Compton had been having trouble getting answers to such questions from the Uranium Committee’s head theorist, Wisconsin’s Gregory Breit. Physical chemists W. K. Lewis from MIT and George Kistiakowsky from Harvard, as well as Robert Mulliken, a physicist at Chicago, had been hurriedly added to the review panel to fill in the gap. Recognizing the urgency of the task, Compton scheduled a meeting of the expanded group for Tuesday, October 21, at General Electric’s research laboratory in Schenectady, New York.114
A week before the meeting, Lawrence cabled Compton with a request that he be allowed to add another name to the roster: “Oppenheimer has important new ideas. Think it desirable he meet with us Tuesday. Can you arrange invitation?”
Compton telegraphed back that Lawrence was welcome to bring Oppenheimer, but suggested instead that Ernest simply relay Oppie’s ideas—“to avoid duplication travel cost.” Lawrence countered that, if necessary, he would use the Loomis fund to pay for his friend’s travel. “I have a great deal of confidence in Oppenheimer,” Ernest added, “and, when I see you, I will tell you why I am anxious to have the benefit of his judgment in our deliberations.”115
3
A USEFUL ADVISER
BY MID - 1941, OPPENHEIMER probably welcomed the opportunity to become involved in the bomb project—if only out of simple loneliness and boredom. “The situation in Berkeley & here in Pasadena is in some ways very gloomy … almost all the men active in physics have been taken away for war work,” he wrote to friends that May.1 Oppie predicted “that physics in our sense will just about stop by next year.”
But Oppenheimer may also have begun to feel guilty about sitting out the war. The German invasion of the Soviet Union in June had caused a sudden turnabout in the Communist Party’s position on intervention.2 There would not be a third Report to Our Colleagues. In October, Lawrence and Oppenheimer—his ticket paid by the Loomis fund—boarded the eastbound streamliner City of San Francisco for the final meeting of Compton’s panel.
Ernest opened the Schenectady meeting by reading aloud Oliphant’s summary of the M.A.U.D. report. The discussion ranged widely, with various techniques for separating uranium being debated. But the group agreed that the electromagnetic method—Lawrence’s approach—deserved “especially urgent attention.”3
Oppenheimer’s contribution included an all-important estimate of how much uranium would be necessary for a bomb. Oppie had calculated that a critical mass of U-235 might weigh more than 200 pounds. This estimate accorded closely with a guess made earlier by Fermi, but was nearly ten times the figure cited in the M.A.U.D. report. The difference depended upon assumptions made about the bomb’s efficiency, one of the most difficult things to calculate.4
Compton confronted the group with other frustrating unknowns: how long would it take to build a weapon, and what would it cost? Unable to prod the engineers on his panel even to speculate, Compton hazarded his own guesses: three to five years to build the bomb, at a cost of “some hundreds of millions of dollars.”5 He decided against including a cost estimate—“lest the government should be frightened off.”
Disappointed and vexed by such indecision, Lawrence and Oppenheimer left for California the following day, October 22. On the streamliner, Lawrence drafted an angry letter to Compton, decrying the panel’s timidity and hinting darkly that any failure would be on Compton’s head.
It will not be a calamity if, when we get the answers to the uranium problem, they turn out negative from the military point of view, but if the answers are fantastically positive and we fail to get them first, the results for our country may well be a tragic disaster.… I feel strongly, therefore, that anyone who hesitates on a vigorous, all-out effort on uranium assumes a grave responsibility.6
What Lawrence did not tell Compton was that he had already decided to proceed on his own in the bomb project—with Oppenheimer’s help.7
* * *
Thus far, Nier’s spectrograph had produced only minute traces of U-235. At the current rate, it would take some 25 million years to produce the amount of uranium that Oppenheimer thought necessary for an atomic bomb.
In early November, Lawrence went to see Nier in Minnesota, “to see if he could not ‘steam up’ his output and produce the needed quantities in a hurry.”8 His visit convinced Ernest that Nier was not up to the task, and that the “only immediate recourse was to undertake the job ourselves at home.” Indeed, Nier himself arrived at the Rad Lab soon afterward to help with the conversion of the 37-inch. The boys began dismantling the cyclotron under Brobeck’s direction later that month.
Originally content to wait for the British to determine the fissionability of U-235, Ernest was no longer willing to let others set the pace.9 Since his return from Schenectady, the cyclotroneers had begun working late into the night and on weekends.
On November 27, 1941, Lawrence received a further push from the final report of Compton’s panel, whose conclusion this time was brief and unequivocal: “A fission bomb of superlative destructive power will result from bringing quickly together a sufficient mass of element U-235.”10 The chief uncertainty remaining was how much uranium would be necessary for a bomb. Here Compton had hedged his bets, citing a range of estimates—from less than 5 to more than 220 pounds—an answer which reflected the persisting ignorance about the properties of U-235.
While Compton’s brief summary noted that both the centrifuge and gaseous diffusion were approaching practical tests, there was only a vague allusion to “other methods … which may ultimately prove superior, but are now farther from the engineering stage.”11 No specific mention was made of the electromagnetic method
