Bohr was happy to force this confrontation between the old physics and the new. He felt that it would be fruitful for physics. Because original work is inherently rebellious, his paper was not only an examination of the physical world but also a political document. It proposed, in a sense, to begin a reform movement in physics: to limit claims and clear up epistemological fallacies. Mechanistic physics had become authoritarian. It had outreached itself to claim universal application, to claim that the universe and everything in it is rigidly governed by mechanistic cause and effect. That was Haeckelism carried to a cold extreme. It stifled Niels Bohr as biological Haeckelism had stifled Christian Bohr and as a similar authoritarianism in philosophy and in bourgeois Christianity had stifled Søren Kierkegaard.
When Rutherford saw Bohr’s Part I paper, for example, he immediately found a problem. “There appears to me one grave difficulty in your hypothesis,” he wrote Bohr on March 20, “which I have no doubt you fully realise, namely, how does an electron decide what frequency it is going to vibrate at when it passes from one stationary state to the other? It seems to me that you would have to assume that the electron knows beforehand where it is going to stop.”282 Einstein showed in 1917 that the physical answer to Rutherford’s question is statistical—any frequency is possible, and the ones that turn up happen to have the best odds. But Bohr answered the question in a later lecture in more philosophical and even anthropomorphic terms: “Every change in the state of an atom should be regarded as an individual process, incapable of more detailed description, by which the atom goes over from one so-called stationary state to another. . . . We are here so far removed from a causal description that an atom in a stationary state may in general even be said to possess a free choice between various possible transitions.”283 The “catchwords” here, as Harald Høffding might say, are individual and free choice. Bohr means the changes of state within individual atoms are not predictable; the catchwords color that physical limitation with personal emotion.
In fact the 1913 paper was deeply important emotionally to Bohr. It is a remarkable example of how science works and of the sense of personal authentication that scientific discovery can bestow. Bohr’s emotional preoccupations sensitized him to see previously unperceived regularities in the natural world. The parallels between his early psychological concerns and his interpretation of atomic processes are uncanny, so much so that without the great predictive ability of the paper its assumptions would seem totally arbitrary.
Whether or not the will is free, for example, was a question that Bohr took seriously. To identify a kind of freedom of choice within the atom itself was a triumph for his carefully assembled structure of beliefs. The separate, distinct electron orbits that Bohr called stationary states recall Kierkegaard’s stages. They also recall Bohr’s attempt to redefine the problem of free will by invoking separate, distinct Riemann surfaces. And as Kierkegaard’s stages are discontinuous, negotiable only by leaps of faith, so do Bohr’s electrons leap discontinuously from orbit to orbit. Bohr insisted as one of the two “principal assumptions” of his paper that the electron’s whereabouts between orbits cannot be calculated or even visualized.284 Before and after are completely discontinuous. In that sense, each stationary state of the electron is complete and unique, and in that wholeness is stability. By contrast, the continuous process predicted by classical mechanics, which Bohr apparently associated with the licentiate’s endless ratiocination, tears the atom apart or spirals it into radiative collapse.
Bohr may have found his way through his youthful emotional crisis in part by calling up his childhood gift of literal-mindedness. He famously insisted on anchoring physics in fact and refused to carry argument beyond physical evidence. He was never a system-builder. “Bohr characteristically avoids such a word as ‘principle,’ ” says Rosenfeld; “he prefers to speak of ‘point of view’ or, better still, ‘argument,’ i.e. line of reasoning; likewise, he rarely mentions the ‘laws of nature,’ but rather refers to ‘regularities of the phenomena.’ ”285 Bohr was not displaying false humility with his choice of terms; he was reminding himself and his colleagues that physics is not a grand philosophical system of authoritarian command but simply a way, in his favorite phrase, of “asking questions of Nature.”286 He apologized similarly for his tentative, rambling habit of speech: “I try not to speak more clearly than I think.”287
“He points out,” Rosenfeld adds, “that the idealized concepts we use in science must ultimately derive from common experiences of daily life which cannot themselves be further analysed; therefore, whenever any two such idealizations turn out to be incompatible, this can only mean that some mutual limitation is imposed upon their validity.”288 Bohr had found a solution to the spiraling flights of doubt by stepping out of what Kierkegaard called “the fairyland of the imagination” and back into the real world.289 In the real world material objects endure; their atoms cannot, then, ordinarily be unstable. In the real world cause and effect sometimes seem to limit our freedom, but at other times we know we choose. In the real world it is meaningless to doubt existence; the doubt itself demonstrates the existence of the doubter. Much of the difficulty was language, that slippery medium in which Bohr saw us inextricably suspended. “It is wrong,” he told his colleagues repeatedly, “to think that the task of physics is to find out how nature is”—which is the territory classical physics had claimed for itself. “Physics concerns what we can say about nature.”290
Later Bohr would develop far more elaborately the idea of mutual limitations as a guide to greater understanding. It would supply a deep philosophical basis for his statecraft as well as for his physics. In 1913 he first demonstrated its resolving power. “It was clear,” he remembered at the end of his life, “and that was the point about the Rutherford atom, that we had something from which we could not proceed at all in any other way than by radical change. And that was the reason then that [I] took it up so seriously.”291
4
The Long Grave Already Dug
Otto Hahn cherished the day the Kaiser came to visit. The official dedication of the first two Kaiser Wilhelm Institutes, one for chemistry, one for physical chemistry, on October 23, 1912—Bohr in Copenhagen was approaching his quantized atom—was a wet day in the suburb of Dahlem southwest of Berlin.292, 293 The Kaiser, Wilhelm II, Victoria’s eldest grandson, wore a raincloak to protect his uniform, the dark collar of his greatcoat turned out over the lighter shawl of the cloak. The officials who walked the requisite paces behind him, his scholarly friend Adolf von Harnack and the distinguished chemist Emil Fischer foremost among them, made do with dark coats and top hats; those farther back in the procession who carried umbrellas kept them furled. Schoolboys, caps in hand, lined the curbs of the shining street like soldiers on parade. They stood at childish attention, awe dazing their dreamy faces, as this corpulent middle-aged man with upturned dark mustaches who believed he ruled them by divine right passed in review. They were thirteen, perhaps fourteen years old. They would be soldiers soon enough.
Officials in the Ministry of Culture had encouraged His Imperial Majesty to support German science. He responded by donating land for a research center on what had been a royal farm. Industry and government then lavishly endowed a science foundation, the Kaiser Wilhelm Society, to operate the proposed institutes, of which there would be seven by 1914.294
The society began its official life early in 1911 with von Harnack, a theologian who was the son of a chemist, as its first president. The imperial architect, Ernst von Ihne, went briskly to work. The Kaiser came to Dahlem to dedicate the first two finished buildings, and the Institute for Chemistry especially must have pleased him. It was set back on a broad lawn at the corner of Thielallee and Faradayweg: three stories of cut stone filigreed with six-paned windows, a steep, gabled slate roof and at the roofline high above the entrance a classical pediment supported by four Doric columns. A wing angled off paralleling the cross street. Fitted between the main building and the wing like a hin
ge, a round tower rose up dramatically four stories high. Von Ihne had surmounted the tower with a dome. Apparently the dome was meant to flatter the Kaiser’s taste. A sense of humor was not one of Wilhelm II’s strong points and no doubt it did. The dome took the form of a giant Pickelhaube, the comic-opera spiked helmet that the Kaiser and his soldiers wore.
Leaving Ernest Rutherford in Montreal in 1906 Hahn had moved to Berlin to work with Emil Fischer at the university. Fischer was an organic chemist who knew little about radioactivity, but he understood that the field was opening to importance and that Hahn was a first-rate man. He made room for Hahn in a wood shop in the basement of his laboratories and arranged Hahn’s appointment as a Privatdozent, which stirred less forward-looking chemists on the faculty to wonder aloud at the deplorable decline in standards. A chemist who claimed to identify new elements with a gold-foil electroscope must be at least an embarrassment, if not in fact a fraud.295
Hahn found the university’s physicists more congenial than its chemists and regularly attended the physics colloquia. At one colloquium at the beginning of the autumn term in 1907 he met an Austrian woman, Lise Meitner, who had just arrived from Vienna.296 Meitner was twenty-nine, one year older than Hahn. She had earned her Ph.D. at the University of Vienna and had already published two papers on alpha and beta radiation. Max Planck’s lectures in theoretical physics had drawn her to Berlin for postgraduate study.
Hahn was a gymnast, a skier and a mountain climber, boyishly goodlooking, fond of beer and cigars, with a Rhineland drawl and a warm, selfdeprecating sense of humor. He admired attractive women, went out of his way to cultivate them and stayed friends with a number of them throughout his happily married life. Meitner was petite, dark and pretty, if also morbidly shy. Hahn befriended her. When she found she had free time she decided to experiment. She needed a collaborator. So did Hahn. A physicist and a radiochemist, they would make a productive team.
They required a laboratory. Fischer agreed that Meitner could share the wood shop on condition that she never show her face in the laboratory upstairs where the students, all male, worked.297 For two years she observed the condition strictly; then, with the liberalization of the university, Fischer relented, allowed women into his classes and Meitner above the basement. Vienna had been only a little more enlightened. Meitner’s father, an attorney—the Meitners were assimilated Austrian Jews, baptized all around—had insisted that she acquire a teacher’s diploma in French before beginning to study physics so that she would always be able to support herself. Only then could she prepare for university work. With the diploma out of the way Meitner crammed eight years of Gymnasium preparation into two. She was the second woman ever to earn a Ph.D at Vienna. Her father subsidized her research in Berlin until at least 1912, when Max Planck, by now a warm supporter, appointed her to an assistantship. “The German Madame Curie,” Einstein would call her, characteristically lumping the Germanic peoples together and forgetting her Austrian birth.
“There was no question,” says Hahn, “of any closer relationship between us outside the laboratory. Lise Meitner had had a strict, lady-like upbringing and was very reserved, even shy.” They never ate lunch together, never went for a walk, met only in colloquia and in the wood shop. “And yet we were really close friends.”298 She whistled Brahms and Schumann to him to pass the long hours taking timed readings of radioactivity to establish identifying half-lives, and when Rutherford came through Berlin in 1908 on his way back from the Nobel Prize ceremonies she selflessly accompanied Mary Rutherford shopping while the two men indulged themselves in long talks.
The close friends moved together to the new institute in 1912 and worked to prepare an exhibit for the Kaiser. In his first venture into radiochemistry, in London before he went to Montreal, Hahn had spied out what he took to be a new element, radiothorium, that was one hundred thousand times as radioactive as its modest namesake. At McGill he found a third substance intermediate between the other two; he named it “meso thorium” and it was later identified as an isotope of radium. Mesothorium compounds glow in the dark at a different level of faint illumination from radiothorium compounds. Hahn thought the difference might amuse his sovereign. On a velvet cushion in a little box he mounted an unshielded sample of mesothorium equivalent in radiation intensity to 300 milligrams of radium. He presented his potent offering to the Kaiser and asked him to compare it to “an emanating sample of radiothorium that produced in the dark very nice luminous moving shapes on [a] screen.”299 No one warned His Majesty of the radiation hazard because no safety standards for radiation exposure had yet been set. “If I did the same thing today,” Hahn said fifty years later, “I should find myself in prison.”300
The mesothorium caused no obvious harm. The Kaiser passed on to the second institute, half a block up Faradayweg northwest beyond the angled wing. Two senior chemists managed the Chemistry Institute where Hahn and Meitner worked, but the Institute for Physical Chemistry and Electrochemistry, to give it its full name, was established specifically for the man who was its first director, a difficult, inventive German-Jewish chemist from Breslau named Fritz Haber. It was a reward of sorts. A German industrial foundation paid for it and endowed it because in 1909 Haber had succeeded in developing a practical method of extracting nitrogen from the air to make ammonia. The ammonia would serve for artificial fertilizer, replacing Germany’s and the world’s principal natural source, sodium nitrate dug from the bone-dry northern desert of Chile, an expensive and insecure supply. More strategically, the Haber process would be invaluable in time of war to produce nitrates for explosives; Germany had no nitrates of its own.
Kaiser Wilhelm enlarged at the dedication on the dangers of firedamp, the explosive mixture of methane and other gases that accumulates in mines. He urged his chemists to find some early means of detection. That was a task, he said, “worthy of the sweat of noble brows.”301 Haber, noble brow—he shaved his bullet head, wore round horn-rimmed glasses and a toothbrush mustache, dressed well, wined and dined in elegance but suffered bitter marital discord—set out to invent a firedamp whistle that would sound a different pitch when dangerous gases were present. With a fine modern laboratory uncontaminated by old radioactivity Hahn and Meitner went to work at radiochemistry and the new field of nuclear physics. The Kaiser returned from Dahlem to his palace in Berlin, happy to have lent his name to yet another organ of burgeoning German power.
* * *
In the summer of 1913 Niels Bohr sailed with his young wife to England. He followed the second and third parts of his epochal paper, which he had sent ahead by mail to Rutherford; he wanted to discuss them before releasing them for publication. In Manchester he met his friend George de Hevesy again and some of the other research men. One he met, probably for the first time, was Henry Gwyn Jeffreys Moseley, called Harry, an Eton boy and an Oxford man who had worked for Rutherford as a demonstrator, teaching undergraduates, since 1910.302 Harry Moseley at twenty-six was poised for great accomplishment. He needed only the catalyst of Bohr’s visit to set him off.
Moseley was a loner, “so reserved,” says A. S. Russell, “that I could neither like him nor not like him,” but with the unfortunate habit of allowing no loose statement of fact to pass unchallenged.303 When he stopped work long enough to take tea at the laboratory he even managed to inhibit Ernest Rutherford. Rutherford’s other “boys” called him “Papa.” Moseley respected the boisterous laureate but certainly never honored him with any such intimacy; he rather thought Rutherford played the stage colonial.
Harry came from a distinguished line of scientists. His great-grandfather had operated a lunatic asylum with healing enthusiasm but without benefit of medical license, but his grandfather was chaplain and professor of natural philosophy and astronomy at King’s College and his father had sailed as a biologist on the three-year voyage of H.M.S. Challenger that produced a fifty-volume pioneering study of the world ocean. Henry Moseley—Harry had his father’s first name—won the friendly praise of Charle
s Darwin for his one-volume popular account, Notes by a Naturalist on the ‘Challenger’; Harry in his turn would work with Darwin’s physicist grandson Charles G. Darwin at Manchester.
If he was reserved to the point of stuffiness he was also indefatigable at experiment. He would go all out for fifteen hours, well into the night, until he was exhausted, eat a spartan meal of cheese sometime before dawn, find a few hours for sleep and breakfast at noon on fruit salad. He was trim, carefully dressed and conservative, fond of his sisters and his widowed mother, to whom he regularly wrote chatty and warmly devoted letters. Hay fever threw off his final honors examinations at Oxford; he despised teaching the Manchester undergraduates—many were foreigners, “Hindoos, Burmese, Jap, Egyptian and other vile forms of Indian,” and he recoiled from their “scented dirtiness.”304 But finally, in the autumn of 1912, Harry found his great subject.
“Some Germans have recently got wonderful results by passing X rays through crystals and then photographing them,” he wrote his mother on October 10.305 The Germans, at Munich, were directed by Max von Laue. Von Laue had found that the orderly, repetitive atomic structure of a crystal produces monochromatic interference patterns from X rays just as the mirroring, slightly separated inner and outer surfaces of a soap bubble produce interference patterns of color from white light. X-ray crystallography was the discovery that would win von Laue the Nobel Prize. Moseley and C. G. Darwin set out with a will to explore the new field. They acquired the necessary equipment and worked through the winter. By May 1913 they had advanced to using crystals as spectroscopes and were finishing up a first solid piece of work. X rays are energetic light of extremely short wavelength. The atomic lattices of crystals spread out their spectra much as a prism does visible light. “We find,” Moseley wrote his mother on May 18, “that an X ray bulb with a platinum target gives out a sharp line spectrum of five wavelengths. . . . Tomorrow we search for the spectra of other elements. There is here a whole new branch of spectroscopy, which is sure to tell one much about the nature of the atom.”306
Making of the Atomic Bomb Page 11
