The Private Heisenberg and the Absent Bomb | Hacker News Reader

The Private Heisenberg and the Absent Bomb

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40 pointsal_olpimo16 comments

That's been a speculation for decades. Here's a more technical analysis of Heisenberg's calculation of critical mass.[1] He had a figure of tons of uranium. In reality, the bare-sphere critical mass of U-235 is 52Kg. The Hiroshima bomb, which was a very simple design, used 62Kg. With reflectors and compression, smaller amounts can be used.

Whether Heisenberg miscalculated this by intent or mistake remains unknown.

[1] https://www.mpiwg-berlin.mpg.de/sites/default/files/p467_3.p...

I like the irony of Heisenberg leaving a legacy of uncertainty.

Hitler's policies in Poland and elsewhere from 1939 on may have swayed Heisenberg from contributing to the German war effort. Thankfully, there never was a nazi A-bomb - paired with their cruise and ballistic missiles, the tide of war could have turned again even fairly late in 1944.

It's an interesting and somewhat romantic idea, but frankly I doubt that someone as intelligent as Heisenberg wouldn't have understand that whatever his calculation claimed, this wasn't going to stop with him.

But as the last part of the article explains, Heisenberg could probably count on his peers not looking too closely at whatever calculation he made, so long as it discouraged the project. And his peers, in this matter, at that time, were not many.

Popp 2016: "Misinterpreted Documents and Ignored Physical Facts: The History of ‘Hitler's Atomic Bomb’ needs to be corrected" is obviously unknown to the author of this article:

http://onlinelibrary.wiley.com/doi/10.1002/bewi.201601794/ab...

"It is shown that until the end of the war the German physicists did not know that an atomic bomb can only be made with fast neutrons, except Heisenberg, who, however, discovered it rather late, did not communicate it clearly and did not study any bomb physics. The physically correct interpretation of the documents reveals that the German physicists worked unsuccessfully on a reactor, which would have been a prerequisite for a plutonium bomb. But they did not know how to build a bomb because they never worked on a realistic bomb theory."

I don't know whether Thomas Powers is acquainted with this particular paper, but the paper itself makes it clear that Mr. Powers is well acquainted with many of the documents that form the basis of the paper. Popp's paper and Powers' article are about two different, albeit related, issues: Popp's purpose is to show that the German scientists' grasp of bomb-making has often been exaggerated (though not particularly so by Powers, who has been criticized by Walker for the opposite), while Powers' article considers whether Heisenberg's recently-published letters to his wife shed any more light on his purpose and motives. While knowing what he knew (and thought he knew) of bomb-making helps in analyzing his words and actions, physics alone cannot resolve the matter.

It's fairly fictionalized but the play Copenhagen uses a visit between Heisenberg and Bohr to explore this topic. There's a decent BBC version.

My impression (recalled over a decade or more) is that the play uses the meeting to launch into an exploration of the moral ambiguity and - yes - uncertainty surrounding Heisenberg's wartime role. The fictional dialog is much longer than the actual meeting apparently was, and it refers to events that were subsequent to that meeting. IIRC, it followed the publication of Thomas Powers' book on the topic but preceded the publication of the Farm Hall transcripts. I thoroughly recommend it.

There's also a play (Operation Epsilon) based on the Farm Hall transcripts. It's perhaps a bit too literal and has a lot of characters. That said, while I don't think it's in the same class as a work of theater as Copenhagen, I definitely recommend it if it comes around.

I think the play reverses the facts and their meaning. Bohr's response to the meeting included communications that jeopardized Heisenberg's life. It seems clear that Heisenberg was trolling for any excuse he could give to his German team to drag their feet, such as word from Bohr (true or false) that scientists on the other side would likely refuse to work on atomic weapons, or would do so if they knew the Germans would. Bohr refused to give that word, making a German bomb more likely, not less. This new article reinforces such a view.

And, I should add, starring Daniel Craig as Heisenberg.

A lot has been said about Heisenberg’s calculation of the critical mass of U 235. Many believe it to be his miscalculation. I think most people would agree that he was quite a ’good’ mathematician and yet the analysis in the Farm Hall transcript is at a level one would expect from a first year undergraduate. No mention of ’Laplace transform into spherical coordinates’, or more simply ’Fick Law’ on diffusion. When he talks about 10 tons of U235, Hahn (a chemist) reminds him that he has told him that only 50 Kg is needed. And later when Hahn askes how the bomb works Heisenberg talks of ’each neutron begets two children’ and that 1 ton is needed. A week later Heisenberg gives a very ‘polished’ lecture on the subject using the appropriate mathematical concepts. The question is did he work this all out in a few days or did he already know? Perhaps he had some ambivalence about putting such a weapon in the hands of someone slightly ‘unhinged’, a dilemma we have today!

As a foot note. Heisenberg was not the only one to foster the idea that the weight of such a bomb would be an impediment to its realisation. Both Heisenberg and Yoshio Nishina were students under Niels Bohr. Nishina went on to become Japan’s eminent physicist and to work on Japan’s own atomic bomb but even he had some ambivalence about such a weapon. As recorded in the minutes of the meeting on the 2nd July 1943 at Riken, Tokyo, after describing some technical aspects to Lt. Gen. Nobu-uji, Nishina adds “ that is to say, the weight of this thing would be enormous and because of this, the opinion is that it would not be suitable (as a bomb)”. すなわちボンブの重量甚大なるものとなるを以て、適当ならざるべしとの見解なり Sunawachi bombu no jyuryo jindai naru mono to naru wo motte tekito narazarubeshi tono kenkai nari.”

"Heisenberg's War" is about the possibility that Heisenberg either didn't try very hard or perhaps deliberately sabotaged the German bomb effort. Very controversial, great read.

https://www.amazon.com/Heisenbergs-War-Secret-History-German...

Heisenberg is a smaller part of this book; gripping read: https://en.wikipedia.org/wiki/The_Making_of_the_Atomic_Bomb

I think it would be horrible to be in a country with a leader like Hitler knowing a way to deliver them extraordinary power to do damage and destruction.

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