E=mc2

by David Bodanis

  As a result, Oppenheimer was superb at identifying weaknesses or inner doubts in others. When he lashed out at fellow researchers throughout his time as a Berkeley professor, he could unerringly select whatever area they felt weakest about, for he knew very well what it was to have an area to feel weak about. Even in his own physics he was aware of his own weaknesses, and felt a crushing sense of self-loathing at the way he regularly pulled back, ever so slightly, just when he might make a major breakthrough.

  And then, at Los Alamos, he switched. The sarcasm was dropped, for the duration of the war. But the ability to detect other people's deepest fears or desires remained, and this meant that he became a superb leader of men.

  He knew—instantly—that the young postgraduate physicists he needed in large numbers wouldn't pass up work at MIT's radar lab or other famous wartime projects to head to this unknown New Mexico site, simply on the basis of salaries, or offers of future jobs. They'd come only if they thought the top physicists in America were going there. Oppenheimer, accordingly, recruited the senior physicists first; the postgrads followed fast. He even got the authority-resistant genius Richard Feynman on his side. (Tell Feynman that something was a national emergency and his country needed him, and he'd give his mocking New York snort and tell you to get lost.) But Oppenheimer understood that Feynman was so hostile in large part out of furious anger: his young wife had tuberculosis, and in this era before antibiotics it was likely she would soon die. Oppenheimer obtained a rare-as-gold wartime train pass so she could come to New Mexico; he also arranged a place in a hospital close enough to Los Alamos so that Feynman could visit her regularly. In his later memoirs, Feynman joyously mocked every administrator he worked for—with the exception of the two years at Los Alamos, where he did everything Oppenheimer asked.

  Oppenheimer's skills came to the fore in the hardest problem Los Alamos needed to solve. America was building two entirely different sorts of bombs. One team, led by Lawrence in Tennessee, took a blunt approach, and was simply trying to extract the most explosive component in natural uranium. When enough of that was accumulated, there'd be a bomb. The Tennessee factories followed the sort of straightforward engineering that Lawrence and other plain-talking Americans liked. Although there were exceptions, it was largely pushed by native-born Americans.

  Another team, up in Washington State, was taking a more subtle approach. They were starting with ordinary uranium, and then hoping to transform that to an entirely new element, in a process of transmutation much like the one medieval alchemists and even Newton had struggled with in past centuries. The alchemists had wanted to turn lead into gold. The Washington State team, if they succeeded, would transform ordinary uranium into the wickedly powerful, new plutonium metal. Although again there were exceptions, this abstruse approach had been promoted more by the European refugees, educated in a more theoretical tradition.

  The Pentagon liked Lawrence and the blunt Americans down in Tennessee, but it turned out that the foreigners' Washington project did best of all. Despite all of Lawrence's screaming and haranguing and threats, even after months of operation the Tennessee factories—giant factories, over a mile in total length; costing over a billion dollars (even in 1940s currency)—could barely sieve out enough purified uranium to stuff into a single envelope. No one was going to be able to make a bomb with that.

  But although the Washington team did manage to create its promised plutonium, pretty soon the Los Alamos staff realized that no one could get it to ignite as a bomb. The problem wasn't that plutonium didn't explode. Rather, this new element exploded too easily. To make a simple uranium bomb—if the Tennessee team ever got enough purified uranium together—wouldn't be hard. If the amount that would make an explosion was 50 pounds, then you could make a 40-pound ball, and carve a hole in it, and then get a big gun, aim it at the hole, and fire—fast!—the remaining 10 pounds into it. The threshold would be reached so quickly, and the reaction would take place in such a small concentrated area, that much of the explosive U235 form of uranium would convert into energy before it blew itself apart.

  The fragile and new plutonium was different. Fire two segments at each other and the plutonium would start exploding before the two halves completely clanged together. You wouldn't want to stand nearby when this started, of course, for there would be a gush of liquefied or gaseous plutonium where the reaction began. But that would be all. There would be almost no nuclear reaction: most of the raw plutonium, not transformed, would simply spatter away.

  This is where Oppenheimer's insight and managerial gift came in. Forget about trying to clang two separate pieces of plutonium together. The way to get the plutonium fuel from Washington State to work, he realized, would be to start with a ball of plutonium that was fairly low density. That wouldn't explode. But then you'd wrap explosives around it, and set them off, all at precisely the same instant. Do it right, and the ball would crumple inward, so fast that the cascading sequence of E=mc2 blasts that started spreading within would have enough time to accumulate before the plutonium flew apart.

  The technique was called implosion, but the calculations were so hard—how do you make sure the plutonium ball doesn't crumple unevenly?—that there was a great deal of cynicism about whether it could work. (When Feynman first saw what the implosion theorists were trying, he pronounced simply: "It stinks!") Oppenheimer overcame that. He nurtured the first theorists who proposed implosion; he assembled the right explosives experts; as the project grew to a level that under anyone else's supervision it might have fallen apart in a mess of squabbling egos, he deftly manipulated the participants so that all the different groups involved worked together in parallel.

  At one point he had the top U.S. explosives expert, and the top UK explosives expert, and the Hungarian John von Neumann—the quickest mathematician anyone had met, who would also help create the computer in his long career—and a host of other nationalities all working on it. He even had Feynman joining in! The one prima donna who might have destroyed the effort was the embarrassingly egocentric Hungarian physicist Edward Teller. Oppenheimer neatly led him away, and granted him his own office and work team, even amid the shortages of skilled manpower, to concentrate on his own prize ideas. Teller was vain enough—as Oppenheimer of course understood—that he simply took it as his due; in his pleasure he no longer bothered everyone else.

  Paralleling the whole team was a purely British effort, which touched on these theoretical matters as well as practical isotope separation, at Chalk River, near Ottawa. Groves had been suspicious of this group, but Oppenheimer wanted all the help he could get.

  Money didn't count. Everyone knew the level Germany was starting from. At one time, at Los Alamos, calculations suggested that a casing of solid gold might help bounce escaped neutrons back into an exploding bomb. (Its weight would also help keep the exploding plutonium bomb intact.) A little later, Charlotte Serber, who ran the library cum document storage room at Los Alamos, received a small package, about the size of a brown paper lunch bag.

  "All that day Serber amused herself and the women who worked for her by saying to innocent would-be readers 'Please move these little packages to the next table for me.'

  But they couldn't move the one that came from Fort Knox. Gold is denser than lead (that's why it was chosen), and the little 6-inch solid gold sphere inside weighed as much as an eighty-pound barbell.

  But yet, despite the dozens of top researchers and the nearly unlimited funds, the plutonium problem still wasn't being solved. Was it possible, Oppenheimer and others worried, that no full bomb could be made this way? In that case, the best that might result would be an accumulation of radioactive plutonium. Maybe that was even what Heisenberg's heavy water reactor was being designed to cook up. Oppenheimer was informed, in a memorandum of August 21,1943:

  It is possible . . . that [the Germans] will have a production, let us say, of two gadgets a month. This would place particularly Britain in an extremely serious position but there would be
hope for counteraction from our side before the war is lost. . . .

  One of the memo authors was Teller, who could be discounted, but the other was Hans Bethe, an eminently sensible man. He was the head of the theoretical division at Los Alamos, and he'd been a faculty member with Geiger until 1933 in Tubingen. He had excellent contacts with physicists who'd remained on the Continent. The "gadgets" Bethe and Teller had in mind were full bombs, which were unlikely at this stage, but who knew what else the Germans might build?

  Even a few pounds of powdered radioactive metal released over London could make parts of that city uninhabitable for years. There already were worrying reports of the advanced delivery weapons Germany was working on, and one of Heisenberg's men was later seen at Peenemtinde, where the supersonic "vengeance" weapon—the V-2 missile—was being built. Much simpler jet drones were also being constructed—the V-is—and if those crashed highly radioactive warheads into Allied troop emplacements, in the south of England before D-Day or in France afterward, there could be casualties of a level that had never before been seen.

  The threats were taken so seriously that Eisenhower accepted Geiger counters, and specialists trained in their use, to be ready to go with his troops building up in England for D Day. And then, at the very end of 1943, when Oppenheimer was most lost in the plutonium implosion problem, Niels Bohr arrived at Los Alamos, after an escape from his institute in Copenhagen. Bohr was the kindly elder statesman of physics. Over the years everyone who counted, from Heisenberg to Oppenheimer to Meitner's nephew Robert Frisch, had stayed at his institute and worked with him.

  Now Bohr brought serious news. On December 6— after he'd fled—German military police had invaded his institute. They hadn't managed to steal the Nobel gold medals stored there, for George de Hevesy had dissolved them in a jar of strong acid, and left them—in liquid suspension—unobtrusively on a back shelf. But they had bullied their way around, arresting one of Bohr's colleagues who lived in the building. Most seriously, there were rumors that the institute's powerful cyclotron, an early form of particle accelerator, was going to be broken apart and sent back to Germany. Cyclotrons can make plutonium.

  And then British military intelligence reported that, despite the sabotage and even a later Allied bombing raid, the factory at Vemork had been restarted. I. G. Farben engineers had been working frantically to repair it: replacement parts had been hurried in, and production now was higher than ever. In February 1944 the Norwegian Resistance reported that the entire heavy water stock was about to be sent back to Germany.

  What to do? It was an excruciating moment, previewing the dilemmas the Allied physicists would face in the decision to use the bomb one year later. Another direct assault wasn't possible, for the Vemork factory was too heavily barricaded. The main train tracks out were heavily guarded as well—there were regular Army troops; SS detachments; auxiliary airfields that would be opened for spotter aircraft.

  The sole weak spot for attacking the shipment back to Germany was where the train cars with the heavy water from Vemork had to be loaded onto a ferry to cross Lake Tinnsjo, on their way to the Norwegian coast. That was scheduled to take place in mid-February 1944.

  If the train was sunk while it was on the ferry, no German divers could bring it up from the lake's depths. But Tinnsjo was also the main crossing to the rest of Norway for the factory workers at Vemork plus their families; it was also a popular tourist crossing. Ordinary families out for the day always were on the ferry.

  Whom do you kill for a greater good?

  Because of the equation—these powers E=mc2 was offering—the physicists were demanding an awful moral trade-off, greater than anyone should be required to make. Knut Haukelid was one of the Norwegians who had remained behind after the factory raid, living rough on the Hardanger plateau, surviving massive manhunts. By now he was very experienced at the skills needed for sabotage: smuggling himself into a town; working out whom to trust; assembling and testing whatever explosives and timers would be needed. But that wasn't the issue. He had traveled this far, and lived this harshly, to save his countrymen. Now he would be killing them, drowning them in deep cold water.

  Norway command to London:

  REPORTS AS FOLLOWS: . . . DOUBT IF RESULT OF OPERATION IS WORTH REPRISALS STOP WE CANNOT DECIDE HOW IMPORTANT THE OPERATIONS ARE STOP PLEASE REPLYTHIS EVENING IF POSSIBLE STOP

  London to Norway command:

  MATTER HAS BEEN CONSIDERED STOP IT IS THOUGHT VERY IMPORTANT THAT THE HEAVY WATER SHALL BE DESTROYED STOP HOPE IT CAN BE DONE WITHOUTTOO DISASTROUS RESULTS STOP SEND OUR BEST WISHES FOR SUCCESS IN THE WORK STOP GREETINGS

  The best Haukelid could do was arrange with the Vemork transport engineer that the shipment would only come out on Sunday the 20th, when traffic would be light. (Trade union activity had always been strong in Vemork, and as a result the Resistance had high membership—and higher support—in the factory.) Late the Saturday night before, Haukelid arrived with two locals at the berthed ferry. They got on board safely, but when they were hunting for a spot below-decks to lay their explosives, the night watchman, a young Norwegian, found them. He knew one of Haukelid's companions, though, from a local sports club, and quickly nodded his agreement when they gave him their cover story: that Haukelid and the other man, Rolf Sorlie, had to hide from the Germans, and needed somewhere to store their packages. While the first two men stayed behind talking, Haukelid and Sorlie set the charges: right against the front hull, so the explosion would tip the boat forward, lifting the propeller uselessly up in the air, and would cause the tipped boat to fill with water and sink immediately. It was a half hour before Haukelid was done.

  When I left the watchman, I was not clear in my mind as to what I ought to do. . . . I remembered the fate of the two Norwegian guards at Vemork, who had been sent to a German concentration camp after the attack there. I did not want to hand over a Norwegian to the Germans. But if the watchman disappeared, there was danger of the Germans' suspicions being aroused next morning.

  I contented myself with shaking hands with the watchman and thanking him—which obviously puzzled him.

  Lake Tinnsjo ferry

  NORSK HYDRO

  Everyone involved was in Haukelid's position. Alf Larsen, chief engineer at Vemork, had been at a dinner party earlier that evening, where a visiting violinist said that he'd be taking the boat the next day. Larsen had tried to say no, that he should stay longer in this beautiful region, the skiing was so excellent. But when the violinist waved that off, Larsen hadn't been able to insist. A contact at the factory had told him that his elderly mother, too, was planning to take the ferry.

  The bomb went off at 10:45 A.M.; the boat was in 1,300 feet of water. The flatcars from the train broke loose in the sudden tilt, their doors bursting open. The factory worker's mother wasn't on board—her son hadn't let her out of the house—but the violinist was. There were fifty-three people on board. Most of the sturdy German guards managed to fight their way off the tumbling ship in time, but many of the women and children were pushed aside. Over a dozen passengers were caught inside.

  A few of the barrels that had been only slightly purified bobbed on the top of the lake, and the passengers who'd managed to get off but hadn't made it into lifeboats—although the violinist did—grabbed on till a rescue boat came. But the barrels that contained the concentrated heavy water demonstrated, in slow-motion free fall, what they contained. Since the H 2 0 molecules are composed of a nucleus heavier than ordinary water, the barrels sank as if weighted, swirling around the ferry and its innocent trapped passengers down to the bottom.

  One year and six months later, in August 1945, 50 pounds of purified Uranium 235, encased within 10,000 pounds of cordite, steel tamper, casing, and firing controls, was waiting on a heavy trolley, about to be loaded onto a B-29 on the island of Tinian, six hours' flying time from Japan. Oppenheimer was back in Los Alamos, monitoring this final operation.

  If he were a simpler man, he might have been proud. The constru
ction "machine" of researchers and factories and assembly units, which Heisenberg had abortively tried to put together in Germany, had here—on American shores, and under Oppenheimer's direction— finally been achieved. Rivers had been tapped to supply the processing plants and reactors; whole cities had been built to house tens of thousands of workers; a new element had been created through transmutation. It was an immense achievement.

  Fermi's first neutron source, the one he'd used in Rome, based on Chadwick's design, could be held on the palm of one hand. The next device Fermi built, scraping together minor funds in New York in 1940, was about the size of a few large filing cabinets. By late 1942, with Oppenheimer overseeing the first substantial U.S. government funding, Fermi had built an enhanced device that filled much of a competition squash court, underneath the stands of the University of Chicago stadium. The final versions, constructed two years later, when atomic bomb funding was at full tilt, were the centerpieces of a 300,000-acre site in central Washington, near Hanford. With their supporting structures, they stretched taller than the entire Rome institute where Fermi had begun in 1934. Individuals who were aware of the full history could only stand in front of it in awe.

  The plutonium problem had been solved, through mathematicians and explosives experts finding a shape for the ordinary explosives that would smoothly implode the plutonium ball. Regular supplies of the Washington site's output could now be machined for more bombs. The less successful Tennessee factories had also managed to produce a small amount of explosive, and it was Tennessee's total output—almost the complete amount of U235 the United States had—that was being loaded on Saipan.