equations. And thus he produced in time for his final lecture—“The Field Equations of Gravitation,” on November 25, 1915—a set of covariant equations that capped his general theory of relativity.

Einstein was thrilled by his success, but at the same time he was worried that Hilbert, who had presented his own version five days earlier in Göttingen, would be accorded some of the credit for the theory. “Only one colleague has really understood it,” he wrote to his friend Heinrich Zangger, “and he is seeking to nostrify it (Abraham’s expression) in a clever way.” [...] “In my personal experience I have hardly come to know the wretchedness of mankind better.” In a letter to Besso a few days later, he added, “My colleagues are acting hideously in this affair. You will have a good laugh when I tell you about it.”

[...] In the original version, Hilbert’s equations differed in a small but important way from Einstein’s final version of the November 25 lecture. They were not actually generally covariant, and he did not include a step that involved contracting the Ricci tensor and putting the resulting trace term, the Ricci scalar, into the equation. Einstein did this in his November 25 lecture. Apparently, Hilbert made a correction in the revised version of his article to match Einstein’s version. His revisions, quite generously, also added the phrase “first introduced by Einstein” when he referred to the gravitational potentials.

[...] Either way, it was, without question, Einstein’s theory that was being formalized by these equations, one that he had explained to Hilbert during their time together in Göttingen that summer. Even the physicist Kip Thorne, one of those who give Hilbert credit for producing the correct field equations, nonetheless says that Einstein deserves credit for the theory underlying the equations. “Hilbert carried out the last few mathematical steps to its discovery independently and almost simultaneously with Einstein, but Einstein was responsible for essentially everything that preceded these steps,” Thorne notes. “Without Einstein, the general relativistic laws of gravity might not have been discovered until several decades later.”

Hilbert, graciously, felt the same way. As he stated clearly in the final published version of his paper, “The differential equations of gravitation that result are, as it seems to me, in agreement with the magnificent theory of general relativity established by Einstein.” Henceforth he would always acknowledge (thus undermining those who would use him to diminish Einstein) that Einstein was the sole author of the theory of relativity. “Every boy in the streets of Göttingen understands more about four-dimensional geometry than Einstein,” he reportedly said. “Yet, in spite of that, Einstein did the work and not the mathematicians.”

The answer, which he triumphantly announced in the third of his four November lectures, came out right: 43 arc-seconds per century. “This discovery was, I believe, by far the strongest emotional experience in Einstein’s scientific life, perhaps in all his life,” Abraham Pais later said. He was so thrilled he had heart palpitations, as if “something had snapped” inside. “I was beside myself with joyous excitement,” he told Ehrenfest. To another physicist he exulted: “The results of Mercury’s perihelion movement fills me with great satisfaction. How helpful to us is astronomy’s pedantic accuracy, which I used to secretly ridicule!”

Together, this left side of the equation—which is now known as the Einstein tensor and can be written simply as Gmn—compresses together all of the information about how the geometry of spacetime is warped and curved by objects.

The right side describes the movement of matter in the gravitational field. The interplay between the two sides shows how objects curve spacetime and how, in turn, this curvature affects the motion of objects. As the physicist John Wheeler has put it, “Matter tells space-time how to curve, and curved space tells matter how to move.”

Einstein’s pride of authorship was understandable. As soon as he got printed copies of his four lectures, he mailed them out to friends. “Be sure you take a good look at them,” he told one. “They are the most valuable discovery of my life.” To another he noted, “The theory is of incomparable beauty.”

Another of the great giants of twentieth-century physics, Max Born, called it “the greatest feat of human thinking about nature, the most amazing combination of philosophical penetration, physical intuition and mathematical skill.”

The entire process had exhausted Einstein but left him elated. His marriage had collapsed and war was ravaging Europe, but Einstein was as happy as he would ever be. “My boldest dreams have now come true,” he exulted to Besso. “General covariance. Mercury’s perihelion motion wonderfully precise.” He signed himself “contented but kaput.”

Now, with his general version of the theory, this fabric of spacetime became not merely a container for objects and events. Instead, it had its own dynamics that were determined by, and in turn helped to determine, the motion of objects within it—just as the fabric of a trampoline will curve and ripple as a bowling ball and some billiard balls roll across it, and in turn the dynamic curving and rippling of the trampoline fabric will determine the path of the rolling balls and cause the billiard balls to move toward the bowling ball.

Is the trampoline analogy really good, albeit so frequently used? When the trampoline is regarded as a 2D universe, we can't let the earth's gravity be added to this model. But without the earth's gravitational field, would the bowling balls and the billiard balls move in the way through which I try to understand how real 3D objects curve the 4D spacetime, which in turn causes the objects to move in a particular way within it? For example, in "empty space", the balls can sit on the trampoline without distorting the membrane at all. If you slam the bowling ball onto the membrane, causing it to depress, that won't make the billiard balls descend into the depress, instead it will float motionless, until the membrane's elasticity kicks back and pushes the billiard balls in the opposite direction, and then they will be gone. I guess the more accurate analogy should be set in a strictly 2D universe where the balls can never leave the membrane (so they are really just circles with mass, living on the surface). But then, what intuition do we gain from such a world? How does this 2D universe help us understand why the bowling circle is able to attract the billiard circles?

[...] a book for the lay reader, Relativity: The Special and the General Theory, that remains popular to this day. To make sure that the average person would fathom it, he read every page out loud to Elsa’s daughter Margot, pausing frequently to ask whether she indeed got it. “Yes, Albert,” she invariably replied, even though (as she confided to others) she found the whole thing totally baffling.

Naturally she was overjoyed and excited, but Einstein was quite calm. “I knew the theory was correct,” he told her.

But, she asked, what if the experiments had shown his theory to be wrong?He replied, “Then I would have been sorry for the dear Lord; the theory is correct.”

“The intimate union between the beautiful, the true and the real has again been proved.” Einstein replied to Planck with a veneer of humility: “It is a gift from gracious destiny that I have been allowed to experience this.”

Einstein was back in Berlin, so he missed the excitement. He celebrated by buying a new violin. But he understood the historic impact of the announcement that the laws of Sir Isaac Newton no longer fully governed all aspects of the universe. “Newton, forgive me,” Einstein later wrote, noting the moment. “You found the only way which, in your age, was just about possible for a man of highest thought and creative power.”

Ether Reincarnated

Among other things, Mach’s idea that inertia is caused by the presence of all of the distant bodies in the universe implied that these bodies could instantly have an effect on an object, even though they were far apart. Einstein’s theory of relativity did not accept instant actions at a distance. Even gravity did not exert its force instantly, but only through changes in the gravitational field that obeyed the speed limit of light.

“In contradiction to what Mach would have predicted,” Brian Greene writes, “even in an otherwise empty universe, you will feel pressed against the inner wall of the spinning bucket... In general relativity, empty spacetime provides a benchmark for accelerated motion.”

The inertia pushing the water up the wall was caused by its rotation with respect to the metric field, which Einstein now reincarnated as an ether. As a result, he had to face the possibility that general relativity did not necessarily eliminate the concept of absolute motion, at least with respect to the metric of spacetime.

This clearly made Einstein uncomfortable. The best way to eliminate the need for an ether that existed separately from matter, he concluded, would be to find his elusive unified field theory.

Cosmology

In 1939, for example, he produced a paper that provided, he said, “a clear understanding as to why these ‘Schwarzschild singularities’ do not exist in physical reality.” A few months later, however, J. Robert Oppenheimer and his student Hart-land Snyder argued the opposite, predicting that stars could undergo a gravitational collapse.

“Black holes are not rare, and they are not an accidental embellishment of our universe,” says Dyson. “They are the only places in the universe where Einstein’s theory of relativity shows its full power and glory. Here, and nowhere else, space and time lose their individuality and merge together in a sharply curved four-dimensional structure precisely delineated by Einstein’s equations.”

[...] inertia (or centrifugal forces) would not exist for something spinning in a completely empty universe. * Instead, inertia was caused only by rotation relative to all the other objects in the universe. “According to my theory, inertia is simply an interaction between masses, not an effect in which ‘space’ of itself is involved, separate from the observed mass,” Einstein told Schwarzschild.

His new idea was published that month in what became yet another seminal Einstein paper, “Cosmological Considerations in the General Theory of Relativity.” 9 On the surface, it did indeed seem to be based on a crazy notion: space has no borders because gravity bends it back on itself.

To keep the matter in the universe from imploding, Einstein added a “repulsive” force: a little addition to his general relativity equations to counterbalance gravity in the overall scheme.

In his revised equations, this modification was signified by the Greek letter lambda, λ, which he used to multiply his metric tensor gμν in a way that produced a stable, static universe. In his 1917 paper, he was almost apologetic: “We admittedly had to introduce an extension of the field equations that is not justified by our actual knowledge of gravitation.”

Later, when it was discovered that the universe was in fact expanding, Einstein would call it his “biggest blunder.” But even today, in light of evidence that the expansion of the universe is accelerating, it is considered a useful concept, indeed a necessary one after all.

[...] the cosmological constant, which he had reluctantly concocted to account for a static universe, was apparently not necessary, for the universe was in fact expanding. “The situation is truly exciting,” he exulted to Besso.

Of course, it would have been even more exciting if Einstein had trusted his original equations and simply announced that his general theory of relativity predicted that the universe is expanding. If he had done that, then Hubble’s confirmation of the expansion more than a decade later would have had as great an impact as when Eddington confirmed his prediction of how the sun’s gravity would bend rays of light. The Big Bang might have been named the Einstein Bang, and it would have gone down in history, as well as in the popular imagination, as one of the most fascinating theoretical discoveries of modern physics.

“When I was discussing cosmological problems with Einstein,” George Gamow later recalled, “he remarked that the introduction of the cosmological term was the biggest blunder he ever made in his life.”

[...] “Unfortunately,” says Nobel laureate Steven Weinberg, “it was not so easy just to drop the cosmological constant, because anything that contributes to the energy density of the vacuum acts just like a cosmological constant.”

[...] The mysterious dark energy that seems to cause this expansion behaves as if it were a manifestation of Einstein’s constant.

Unified Field Theory

Among those who were dismayed was Wolfgang Pauli. Einstein’s new approaches “betrayed” his general theory of relativity, Pauli sharply told him, and relied on mathematical formalism that had no relation to physical realities. He accused Einstein of “having gone over to the pure mathematicians,” and he predicted that “within a year, if not before, you will have abandoned that whole distant parallelism, just as earlier you gave up the affine theory.”

Pauli was right. Einstein gave up the theory within a year. But he did not give up the quest. Instead, he turned his attention to yet another revised approach that would make more headlines but not more headway in solving the great riddle he had set for himself. “Einstein Completes Unified Field Theory,” the New York Times reported on January 23, 1931, with little intimation that it was neither the first nor would it be the last time there would be such an announcement. And then again, on October 26 of that year: “Einstein Announces a New Field Theory.”

Finally, the following January, he admitted to Pauli, “So you were right after all, you rascal.”

And so it went, for another two decades. None of Einstein’s offerings ever resulted in a successful unified field theory. Indeed, with the discoveries of new particles and forces, physics was becoming less unified. At best, Einstein’s effort was justified by the faint praise from the French mathematician Elie Joseph Cartan in 1931: “Even if his attempt does not succeed, it will have forced us to think about the great questions at the foundation of science.”

“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.”

Careers

University of Berlin

And even though he had been publishing outlines and papers describing his ongoing efforts to generalize relativity, it was unclear whether he would succeed in that quest. “The Germans are gambling on me as they would on a prize-winning hen,” he told a friend as they were leaving a party, “but I don’t know if I can still lay eggs.”

However, to the venerable Hendrik Lorentz in Holland Einstein displayed more gravitas: “I could not resist the temptation to accept a position in which I am relieved of all responsibilities so that I can give myself over completely to rumination.”

There was, of course, another factor that made the new job enticing: the chance to be with his cousin and new love, Elsa. As he would later admit to his friend Zangger, “She was the main reason for my going to Berlin, you know.”

1918

He retained his position in Berlin but agreed to be a guest lecturer in Zurich, making month-long visits there twice a year. That, he thought, could give him the best of both worlds.

In what seemed like an excess of Swiss caution, the Zurich authorities approved the lecture contract, which paid Einstein his expenses but no fee, “by way of experiment.” They were in fact wise; Einstein’s lectures were initially very popular, but eventually attendance dwindled and they would be canceled after two years.

America

When he gave a speech to an international relations group, in which he denounced arms-control compromises and advocated complete disarmament, his audience seemed to treat him as celebrity entertainment.

[...] As a result, he was dismissive when his friend Ehrenfest in Leiden wrote to ask for his help in getting a job in America. “I must tell you honestly that in the long term I would prefer to be in Holland rather than in America,” Einstein replied. “Apart from the handful of really fine scholars, it is a boring and barren society that would soon make you shiver.”

He clearly enjoyed America’s freedom, excitement, and even (yes) the celebrity status it conferred upon him. Like many others, he could be critical of America yet also attracted to it. He could recoil at its occasional displays of crassness and materialism, yet find himself powerfully drawn to the freedoms and unvarnished individuality that were on the flip side of the same coin.

Einstein went to Oxford to give another series of lectures. Once again, he found its refined formality oppressive, especially in contrast to America. [...] He came to realize, once again, that America, for all of its lapses of taste and excesses of enthusiasm, offered freedoms he might never find again in Europe.

The interview dragged on for forty-five minutes, and Einstein became increasingly impatient. When he was asked whether he was a sympathizer of any communist or anarchist parties, Einstein lost his temper. “Your countrymen invited me,” he said. “Yes, begged me. If I am to enter your country as a suspect, I don’t want to go at all. If you don’t want to give me a visa, please say so.”

Then he reached for his coat and hat. “Are you doing this to please yourselves,” he asked, “or are you acting on orders from above?” Without waiting for an answer, he left with Elsa in tow.

As the Times correctly reported, “He is not a Communist and has declined invitations to lecture in Russia because he did not want to give the impression that he was in sympathy with the Moscow regime.” What none of the papers reported, however, was that Einstein did agree to sign a declaration, requested by the consulate, that he was not a member of the Communist Party or any organization intent on overthrowing the U.S. government.

Politics

From his youth as an admirer of Jost Winteler and a friend of Friedrich Adler, Einstein had been attracted to the ideal of socialism as well as that of individual freedom. The revolution in Berlin—led by a collection of socialists, workers’ councils, communists, and others on the left—caused him to confront cases when these two ideals conflicted.

For the rest of his life Einstein would expound a democratic socialism that had a liberal, anti-authoritarian underpinning. He advocated equality, social justice, and the taming of capitalism. He was a fierce defender of the underdog. But to the extent that any revolutionaries edged over toward a Bolshevik desire to impose centralized control, or to the extent that a regime such as Russia’s struck him as authoritarian, Einstein’s instinctive love of individual liberty usually provoked a disdainful reaction.

Some people are innately conditioned to hedge their words, try to please their listeners, and enjoy the comfort that comes from conforming. Not Einstein. Instead, he responded critically. “I have always thought that the German university’s most valuable institution is academic freedom, whereby the lecturers are in no way told what to teach, and the students are able to choose what lectures to attend, without much supervision and control,” he said. “Your new statutes seem to abolish all of this. I would be very sorry if the old freedom were to come to an end.” At that point, Born recalled, “the high and mighty young gentlemen sat in perplexed silence.”

Calling himself “an old-time believer in democracy,” he again made clear that his socialist sentiments did not make him sympathetic to Soviet-style controls. “All true democrats must stand guard lest the old class tyranny of the Right be replaced by a new class tyranny of the Left,” he said.

Some on the left insisted that democracy, or at least multiparty liberal democracy, needed to be put aside until the masses could be educated and a new revolutionary consciousness take hold. Einstein disagreed. “Do not be seduced by feelings that a dictatorship of the proletariat is temporarily needed in order to hammer the concept of freedom into the heads of our fellow countrymen,” he told the rally. Instead, he decried Germany’s new left-wing government as “dictatorial,” and he demanded that it immediately call open elections, “thereby eliminating all fears of a new tyranny as soon as possible.”

As Sigmund Freud pointed out, part of the success of Jewish scientists was their “creative skepticism,” which arose from their essential nature as outsiders.

Then he made a larger point designed to disparage Edison’s view of education. “The value of a college education is not the learning of many facts but the training of the mind to think,” he said.

“In view of the attitude that large numbers of educated Germans have towards Jews, I have always thought that the proper conduct of the Jews in public life should be one of proud reserve.”

To Marie Curie he confided that he would probably quit his positions in Berlin and find someplace else to live. She urged him to stay and fight instead: “I think that your friend Rathenau would have encouraged you to make an effort.”

But Einstein’s deepening love for his Jewish heritage did not instill any new appreciation for the Jewish religion. “Dull-minded tribal companions are praying, faces turned to the wall, rocking their bodies forward and back,” he recorded in his diary. “A pitiful sight of men with a past but without a future.”

There was, however, one question that he tried to answer seriously, and which he alas got wrong. It was about a politician whose party had risen from obscurity three months earlier to win 18 percent of the vote in the German elections. “What do you think of Adolf Hitler?” Einstein replied, “He is living on the empty stomach of Germany. As soon as economic conditions improve, he will no longer be important.”

His sermon, grounded in his humanistic outlook, was on how science had not yet been harnessed to do more good than harm. During war it gave people “the means to poison and mutilate one another,” and in peacetime it “has made our lives hurried and uncertain.” Instead of being a liberating force, “it has enslaved men to machines” by making them work “long wearisome hours mostly without joy in their labor.” Concern for making life better for ordinary humans must be the chief object of science. “Never forget this when you are pondering over your diagrams and equations!”

The economic depression, especially in America, seemed to be caused, he said, mainly by technological advances that “decreased the need for human labor” and thereby caused a decline in consumer purchasing power.

“The only way to be effective is through the revolutionary method of refusing military service,” he declared. “Many who consider themselves good pacifists will not want to participate in such a radical form of pacifism; they will claim that patriotism prevents them from adopting such a policy. But in an emergency, such people cannot be counted on anyhow.”

[...] “If in time of peace members of pacifist organizations are not ready to make sacrifices by opposing authorities at the risk of imprisonment, they will certainly fail in time of war, when only the most steeled and resolute person can be expected to resist.” The crowd erupted in delirium, with overwrought pacifists rushing up to kiss his hand and touch his clothing.

[...] Even as the Nazis began their rise to power, Einstein refused to admit, at least initially, that there might be exceptions to his pacifist postulate. What would he do, a Czech journalist asked, if another European war broke out and one side was clearly the aggressor? “I would unconditionally refuse all war service, direct or indirect, and would seek to persuade my friends to adopt the same position, regardless of how I might feel about the causes of any particular war,” he answered.

[...] Such sentiments were not unusual at the time. The First World War had shocked people by being so astonishingly brutal and apparently unnecessary. Among those who shared Einstein’s pacifism were Upton Sinclair, Sigmund Freud, John Dewey, and H. G. Wells. “We believe that everybody who sincerely wants peace should demand the abolition of military training for youth,” they declared in a 1930 manifesto, which Einstein signed. “Military training is the education of the mind and body in the technique of killing. It thwarts the growth of man’s will for peace.”

[...] “Mere agreements to limit armaments confer no protection,” he said. Instead, there should be an international body empowered to arbitrate disputes and enforce the peace. “Compulsory arbitration must be supported by an executive force.”

“Einstein tended to become impractical once outside the scientific field,” his novelist friend and fellow pacifist Romain Rolland commented. It is true that, given what was about to happen in Germany, disarmament was a chimera, and pacifist hopes were, to use a word sometimes flung at Einstein, naïve. Yet it should be noted that there was some merit to his criticisms. The arms-control acolytes in Geneva were no less naïve. They spent five years in futile, arcane debates as Germany rearmed itself.

This wariness of authority reflected the most fundamental of all of Einstein’s moral principles: Freedom and individualism are necessary for creativity and imagination to flourish. He had demonstrated this as an impertinent young thinker, and he proclaimed the principle clearly in 1931. “I believe that the most important mission of the state is to protect the individual and to make it possible for him to develop into a creative personality,” he said.

He had come to some somber conclusions about Russia, he added. “At the top there appears to be a personal struggle in which the foulest means are used by power-hungry individuals acting from purely selfish motives. At the bottom there seems to be complete suppression of the individual and freedom of speech. One wonders whether life is worth living under such conditions.”

“Violence breeds violence,” he wrote Levine in a letter of praise. “Liberty is the necessary foundation for the development of all true values.”

Millikan thought Einstein naïve in his politics, as did many people. To some extent he was, but it should be remembered that his qualms about the convictions of the Scottsboro Boys and Mooney proved justified, and his advocacy of racial and social justice turned out to be on the right side of history.

Despite his association with the Zionist cause, Einstein’s sympathies extended to the Arabs who were being displaced by the influx of Jews into what would eventually be Israel. His message was a prophetic one. “Should we be unable to find a way to honest cooperation and honest pacts with the Arabs,” he wrote Weizmann in 1929, “then we have learned absolutely nothing during our 2,000 years of suffering.”

[...] “The two great Semitic peoples,” he said, “have a great common future.” If the Jews did not assure that both sides lived in harmony, he warned friends in the Zionist movement, the struggle would haunt them in decades to come. 78 Once again, he was labeled naïve.

Viereck began by asking Einstein whether he considered himself a German or a Jew. “It’s possible to be both,” replied Einstein. “Nationalism is an infantile disease, the measles of mankind.”

A week later, all of these items—German-American friendship, debt payments, war resistance, even Einstein’s pacifism—were dealt a blow that would render them senseless for more than a decade. On January 30, 1933, while Einstein was safely in Pasadena, Adolf Hitler took power as the new chancellor of Germany.

Einstein had begun to mute his pacifist rhetoric. At a birthday luncheon that day in Chicago, he spoke vaguely about the need for international organizations to keep the peace, but he refrained from repeating his calls for war resistance.

Einstein replied by saying how pleased he was that “your former love for the blond beast has cooled off a bit.” The Germans were all a bad breed, Einstein insisted, “except a few fine personalities (Planck 60% noble, and Laue 100%).” Now, in this time of adversity, they could at least take comfort that they were thrown together with their true kinsmen. “For me the most beautiful thing is to be in contact with a few fine Jews—a few millennia of a civilized past do mean something after all.”

“Jewish intellectualism is dead,” propaganda minister Joseph Goebbels, his face fiery, yelled from the podium. “The German soul can again express itself.”

What happened in Germany in 1933 was not just a brutality perpetrated by thuggish leaders and abetted by ignorant mobs. It was also, as Einstein described, “the utter failure of the so-called intellectual aristocracy.” Einstein and other Jews were ousted from what had been among the world’s greatest citadels of open-minded inquiry, and those who remained did little to resist.

The target of his ire was the [Hebrew] university’s president, Judah Magnes, a former rabbi from New York who felt a duty to please his wealthy American backers, including on faculty appointments, even if this meant compromising on scholarly distinction. Einstein wanted the university to operate more in the European tradition, with the academic departments given great power over curriculum and tenured faculty decisions.

Instead of pushing pacifism, he redoubled his commitment to a world federalist organization, like a League of Nations with real teeth, that would have its own professional army to enforce its decisions. “It seems to me that in the present situation we must support a supranational organization of force rather than advocate the abolition of all forces,” he said. “Recent events have taught me a lesson in this respect.”

In the wake of the new threat arising in Germany, his new philosophy, he wrote, was “no disarmament without security.”

“Men who, by their religious and moral convictions, are constrained to refuse military service should not be treated as criminals,” he argued. “They should be offered the alternative of accepting more onerous and hazardous work than military service.” For example, they could be put to work as low-paid conscripts doing “mine labor, stoking furnaces aboard ships, hospital service in infectious disease wards or in certain sections of mental institutions.”

To an American professor: “To prevent the greater evil, it is necessary that the lesser evil—the hated military—be accepted for the time being.”

“I am the same ardent pacifist I was before. But I believe that we can advocate refusing military service only when the military threat from aggressive dictatorships toward democratic countries has ceased to exist.”

“Einstein, a genius in his scientific field, is weak, indecisive and inconsistent outside it,” the dedicated pacifist Romain Rolland wrote in his diary. The charge of inconsistency would have amused Einstein. For a scientist, altering your doctrines when the facts change is not a sign of weakness.

At lunch in the gardens of Churchill’s home, Chartwell, they discussed Germany’s rearmament. “He is an eminently wise man,” Einstein wrote Elsa that day. “It became clear to me that these people have made preparations and are determined to act resolutely and soon.” 70 It sounded like an assessment from someone who had just eaten lunch with Churchill.

“I am a convinced democrat,” he told fellow German refugee Leo Lania for the New York World Telegram. “It is for this reason that I do not go to Russia, although I have received very cordial invitations. My voyage to Moscow would certainly be exploited by the rulers of the Soviets to profit their own political aims. Now I am an adversary of Bolshevism just as much as of fascism. I am against all dictatorships.”

[...] The essence of his political belief was to oppose any power that “enslaves the individual by terror and force, whether it arises under a Fascist or Communist flag.”

“Without such freedom there would have been no Shakespeare, no Goethe, no Newton, no Faraday, no Pasteur, no Lister.” Freedom was a foundation for creativity.

[...] “The monotony of a quiet life stimulates the creative mind,” he said, and he repeated a suggestion he had made when younger that scientists might be employed as lighthouse keepers so they could “devote themselves undisturbed” to thinking. [...] he seemed not to realize that for others it could be far more fruitful when pursued collaboratively. In Copenhagen and elsewhere, the quantum mechanics team had been building on one another’s ideas with a frenzy.

That was especially true in Princeton, which was a conservative town, and at its university, which harbored a surprising number of students who shared the amorphous anti-Semitic attitude found among some in their social class. A survey of incoming freshmen in 1938 produced a result that is now astonishing, and should have been back then as well: Adolf Hitler polled highest as the “greatest living person.” Albert Einstein was second.

when his friend Isaac Don Levine, whose anticommunist writings Einstein had previously endorsed, asked him to sign a petition in 1934 condemning Stalin’s murder of political prisoners, this time Einstein balked. “I, too, regret immensely that the Russian political leaders let themselves be carried away,” Einstein wrote. “In spite of this, I cannot associate myself with your action. It will have no impact in Russia. The Russians have proved that their only aim is really the improvement of the lot of the Russian people.”

It was a gauzy view of the Russians and of Stalin’s murderous regime, one that history would prove wrong. Einstein was so intent on fighting the Nazis, and so annoyed that Levine had shifted so radically from left to right, that he reacted strongly against those who would equate the Russian purges with the Nazi holocaust.

[...] in 1949 he wrote an influential essay for the inaugural issue of the Monthly Review titled “Why Socialism?”

In it he argued that unrestrained capitalism produced great disparities of wealth, cycles of boom and depression, and festering levels of unemployment. The system encouraged selfishness instead of cooperation, and acquiring wealth rather than serving others. People were educated for careers rather than for a love of work and creativity. And political parties became corrupted by political contributions from owners of great capital.

These problems could be avoided, Einstein argued in his article, through a socialist economy, if it guarded against tyranny and centralization of power. “A planned economy, which adjusts production to the needs of the community, would distribute the work to be done among all those able to work and would guarantee a livelihood to every man, woman, and child,” he wrote. “The education of the individual, in addition to promoting his own innate abilities, would attempt to develop in him a sense of responsibility for his fellow-men in place of the glorification of power and success in our present society.”

He added, however, that planned economies faced the danger of becoming oppressive, bureaucratic, and tyrannical, as had happened in communist countries such as Russia. “A planned economy may be accompanied by the complete enslavement of the individual,” he warned. It was therefore important for social democrats who believed in individual liberty to face two critical questions: “How is it possible, in view of the far-reaching centralization of political and economic power, to prevent bureaucracy from becoming all-powerful and overweening? How can the rights of the individual be protected?”

“The Germans, as a whole nation, are responsible for these mass killings and should be punished as a people,” he declared.

[...] “The Germans butchered millions of civilians according to a well-prepared plan,” he wrote. “They would do it again if only they were able to. Not a trace of guilt or remorse is to be found among them.”

After rattling around in the kitchen to make Eban a cup of coffee, Einstein told him that he saw the birth of Israel as one of the few political acts in his lifetime that had a moral quality. But he was concerned that the Jews were having trouble learning to live with the Arabs. “The attitude we adopt toward the Arab minority will provide the real test of our moral standards as a people,” he had told a friend a few weeks earlier.

Nuclear Bomb

Sitting at a bare wooden table on the screen porch of the sparsely furnished cottage, Szilárd explained the process of how an explosive chain reaction could be produced in uranium layered with graphite by the neutrons released from nuclear fission. “I never thought of that!” Einstein interjected. He asked a few questions, went over the process for fifteen minutes, and then quickly grasped the implications. Instead of writing to the queen mother, Einstein suggested, perhaps they should write to a Belgian minister he knew.

Hoover went on to say that Einstein had been involved in the World Antiwar Congress in Amsterdam in 1932, which had some European communists on its committee. This was the conference that Einstein, as noted earlier, had specifically and publicly declined to attend or even support; as he wrote the organizer, “Because of the glorification of Soviet Russia it includes, I cannot bring myself to sign it.” Einstein had gone on in that letter to denounce Russia, where “there seems to be complete suppression of the individual and of freedom of speech.” Nevertheless, Hoover implied that Einstein had supported the conference and was thus pro-Soviet.

World Government

One issue that Einstein could not resolve neatly was what right this world government would have to intervene in the internal affairs of nations. It must be able “to interfere in countries where a minority is oppressing a majority,” he said, citing Spain as an example. Yet that caused him contortions about whether this standard applied to Russia. “One must bear in mind that the people in Russia have not had a long tradition of political education,” he rationalized. “Changes to improve conditions in Russia had to be effected by a minority because there was no majority capable of doing so.”

This is double-standard (Spain vs. Russia), and contradicts himself:

Some on the left insisted that democracy, or at least multiparty liberal democracy, needed to be put aside until the masses could be educated and a new revolutionary consciousness take hold. Einstein disagreed. “Do not be seduced by feelings that a dictatorship of the proletariat is temporarily needed in order to hammer the concept of freedom into the heads of our fellow countrymen,” he told the rally. Instead, he decried Germany’s new left-wing government as “dictatorial,” and he demanded that it immediately call open elections, “thereby eliminating all fears of a new tyranny as soon as possible.”

“If the idea of world government is not realistic,” he said in 1948, “then there is only one realistic view of our future: wholesale destruction of man by man.”

Soviet Russia

He disliked communist authoritarianism, but he did not see it as an imminent danger to American liberty. The greater danger, he felt, was rising hysteria about the supposed Red menace.

As for the repression inside Russia, Einstein tended to offer only mild condemnations diluted by excuses. “It is undeniable that a policy of severe coercion exists in the political sphere,” he said in one talk. “This may, in part, be due to the need to break the power of the former ruling class and to convert a politically inexperienced, culturally backward people into a nation well organized for productive work. I do not presume to pass judgment in these difficult matters.”

An outsider is hardly able to judge the facts and possibilities. In any case it cannot be doubted that the achievements of the Soviet regime are considerable in the fields of education, public health, social welfare, and economics, and that the people as a whole have greatly gained by these achievements.

“We should not make the mistake of blaming capitalism for all existing social and political evils, nor of assuming that the very establishment of socialism would be sufficient to cure the social and political ills of humanity,” he wrote. Such thinking led to the “fanatical intolerance” that infected the Communist Party faithful, and it opened the way to tyranny.

McCarthyism

On the other hand, he stressed in scores of letters and statements that Americans should not let the fear of communism cause them to surrender the civil liberties and freedom of thought that they cherished. There were a lot of domestic communists in England, but the people there did not get themselves whipped into a frenzy by internal security investigations, he pointed out. Americans need not either.

Einstein’s lifelong comfort in resisting prevailing winds made him serenely stubborn during the McCarthy era. At a time when citizens were asked to name names and testify at inquiries into their loyalty and that of their colleagues, he took a simple approach. He told people not to cooperate.

Standing up for the First Amendment was particularly a duty of intellectuals, he said, because they had a special role in society as preservers of free thought. He was still horrified that most intellectuals in Germany had not risen in resistance when the Nazis came to power.

Senator McCarthy also issued a denunciation, though it seemed slightly muted due to Einstein’s stature. “Anyone who advises Americans to keep secret information which they have about spies and saboteurs is himself an enemy of America,” he said, not quite aiming directly at Einstein or what he had written.

Among the more amusing ripostes came from his friend Bertrand Russell. “You seem to think that one should always obey the law, however bad,” the philosopher wrote to the New York Times. “I am compelled to suppose that you condemn George Washington and hold that your country ought to return to allegiance to Her Gracious Majesty, Queen Elisabeth II. As a loyal Briton, I of course applaud this view; but I fear it may not win much support in your country.” Einstein wrote Russell a thank-you letter, lamenting, “All the intellectuals in this country, down to the youngest student, have become completely intimidated.”

Indeed, he took a boyish American glee at his freedom to say whatever he felt. “I have become a kind of enfant terrible in my new homeland due to my inability to keep silent and to swallow everything that happens,” he wrote Queen Mother Elisabeth. “Besides, I believe that older people who have scarcely anything to lose ought to be willing to speak out in behalf of those who are young and are subject to much greater restraint.”

“If I were a young man again and had to decide how to make a living, I would not try to become a scientist or scholar or teacher,” he intoned to Theodore White of the Reporter magazine. “I would rather choose to be a plumber or a peddler, in the hope of finding that modest degree of independence still available.”

Einstein and some other refugees tended, understandably, to view McCarthyism as a descent into the black hole of fascism, rather than as one of those ebbs and flows of excess that happen in a democracy. As it turned out, American democracy righted itself, as it always has.

Einstein was not used to self-righting political systems. Nor did he fully appreciate how resilient America’s democracy and its nurturing of individual liberty could be. So for a while his disdain deepened. But he was saved from serious despair by his wry detachment and his sense of humor. He was not destined to die a bitter man.

McCarthyism had died down, and Eisenhower had proved a calming influence. “God’s own country becomes stranger and stranger,” Einstein wrote Hans Albert that Christmas, “but somehow they manage to return to normality. Everything—even lunacy—is mass produced here. But everything goes out of fashion very quickly.”

Fame

This was, in fact, as the newspaper would say, “a pile of soft rubbish.” Einstein had done his thought experiment while working in the Bern patent office in 1907, not in Berlin, and it had not involved a person actually falling. “The newspaper drivel about me is pathetic,” he wrote Zangger when the article came out. But he understood, and accepted, how journalism worked. “This kind of exaggeration meets a certain need among the public.”

Einstein’s aversion to publicity, however, existed a bit more in theory than in reality. It would have been possible, indeed easy, for him to have shunned all interviews, pronouncements, pictures, and public appearances. Those who truly dislike the public spotlight do not turn up, as the Einsteins eventually would, with Charlie Chaplin on a red carpet at one of his movie premieres.

One reason that Einstein—unlike Planck or Lorentz or Bohr—became such an icon was because he looked the part and because he could, and would, play the role. “Scientists who become icons must not only be geniuses but also performers, playing to the crowd and enjoying public acclaim,” the physicist Freeman Dyson (no relation to the Astronomer Royal) has noted. Einstein performed. He gave interviews readily, peppered them with delightful aphorisms, and knew exactly what made for a good story.

Einstein’s detachment allowed him to affect an air of amusement rather than anxiety. “The whole affair is a matter of indifference to me, as is all the commotion, and the opinion of each and every human being,” he said. “I will live through all that is in store for me like an unconcerned spectator.”

[...] In retrospect, the controversy over publicity seems quaint and the book harmless fluff. “I have browsed through it a little, and find it not quite as bad as I had expected,” Born later admitted. “It contains many rather amusing stories and anecdotes which are characteristic of Einstein.”

“With fame I become more and more stupid, which of course is a very common phenomenon,” Einstein told Zangger.

"The cult of individual personalities is always, in my view, unjustified... It strikes me as unfair, and even in bad taste, to select a few for boundless admiration, attributing superhuman powers of mind and character to them. This has been my fate, and the contrast between the popular estimate of my achievements and the reality is simply grotesque. This extraordinary state of affairs would be unbearable but for one great consoling thought: it is a welcome symptom in an age, which is commonly denounced as materialistic, that it makes heroes of men whose ambitions lie wholly in the intellectual and moral sphere."

The next morning, before he could depart, a young man tracked him down at Frank’s office and insisted on showing him a manuscript. On the basis of his E=mc2 equation, the man insisted, it would be possible “to use the energy contained within the atom for the production of frightening explosives.” Einstein brushed away the discussion, calling the concept foolish.

Einstein would have been, and later was, appalled at the conflation of relativity with relativism. As noted, he had considered calling his theory “invariance,” because the physical laws of combined spacetime, according to his theory, were indeed invariant rather than relative.

What ramifications, His Grace inquired, did the theory of relativity have for religion?

The answer probably disappointed both the archbishop and their host. “None,” Einstein said. “Relativity is a purely scientific matter and has nothing to do with religion.”

The Japanese people struck him as gentle and unpretentious, with a deep appreciation for beauty and ideas. “Of all the people I have met, I like the Japanese most, as they are modest, intelligent, considerate, and have a feel for art,” he wrote his two sons.

But he knew, as he confided to one of his hosts, that if he came back [to Jerusalem] he would be “an ornament” with no chance of peace or privacy. As he noted in his diary, “My heart says yes, but my reason says no.”

Nobel Prize

The Swedish committee was mindful of the charge in Alfred Nobel’s will that the prize should go to “the most important discovery or invention,” and it felt that relativity theory was not exactly either of those.

Three out of the committee’s five members throughout the period from 1910 to 1922 were experimentalists from Sweden’s Uppsala University, known for its fervent devotion to perfecting experimental and measuring techniques.

As Lorentz’s letter declared, Einstein “has placed himself in the first rank of physicists of all time.” Bohr’s letter was equally clear: “One faces here an advance of decisive significance.”

To his critics, the fact that he had suddenly achieved superstar status as the most internationally celebrated scientist since the lightning-tamer Benjamin Franklin was paraded through the streets of Paris was evidence of his self-promotion rather than his worthiness of a Nobel.

“Einstein stands above his contemporaries even as Newton did,” wrote Eddington, offering the highest praise a member of the Royal Society could muster.

Einstein gave his official acceptance speech the following July at a Swedish science conference with King Gustav Adolf V in attendance. He spoke not about the photoelectric effect, but about relativity, and he concluded by emphasizing the importance of his new passion, finding a unified field theory that would reconcile general relativity with electromagnetic theory and, if possible, with quantum mechanics.

Hans Albert complained that the trust arrangement, which had previously been agreed to, made only the interest on the money accessible to the family. Once again, Zangger intervened and calmed the dispute. Einstein jokingly wrote to his sons, “You all will be so rich that some fine day I may ask you for a loan.” The money was eventually used by Mari to buy three homes with rental apartments in Zurich.

Peers

Max Planck

It was unclear, even to Einstein, whether Planck was persuaded of the reality of quanta. “I largely succeeded in convincing Planck that my conception is correct, after he has struggled against it for so many years,” Einstein wrote his friend Heinrich Zangger. But a week later, Einstein gave Zangger another report: “Planck stuck stubbornly to some undoubtedly wrong preconceptions.”

Hendrik Lorentz

As for Lorentz, Einstein remained as admiring as ever: “A living work of art! He was in my opinion the most intelligent of the theoreticians present.”

Henri Poincaré

He dismissed Poincaré, who paid little attention to him, with a brusque stroke: “Poincaré was simply negative in general, and, all his acumen notwithstanding, he showed little grasp of the situation.”

Adding to the irony was that his other main letter of recommendation came from Henri Poincaré, the man who had almost come up with the special theory of relativity but still had not embraced it. Einstein was “one of the most original minds I have ever come across,” he said. Particularly poignant was his description of Einstein’s willingness, which Poincaré himself lacked, to make radical conceptual leaps: “What I admire in him in particular is the facility with which he adapts himself to new concepts. He does not remain attached to classical principles, and, when presented with a problem in physics, is prompt to envision all the possibilities.” Poincaré, however, could not resist asserting, perhaps with relativity in mind, that Einstein might not be right in all his theories: “Since he seeks in all directions one must expect the majority of the paths on which he embarks to be blind alleys.”

Marie Curie

She was bereft, and so was her late husband’s protégé, Langevin, who taught physics at the Sorbonne with the Curies. Langevin was trapped in a marriage with a wife who physically abused him, and soon he and Marie Curie were having an affair in a Paris apartment. His wife had someone break into it and steal their love letters.

Just as the Solvay Conference was getting under way, with both Curie and Langevin in attendance, the purloined letters began appearing in a Paris tabloid as a prelude to a sensational divorce case. In addition, at that very moment, it was announced that Curie had won the Nobel Prize in chemistry, for discovering radium and polonium. A member of the Swedish Academy wrote her to suggest that she not appear to receive it, given the furor raised by her relationship with Langevin, but she coolly responded, “I believe there is no connection between my scientific work and the facts of private life.” She headed to Stockholm and accepted the prize.

David Hilbert

After expressing his thanks, Einstein added, “I feel compelled to say something else to you.” He explained:

There has been a certain ill-feeling between us, the cause of which I do not want to analyze. I have struggled against the feeling of bitterness attached to it, with complete success. I think of you again with unmixed geniality and ask you to try to do the same with me. It is a shame when two real fellows who have extricated themselves somewhat from this shabby world do not afford each other mutual pleasure.

Lovers

Mileva Marić

As Einstein wandered around Europe giving speeches and basking in his rising renown, his wife stayed behind in Prague, a city she hated, and brooded about not being part of the scientific circles that she once struggled to join. “I would like to have been there and listened a little, and seen all these fine people,” she wrote him after one of his talks in October 1911. “It is so long since we saw each other that I wonder if you will recognize me.” She signed herself, “Deine alte D,” your old D, as if she were still his Dollie, albeit a bit older.

Despite being back with such friends and diversions, Marić’s depression continued to deepen, and her health to decline. She developed rheumatism, which made it hard for her to go out, especially when the streets became icy in winter. She attended the Hurwitz recitals less frequently, and when she did show up her gloom was increasingly evident. In February 1913, to entice her out, the Hurwitz family planned an all-Schumann recital. She came, but seemed paralyzed by pain, both mental and physical.

Personal relationships involve nature’s most mysterious forces. Outside judgments are easy to make and hard to verify. Einstein repeatedly and plaintively stressed to all of their mutual friends—especially the Bessos, Habers, and Zanggers—that they should try to see the breakup of his marriage from his perspective, despite his own apparent culpability.It is probably true that he was not solely to blame. The decline of the marriage was a downward spiral. He had become emotionally withdrawn, Marić had become more depressed and dark, and each action reinforced the other. Einstein tended to avoid painful personal emotions by immersing himself in his work. Marić, for her part, was bitter about the collapse of her own dreams and increasingly resentful of her husband’s success.

Marić and the two boys left Berlin, accompanied by Michele Besso, aboard the morning train to Zurich on Wednesday, July 29, 1914. Haber went to the station with Einstein, who “bawled like a little boy” all afternoon and evening. It was the most wrenching personal moment for a man who took perverse pride in avoiding personal moments. For all of his reputation of being inured to deep human attachments, he had been madly in love with Mileva Marić and bonded to his children. For one of the few times in his adult life, he found himself crying.

Einstein backed down from his charge that Mari was faking illness, but railed that her emotional distress was unwarranted. “She leads a worry-free life, has her two precious boys with her, lives in a fabulous neighborhood, does what she likes with her time, and innocently stands by as the guiltless party,” he wrote Besso.

“Why do you torment me so endlessly? I really don’t deserve this from you.”

But within a few days, she began to assess the situation more clinically. Her life had reached a low point. She suffered pains, anxieties, and depression. Her younger son was in a sanatorium. The sister who had come to help her succumbed to depression and had been committed to an asylum. And her brother, who was serving as a medic in the Austrian army, had been captured by the Russians. Perhaps an end to the battles with her husband and the chance of financial security might, in fact, be best for her.

A few days later she decided to take the deal. “Have your lawyer write Dr. Zürcher about how he envisions it, how the contract should be,” she replied. “I must leave upsetting things to objective persons. I do not want to stand in the way of your happiness, if you are so resolved.”

“I am curious what will last longer, the world war or our divorce proceedings,” he complained lightly at one point. But as things were progressing the way he wanted, he merrily added, “In comparison, this little matter of ours is still much the more pleasant. Amiable greetings to you and kisses to the boys.”

“I plan on coming to Zurich soon, and we should put all the bad things behind us. You should enjoy what life has given you—like the wonderful children, the house, and that you are not married to me anymore.”

One cold day later that winter, she slipped on the ice on the way to see Eduard and ended up lying unconscious until strangers found her. She knew she was going to die soon, and she had recurring nightmares about struggling through the snow, unable to reach Eduard. She was panicked about what would happen to him, and wrote heart-wrenching letters to Hans Albert.

Einstein succeeded in selling her house by early 1948, but with her power of attorney she blocked the proceeds from being sent to him. He wrote to Hans Albert, giving him all the details and promising him that, whatever happened, he would take care of Eduard “even if it costs me all my savings.” 27 That May, Mari had a stroke and lapsed into a trance in which she repeatedly muttered only “No, no!” until she died three months later. The money from the sale of her apartment, 85,000 Swiss francs, was found under her mattress.

Elsa Einstein

The contrast with Einstein’s wife was stark. Mileva Marić was exotic, intellectual, and complex. Elsa wasn’t. Instead, she was conventionally handsome and domestically nurturing. She loved heavy German comfort foods and chocolate, which tended to give her a rather ample, matronly look. Her face was similar to her cousin’s, and it would become strikingly more so as they aged.

Einstein was looking for new companionship, and he first flirted with Elsa’s sister. But by the end of his Easter visit, he had settled on Elsa as offering the comfort and nurturing that he now craved. The love he was seeking, it seems, was not wild romance but uncomplicated support and affection.

A decade earlier, when he was writing his love letters to Marić that celebrated their own rarefied and bohemian approach to life, Einstein would likely have lumped relatives such as Elsa into the category of “bourgeois philistines.” But now, in letters that were almost as effusive as the ones he had written to Marić, he professed his new passion for Elsa. “I have to have someone to love, otherwise life is miserable,” he wrote. “And this someone is you.”

Elsa’s home cooking, a hearty pleasure she lavished on him like a mother, became a theme in their letters. Their correspondence, like their relationship, was a stark contrast to that between Einstein and Mari a dozen years earlier. He and Elsa tended to write to each other about domestic comforts—food, tranquillity, hygiene, fondness—rather than about romantic bliss and planted kisses, or intimacies of the soul and insights of the intellect.

But after returning to Prague from Berlin, Einstein seemed to develop qualms about his affair with his cousin. He tried, in two letters, to put an end to it. “There would only be confusion and misfortune if we were to give into our mutual attraction,” he wrote Elsa.

Later that month, he tried to be even more definitive. “It will not be good for the two of us, as well as for the others, if we form a closer attachment. So, I am writing to you today for the last time and am submitting again to the inevitable, and you must do the same. You know that it is not hardness of heart or lack of feeling that makes me talk like this, because you know that, like you, I bear my cross without hope.”

He made clear, however, that she should not expect him to abandon his wife: “You and I can very well be happy with each other without her having to be hurt.”

In return, he wanted the right to have his sons visit him in Berlin. They would not come into contact with Elsa, he pledged. He even added a somewhat surprising promise: he would not be living with Elsa even if they got married. Instead, he would keep his own apartment. “For I shall never give up the state of living alone, which has manifested itself as an indescribable blessing.”

Just after the war ended, so did Einstein’s divorce proceedings. As part of the process, he had to give a deposition admitting adultery. On December 23, 1918, he appeared before a court in Berlin, stood before a magistrate, and declared,“I have been living together with my cousin, the widow Elsa Einstein, divorced Löwenthal, for about 4½ years and have been continuing these intimate relations since then.”

As was customary, the decree included the order that “the Defendant [Einstein] is restrained from entering into a new marriage for the period of two years.” Einstein had no intention of obeying that provision. He had decided that he would marry Elsa, and he would end up doing so within four months.

The letter is so striking and curious it bears being quoted at length:

You are the only person to whom I can entrust the following and the only one who can give me advice ... You remember that we recently spoke about Albert’s and Mama’s marriage and you told me that you thought a marriage between Albert and me would be more proper. I never thought seriously about it until yesterday. Yesterday, the question was suddenly raised about whether Albert wished to marry Mama or me. This question, initially posed half in jest, became within a few minutes a serious matter which must now be considered and discussed fully and completely. Albert himself is refusing to take any decision, he is prepared to marry either me or Mama. I know that Albert loves me very much, perhaps more than any other man ever will. He told me so himself yesterday. On the one hand, he might even prefer me as his wife, since I am young and he could have children with me, which naturally does not apply at all in Mama’s case; but he is far too decent and loves Mama too much ever to mention it. You know how I stand with Albert. I love him very much; I have the greatest respect for him as a person. If ever there was true friendship and camaraderie between two beings of different types, those are quite certainly my feelings for Albert. I have never wished nor felt the least desire to be close to him physically. This is otherwise in his case—recently at least. He admitted to me once how difficult it is for him to keep himself in check. But now I do believe that my feelings for him are not sufficient for conjugal life . . . The third person still to be mentioned in this odd and certainly also highly comical affair would be Mother. For the present—because she does not yet firmly believe that I am really serious. She has allowed me to choose completely freely. If she saw that I could really be happy only with Albert, she would surely step aside out of love for me. But it would certainly be bitterly hard for her. And then I do not know whether it really would be fair if—after all her years of struggle—I were to compete with her over the place she had won for herself, now that she is finally at the goal. Philistines like the grandparents are naturally appalled about these new plans. Mother would supposedly be disgraced and other such unpleasant things . . . Albert also thought that if I did not wish to have a child of his it would be nicer for me not to be married to him. And I truly do not have this wish. It will seem peculiar to you that I, a silly little thing of a 20-year-old, should have to decide on such a serious matter; I can hardly believe it myself and feel very unhappy doing so as well. Help me! Yours, Ilse.

She wrote a big note on top of the first page: “Please destroy this letter immediately after reading it!” Nicolai didn’t.

Was it true? Was it half-true? Was the truth relative to the observer? The only evidence we have of Einstein’s mother-daughter dithering is this one letter. No one else, then or in recollections, ever mentioned the issue. The letter was written by an intense and love-struck young woman to a dashing philanderer whose attentions she craved. Perhaps it was merely her fantasy, or her ploy to provoke Nicolai’s jealousy. As with much of nature, especially human nature, the underlying reality, if there is such a thing, may not be knowable.

As it turned out, Einstein married Elsa in June 1919, and Ilse ended up remaining close to both of them.

Einstein’s new marriage was different from his first. It was not romantic or passionate. From the start, he and Elsa had separate bedrooms at opposite ends of their rambling Berlin apartment. Nor was it intellectual. Understanding relativity, she later said, “is not necessary for my happiness.”

The marriage was, in fact, a solid symbiosis, and it served adequately, for the most part, the needs and desires of both partners. Elsa was an efficient and lively woman, who was eager to serve and protect him. She liked his fame, and (unlike him) did not try to hide that fact. She also appreciated the social standing it gave them, even if it meant she had to merrily shoo away reporters and other invaders of her husband’s privacy.

“The Lord has put into him so much that’s beautiful, and I find him wonderful, even though life at his side is enervating and difficult,” she once said.

Yet beneath the surface of many romances that evolve into partnerships, there is a depth not visible to outside observers. Elsa and Albert Einstein liked each other, understood each other, and perhaps most important (for she, too, was actually quite clever in her own way) were amused by each other. So even if it was not the stuff of poetry, the bond between them was a solid one. It was forged by satisfying each other’s desires and needs, it was genuine, and it worked in both directions.

Misc

In 1923, after marrying Elsa, he had fallen in love with his secretary, Betty Neumann. Their romance was serious and passionate, according to newly revealed letters. That fall, while on a visit to Leiden, he wrote to suggest that he might take a job in New York, and she could come as his secretary. She would live there with him and Elsa, he fantasized. “I will convince my wife to allow this,” he said. “We could live together forever. We could get a large house outside New York.”

She replied by ridiculing both him and the idea, which prompted him to concede how much of a “crazy ass” he had been. “You have more respect for the difficulties of triangular geometry than I, old mathematicus, have.”

He finally terminated their romance with the lament that he “must seek in the stars” the true love that was denied to him on earth. “Dear Betty, laugh at me, the old donkey, and find somebody who is ten years younger than me and loves you just as much as I do.”

But the relationship lingered. The following summer, Einstein went to see his sons in southern Germany, and from there he wrote to his wife that he could not visit her and her daughters, who were at a resort nearby, because that would be “too much of a good thing.” At the same time, he was writing Betty Neumann saying that he was going secretly to Berlin, but she should not tell anyone because if Elsa found out she “will fly back.”

After he built the house in Caputh, a succession of women friends visited him there, with Elsa’s grudging acquiescence. Toni Mendel, a wealthy widow with an estate on the Wannsee, sometimes came sailing with him in Caputh, or he would pilot his boat up to her villa and stay late into the night playing the piano. They even went to the theater together in Berlin occasionally. Once when she picked Einstein up in her chauffeured limousine, Elsa got into a furious fight with him and would not give him any pocket money.

When Elsa found out that Michanowski had visited Einstein in Oxford, she was furious, particularly at Michanowski for misleading her about where she was going. Einstein wrote from Oxford to tell Elsa to calm down. “Your dismay toward Frau M is totally groundless because she behaved completely according to the best Jewish-Christian morality,” he said. “Here is the proof: 1) What one enjoys and doesn’t harm others, one should do. 2) What one doesn’t enjoy and only aggravates others, one should not do. Because of #1, she came with me, and because of #2 she didn’t tell you anything about it. Isn’t that impeccable behavior?” But in a letter to Elsa’s daughter Margot, Einstein claimed that Michanowski’s pursuit was unwanted. “Her chasing me is getting out of control,” he wrote Margot, who was Michanowski’s friend. “I don’t care what people are saying about me, but for mother [Elsa] and for Frau M, it is better that not every Tom, Dick and Harry gossip about it.”

On one visit, Lebach left a piece of clothing in Einstein’s sailboat, which caused a family row and prompted Elsa’s daughter to urge her to force Einstein to end the relationship. But Elsa was afraid that her husband would refuse. He had let it be known that he believed that men and women were not naturally monogamous. In the end, she decided that she was better off preserving what she could of their marriage. In other respects, it suited her aspirations.

She realized that she must accept him with all of his complexities, especially since her life as Mrs. Einstein included much that made her happy. “Such a genius should be irreproachable in every respect,” she told the artist and etcher Hermann Struck, who did Einstein’s portrait around the time of his fiftieth birthday (as he had done a decade earlier). “But nature does not behave this way. Where she gives extravagantly, she takes away extravagantly.” The good and the bad had to be accepted as a whole. “You have to see him all of one piece,” she explained. “God has given him so much nobility, and I find him wonderful, although life with him is exhausting and complicated, and not only in one way but in others.”

Friends

Paul Ehrenfest

Ehrenfest was a mousy and insecure man, but his eagerness for friendship and his love of physics made it easy for him to forge a bond with Einstein. 23 They both seemed to crave arguing about science, and Einstein later said that “within a few hours we were friends as if Nature created us for each other.” [...]

Matters eventually came to a happy resolution when Ehrenfest accepted an offer, which Einstein had earlier received but declined, to replace the revered Lorentz, who was cutting back from full-time teaching at the University of Leiden. Einstein was thrilled, for it meant he would now have two friends there to visit regularly. It became, for Einstein, almost a second academic home and a way to escape the oppressive atmosphere he later found in Berlin. Almost every year for the next two decades, until 1933 when Ehrenfest committed suicide and Einstein moved to America, Einstein would make regular pilgrimages to see him and Lorentz in Leiden or at the seaside resorts nearby.

Parents

Hermann Einstein was not destined to see his son become anything more successful than a third-class patent examiner. In October 1902, when Hermann’s health began to decline, Einstein traveled to Milan to be with him at the end. Their relationship had long been a mix of alienation and affection, and it concluded on that note as well. “When the end came,” Einstein’s assistant Helen Dukas later said, “Hermann asked all of them to leave the room, so he could die on his own.”

Einstein felt, for the rest of his life, a sense of guilt about that moment, which encapsulated his inability to forge a true bond with his father. For the first time, he was thrown into a daze, “overwhelmed by a feeling of desolation.” He later called his father’s death the deepest shock he had ever experienced. The event did, however, solve one important issue. On his deathbed, Hermann Einstein gave his permission, finally, for his son to marry Mileva Marić.

Dying from stomach cancer, she had moved in with him and Elsa at the end of 1919, and watching her suffer overwhelmed whatever human detachment he usually felt or feigned. When she died in February 1920, Einstein was exhausted by the emotions. “One feels right into one’s bones what ties of blood mean,” he wrote Zangger. Käthe Freundlich had heard him boast to her husband, the astronomer, that no death would affect him, and she was relieved that his mother’s death proved that untrue. “Einstein wept like other men,” she said, “and I knew that he could really care for someone.”

Children

I would raise the two boys myself,” he said. “They would be taught at home, as far as possible by me personally.” In various letters over the next few months, Einstein described his different ideas and fantasies for home-schooling his sons, what he would teach, and even the type of walks they would take.

“I believe that his attitude toward me has fallen below the freezing point,” Einstein lamented to Besso. “Under the given circumstances, I would have reacted in the same way.” After three letters to his son went unanswered in three months, Einstein plaintively wrote him: “Don’t you remember your father anymore? Are we never going to see each other again?”

Finally, the boy replied by sending a picture of a boat he was constructing out of wood carvings. He also described his mother’s return from the sanatorium. “When Mama came home, we had a celebration. I had practiced a sonata by Mozart, and Tete had learned a song.”

After receiving a pessimistic medical prognosis, Einstein lamented to Besso, “My little boy’s condition depresses me greatly. It is impossible that he will become a fully developed person. Who knows if it wouldn’t be better for him if he could depart before coming to know life properly.”

To Zangger, he ruminated about the “Spartan’s method”—leaving sickly children out on a mountain to die—but then said he could not accept that approach. Instead, he promised to pay whatever it took to get Eduard care, and he told Zangger to send him to whatever treatment facility he thought best. “Even if you silently say to yourself that every effort is futile, send him anyway, so that my wife and my Albert think that something is being done.”

Shortly after his remarriage, Einstein visited Zurich to see his sons. Hans Albert, then 15, announced that he had decided to become an engineer.

“I think it’s a disgusting idea,” said Einstein, whose father and uncle had been engineers.

“I’m still going to become an engineer,” replied the boy.Einstein stormed away angry, and once again their relationship deteriorated, especially after he received a nasty letter from Hans Albert. “He wrote me as no decent person has ever written their father,” he explained in a pained letter to his other son, Eduard. “It’s doubtful I’ll ever be able to take up a relationship with him again.”

But Mari by then was intent on improving rather than undermining his relationship with his sons. So she emphasized to the boys that Einstein was “a strange man in many ways,” but he was still their father and wanted their love. He could be cold, she said, but also “good and kind.” According to an account provided by Hans Albert, “Mileva knew that for all his bluff, Albert could be hurt in personal matters—and hurt deeply.”

Especially after he scored first in his exams, his father not only became reconciled, but proud. “My Albert has become a sound, strong chap,” Einstein wrote Besso in 1924. “He is a total picture of a man, a first-rate sailor, unpretentious and dependable.”

Einstein eventually said the same to Hans Albert, adding that he may have been right to become an engineer. “Science is a difficult profession,” he wrote.“Sometimes I am glad that you have chosen a practical field, where one does not have to look for a four-leaf clover.”

Einstein conceded that he couldn’t stop him, but he urged his son to promise not to have children. “And should you ever feel like you have to leave her, you should not be too proud to come talk to me,” Einstein wrote. “After all, that day will come.”

Hans Albert and Frieda married in 1927, had children, and remained married until her death thirty-one years later. As Evelyn Einstein, their adopted daughter, recalled years later, “Albert had such a hell of a time with his parents over his own marriage that you would think he would have had the sense not to interfere with his son’s. But no. When my father went to marry my mother, there was explosion after explosion.”

[...] But within two years, Einstein had begun to accept Frieda. The couple came to visit him in the summer of 1929, and he reported back to Eduard that he had made his peace. “She made a better impression than I had feared,” he wrote. “He is really sweet with her. God bless those rose-colored spectacles.”

“It’s at times difficult to have such an important father, because one feels so unimportant,” he [Eduard] wrote at one point. A few months later, he poured out more insecurities: “People who fill their time with intellectual work bring into the world sickly, nervous at times even completely idiotic children (for example, you me).”

Margot was so painfully shy that she often hid from strangers, but Marianoff’s wiles soon brought her out of her shell. Their wedding occurred a few days after Eduard had tried to commit suicide, and a distraught Mari made an unannounced visit to Berlin to ask her former husband for help. Marianoff later described the scene at the end of his wedding ceremony: “As we came down the steps I noticed a woman standing near the portico. I would not have noticed her, except that she looked at us with such an intensely burning gaze that it impressed me. Margot said under her breath, ‘It’s Mileva.’ ”

Einstein was shaken deeply by his son’s illness. “This sorrow is eating up Albert,” Elsa wrote. “He finds it difficult to cope with.”

There was, however, not much he could do. The morning after the wedding, he and Elsa left by train to Antwerp, from which they would sail for their second voyage to the United States.

Einstein replied that he hoped to take Eduard with him to visit Princeton. “Unfortunately, everything indicates that strong heredity manifests itself very definitely,” he lamented. “I have seen that coming slowly but inexorably since Tete’s youth. Outside influences play only a small part in such cases, compared to internal secretions, about which nobody can do anything.”

Seelig hoped to get him to make contact with his son, but he never did. “There is something blocking me that I am unable to analyze fully,” Einstein told Seelig. “I believe I would be arousing painful feelings of various kinds in him if I made an appearance in whatever form.”

Einstein, thanks to a reminder from his son’s wife, wrote him [Hans] a letter that was slightly formal, as if created for a special occasion. But it contained a nice tribute both to his son and to the value of a life in science: “It is a joy for me to have a son who has inherited the main traits of my personality: the ability to rise above mere existence by sacrificing one’s self through the years for an impersonal goal.”