The Making of the Atomic Bomb

Copenhagen in the mid-1930s and would be working with him again at Princeton, joined them on the crowded West 57th Street pier. He had taught his regular Monday morning class, then caught a midday train.

As the Drottningholm berthed, at 1 p.m. on January 16, Laura Fermi saw Bohr on an upper deck leaning on the railing searching the crowd. She thought him worn when they met: “During the short time that had elapsed since our visit to his home, Professor Bohr seemed to have aged. For the last few months he had been extremely preoccupied about the political situation in Europe, and his worries showed on him. He stooped like a man carrying a heavy burden. His gaze, troubled and insecure, shifted from the one to the other of us, but stopped on none.” No doubt Bohr was worried about Europe. He had also been seasick.

He had business in New York; he and Erik went off with the Fermis. Wheeler took L6on Rosenfeld along to Princeton. Keeping his promise to Frisch, Bohr had not mentioned the Hahn-Strassmann discovery and the Frisch- Meitner interpretation to either Fermi or Wheeler, but he had neglected to tell Rosenfeld of his pledge. Rosenfeld thought Frisch and Meitner had already sent off the paper that would give their work of interpretation priority. He passed on to Wheeler what Bohr had passed on to him. “In those days,” Wheeler remembers, “I was in charge of the Monday evening journal club” — a weekly gathering of Princeton physicists to discuss the latest studies they found in physics journals, a way of keeping up. “It was the custom to get three things reported then, and here was something hot, as I had learned from Rosenfeld on the train.” America first heard the news of the splitting of uranium — the term “fission” had not yet crossed the Atlantic — at the Princeton physics department journal club on the chill Monday evening of January 16, 1939. “The effect of my talk on the American physicists,” says Rosenfeld ruefully, “was more spectacular than the fission phenomenon itself. They rushed about spreading the news in all directions.”

Bohr arrived in Princeton the next day to take up residence and Rosenfeld casually mentioned the journal club talk. “I was immediately frightened,” Bohr wrote his wife that night, “as I had promised Frisch I would wait until Hahn's note appeared and his own was sent off.” It was more than a point of honor, though that would have been sufficient in itself to trigger the Bohr conscience. It was also that Meitner and Frisch were refugees who could use so spectacular a coup to establish themselves securely in exile. Bohr had at hand the work he and Rosenfeld had accomplished aboard the Drottningholm; for the next three days he labored to convert it into a letter to Nature that would give credit pointedly at the outset to Meitner and Frisch. Three days to produce a seven-hundred-word paper was for Niels Bohr great haste.

“Can you guess where I found out about [Bohr's news]?” asks Eugene Wigner. “In… the [Princeton] infirmary. Because I contracted jaundice and was in the infirmary for six weeks.” Wigner and Princeton had not immediately got along; in 1936 “they said I should look for another job.” Princeton then, he thought, was “an ivory tower; people did not have any normal thinking about the facts of life and so forth and they looked down upon me.” He sought another job and found one at the University of Wisconsin at Madison. “From the second day on I felt at home there. Somebody suggested we go to the track and we ran around the track and we were friends. We talked not only about the most difficult problems but about the daily events. We got down to earth almost.” He met a young American woman in Wisconsin; they were quickly married. She became ill:

I tried to conceal it from her that she had cancer and that there was no hope for her surviving. She was in a hospital in Madison and then she went to see her parents and I went with her but I didn't want to stay with her parents, of course, because I was, after all, a stranger to her parents. I went for a little while away to Michigan, Ann Arbor, and then I came back and saw her in her bed at her parents'. And then she told me essentially that she knows that she is close to death. She said, “Should I tell you where our suitcases are?” So she knew when she talked to me. I tried to conceal it from her because I felt that it would be better if a reasonably young person does not realize that she is doomed. Of course, we are all doomed.

He returned to Princeton in 1938, the university by then having more sensibly assessed bis worth (a sophisticated and highly respected theoretician, Wigner shared the Nobel Prize in Physics in 1963 for his work on the structure of the nucleus).

After Bohr's arrival Szilard traveled down from New York to visit his sick friend and won a long-overdue surprise:

Wigner told me of Hahn's discovery. Hahn found that uranium breaks into two parts when it absorbs a neutron… When I heard this I immediately saw that these fragments, being heavier than corresponds to their charge, must emit neutrons, and if enough neutrons are emitted… then it should be, of course, possible to sustain a chain reaction. All the things which H. G. Wells predicted appeared suddenly real to me.

At Wigner's bedside in the Princeton infirmary the two Hungarians debated what to do.

In the meantime Bohr had sent his letter for Nature to Frisch in Copenhagen, asking him to forward it on “if, as I hope, Hahn's article has already been published and your and your aunt's note has already been submitted.” He asked for the “latest news” on that front and wondered “how the experiments are proceeding.” In a postscript he added that he had just seen the Hahn-Strassmann paper in Naturwissenschaften.

Ideas infect like viruses. The point of origin of the fission infection was Dahlem. From there it spread to Stockholm, to Kungalv, to Copenhagen. It crossed the Atlantic with Bohr and Rosenfeld. I. I. Rabi and the young California-born theoretician Willis Eugene Lamb, Jr., two Columbia men working at Princeton that week, both heard the news, Lamb perhaps from Wheeler, Rabi from Bohr himself. They returned to New York — “probably Friday night,” Lamb thinks. Rabi says he told Fermi. In 1954 Fermi credited Lamb: “I remember one afternoon Willis Lamb came back very excited and said that Bohr had leaked out great news.” Lamb recalls “spreading it around” but does not recall specifically telling Fermi. Possibly both men talked to the Italian laureate within a space of hours; it was information he of all physicists would most need to hear, since the Nobel lecture he had delivered only a month earlier, not yet printed, was now partly obsolete and an embarrassment. (Fermi confined revision to a footnote: “The discovery by Hahn and Strassmann… makes it necessary to reexamine all the problems of the transuranic elements, as many of them might be found to be products of a splitting of uranium.” The many other radioactivities he and his group identified and his slow-neutron discovery still secured his Nobel Prize.)

Szilard also hoped to talk to Fermi: “I thought that if neutrons are in fact emitted in fission, this fact should be kept secret from the Germans. So I was very eager to contact Joliot and to contact Fermi, the two men who were most likely to think of this possibility.” He had borrowed Wigner's apartment and had not yet left Princeton. “I got up one morning and wanted to go out. It was raining cats and dogs. I said, ‘My God, I am going to catch cold!’ Because at that time, the first years I was in America, each time I got wet I invariably caught a bad cold.” He had to go out anyway. “I got wet and came home with a high fever, so I was not able to contact Fermi.”

Fever or not, by January 25 — Wednesday — Szilard had returned to New York, had seen the Hahn- Strassmann paper and was writing Lewis Strauss, whose patronage might now be more important than ever:

I feel I ought to let you know of a very sensational new development in nuclear physics. In a paper… Hahn reports that he finds when bombarding uranium with neutrons the uranium breaking up… This is entirely unexpected and exciting news for the average physicist. The Department of Physics at Princeton, where I spent the last few days, was like a stirred-up ant heap.

Apart from the purely scientific interest there may be another aspect of this discovery, which so far does not seem to have caught the attention of those to whom I spoke. First of all it is obvious that the energy released in this new reaction must be very much higher than all previously known cases… This in itself might make it possible to produce power by means of nuclear energy, but I do not think that this possibility is very exciting, for… the cost of investment would probably be too high to make the process worthwhile… I see… possibilities in another direction. These might lead to large-scale production of energy and radioactive elements, unfortunately also perhaps to atomic bombs. This new discovery revives all the hopes and fears in this respect which I had in 1934 and 1935, and which I have as good as abandoned in the course of the last two years. At present I am running a high temperature and am therefore confined to my four walls, but perhaps I can tell you more about these new developments some other time.

The same day Fermi stepped into the office of John R. Dunning, a Columbia experimentalist whose specialty