How Was the Atomic Bomb Made?

Summary

Hi everyone, welcome to Cold-Knowledge Blind Box. I'm your user host, Qiao Yulan. Autumn is slowly settling in here in Shenzhen. This episode, let's get straight to some "hot" knowledge: how the first atomic bomb was made. Doing something big comes down to unity of knowledge and action. First you need an understanding of the principles of the atomic bomb, then you verify them in the laboratory, and finally you achieve mass production.

When it comes to the theoretical foundation of the atomic bomb, everyone's first reaction is probably Einstein, sticking out his tongue, writing E=mc² on a blackboard. That's the mass-energy equivalence equation.

E stands for energy, m is the mass of the object at rest, and c is the speed of light. Put in just 1 gram of mass, and you get the terrifying amount of energy that would take 21,400 tons of TNT to produce. The formula is so elegant and concise that with just a little explanation, most people can grasp how one could obtain enormous energy.

But to invent the atomic bomb from that formula alone would be too much like a fairy tale. Einstein proposed the mass-energy equivalence in 1905, but it was only a by-product of special relativity. Even Einstein thought that converting mass into energy was theoretically feasible, but with the engineering capabilities of the 20th century, it was basically impossible in reality.

So at that time, no scientist was seriously trying to figure out how to turn mass into energy. As a result, for the 28 years after the mass-energy formula was proposed, exploration in this area basically stagnated.

Then came 1933, a year that would change the fate of every European. The gears of destiny began to turn. The London Times ran a report: scientists at Cambridge University had discovered a fundamental particle called the neutron. If you used the neutron as a projectile to strike an atomic nucleus, it would cause the nucleus to split and release new neutrons.

Meanwhile, the headline in German news was that the Nazi Party had won the majority of seats in the Reichstag, and Hitler was about to become German chancellor. Putting the two side by side, a Jewish scientist named Leo Szilard decisively chose to flee to England. He even tried earnestly to persuade another Jew to leave too, and that was Einstein. Of course, this was not the only thing Szilard contributed, and we'll come back to him later.

After arriving in England, Szilard studied the research done at Cambridge carefully, and suddenly realized that it was essentially a positive feedback system. As long as you controlled the various input parameters, choosing whether to release or absorb neutrons, you could decide whether the splitting of the nuclei could be sustained. This is the basic principle of the chain reaction. At that point, the theoretical barriers to the atomic bomb were basically cleared away, and what remained was to verify the theory in the laboratory.

In 1938, Germany formally annexed Austria, and Hitler revealed his ambitions. At this critical moment, the German scientist Otto Hahn, while cleaning up the products of nuclear fission, unexpectedly found that the mass of the products seemed a little less than that of the original material. After ruling out measurement error, Hahn still couldn't find a suitable theory to explain the phenomenon. After all, Einstein had already left Germany, and normal communication among scientists had been cut off by the shadow of war. So Hahn wrote to another scientist, Lise Meitner, to ask.

Ms. Meitner was herself a heavyweight. She had been nominated 29 times for the Nobel Prize in Physics and 19 times for the Nobel Prize in Chemistry. After seeing the results in Hahn's letter, she proposed a bold hypothesis: that the missing mass had been converted into energy. Not only that, she quickly calculated that each fissioned nucleus would release roughly 200 million electronvolts of energy.

Ms. Meitner sent the results back to Hahn, and she also shared her findings with another giant of quantum physics, Bohr.

Yes, if you look at this round of events, you'll notice that the major discoveries and progress were basically made by German scientists, or by foreign scholars teaching at German universities. If history had taken a different turn, then in some parallel universe, the first foreign language we'd have to learn might be German, not English.

Bohr was a Danish scientist and a towering figure in atomic physics. We'll mention him many more times later. In 1939 he set off for the United States, and in Washington he gave an academic lecture on what Hahn had discovered about nuclear fission and the latest developments. The lecture was held in the morning, and it stunned the audience. Many scientists rushed back to their labs that very afternoon and worked through the night to reproduce the experimental results. The scene was as lively as the earlier rush to verify superconductivity.

Soon, the experimental results came out. But American physicists felt a chill run down their spines, because the Germans had taken a comprehensive lead over the Americans, and at any moment they might develop a world-destroying atomic bomb. At this point, awareness among a small circle of physicists was not enough. They had to persuade the government to invest massive resources to catch up immediately!

In August 1939, the far-sighted Szilard found Einstein, who was already in America, and explained his concerns. He hoped that, with Einstein's influence, Einstein would write to the President to convey how serious the situation was. Also present were two other Jewish scientists, Eugene Wigner and Edward Teller. By the way, Teller also has another name: the "father of the hydrogen bomb."

These four Jewish scientists discussed together the letter to be sent to Roosevelt, and clearly explained the terrifying power of the atomic bomb, which could destroy an entire city. America was seriously behind, and had to catch up at once. The letter was written. Now, just send it to the President quickly. With Einstein's prestige behind it, surely the President would take a look?

That's a bit naive. Imagine one day a highly respected physicist hands you a letter full of technical jargon. You can half-guess that the conclusion is that you only need one AA battery to power your NIO car for days and nights on end. What's your reaction? Don't you have a bit of doubt in your heart too?

What's more, at that time Germany was only 29 days away from invading Poland, and America was still following a policy of isolationism. How could a President who was busy with countless affairs be persuaded to make a decision that would change the fate of mankind on the spot?

Even more awkward, none of the four people knew President Roosevelt personally, and they had hardly dealt with government officials. If they had simply stuck stamps on the letter and mailed it to the White House, the most likely result would have been a thank-you card from the White House, and nothing would have changed.

In the end, they still had to rely on Szilard. He had an old friend named Sachs, who frequented the glittering world of Wall Street and was then serving as an economic adviser at Roosevelt's side. After a brief explanation from Szilard, Sachs understood how important the matter was, and patted his chest to say that stopping the Nazis was no trouble at all.

Don't underestimate this seemingly insignificant task of delivering the letter. It's fair to say that without Sachs's cleverness and erudition, even if the letter had actually been shown to Roosevelt, it would not have had much effect. Let me describe a suffocating scene to show you how hard it was: how would you report to your boss, and persuade him to tilt a huge amount of resources toward a pie you've drawn for him?

The full name of this letter is the "Einstein–Szilard Letter." If you have the chance, you can look it up yourself, and you'll understand how far from easy this whole thing was.

Sachs waited until Hitler formally invaded Poland, then found the right moment to hand the letter to Roosevelt. At first Roosevelt was very reluctant to read the letter, because it was full of physics terminology. As the President grew more and more impatient, Sachs slowly told him a historical story. In 1803, the American Robert Fulton invented the world's first steamboat. He then went to see the French Emperor Napoleon, hoping to persuade Napoleon to invest in and build the project, arguing that it could be used to defeat the British navy. But Napoleon bluntly pointed out the flaws of the steamboat, declaring that the technology was far too immature and could never cross the English Channel. As a result, France's naval construction fell far behind Britain's.

Sachs then changed the subject: the atomic bomb is the steamboat of our era, a revolutionary new invention. Mr. President, you must not play the second Napoleon! Roosevelt was deeply shaken by this, and immediately agreed that the government would take action right away. You see, listening to Cold-Knowledge Blind Box really does help. Who knows, a single story might be exactly what wakes a person from their dream!

So did America then rush headlong into building the bomb? Roosevelt's next move was merely to agree to set up an advisory committee specifically responsible for researching the atomic bomb. That was still a very long way from actually starting to make one. And at the time, the timing, the geography and the human factors were all against America.

In the next episode of Cold-Knowledge Blind Box, we'll introduce the key figure, Oppenheimer, and how he efficiently organized and managed a team of scientists. In a sealed-off desert, within three years, they caught up with the Germans, who had been far ahead, and finally built the atomic bomb, achieving a miracle in the history of human science and engineering.

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