Andrej Karpathy's Reviews > The Making of the Atomic Bomb

The Making of the Atomic Bomb by Richard Rhodes
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Dec 13, 2016

it was amazing

For thousands of years man's capacity to destroy was limited to spears, arrows and fire. 120 years ago we learned to release chemical energy (e.g. TNT), and 70 years ago we learned to be 100 million times+ more efficient by harnessing the nuclear strong force energy with atomic weapons, first through fission and then fusion. We've also miniaturized these brilliant inventions and learned to mount them on ICBMs traveling at Mach 20. Unfortunately, we live in a universe where the laws of physics feature a strong asymmetry in how difficult it is to create and to destroy. This observation is also not reserved to nuclear weapons - more generally, technology monotonically increases the possible destructive damage per person per dollar. This is my favorite resolution to the Fermi paradox.

But I digress. Rhodes' "The Making of the Atomic Bomb" is a wonderful and exhaustingly detailed case study of the development of a transformative technology - the atomic bomb. The book is very thorough and covers the initial discoveries in nuclear physics, the early experiments, the government's intervention, the massive Manhattan project and its parallels in 4 other world powers, the associated secrecy, diplomacy, sabotage and espionage, and finally culminates with death and destruction at Hiroshima/Nagasaki and the associated political and ethical dilemmas.

I'll summarize the book to give an idea of what it's about and highlight some parts I found interesting.

The story of the bomb begins circa 1938 against the backdrop of an imminent second world war with a series of rapid discoveries that showed that if you shoot a neutron into a Uranium 235 isotope atom, the atom rapidly becomes unstable, breaks up and gives off 1) a lot of energy and 2) an average of 2.5 more neutrons. A number of scientists immediately realized that if you "chain" this effect you'd make a bomb. Making an atomic bomb therefore amounts to 1) isolating the U-235 isotope from natural Uranium (which is mostly (99.3%) an un-fissionable U-238), and 2) shooting one handful of U-235 into another at a high speed with some conventional explosive. Alternatively, a completely separate path was discovered: you could transform Uranium to Plutonium (which is much easier to separate) and create a bomb using a more complex implosion mechanism. Not knowing which path to take, the US ended up pursuing both a U-235 bomb ("Little Boy") and a Plutonium bomb ("Fat Man") with their entirely separate industrial processes. Amusingly, both paths converged within 3 days of each other in the summer of 1945, and the bombs were dropped on Hiroshima/Nagasaki respectively. This terrifying display of technological superiority forced Japan to accept an unconditional surrender and ended the second world war.

It was quite interesting to follow the political commitment of each world power in response to the scientific developments. The US established a committee in 1939 to investigate the potential of building a nuclear bomb but it crawled at a snail's speed for 3 years until almost half of the second world war was over, mostly due to the incompetence of key individuals (e.g. Lyman Briggs, who sat on the UK's MAUD report, or possibly Enrico Fermi who in an early meeting with Admiral Hopper cited the necessary critical mass as possibly being on the order of a small sun when he knew better). However, with the intervention of Oliphant et al. the US finally stirred in 1942 and started the Manhattan project. As for the other countries, paraphrasing, the UK was like: "Here US, we did a lot of the theory work but we're kind of busy dealing with Germany over here.", Germany was like: "This isn't going to be ready in 3-5 year time horizon and we're kind of in a lot of trouble, so we're going to poke at it a bit at most. Also, our anti-semitism cost us half of all nuclear physicists so that wasn't ideal.", Japan was like: "We can try our best but we don't really have the resources", and the Soviet Union was like: "We're kind of behind here so we're going to go all out on espionage."

The Manhattan project was a spectacular display of national technical achievement. Niels Bohr has said that "[building the bomb] can never be done unless you turn the United States into one huge factory". Luckily, it wasn't nearly as bad. In a few years, The Manhattan Project took ~$50B 2016 dollars, which was about 0.4% of the US GDP in its peak or only about 9 days of the total war spending. In its peak it employed about 125,000 people (about 0.1% of all workforce) and grew to be about as large as the 1945 US automobile industry. Most of its complexity went into the laborious process of isolating U-235/Plutonium from natural Uranium. Once the infrastructure was in place it was possible to produce several atomic bombs per month.

The bombs were not ready in time for the defeat of Germany in 1945, but Truman decided to use the bombs on Japan to 1) prevent further loss of American lives in face of Japan that was deeply dug in and clearly unwilling to surrender and, as is hinted at, 2) to justify the costs of the project. The Little Boy was dropped on Hiroshima and killed an estimated 70K people (eventually 200K by 5 years). The Fat Man was dropped on Nagasaki a few days later and caused 60% of that. What I did not realize was that these casualties were large but not astronomical. For example, a single day of bombing Tokyo with conventional explosives killed 100K people and injured 1M. What I also didn't know is that Liutenant General Leslie Groves (who was in charge of the Manhattan Project) was strongly in favor of dropping one of the bombs on Kyoto, the serene "Rome of Japan" established back in 793. Luckily, his plan was vetoed by the Secretary of War Stimson who refused to bomb the city due to its cultural significance. What the hell, Leslie? Unbelievable.

As I am a scientist myself, I was particularly curious about the extent to which the nuclear scientists who conceived and designed the bomb influenced the ethical/political discussions. Unfortunately, it is clearly the case that the scientists were quickly marginalized and, in effect, told to shut up and just help build the bomb. From the very start, Roosevelt explicitly wanted policy considerations restricted to a small group that excluded any scientists. As some of the more prominent examples of scientists trying to influence policy, Bohr advocated for establishing an "Open World Consortium" and sharing information about the bomb with the Soviet Union, but this idea was promptly shut down by Churchill. In this case it's not clear what effect it would have had and, in any case, the Soviets already knew a lot through espionage. Bohr also held the seemingly naive notion that scientists should continue publishing all nuclear research during the second world war as he felt that science should be completely open and rise above national disputes. Szilard strongly opposed this openness internationally, but advocated for more openness within the Manhattan project for sake of efficiency. This outraged Groves who was obsessed with secrecy. In fact, Szilard was almost arrested, suspected to be a spy, and placed under a comical surveillance that mostly uncovered his frequent visits to a chocolate store.

As a last curious historical note, World War 2 came at exactly the time when the very last conventional war could be fought. Given the advances in nuclear physics, starting a conflict a few years after 1939 would have been impossible due to the danger of all-out nuclear war in which everyone loses. I had also often thought about what would have happened if Germany did not execute Operation Barbarossa and open the Eastern front with the Soviet Union, which could have bought it extra time and resources to cause more havoc elsewhere in Europe/North Africa. This book provides the answer - the US nuclear weapon program was so far ahead of the German program that even if the war dragged on longer, Germany would have been reduced to irradiated ash.

It is almost impossible to do justice to this tome, so let me conclude by saying that the story includes awesome nuclear physics, science superheros, fanatical supervillans, massive factories appearing in the desert, political intrigue, British commandos on secret missions, explosions, oh and - it all actually happened. Great read, 5/5.



Additional Reading:

- Operation Epsilon, Captured Nazi Scientists at Farm Hall learning about the US dropping the Atomic Bomb: transcripts http://germanhistorydocs.ghi-dc.org/p... . Very interesting reading that features Heisenberg, Hahn et al. confronting the fact that US built and used nuclear weapons.
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Reading Progress

September 7, 2015 – Shelved
September 7, 2015 – Shelved as: to-read
September 20, 2016 – Started Reading
December 13, 2016 – Finished Reading

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