The First War of Physics (34 page)

This meant that the risk of pre-detonation in a U-235 bomb could be greatly reduced simply by shielding the bomb core from stray neutrons. The core material would no longer need to be quite as pure as had first been thought. And the muzzle velocity of the gun used to assemble the super-critical mass could also be reduced, shortening the length of the gun barrel and making the uranium bomb much more compact. Instead of Thin Man’s seventeen feet, the bomb would now need to be no more than about six feet in length. This new design was codenamed ‘Little Boy’, Thin Man’s smaller brother. The uranium bomb was now definitely a ‘sure thing’.

But the fact remained that according to Lawrence’s latest estimates, within the timescale envisaged for the Manhattan Project there was likely to be enough U-235 to build only one bomb. The threat of an atomic bomb would not be an empty one, but if the Allies used the bomb in the war against Nazi Germany sometime in early 1945 they would be unable to
follow this with the threat of a second weapon, except through a very dangerous bluff. And if the Germans retaliated with a bomb of their own …

Father confessor

Following their arrival at Newport News, Virginia in early December 1943, the physicists of the British Tube Alloys delegation had separated. Peierls, Frisch, Penney and Tuck went on to Los Alamos, although Peierls’ stay was short. He and Fuchs had been assigned to join the work on gaseous diffusion and the problems associated with the operation of the large-scale diffusion plant at Oak Ridge. They worked from offices near Wall Street in New York rented by the British Ministry of Supply, and were officially listed as consultants to the Kellex Corporation, a subsidiary of the Kellogg engineering firm which was building the plant in Tennessee.

Chadwick and his wife Aileen arrived at Los Alamos in early 1944, after having taken a detour to see their daughters in Halifax, Canada, where they had lived since the summer of 1940, safe from German air raids. Rotblat arrived towards the end of February, and stayed in a spare room in the Chadwicks’ relatively prestigious log cabin.

To the American physicists at Los Alamos, contact with colleagues who had so recently experienced life in war-torn Europe and who had lived for so long under the shadow of the Nazi threat brought home to them the real reason why they were all there, and what they were doing. The Britons’ war-stories were sobering. Penney gave a colloquium on the destruction caused by the German aerial bombardment of London, in the detached, matter-of-fact style typical of a scientific discussion, a smile firmly affixed to his face. The smile hid much. Penney had lost his wife in the Blitz.

Niels and Aage Bohr had arrived in New York on 6 December, where they were hustled from the harbour to a hotel by intelligence agents concerned to keep secret their identity. Only when they were safely in their hotel room did they notice that their attempts to conceal their identities beneath pseudonyms had been rather frustrated by Bohr’s luggage, which was boldly labelled
NIELS BOHR.

Of course, not everyone whom Bohr met in his first days in America was aware of the pseudonym or the need for secrecy. In a Washington hotel, Bohr encountered a familiar face in the hotel elevator. It was Else von Halban, Hans von Halban’s wife.

‘Good evening, Mrs von Halban’, he said.

‘I’m not Mrs von Halban now,’ she explained, ‘I’m Mrs Placzek. Good evening Professor Bohr.’

‘I’m not Professor Bohr now; I’m Mr Baker.’

Else had divorced Halban and married George Placzek in Montreal.

The Bohrs were met at the railway station in Lamy, New Mexico, and driven to a quiet stretch of road where they changed vehicles before driving on to Los Alamos. Their cover names Nicholas and James Baker were reinterpreted by the Los Alamos scientists as ‘Uncle Nick’ and ‘Jim’. Oppenheimer organised a meeting on 31 December to give Bohr an opportunity to recount his visit from Heisenberg and to discuss the drawing he had carried with him from Denmark.

The physicists were puzzled by the crude drawing. Bohr referred to it as a drawing of a bomb, but it was clearly a drawing of a reactor. It showed alternating layers of uranium and heavy water moderator rather than the favoured lattice configuration that had been adopted in the construction of Fermi’s first uranium–graphite pile. Bethe wondered if the Germans were so crazy that they wanted ‘to throw a reactor down on London’. Bethe and Teller quickly estimated the explosive force of a uranium–heavy water pile, and concluded that it would be no greater than an equivalent mass of TNT.

But the general climate of fear fostered another possible conclusion. Perhaps Heisenberg had simply managed to keep the real intentions of the German programme secret, even from Bohr.

Bohr was apprised of the progress at Los Alamos. He quickly realised that ‘they did not need my help in making the atom bomb’. His was to be a relatively modest, though vitally important, role on the Manhattan Project. Many of the physicists, now working long hours, six days a week to create the world’s most dreadful weapon, had not themselves lived beneath the shadow of war. However, Bohr had directly experienced life as a Danish
half-Jew under Nazi domination. He had been threatened with arrest by the Gestapo and had escaped in dramatic fashion with the help of the Danish resistance. His September 1941 conversation with Heisenberg had left him in no doubt that, under Heisenberg’s leadership, everything was being done in Germany to develop atomic weapons. He provided a forceful and timely reminder of the threat of a Nazi weapon, and everything that this implied.

Bohr, revered by many gathered on the Hill as a father figure, became a father confessor, particularly for some of the younger physicists such as Feynman. Any scientist wrestling with his conscience over what he was helping to build would find the moral justification for it in Bohr’s own experiences. ‘He made the enterprise seem hopeful,’ Oppenheimer observed after the war of Bohr’s role, ‘when many were not free of misgiving.’ Bohr had a salutary effect on the morale of the Los Alamos physicists.

If Heisenberg’s intention in September 1941 had really been to convince nuclear scientists not to engage in building weapons of mass destruction, then his failure was now complete, and utter.

Bohr paid frequent visits to the Chadwicks’ cabin and got to know Rotblat, who had acquired a short-wave radio. Together they would listen to news of the war broadcast by the BBC World Service. Bohr maintained that: ‘We must hear all the rumours before they are denied.’

A remark made by Groves over dinner one evening left a lasting impression on. Rotblat. Groves volunteered the opinion that of course the real purpose of the atomic bomb was to subdue the Soviet Union. Rotblat had no illusions about the Soviet regime, but the Soviet Union was an ally in the war against Germany, and a nation whose people were making incredible sacrifices. Rotblat felt keenly ‘the sense of betrayal of an ally’. His discussions with Bohr about the post-war implications of the bomb became more intense.

Complementarity of the bomb

If Bohr did not eventually contribute much of technical substance to the Manhattan Project, it was not only because he perceived the project to be
in more capable hands, but also because his mind had already jumped a further step ahead. From what he could see and what he was told at Los Alamos, it was easy to conclude that atomic weapons were soon to be a hard fact of political life. He was astonished to learn that the British and American administrations had given little – if any – thought to the postwar challenges posed by the threat of the weapons that would soon be available. He had no doubt that there were scientists in the Soviet Union equally capable of building atomic weapons of their own.

He perceived parallels with
complementarity
, one of the central planks of his own philosophy of physics which he believed had implications for the way we can interpret aspects of our wider world. In the sub-atomic quantum world, complementarity attempts to rationalise the dual wave–particle behaviour of fundamental particles such as electrons. Under different, mutually exclusive circumstances, electrons will exhibit both wave-like behaviour and particle-like behaviour. It is impossible to rationalise this in terms of some kind of underlying reality because, according to Bohr’s philosophy, such a reality is simply beyond the reach of our instruments, our observations and our understanding. We are therefore left with seeming contradictions. Here the electron is a wave. Here it is a particle. Bohr had argued in 1927 that although these behaviours are mutually exclusive, they are not actually contradictory. They are complementary behaviours of a deeper, forever unknowable, reality.

Atomic weapons have similar complementary properties, Bohr now realised. Under one set of circumstances, atomic weapons heralded an arms race leading, perhaps inevitably, to nothing less than the destruction of human civilisation. At the same time, under different circumstances, atomic weapons heralded the end of war, because in a war fought with atomic weapons there could be no victor. If political, cultural or religious differences were to be settled without an end-of-the-world, no-win scenario, then the advent of atomic weapons meant that recourse to war would no longer be thinkable. Differences would have to be settled in other, less violent, ways. The choice was plain. Arms race or international arms control?

An electron has no choice about how it is to behave, but a political organisation of society is in principle free to make choices, provided these are first recognised. Bohr believed that an arms race was not an inevitable consequence of the work now in hand at Los Alamos. Such a race could yet be avoided. He reasoned that the only way to achieve this was to adopt an ‘open world’ policy, taking potential enemies into confidence and building trust through dialogue. In early 1944 this meant gaining the confidence of the Soviet Union, now an ally in the war against Nazi Germany and Japan, but acknowledged by many as an enemy in waiting.

Sinking of the
Hydro

The bombing raid on the Vemork plant convinced the Germans to rebuild the heavy water facility in Germany, and plans were laid to transport the last of the heavy water by sea, under armed guard. Rosbaud alerted the SOE to these plans early in January 1944, and Haukelid was asked to look at ways to prevent the heavy water from leaving Rjukan.

A one-man attack on the plant itself was impossible, so Haukelid turned his attention to the transport arrangements. The drums containing the heavy water, labelled ‘Potash-lye’, were to be moved by train from Vemork to the
Hydro
, a ferry that would cross Lake Tinnsjø, and thence by rail to a port and a waiting ship to Germany. The ferry itself was the least guarded and offered the prospect of minimising civilian casualties. On 9 February he sent a telegram back to London suggesting sabotage of the ferry. Although the saboteurs went on to express their misgivings that the operation was not worth the risk of reprisals that would certainly follow, the response from London was clear. The heavy water had to be destroyed.

Haukelid, Skinnarland and Rolf Sørlie laid plans to sink the ferry at the deepest point in the lake, sending the drums of heavy water to the bottom. The battle for heavy water was about to claim its last casualties.

Armed with sten guns, pistols and grenades, Haukelid and Sørlie smuggled themselves aboard the ferry in the early morning of Sunday, 20 February. On the inside of the hull they placed nineteen pounds of
plastic explosive, high-speed fuses, detonators and timers hastily assembled from old alarm clocks. They set the clocks for 10:45am. They then made their escape.

The
Hydro
sailed on time at 10:00am carrying 53 passengers, crew and German guards, and 39 drums containing over 3,600 gallons of heavy water. The explosion ripped a hole eleven feet square out of the side of the 493-ton ferry. It sank within three minutes. Twenty-six drowned, including fourteen civilians, among them a couple and their three-year-old daughter. The other 27 managed to jump from the ferry as it sank, and were rescued from the icy water by local farmers and fishermen.

The heavy water sank to the bottom of Lake Tinnsjø, where it remains today.

Life on the Hill

Groves’ belief in Oppenheimer’s capabilities was genuine. The mismanagement that had characterised the first few months of Oppenheimer’s tenure had given way to strong and effective leadership. Oppenheimer the scientific director of the Los Alamos laboratory emerged as a very different personality from Oppenheimer the academic physicist. He had adapted, chameleon-like, to the very different environment and the demands he now faced.

His was not a dictatorial style of leadership. For that he could always rely on Groves, more used to barking orders to army personnel than looking after the well-being of awkward, argumentative civilians. Instead, Oppenheimer would simply put forward persuasive and compelling arguments why someone on the project should do things his way rather than their way. He directed the work through politics and manipulation, carried out with considerable charisma and finesse. Most of the scientists on the project were aware they were being manipulated, but many accepted and welcomed it. ‘I think that he really realised that the other person knew that this was going on,’ explained one Los Alamos physicist, ‘it was like a ballet, each one knowing the part and the role he’s playing, and there wasn’t any subterfuge to it.’

Subterfuge or not, Oppenheimer’s concern for the well-being of the new citizens of Los Alamos transcended a strict interpretation of his duties as scientific director. A career in academic physics had hardly prepared him for the management problems he now faced in the closed and claustrophobic micro-society taking shape on the Hill. He was obliged to adopt roles ranging from mayor of a small boom-town to personnel manager to local priest.

He was daily confronted with the problems of squalid army buildings, poor facilities, a constant housing shortage, lack of suitable water supplies and intermittent electricity. He often found himself caught between his staff and Groves’ almost criminal lack of diplomacy.
⁵
He had to deal with minor insurrections mounted by the scientists’ wives, as they sought to improve their living conditions. Investigation of some minor infringements uncovered the ‘WAC shack’, a flourishing business conducted by a few young girls of the Women’s Army Corps offering personal services to men stuck on the Hill with irrepressible desires, and money in their pockets. He got caught up in the often petty domestic troubles of his staff. As romances blossomed, Oppenheimer frequently attended the resulting wedding ceremonies, sometimes acting as a witness and occasionally giving away the bride.