Steven Shapin · Barrel of Greenbacks: Luis Alvarez and the Bomb

Luis Alvarez gets only a bit part in Christopher Nolan’s movie Oppenheimer. In January 1939, the news arrives in Berkeley that two German scientists have split the uranium atom. Oppenheimer, who hasn’t yet heard, sees an excited Alvarez dashing out of a barber shop mid-haircut, newspaper in hand. He catches up with him at the physics department, where they’re joined by E.O. Lawrence, the director of Berkeley’s Radiation Laboratory. As a theoretical physicist, Oppenheimer doesn’t believe the story. ‘It’s not possible,’ he says: the massive uranium atom is too stable; splitting it into two other largish nuclei would go against all previous findings about nuclear interactions. He heads over to a blackboard to sketch out the mathematics. Alvarez reacts differently: ‘I’m going to try to reproduce it,’ he says, and leaves the room. A short time passes; Oppenheimer’s scepticism is well supported by theory but, Lawrence tells him, there’s ‘just one problem … Alvarez did it.’ They go next door to look at the experimental evidence that Alvarez has just produced. Oppenheimer is persuaded, and immediately understands what it means. He tells the younger physicist that splitting the uranium nucleus can cause a neutron chain reaction and the release of an enormous amount of energy: ‘A bomb, Alvarez, a bomb.’The Manhattan Project, which built the atomic bomb, transmuted pure theory into mass slaughter, and it changed everything for the scientists who did the work. For Oppenheimer, as its scientific director, it brought first power, then fame, then banishment. For Alvarez, the bomb was a launchpad to a brilliant life as an experimental physicist and counsellor to the Cold War state. Oppenheimer did little physics after Los Alamos. He wrote limpid essays on the nature of science, directed the Princeton Institute for Advanced Study and, after the withdrawal of his security clearance in 1954, emerged as a tragic hero of the American left. Alvarez went on to very great scientific things, and in 1968 was finally awarded the Nobel Prize in Physics, which Oppenheimer never won.Alvarez enjoyed doing lots of different things and, for much of his life, worked in institutional environments that gave him free range. Towards the end of his career, his curiosity turned to things outside physics.

He inserted himself into the controversy over whether there had been a ‘second gunman’ in the Kennedy assassination (there hadn’t), suggested an explanation for the extinction of the dinosaurs (it was caused by the impact of an enormous asteroid), and used radiation-detection techniques in an effort to establish whether there were as yet undiscovered chambers in the Egyptian pyramids (there weren’t). Alec Nevala-Lee is an American writer of science fiction, detective thrillers and biographies, whose previous work includes a life of Buckminster Fuller. He likes to write about creative risk-takers. Alvarez is a natural subject for him.Oppenheimer and Alvarez both came from privilege: Oppenheimer’s father was a wealthy New York merchant; Alvarez’s was a prosperous Californian physician and author. Alvarez, who shared his name with his paternal grandfather, was a tall, blue-eyed blond – as one historian recently put it, ‘a white man with a Hispanic name’. He took his doctorate in physics at the University of Chicago in 1936, then went to Lawrence’s Radiation Laboratory at Berkeley, where he was based for the rest of his academic career.Lawrence built cyclotrons, complex instruments that used electric and magnetic fields to accelerate charged particles to enormous energies and then smash them into target materials. Cyclotrons were used to make radioactive isotopes for medical purposes but, more significant, they were the principal means of discovering new subatomic particles. At that time it was scarcely considered that there would be military uses for this sort of equipment. Alvarez’s first notable achievement at Berkeley was the experimental confirmation of the theoretically predicted phenomenon of K-capture: an electron in the orbit closest to the nucleus combines with a proton to produce a neutron, so transmuting one element into another.Experimental nuclear physics was, even then, very expensive. But the war profoundly changed the financial and political environment of American science. It’s been said that ‘radar won the war; the atomic bomb ended it.’ In 1940 Alvarez was sent off to the MIT Radiation Laboratory in Cambridge, Massachusetts to help develop the British invention of the cavity magnetron into usable ground and aircraft-based radar systems. This was his first involvement with large, multi-skilled teams working towards military ends, and with the vast resources made available for this sort of research and development.

At its peak, the Rad Lab absorbed close to $4 million per month and employed 4000 people – small beer compared to the more charismatic Manhattan Project, though it employed twice as many academic physicists.Alvarez was a brilliant and prolific inventor. The Rad Lab made him a kind of minister without portfolio, tasked with doing pretty much whatever he thought was needed. His versatility became a personal brand – the Special Systems Division was known as ‘Luie’s Gadgets’. A suite of ‘war-winning’ radar inventions is owed to Alvarez and his colleagues: the ground-controlled approach radar that helped land planes in poor visibility; the ground-based microwave early warning system; the Eagle high-altitude bombing system; and the Vixen radar technique used so effectively against U-boats.The call to Los Alamos came late in the game, and the approach was made directly by Oppenheimer, who put Alvarez to work on problems with detonation of the plutonium bomb – the sort tested at Alamogordo and then dropped on Nagasaki. To effectively detonate a subcritical mass of plutonium, it had to be compressed to criticality by perfectly spherical waves produced by more than thirty simultaneously firing explosive lenses. The technical problems of achieving this simultaneity were enormous; if the firing times varied even by as little as a few nanoseconds, the result would be a ‘fizzle’ rather than a full-blooded blast. But Alvarez solved the problem.Oppenheimer next tasked him with developing gauges that would accurately measure the force of the blasts. When the Trinity Test took place, Alvarez was in a B-29, but Oppenheimer had insisted that he keep 25 miles away from Ground Zero because of weather and safety concerns, meaning that the measuring instruments he had devised couldn’t be deployed. Alvarez did as he was told, and may have been the first person to describe the appearance of the ‘mushroom cloud’. But he had desperately wanted to be there for the big moment, and even forty years later could still recall his rage: ‘I was absolutely furious, angry with [Oppenheimer] as I have never been angry with anyone before or since.’Alvarez always wanted to be where the action was. Associates remarked on his ‘cowboy spirit’, his appetite for both scientific and personal risk.

Oppenheimer agreed that Alvarez should be dispatched to Tinian Island in the Marianas, where the uranium bomb was being made ready for Hiroshima; he was charged with installing the gauges that would measure its explosive energy. Determined to be aboard Great Artiste, the observation B-29 that would accompany the Enola Gay as it dropped the bomb, Alvarez shrewdly decided not to lobby Oppenheimer, instead going straight to the military director of the Manhattan Project, General Leslie Groves, who gave his approval: Oppenheimer was called the Father of the Bomb, but Alvarez was the scientist in the delivery room. At the moment the bomb was released over Hiroshima, Alvarez was fully occupied watching the oscilloscope screen that recorded data from the gauges slung under parachutes. Minutes later, he ‘looked in vain for the city that had been our target’, seeing no man-made structures on the ground. He worried that the Enola Gay bombardier had missed, but the crew on the observation plane reassured him that Hiroshima had been annihilated: ‘It was a beautiful job of bombing.’After the war, Oppenheimer said that the scientists had ‘known sin’, but Alvarez had no qualms. On the plane back from Hiroshima, he wrote a letter to his son, explaining why it was the right thing to do: many more lives would have been lost if the war went on; the horror of the destruction would guarantee perpetual world peace. The bomb, he said, was ‘one of the most life-saving decisions in the history of mankind’. Alvarez was far from alone in thinking that, but on his return to Los Alamos, he was irritated by the handwringing of colleagues: ‘Many of my friends felt responsible for killing Japanese civilians, and it upset them terribly. I could muster very little sympathy for their point of view.’Even before Hiroshima, Alvarez was thinking about what he might do when he re-entered academic life. Two things were clear: that the future of physics lay in investigating fundamental atomic particles, and that this work involved the construction of ever more powerful particle accelerators. He was made a full professor at the University of California, though most of his salary was paid by the Atomic Energy Commission. The lab at Berkeley had been profoundly changed by the wartime mobilisation of physics; it’s hard now to recover the prewar sense that atomic physics was as pure as pure science could be.

But, after 1939, the physicists understood very well the explosive implications of atom-splitting, and, once the Manhattan Project had proved them right, the politicians and generals were easily persuaded – or persuaded themselves – that advances in nuclear physics would be central to the fight against communism. Lawrence was skilled in the political arts, and he ensured that the commitment of enormous government resources to nuclear physics was made permanent. As his protégé, Alvarez followed suit; torrents of government money were directed to the Berkeley lab. ‘We ran it,’ he bragged, ‘with a big barrel of greenbacks.’Lawrence and Alvarez wanted atomic physics to grow big – financially, instrumentally, organisationally. Theory came cheap; experimental equipment was expensive. The instruments used to find out new things about atomic structure have been some of the most costly scientific kit ever constructed. Most commentary on postwar physics dwells on the knowledge that was produced, but the equipment that was built to obtain that knowledge played an enormous role in the lives of scientists and in defining what it was they wanted. It was their military and political allies who made possible the colossally expensive instrumentation that transformed atomic physics into the biggest bit of Big Science.The primary scientific task was to discover new subatomic particles. Cosmic rays had enormous energies and they came free, streaming down from the sky, but accelerators could manipulate particle beams and make collisions more controllable. There were physicists who hoped for ‘some easy way’ to generate high-energy beams, but Alvarez thought ‘the best thing to do was use brute force.’ Lawrence’s cyclotrons accelerated charged particles in a spiral path; the larger the radius of the spiral, the higher the energy of the particles. Alvarez wanted to build a linear accelerator – a ‘linac’ – which could generate much greater energies. (When the particle beam travels in a straight line, it doesn’t lose energy through curving.) The linearity made it a simpler matter to boost the energy of the beam at intervals along its path, and the instrument could be made as long as you liked and had the real estate to accommodate it – Alvarez’s first design for a linac in the Berkeley hills was two thousand feet long. Radio frequency oscillators were used as the boosters: the military had mountains of surplus radar sets to do the job, six hundred of which General Groves secured for Alvarez.