The two brightest stars arrived together on a train from the east. Hans Bethe was working at MIT’s radar lab when Oppenheimer’s summons reached him. Believing the atomic bomb an unlikely prospect anytime soon, Bethe had to be persuaded by Van Vleck to attend; Hans brought his wife, Rose, along for a California vacation. Joining them in Chicago, Edward Teller and his wife, Mici, shared a compartment on the streamliner with the Bethes. Since writing his paper with Bethe on ballistics, Teller had left Columbia to go to Chicago and work with Fermi, but he had not yet been given an assignment at the Met Lab.8
Although Bethe and Teller had first met as graduate students in Germany during the late 1920s, the two did not get to know each other until 1937, when they spent a summer driving through the western United States, camping and discussing physics.9 They discovered they had much in common.
Born in Alsace of a Jewish mother, Bethe had been fired from his position at the University of Tübingen in 1933—the victim of Hitler’s racial purity laws—about the same time that Teller was forced from his teaching post at Göttingen’s Institute of Physical Chemistry. Following a brief respite in Copenhagen to study under Bohr, and then England, both men found refuge in professorships at American universities. In 1938, Teller had persuaded Bethe to attend a conference on stellar evolution, a topic on which Bethe would become the world’s expert. Bethe picked Teller as his replacement the following summer at Columbia.10
But in other respects—including temperament—Bethe and Teller were strikingly different. In contrast to Teller’s often gloomy persona, Bethe seemed unfailingly affable and outgoing, with twinkling eyes and a cherubic face.
Teller had also met Lawrence and Oppenheimer in the vagabond summer of 1937, when he came to Berkeley at Oppie’s invitation to give a seminar. Edward’s lasting memory of Oppenheimer—whose personality he reportedly found “overpowering”—would always be associated with the spicy meal they shared before the seminar at a Mexican restaurant. The hot food caused the guest lecturer to temporarily lose his voice. It was perhaps the only time that Edward would be speechless in Oppie’s presence.11
Ernest, too, left an indelible impression by taking Teller out on the Bay in his new boat, on a cruise memorable for strong winds and high seas. (“I withstood the choppy waters with a little less than complete equanimity,” Edward later wrote. “Californians seemed to be more than I could handle comfortably.”)
Arriving in Berkeley in early July 1942, Bethe and Teller looked forward to a pleasant interlude and a welcome break from the war. The two families shared with Konopinski a large house overlooking the Bay on the north side of campus. Teller found it amusing that Konopinski—a big, burly man—wound up with the frilly pink bedroom that had formerly been occupied by the landlord’s daughter. “We have rented, with the Bethes, a palace and enjoy life very greatly,” Teller wrote to Fermi at Chicago.12
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The Berkeley seminar began at the start of the second week of July in a seminar room adjacent to Oppie’s office at LeConte. The site had been made secure for the purpose by stretching wire netting over the balcony and posting a campus policeman downstairs. Serber began the first session by describing the current state of knowledge regarding the atomic bomb—how it might work and what it would look like. Oppenheimer relieved the tension that evening by taking his guests to dinner at Spengers, a seafood restaurant near the train tracks in Berkeley.13
The figures derived by Nelson and Frankel indicated that a 6-inch-diameter sphere of U-235, weighing about 33 pounds, would be needed for a fission weapon. They calculated that the core of a plutonium bomb would be just over 2 inches across and would weigh about 9 pounds. Breit’s estimates of critical mass had been too high by a factor of eight.14
Near the end of the seminar’s second day, Teller sidetracked the discussion onto an idea that he and Fermi had talked about at Columbia the previous winter. Over lunch, Fermi had made the simple observation that an atomic bomb might release enough energy to start the thermonuclear reaction that fueled the Sun and other stars. Powerful as a fission bomb might be, it would then be only an initiator for a very much larger bomb of a different sort—fusing hydrogen into helium. A so-called hydrogen bomb could theoretically be of virtually unlimited power.
Teller had discussed this possibility with Konopinski at Chicago and during the train trip west with Bethe.15 The prospective thermonuclear fuel that Teller and Konopinski had looked at was liquid deuterium, which was easier to separate from heavy water than U-235 was from U-238. They calculated that a cubic meter of deuterium, heated to a temperature of 400 million degrees by an atomic bomb, would release the explosive energy of 1 million tons of TNT.
Teller had already made it plain at the Berkeley seminar that he regarded the atomic bomb as essentially an engineering problem. His enthusiasm was reserved for the deuterium superbomb, which, he argued, would guarantee victory to the first country that possessed it. The physicists in Oppie’s office began to refer to Edward’s hypothetical weapon as the “Super.”16 When Teller had left Chicago, he and Konopinski had tentatively concluded that the Super would not work. By the time Teller arrived in Berkeley, he was no longer so sure.
Serber recalled that the effect of Teller’s revelation concerning the Super was electric: “Everybody forgot about the A-bomb as if it were old hat.”17 Yet, horrific as the theoretical Super might be, there was still another, even grimmer specter that haunted the theorists: the possibility that an exploding superbomb might release enough energy to ignite the nitrogen in the atmosphere, incinerating the planet. Bethe dismissed that possibility instinctively and later claimed to have disproved it with a few quick calculations.
Oppenheimer, however, remained so taken with the notion of the Super and the possibility of atmospheric ignition that he decided to contact
