Richard Rhodes - The Making of the Atomic Bomb

He returned to the parsonage at Vissenbjerg in the autumn of 1910. His work slowed. He may have recalled the licentiate’s dissertation problems, for he again turned to Kierkegaard. “He made a powerful impression on me when I wrote my dissertation in a parsonage in Funen, and I read his works night and day,” Bohr told his friend and former student J. Rud Nielsen in 1933. “His honesty and his willingness to think the problems through to their very limit is what is great. And his language is wonderful, often sublime. There is of course much in Kierkegaard that I cannot accept. I ascribe that to the times in which he lived. But I admire his intensity and perseverance, his analysis to the utmost limit, and the fact that through these qualities he turned misfortune and suffering into something good.” 249

He finished his Ph.D. thesis, “Studies in the electron theory of metals,” by the end of January 1911. On February 3, suddenly, at fifty-six, his father died. He dedicated his thesis “in deepest gratitude to the memory of my father.” 250He loved his father; if there had been a burden of expectation he was free of that burden now.

As was customary, he publicly defended his thesis in Copenhagen on May 13. “Dr. Bohr, a pale and modest young man,” the Copenhagen newspaper Dagbladet reported under a crude drawing of the candidate standing in white tie and tails at a heavy lectern, “did not take much part in the proceedings, whose short duration is a record.” 251The small hall was crowded to overflowing. Christiansen, one of the two examiners, said simply that hardly anyone in Denmark was well enough informed on the subject to judge the candidate’s work.

Before he died Christian Bohr had helped arrange a fellowship from the Carlsberg Foundation for his son for study abroad. Niels spent the summer sailing and hiking with Margrethe Nørland, the sister of a friend, a beautiful young student whom he had met in 1910 and to whom, shortly before his departure, he became engaged. Then he went off in late September to Cambridge. He had arranged to study at the Cavendish under J. J. Thomson.

29 Sept. 1911

Eltisley Avenue 10,

Newnham, Cambridge

Oh Harald! 252

Things are going so well for me. I have just been talking to J. J. Thomson and have explained to him, as well as I could, my ideas about radiation, magnetism, etc. If you only knew what it meant to me to talk to such a man. He was extremely nice to me, and we talked about so much; and I do believe that he thought there was some sense in what I said. He is now going to read [my dissertation] and he invited me to have dinner with him Sunday at Trinity College; then he will talk with me about it. You can imagine that I am happy…. I now have my own little flat. It is at the edge of town and is very nice in all respects. I have two rooms and eat all alone in my own room. It is very nice here; now, as I am sitting and writing to you, it blazes and rumbles in my own little fireplace.

Niels Bohr was delighted with Cambridge. His father’s Anglophilia had prepared him to like English settings; the university offered the tradition of Newton and Clerk Maxwell and the great Cavendish Laboratory with its awesome record of physical discovery. Bohr found that his schoolboy English needed work and set out reading David Copperfield with an authoritative new dictionary at hand, looking up every uncertain word. He discovered that the laboratory was crowded and undersupplied. On the other hand, it was amusing to have to go about in cap and gown (once he was admitted to Trinity as a research student) “under threat of high fines,” to see the Trinity high table “where they eat so much and so first-rate that it is quite unbelievable and incomprehensible that they can stand it,” to walk “for an hour before dinner across the most beautiful meadows along the river, with the hedges flecked with red berries and with isolated windblown willow trees—imagine all this under the most magnificent autumn sky with scurrying clouds and blustering wind.” 253, 254He joined a soccer club; called on physiologists who had been students of his father; attended physics lectures; worked on an experiment Thomson had assigned him; allowed the English ladies, “absolute geniuses at drawing you out,” to do their duty by him at dinner parties. 255

But Thomson never got around to reading his dissertation. The first meeting had not, in fact, gone so well. The new student from Denmark had done more than explain his ideas; he had shown Thomson the errors he found in Thomson’s electron-theory work. “I wonder,” Bohr wrote Margrethe soon after, “what he will say to my disagreement with his ideas.” 256And a little later: “I’m longing to hear what Thomson will say. He’s a great man. I hope he will not get angry with my silly talk.” 257

Thomson may or may not have been angry. He was not much interested in electrons anymore. He had turned his attention to positive rays—the experiment he assigned Bohr concerned such rays and Bohr found it distinctly unpromising—and in any case had very little patience with theoretical discussions. “It takes half a year to get to know an Englishman,” Bohr said in his last interview. “…It was the custom in England that they would be polite and so on, but they wouldn’t be interested to see anybody…. 258I went Sundays to the dinner in Trinity College…. I was sitting there, and nobody spoke to me ever in many Sundays. But then they understood that I was not more eager to speak to them than they were to speak to me. And then we were friends, you see, and then the whole thing was different.” The insight is generalized; Thomson’s indifference was perhaps its first specific instance.

Then Rutherford turned up at Cambridge.

He “came down from Manchester to speak at the annual Cavendish Dinner,” says Bohr. “Although on this occasion I did not come into personal contact with [him], I received a deep impression of the charm and power of his personality by which he had been able to achieve almost the incredible wherever he worked. The dinner”—in December—“took place in a most humorous atmosphere and gave the opportunity for several of Rutherford’s colleagues to recall some of the many anecdotes which already then were attached to his name.” 259Rutherford spoke warmly of the recent work of the physicist C. T. R. Wilson, the inventor of the cloud chamber (which made the paths of charged particles visible as lines of water droplets hovering in supersaturated fog) and a friend from Cambridge student days. Wilson had “just then,” says Bohr, photographed alpha particles in his cloud chamber scattering from interactions with nuclei, “the phenomenon which only a few months before had led [Rutherford] to his epoch-making discovery of the atomic nucleus.” 260

Bohr had matters on his mind that he would soon relate to the problem of the nucleus and its theoretically unstable electrons, but it was Rutherford’s enthusiastic informality that most impressed him at the annual dinner. 261Remembering this period of his life long afterward, he would single out for special praise among Rutherford’s qualities “the patience to listen to every young man when he felt he had any idea, however modest, on his mind.” 262In contrast, presumably, to J. J. Thomson, whatever Thomson’s other virtues.

Soon after the dinner Bohr went up to Manchester to visit “one of my recently deceased father’s colleagues who was also a close friend of Rutherford,” whom Bohr wanted to meet. 263The close friend brought them together. Rutherford looked over the young Dane and liked what he saw despite his prejudice against theoreticians. Someone asked him later about the discrepancy. “Bohr’s different,” Rutherford roared, disguising affection with bluster. “He’s a football player!” Bohr was different in another regard as well; he was easily the most talented of all Rutherford’s many students—and Rutherford trained no fewer than eleven Nobel Prize winners during his life, an unsurpassed record. 264, 265