Of Atoms & Atomic Bombs: The Science Behind Oppenheimer

ON VISITING LOS ALAMOS, New Mexico, USA, the sound of silence hits you. No traffic noises, human voices, or drilling at construction sites. Just the swish of massive pine tree branches in the crisp breezes of the Pajarito Range mesa, two kilometres high. Walking gingerly on brown pine needles to the edge of a thirty-meter drop, the nearest town of Santa Fe fifty kilometres away is barely visible in the blue haze, over the empty sagebrush plain far below.

On July 16 1945, the 5.30 am dark and silence were shattered, at an Army munitions test site on the plains of New Mexico. A flash as blinding as a thousand noonday suns. An endless roaring wind, that sounded like the end of the world. And a giant mushroom cloud rising twelve kilometres to the sky, with lightning flashes of yellow, orange and purple. No ordinary bomb was tested at Alamogordo that day, and it came from no ordinary weapons project. Developed in the silent secrecy of Los Alamos Laboratory, it would end World War II, and change forever the world we live in. 

The movie Oppenheimer, directed and written by Christopher Nolan (Dunkirk, Interstellar) tells how J Robert Oppenheimer organised an extraordinary group of physicists, working feverishly from 1942, to merge a new physics of matter with a massive engineering of materials, to develop the world’s first nuclear bomb. The Manhattan Project, initiated by a letter to President Franklin Roosevelt from Leo Szilard and Albert Einstein, was driven by terrible fear. The world was at war for the second time in 25 years, and if Nazi Germany got the bomb first, then Hitler would win the war, control the world, and terminate 'sub-human’ races. 

Nolan’s tightly packed screenplay draws on the Oppenheimer biography American Prometheus by Kai Bird and Martin Sherwin, whose title refers to the Greek hero who stole the secret of fire from the gods. Chained to a rock, he was condemned to life: an eagle ripping at his body, for all eternity. The film is dominated by three characters: Director of the Manhattan Project, General Leslie Groves (Matt Damon, The Martian); Director of Los Alamos Laboratory, Dr Robert Oppenheimer (Cillian Murphy, Peaky Blinders); and Chairman of the Atomic Energy Commission, Commissioner Lewis Strauss (Robert Downey Jr, Ironman).

Also read | Long before Christopher Nolan's Oppenheimer, a 1946 short film featured the scientist as himself

Blockbusters are always entertaining, rarely instructive, and never need prior homework. Oppenheimer is an exception. Because not all viewers might know the technical terms (fission, fusion, critical mass, among others). Or get the context of some scenes (They cry out to Oppie: "You brought us quantum mechanics!"). And many may not catch the blink-and-miss-it 'subsidiary' characters (Bohr, Bethe, Fermi etc). A brief study of historical context pays off, in the delight of a deeper comprehension.

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In 1900, some said that Physics research might be over. Classical Newtonian models yielded universal laws that quantitatively explained the motion of planets around the sun; the nature of heat and efficiency of engines; the elasticity of steel beams; and the discovery that light was an electromagnetic wave moving through space at a speed c= 300,000 kilometres per second.

Only a couple of minor problems were left. When a metal box was heated, and a small hole was cut in the wall to probe the energy distributed over the inside light frequencies, then classical calculations were completely wrong! And the longstanding problem of Chemistry remained. The Periodic Table arranged elements in serial 'atomic numbers’, from Hydrogen (A=1) to Uranium (A=92). Elements showed a mysterious resonance in properties every 8 steps, like musical octaves sa, re, ga, ma... And a heated element emitted its own signature colour (sodium gave yellow light).

Max Planck of Berlin explained in 1900, the hot-box energy distribution, assuming radiant energies were only emitted in multiples 1,2,3…of an energy packet, or quantum. In 1924 Satyendra Nath Bose of Dhaka derived the same Planck distribution differently, by counting the distinct ways these identical light quanta or photons, could occupy energy states. (All photon-like quantum particles are now called Bosons.)

In 1913, Niels Bohr of Copenhagen proposed for Hydrogen a solar-system picture, where a negative electron was in specially allowed orbits around a nucleus of the positive proton. When an electron fell to a lower orbit, the extra energy was emitted as a light quantum of a characteristic colour. 

From 1925 onwards, these early mechanics of the quantum spoke German: it was formulated by Max Born of Goettingen and his PhD student Werner Heisenberg and by Erwin Schroedinger of Vienna. Atomic-number integers were the positive charges on the nucleus. These were also the total number of (negatively charged) electrons, that were in concentric shells. Since a shell was filled up with 8 electrons, before starting the next, the Periodic Table 'octaves' are understood.

A young American J Robert Oppenheimer, came to Goettingen in 1928 for a PhD with Max Born. They developed a 'Born-Oppenheimer' approximation, crucial to applying the new Quantum Mechanics to molecules composed of atoms.

After returning, Oppenheimer introduced Quantum Mechanics to the United States as noted in the movie scene. While in his 30s, he founded a leading school of theoretical physics at Berkeley. Remarkably versatile, he also worked on the unrelated General Theory of Relativity of Einstein, that said matter distorts the space-time around it, like a marble making a downward dip on a rubber sheet. 

Curiously, the mathematics allowed a singular downward spike or 'black hole’, that even trapped light! Oppenheimer and students showed how they could be generated. A star twice the mass of the sun, at the end of its life, could collapse gravitationally to end up as a black hole eventually detected. As seen in the movie, jubilation at this important publication Physical Review vol 55, page 455 (1939) was cut short: it was the day World War II began.

You may have read about recent Nobels awarded for black holes. The physicists Oppenheimer gathered in Los Alamos had also done important research earlier, and many later won the Nobel prize.

In 1927, Enrico Fermi of Rome, in work complementary to Bose, found an electron-like class of quantum particles, now called Fermions. For the Manhattan Project, Fermi set up in 1942, a nuclear reactor at Chicago, proving that controlled fission was possible. Heavy, unstable Uranium nuclei could split, and if each splitting released two speeding neutrons to hit another nucleus, then 2 became 4, 8, 16… in a chain reaction. At each step, a tiny amount of mass was lost, converted through E = mc², into a huge amount of fission energy (since light speed 'c' is a large number). 

Robert Serber wrote up these fission ideas for newcomers to The Lab in the Los Alamos Primer, now declassified as an online historical document. His wife Charlotte Serber was appointed the Group Leader by Oppenheimer for setting up the Los Alamos Library and managing classified research documents. Then, and now, women at Los Alamos are part of the Los Alamos story. Physicist Maria Goeppert-Mayer was later the second woman Nobel Prize winner after Marie Curie.

Hans Bethe of Cornel l was head of the Los Alamos Theoretical Division. In 1938 he found how stars shine. Hydrogen nuclei or protons (A=1), in stars, fuse into heavier Helium nuclei (A=2), again converting a tiny mass loss to a huge amount fusion energy, that we feel as the heat of our distant sun. The movie mentions a conjectured super-bomb, where a fission bomb 'fuse’, might set off a larger fusion bomb: a small piece of the sun. 

After the war, Edward Teller (who wore suntan lotion at the Alamogordo test site), was a strong supporter of developing The Super or fusion bomb. Oppenheimer was not, and was later accused of working against his country.

In striking, repeated scenes in the movie, Oppenheimer adds marbles to large and small fishbowls, to represent the accumulation of rare isotopes for two types of bomb materials. A cheer goes up, as required kilogram-level critical masses are reached.

The Uranium (“Little Boy”) and Plutonium (“Fat Man”) fission bombs killed 2,00,000 at Hiroshima and Nagasaki. Physicists naively thought the terrifying toll would end all wars. Now there are half a dozen nuclear-armed states. A nuclear WW III would kill tens of millions, and mushrooming cancers over decades, hundreds of millions more. 

"Those who do not remember the past are condemned to repeat it". Never again.

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Today, although Los Alamos National Laboratory still has a large X Division dedicated to nuclear stockpile stewardship behind chain-link fences and armed guards, the rest is no longer secret. The log cabin meeting place in the movie is now part of the Manhattan Project Historical National Park.

At the Bradbury Science Museum, wide-eyed schoolchildren click selfies with mock-ups of the human-size casings of Little Boy and Fat Man. The Theoretical Division of LANL has a stream of outside academic visitors, working with permanent Faculty on open problems of basic science. The academic culture is a supportive one, of competitive cooperation. Perhaps it goes back to the openness to thought and discussion of J Robert Oppenheimer.

The past determines the present, that in turn narrows the spray of possible futures. Technologies from 75 years ago are in constant use. Developed for bombing-raid warnings, Radio Detection and Ranging or RADAR now tells you of rainy weather and lands your plane safely. Early Manhattan Project work was done by human teams with mechanical calculators. Later electronic calculators were called by the job title of the young ladies they replaced — computers! Tech jobs directly trace back to the war, through John von Neumann and Alan Turing. Captured German V2 rocket scientists were seeds for the postwar NASA, that in turn inspired our (home-grown) ISRO and Chandrayaan missions. 

The Fermi Paradox says that if evolution is universal, then Where Is Everybody? Exoplanets outside our solar system were first detected in 1992. The nearest ones happen to be those orbiting the stars closest to Earth: the Alpha Centauri triple-star system is 4.4 light-years distant (at 3 lakh kilometres per finger-snap, about 10 trillion kilometres away). Perhaps in a sphere of a million light-years, we are alone.

Then how infinitely precious the blue-and-white marble is that we live on, surfaced with the glowing film of the only life in the galaxy.

Subodh R Shenoy is a theoretical solid-state physicist based in Hyderabad, India. He has made several academic visits to the (no longer secret) Theory Division of Los Alamos National Lab.