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Suppose a message was sent to the past with a diagram, description, and use, of the simplest fission weapon.

It didn't describe how to mine Uranium, enrich it, or even a description of WHY it works or atomic theory, but did indicate "U235 (and indicate element 92) needed to be separated and concentrated from U238".

If the USA or another superpower got the message, took it seriously, and wanted to build it, how early could humans have achieved this? Given that explosives, mining, atomic theory, and industry was pretty well along in 1900, I'd think 1900 or earlier. I suspect a sufficiently large enrichment plant would be the tricky part.

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    $\begingroup$ In 1900 nobody had any idea that isotopes existed; which is to say, they didn't even know that a chemical element might have more than one atomic species. They wouldn't have known that there was anything to separate. It was only in 1913 that Frederick Soddy showed that there were indeed multiple species of atoms with the same chemical properties. (He got a Nobel prize for this.) The first large-scale isotope separation facility was built during WW2, specifically for the purpose to make an atomic bomb, at considerable expense. $\endgroup$
    – AlexP
    Jun 29 at 22:20
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    $\begingroup$ "Considerable expense" is perhaps putting it lightly. The Manhattan project borrowed fifteen thousand tons of silver from the treasury for the centrifuges alone... centrifuges that also couldn't have been constructed much earlier than they were. $\endgroup$
    – jdunlop
    Jun 29 at 22:46
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    $\begingroup$ Yea, this is a material science issue, like Babbage's inability to cut gears with enough precision to make his difference engine work. As a rough estimate, if a person showed up in 1800 with all of the knowledge to build a nuclear bomb, he might crank one out in about seventy years, but he'd have to become an industrial magnate in order to gather the resources. $\endgroup$ Jun 29 at 22:55
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    $\begingroup$ @jdunlop: The funny thing is that the centrifuges failed and centrifugal separation was abandoned for the Manhattan Project. (Only after the war was the Zippe centrifuge invented -- in the Soviet Union by German prisoner engineers! The Americans got the design from one of the POWs when he was released in 1956.) The isotope separation for the Manhattan Project was eventually done using mainly gaseous diffusion and electromagnetic separation. $\endgroup$
    – AlexP
    Jun 29 at 23:03
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    $\begingroup$ Related (almost full duplicate): Nuclear weapons with 1850s technology $\endgroup$
    – Alexander
    Jun 30 at 5:41

1 Answer 1

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Probably Not Much Earlier Than We Did

The problem is less with the concept of a nuclear bomb - Enrico Fermi famously speculated as to the liberation of atomic energy for destructive purposes in the early 20s - and much, much more with the necessary materials science required to make the fissile material. It took thousands of centrifuges, billions of dollars, the accidental discovery of Teflon...

The "billions of dollars" part is also a big deal. It was \$2B to get to the first bomb's worth of material, in 1942 dollars. That would only have been $1.2B in 1900, assuming that individual tasks wouldn't cost more in real values (which it would), but that would have been 10% of the entire GNP of the time. It's hard to imagine, barring an existential threat (which WWI was not!) a country spending an amount of money nearly impossible to contemplate on something that atomic theory didn't yet support.

You'd also need advances in mining. Chemical leaching in place of traditional smelting.

By the time the US felt it needed an atomic bomb, it already had plenty of scientists who postulated that it was possible... and had all the other tools it needed, as long as it had the motivation to spend an enormous sum of money. In 1900, it didn't have the technology, nor any of the other tools. Knowing that it was possible wouldn't magically advance those - particularly lacking the motivation.

Addendum:

Per @AlexP's comment, the centrifuges weren't even successful, though they would be eventually. But I should also point out that prior to WWII, there wasn't really a country on earth that would be called a "superpower". Prior to WWI, the United States barely had an army!

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    $\begingroup$ This is a great answer - I'd also add that, even with a good understanding of the atomic theory, even with the necessary uranium, it's still a pretty daunting task, involving a bunch of accidents (the demon core incident), stuff just not working, and a lot of creative solutions to work round the existing tech and materials science $\endgroup$
    – lupe
    Jun 30 at 5:18
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    $\begingroup$ Great answer, +1, but prior to WWII, there wasn't really a country on earth that would be called a "superpower"': The British empire would have been considered a superpower by the current understanding of the word. $\endgroup$
    – User65535
    Jun 30 at 8:54
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    $\begingroup$ @Hobbamok - they really wouldn't. The USA eclipsed them in terms of gross GNP before 1900. No one had the manpower/resources necessary. $\endgroup$
    – jdunlop
    Jun 30 at 9:11
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    $\begingroup$ @Hobbamok - that's the point. To make an atomic weapon, you need enormous industrial capacity. That is the resource you require, and the resource they lacked. $\endgroup$
    – jdunlop
    Jun 30 at 9:14
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    $\begingroup$ I suspect a sufficiently large enrichment plant would be the tricky part. "When it was built in 1944, the four-story K-25 gaseous diffusion plant was the world's largest building, comprising over 5,264,000 square feet (489,000 m2) of floor space and a volume of 97,500,000 cubic feet (2,760,000 m3)." - "By 31 December 1946, when the Manhattan Project ended, 110,048,961 man-hours of construction work had been performed at the K-25 site. The total cost, including that of K-27, was $479,589,999 (equivalent to $5.57 billion in 2020)." $\endgroup$
    – Mazura
    Jun 30 at 10:27

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