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“There came into the room a slight-looking boy,” Ernest Rutherford’s McGill colleague and biographer A. S. Eve recalls of Manchester days, “whom Rutherford at once took into his study.190, 191 Mrs. Rutherford explained to me that the visitor was a young Dane, and that her husband thought very highly indeed of his work. No wonder, it was Niels Bohr!” The memory is odd. Bohr was an exceptional athlete. The Danes cheered his university soccer exploits. He skied, bicycled and sailed; he chopped wood; he was unbeatable at Ping-Pong; he routinely took stairs two at a time. He was also physically imposing: tall for his generation, with “an enormous domed head,” says C. P. Snow, a long, heavy jaw and big hands.192 He was thinner as a young man than later and his shock of unruly, combed-back hair might have seemed boyish to a man of Eve’s age, twelve years older than Rutherford. But Niels Bohr was hardly “slight-looking.”
Something other than Bohr’s physical appearance triggered Eve’s dissonant memory: probably his presence, which could be hesitant. He was “much more muscular and athletic than his cautious manner suggested,” Snow confirms. “It didn’t help that he spoke with a soft voice, not much above a whisper.” All his life Bohr talked so quietly—and yet indefatigably—that people strained to hear him. Snow knew him as “a talker as hard to get to the point as Henry James in his later years,” but his speech differed dramatically between public and private and between initial exploration of a subject and eventual mastery.193 Publicly, according to Oskar Klein, a student of Bohr’s and then a colleague, “he took the greatest care to get the most accurately shaded formulation of the matter.” Albert Einstein admired Bohr for “uttering his opinions like one perpetually groping and never like one who [believed himself to be] in the possession of definite truth.”194 If Bohr groped through the exploratory phases of his deliberations, with mastery “his assurance grew and his speech became vigorous and full of vivid images,” Lise Meitner’s physicist nephew Otto Frisch noted.195, 196 And privately, among close friends, says Klein, “he would express himself with drastic imagery and strong expressions of admiration as well as criticism.”197
Bohr’s manner was as binary as his speech. Einstein first met Bohr in Berlin in the spring of 1920. “Not often in life,” he wrote to Bohr afterward, “has a human being caused me such joy by his mere presence as you did,” and he reported to their mutual friend Paul Ehrenfest, an Austrian physicist at Leiden, “I am as much in love with him as you are.”198 Despite his enthusiasm Einstein did not fail to observe closely his new Danish friend; his verdict in Bohr’s thirty-fifth year is similar to Eve’s in his twenty-eighth: “He is like an extremely sensitive child who moves around the world in a sort of trance.” At first meeting—until Bohr began to speak—the theoretician Abraham Pais thought the long, heavy face “gloomy” in the extreme and puzzled at that momentary impression when everyone knew “its intense animation and its warm and sunny smile.”199
Bohr’s contributions to twentieth-century physics would rank second only to Einstein’s. He would become a scientist-statesman of unmatched foresight. To a greater extent than is usually the case with scientists, his sense of personal identity—his hard-won selfhood and the emotional values he grounded there—was crucial to his work. For a time, when he was a young man, that identity was painfully divided.
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Bohr’s father, Christian Bohr, was professor of physiology at the University of Copenhagen. In Christian Bohr’s case the Bohr jaw extended below a thick mustache and the face was rounded, the forehead not so high. He may have been athletic; he was certainly a sports enthusiast, who encouraged and helped finance the Akademisk Boldklub for which his sons would one day play champion soccer (Niels’ younger brother Harald at the 1908 Olympics). He was progressive in politics; he worked for the emancipation of women; he was skeptical of religion but nominally conforming, a solid bourgeois intellectual.
Christian Bohr published his first scientific paper at twenty-two, took a medical degree and then a Ph.D. in physiology, studied under the distinguished physiologist Carl Ludwig at Leipzig. Respiration was his special subject and he brought to that research the practice, still novel in the early 1880s, of careful physical and chemical experiment. Outside the laboratory, a friend of his explains, he was a “keen worshipper” of Goethe; larger issues of philosophy intrigued him.200
One of the great arguments of the day was vitalism versus mechanism, a disguised form of the old and continuing debate between those, including the religious, who believe that the world has purpose and those who believe it operates automatically and by chance or in recurring unprogressive cycles. The German chemist who scoffed in 1895 at the “purely mechanical world” of “scientific materialism” that would allow a butterfly to turn back into a caterpillar was disputing the same issue, an issue as old as Aristotle.
In Christian Bohr’s field of expertise it emerged in the question whether organisms and their subsystems—their eyes, their lungs—were assembled to preexisting purpose or according to the blind and unbreathing laws of chemistry and of evolution. The extreme proponent of the mechanistic position in biology then was a German named Ernst Heinrich Haeckel, who insisted that organic and inorganic matter were one and the same. Life arose by spontaneous generation, Haeckel argued; psychology was properly a branch of physiology; the soul was not immortal nor the will free. Despite his commitment to scientific experiment Christian Bohr chose to side against Haeckel, possibly because of his worship of Goethe. He had then the difficult work of reconciling his practice with his views.
Partly for that reason, partly to enjoy the company of friends, he began stopping at a café for discussions with the philosopher Harald Høffding after the regular Friday sessions of the Royal Danish Academy of Sciences and Letters, of which they were both members. The congenial physicist C. Christensen, who spent his childhood as a shepherd, soon added a third point of view. The men moved from café meetings to regular rotation among their homes. The philologist Vilhelm Thomsen joined them to make a formidable foursome: a physicist, a biologist, a philologist, a philosopher. Niels and Harald Bohr sat at their feet all through childhood.
As earnest of his commitment to female emancipation Christian Bohr taught review classes to prepare women for university study. One of his students was a Jewish banker’s daughter, Ellen Adler. Her family was cultured, wealthy, prominent in Danish life; her father was elected at various times to both the lower and upper houses of the Folketing, the Danish parliament. Christian Bohr courted her; they were married in 1881. She had a “lovable personality” and great unselfishness, a friend of her sons would say.201 Apparently she submerged her Judaism after her marriage. Nor did she matriculate at the university as she must originally have planned.
Christian and Ellen Bohr began married life in the Adler family townhouse that faced, across a wide street of ancient cobbles, Christianborg Palace, the seat of the Folketing. Niels Bohr was born in that favorable place on October 7, 1885, second child and first son. When his father accepted an appointment at the university in 1886 the Bohr family moved to a house beside the Surgical Academy, where the physiology laboratories were located. There Niels and his brother Harald, nineteen months younger, grew up.
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As far back as Niels Bohr could remember, he liked to dream of great interrelationships. His father was fond of speaking in paradoxes; Niels may have discovered his dreaming in that paternal habit of mind.202, 203 At the same time the boy was profoundly literal-minded, a trait often undervalued that became his anchoring virtue as a physicist. Walking with him when he was about three years old, his father began pointing out the balanced structure of a tree—the trunk, the limbs, the branches, the twigs—assembling the tree for his son from its parts. The literal child saw the wholeness of the organism and dissented: if it wasn’t like that, he said, it wouldn’t be a tree. Bohr told that story all his life, the last time only days before he died, seventy-eight years old, in 1962. “I was from first you
th able to say something about philosophical questions,” he summarized proudly then. And because of that ability, he said, “I was considered something of a different character.”204
Harald Bohr was bright, witty, exuberant and assumed at first to be the smarter of the two brothers. “At a very early stage, however,” says Niels Bohr’s later collaborator and biographer Stefan Rozental, “Christian Bohr took the opposite view; he realized Niels’ great abilities and special gifts and the extent of his imagination.” The father phrased his realization in what would have been a cruel comparison if the brothers had been less devoted.205 Niels, he pronounced, was “the special one in the family.”206
Assigned in the fifth grade to draw a house, Niels produced a remarkably mature drawing but counted the fence pickets first. He liked carpentry and metalworking; he was household handyman from an early age. “Even as a child [he] was considered the thinker of the family,” says a younger colleague, “and his father listened closely to his views on fundamental problems.” He almost certainly had trouble learning to write and always had trouble writing.207, 208 His mother served loyally as his amanuensis: he dictated his schoolwork to her and she copied it down.
He and Harald bonded in childhood close as twins. “There runs like a leitmotif above all else,” Rozental notices, “the inseparability that characterized the relationship between the two brothers.” They spoke and thought “à deux” recalls one of their friends.209, 210 “In my whole youth,” Bohr reminisced, “my brother played a very large part. . . . I had very much to do with my brother. He was in all respects more clever than I.” Harald in his turn told whoever asked that he was merely an ordinary person and his brother pure gold, and seems to have meant it.211, 212
Speech is a clumsiness and writing an impoverishment. Not language but the surface of the body is the child’s first map of the world, undifferentiated between subject and object, coextensive with the world it maps until awakening consciousness divides it off. Niels Bohr liked to show how a stick used as a probe—a blind man’s cane, for example—became an extension of the arm.213 Feeling seemed to move to the end of the stick, he said. The observation was one he often repeated—it struck his physicist protégés as wondrous—like the story of the boy and the tree, because it was charged with emotional meaning for him.
He seems to have been a child of deep connection. That is a preverbal gift. His father, with his own Goethesque yearnings for purpose and wholeness—for natural unity, for the oceanic consolations of religion without the antique formalisms—especially sensed it. His overvalued expectation burdened the boy.
Religious conflict broke early. Niels “believed literally what he learnt from the lessons on religion at school,” says Oskar Klein. “For a long time this made the sensitive boy unhappy on account of his parents’ lack of faith.” Bohr at twenty-seven, in a Christmastime letter to his fiancée from Cambridge, remembered the unhappiness as paternal betrayal: “I see a little boy in the snow-covered street on his way to church.214 It was the only day his father went to church. Why? So the little boy would not feel different from other little boys. He never said a word to the little boy about belief or doubt, and the little boy believed with all of his heart.”215
The difficulty with writing was a more ominous sign. The family patched the problem over by supplying him with his mother’s services as a secretary. He did not compose mentally while alone and then call in his helper. He composed on the spot, laboriously. That was the whispering that reminded C. P. Snow of the later Henry James. As an adult Bohr drafted and redrafted even private letters. His reworking of scientific papers in draft and then repeatedly in proof became legendary.216 Once after continued appeals to Zurich for the incomparable critical aid of the Austrian theoretical physicist Wolfgang Pauli, who knew Bohr well, Pauli responded warily, “If the last proof is sent away, then I will come.” Bohr collaborated first with his mother and with Harald, then with his wife, then with a lifelong series of younger physicists.217 They cherished the opportunity of working with Bohr, but the experience could be disturbing. He wanted not only their attention but also their intellectual and emotional commitment: he wanted to convince his collaborators that he was right. Until he succeeded he doubted his conclusions himself, or at least doubted the language of their formulation.
Behind the difficulty with writing lay another, more pervasive difficulty. It took the form of anxiety that without the extraordinary support of his mother and his brother would have been crippling. For a time, it was.218
It may have emerged first as religious doubt, which appeared, according to Klein, when Niels was “a young man.” Bohr doubted as he had believed, “with unusual resolution.” By the time he matriculated at the University of Copenhagen in the autumn of 1903, when he was eighteen, the doubt had become pervasive, intoxicating him with terrifying infinities.219
Bohr had a favorite novel. Its author, Poul Martin Møller, introduced En Dansk Students Eventyr (The Adventures of a Danish Student) as a reading before the University of Copenhagen student union in 1824. It was published posthumously. It was short, witty and deceptively lighthearted. In an important lecture in 1960, “The Unity of Human Knowledge,” Bohr described Møller’s book as “an unfinished novel still read with delight by the older as well as the younger generation in [Denmark].” It gives, he said, “a remarkably vivid and suggestive account of the interplay between the various aspects of our position [as human beings].”220 After the Great War the Danish government helped Bohr establish an institute in Copenhagen. The most promising young physicists in the world pilgrimaged to study there.221 “Every one of those who came into closer contact with Bohr at the Institute,” writes his collaborator Léon Rosenfeld, “as soon as he showed himself sufficiently proficient in the Danish language, was acquainted with the little book: it was part of his initiation.”222
What magic was contained in the little book? It was the first Danish novel with a contemporary setting: student life, and especially the extended conversations of two student cousins, one a “licentiate”—a degree candidate—the other a “philistine.” The philistine is a familiar type, says Bohr, “very soberly efficient in practical affairs”; the licentiate, more exotic, “is addicted to remote philosophical meditations detrimental to his social activities.”223 Bohr quotes one of the licentiate’s “philosophical meditations”:
[I start] to think about my own thoughts of the situation in which I find myself. I even think that I think of it, and divide myself into an infinite retrogressive sequence of “I’s” who consider each other. I do not know at which “I” to stop as the actual, and in the moment I stop at one, there is indeed again an “I” which stops at it. I become confused and feel a dizziness as if I were looking down into a bottomless abyss.224
“Bohr kept coming back to the different meanings of the word ‘I,’ ” Robert Oppenheimer remembered, “the ‘I’ that acts, the ‘I,’ that thinks, the ‘I,’ that studies itself.”225
Other conditions that trouble the licentiate in Møller’s novel might be taken from a clinical description of the conditions that troubled the young Niels Bohr. This disability, for example:
Certainly I have seen thoughts put on paper before; but since I have come distinctly to perceive the contradiction implied in such an action, I feel completely incapable of forming a single written sentence. . . . I torture myself to solve the unaccountable puzzle, how one can think, talk, or write. You see, my friend, a movement presupposes a direction. The mind cannot proceed without moving along a certain line; but before following this line, it must already have thought it. Therefore one has already thought every thought before one thinks it. Thus every thought, which seems the work of a minute, presupposes an eternity. This could almost drive me to madness.226
Or this complaint, on the fragmentation of the self and its multiplying duplicity, which Bohr in later years was wont to quote:
Thus on many occasions man divides himself into two persons, one of whom tries to fool the other,
while a third one, who is in fact the same as the other two, is filled with wonder at this confusion. In short, thinking becomes dramatic and quietly acts the most complicated plots with itself and for itself; and the spectator again and again becomes actor.227
“Bohr would point to those scenes,” Rosenfeld notes, “in which the licentiate describes how he loses the count of his many egos, or [discourses] on the impossibility of formulating a thought, and from these fanciful antinomies he would lead his interlocutor . . . to the heart of the problem of unambiguous communication of experience, whose earnestness he thus dramatically emphasized.”228 Rosenfeld worshiped Bohr; he failed to see, or chose not to report, that for Bohr the struggles of the licentiate were more than “fanciful antinomies.”
Ratiocination—that is the technical term for what the licentiate does, the term for what the young Bohr did as well—is a defense mechanism against anxiety. Thought spirals, panicky and compulsive. Doubt doubles and redoubles, paralyzing action, emptying out the world. The mechanism is infinitely regressive because once the victim knows the trick, he can doubt anything, even doubt itself. Philosophically the phenomenon could be interesting, but as a practical matter ratiocination is a way of stalling. If work is never finished, its quality cannot be judged. The trouble is that stalling postpones the confrontation and adds that guilt to the burden. Anxiety increases; the mechanism accelerates its spiraling flights; the self feels as if it will fragment; the multiplying “I” dramatizes the feeling of impending breakup. At that point madness reveals its horrors; the image that recurred in Bohr’s conversation and writing throughout his life was the licentiate’s “bottomless abyss.”229 We are “suspended in language,” Bohr liked to say, evoking that abyss; and one of his favorite quotations was two lines from Schiller:230
Nur die Fülle führt zur Klarheit,231
Und im Abgrund wohnt die Wahrheit