Like we all who built it first and all, but how did the humans know that such a weapon could be possible to build with so much capability? Was there research from older scientists and physicists that led to the idea that such a thing was possible and only needed to be built?
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> Was there research from older scientists and physicists that led to the idea that such a thing was possible
That’s basically all of science. It’s what they mean when they say discoveries are made on the shoulders of giants.
That said, the discovery that introduced the idea of atomic bombs was quantum mechanics. Quantum mechanics was able to explain a lot about how atoms and radioactive decay it worked. Using it, scientists were able to understand that a lot of energy existed in larger atoms and when they decay, they could release a lot of energy. And anything that releases a lot of energy at once can be made into a bomb…
It’s the most cliche physics thing possible, but it all traces back to Einstein.
When he discovered that “General relativity” was a better model of reality than Newtonian physics, one of the consequences was that energy and mass could be substituted for each other. That is to say, you could turn a little bit of mass into a lot of energy.
That’s where Enrico Fermi comes in. He’s faffing about with Uranium, and thinks he created a new element by smashing a neutron into it. But it turns out that he didn’t create a new element, he had instead split that Uranium, and released a lot of energy in the process.
So then all you need is an isotope that releases more than 1 neutron when it is split apart, and you could get a chain reaction that could sustain itself into a bomb.
That isotope is Uranium 235.
There’s a lot of history to this but.
In the early 1930s we discovered the neutron. At this point we had only thought of atoms made up of protons and electrons, the discovery of the neutron filled some holes in physics that were previously very confusing.
A pretty famous physicist named Enrico Fermi ended up trying to run experiments using neutrons to try to create new elements, the idea was that if we threw neutrons at uranium atoms we could get elements beyond uranium as a product of the reaction. So he got to work, and did it. He ton a chunk of uranium, threw neutrons at it, and did the thing that for centuries was thought impossible, transmutation. In that chunk of what was pure uranium they found something that didn’t match the properties of any element they had known so far. This meant they had made a new element. For this Fermi won a Nobel prize in the late 1930s.
Except he was wrong. Fermi only checked for elements up to lead, he didn’t expect there to be any atom smaller than lead. What he had actually done is split the uranium atom into tow smaller atoms. Not just that, based on the elements it created, what we found out was it had also released a few neutrons into the wild when splitting these atoms, a few neutrons ended up missing from the byproducts. Fermi’s mistake was discovered by two German scientists, Hahn and Meitner, at the cusp of World War II.
The fact that this process both cost a neutron and released a neutron lead to the idea that what if there could be a chain reaction, the released neutron could again fuel this reaction in another atom, and with more neutrons released per reaction it would suddenly burn through all the uranium. We had know there was some energy holding these atoms together from the radioactivity they emitted, physicists put two and two together and figured there’s a good chance this could be used to make energy. And a lot of energy, all at the same time, in the same place. In other words, a bomb.
A few scientists were alarmed at this, especially that it was Nazi Germany that had made this discovery. Einstein famously sent a letter to President Roosevelt that this could be possible and that they needed to build it before Germany could. Roosevelt started the Manhattan Project to try to build it, but first they needed to run a proof of concepts.
To test this, Fermi, now in the US because he got run out of Fascist Italy as a Jew, built the worlds first nuclear reactor under the stadium at the University of Chicago, promising that his calculations said it wouldn’t blow up, just heat up a little bit. Essentially this was a larger scale version of fermi’s previous experiment, they got a massive amount of uranium, piled it up, and shot neutrons at it. And low and behold, it warmed up just slightly, just enough to show that energy was in fact being released by this reaction.
This led the green light to start testing different materials for their fission possibilities and start actually working on getting a bomb.
Lise Meitner. She is how.
Lise Meitner (7 November 1878 – 27 October 1968) is the physicist that the element meitnerium (109) is named after. She came up with the theoretical basis for nuclear fission upon receiving the results of an experiment by a colleague of hers, chemist Otto Hahn.
A Jewish woman, she was born in Austria but lived her later life in Sweden, to which she had fled after her citizenship was revoked during the *Anschluss*. Her work discovering fission was done in Sweden, in the forests around Kungälv near Gothenburg, after receiving a correspondence from Hahn containing his results.
[An article by Jeremy Bernstein](https://inference-review.com/article/the-discovery-of-nuclear-fission) describes the historical moment when she discovered that an atomic bomb was possible, as related primarily by her nephew, Otto Frisch:
>>When I came out of my hotel room after my first night in Kungälv I found Lise Meitner studying a letter from Hahn and obviously worried by it. … Its content was indeed so startling that I was at first inclined to be skeptical. Hahn and Strassmann had found that those three substances [formed by bombarding uranium with neutrons] were not radium, chemically speaking; indeed they had found it impossible to separate them from the barium which, routinely, they had added in order to facilitate the chemical separations. They had come to the conclusion, reluctantly and with hesitation, that they were isotopes of barium.
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>Frisch asked whether Hahn and Strassmann might have made a mistake, but his aunt was adamant:
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>>No, said Lise Meitner; Hahn was too good a chemist for that. But how could barium be formed from uranium? No larger particles than protons or helium nuclei (alpha particles) had ever been chipped away from nuclei…
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>>At that point we both sat down on a tree trunk … and started to calculate on scraps of paper. The charge of a uranium nucleus, we found, was indeed large enough to overcome the effect of the surface tension almost completely; so the uranium nucleus might indeed resemble a very wobbly, unstable drop, ready to divide itself at the slightest provocation, such as the impact of a single neutron.
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>The pair then proceeded to work out for the very first time the physical characteristics of nuclear fission:
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>>But there was another problem. After separation, the two drops would be driven apart by their mutual electric repulsion and would acquire high speed and a very large energy, about 200 MeV in all; where could that energy come from? Fortunately Lise Meitner remembered the empirical formula for computing the masses of nuclei and worked out that the two nuclei formed by the division of a uranium nucleus would be lighter than the original uranium nucleus by about one-fifth the mass of a proton. Now whenever mass disappears energy is created, according to Einstein’s formula E = mc2, and one-fifth of a proton mass was just equivalent to 200 MeV. So here was the source for that energy; it all fitted!
Word spread. Danish physicist Niels Bohr took word of the discovery to a lecture he was giving at Princeton. Two Princeton scientists attending the lecture took word back to Columbia University, where Enrico Fermi, an Italian physicist, had recently been offered a job after fleeing Fascist Italy with his Jewish wife. He relates:
>…I remember one afternoon Willis Lamb came back very excited and said that Bohr had leaked out great news. The great news that had leaked out was the discovery of fission and at least the outline of its interpretation. Then, somewhat later that same month, there was a meeting in Washington where the possible importance of the newly discovered phenomenon of fission was first discussed in semi-jocular earnest as a possible source of nuclear power.
Notice how, even on the verge of war, as scientists were fleeing countries left and right to avoid the racial oppression that would become known as the Holocaust, still the memory is not of the bombs that could be made, but of a bright nuclear-powered future.
* On March 18, 1939, Fermi gave a lecture to military leaders at the Navy Department warning them of the potential impact of nuclear power.
* On August 2, 1939, four scientists, including Einstein, sent a letter to President Roosevelt asserting that Nazi Germany would probably try to build an atomic bomb. Roosevelt took notice.
* The Manhattan Project developed a bomb, and the rest is history.
Think about how food gives you energy (literally in this case). For reference, a jelly donut has about as much energy (measured in calories) as a stick of dynamite.
Once you get a sense for how much energy is locked up in boring stuff like food, and then find something that is much more interesting (like plutonium), an atom bomb is a more natural thought.
If you have time in your hands, Richard Rhodes’s book ‘The Making of the Atomic Bomb’ is a superb story of how a crisis in 19th Century physics led to the discovery of the atom, then the nucleus, then the neutron – and from there how the energy in the uranium nucleus was first liberated through to the destruction of Hiroshima and Nagasaki. It puts the bomb in context and makes it clear that the bomb was inevitable and its use almost certain.
After Hahn and Meitner’s experiment, it was a conversation with Otto Frisch that produced the idea of fission and the very first estimate of how much energy was released when uranium was split. Their work suggested that each fission would release one or two neutrons, and that inspired Leo Szilard who had already come up with the idea of a chain reaction in 1933, but had never considered uranium. In 1939, the idea of a chain reaction in uranium was patented by a team led by Frederic Joliot-Curie – including the idea for a nuclear bomb.
Szilard and Fermi had come to the same conclusion about the same time and alerted the American government to the possibility by a letter signed by Einstein. Meanwhile, the British were taking an early lead; Otto Frisch and Rudolf Peierls had fled Nazi Germany and were working at the University of Birmingham. They produced the first broad outline of a theoretical bomb, including an estimate of the critical mass of uranium needed in early 1940.
Their work became a government project called TUBE ALLOYS which worked out many of the techniques needed to build a uranium bomb, but the UK did not have the spare industrial capacity and was too close to German bombing to realistically build a bomb, so the project was shared with the United States who made up for lost time and actually did it.
If you’re really interested in this, Richard Rhodes’ “The Making of the Atomic Bomb” is a great read (Pulitzer Prize and National Book Award).
And, fun fact – the Hiroshima bomb was never even fully tested – it was an absurdly simple (and inefficient) design, where only a tablespoon or so of matter was converted to energy. It was so basic “it had to work”. The Trinity test (and the Nagasaki bomb) was a much more complicated design – almost impossibly complex, using shaped high explosives with precision-timed detonators to compress a perfect sphere about the size of a basketball down to a perfect sphere the size of a marble. Nobody had “assembled” anything with explosives before.
Lise Meitner was researching physics in the 1920’s and 30’s, and she figured how how to shoot a neutron at an atom, and was able to split an atom. The resulting reaction released a lot of energy.
https://en.wikipedia.org/wiki/Lise_Meitner
The Pulitzer Prize-winning book on this is “The Making of the Atomic Bomb” by Richard Rhodes. Chapter 1 is a classic.
“In London, where Southampton Row passes Russell Square, across from the British Museum in Bloomsbury, Leo Szilard waited irritably one gray Depression morning for the stoplight to change. A trace of rain had fallen during the night; Tuesday, September 12, 1933, dawned cool, humid and dull. Drizzling rain would begin again in early afternoon. When Szilard told the story later he never mentioned his destination that morning. He may have had none; he often walked to think. In any case another destination intervened. The stoplight changed to green. Szilard stepped off the curb. As he crossed the street time cracked open before him and he saw a way to the future, death into the world and all our woe, the shape of things to come.”
Excerpt From
Making of the Atomic Bomb
Richard Rhodes
https://books.apple.com/us/book/the-making-of-the-atomic-bomb/id424597501
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the making of the atomic bomb is one the best books ive ever read
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