Slashdot Mirror
Followup To Bohr-Heisenberg Meeting
December writes "As a follow up to this slashdot article, "The family of Niels Bohr has decided to release all documents deposited at the Niels Bohr Archive, either written or dictated by Niels Bohr, pertaining specifically to the meeting between Bohr and Heisenberg in September 1941. There are in all eleven documents. The decision has been made in order to avoid possible misunderstandings regarding the contents of the documents."
See the Niels Bohr Archive at http://www.nba.nbi.dk/"
One very important fact to remember is that the Russians (and Germans) around this time were using an incorrect estimate of the cross section of uranium, which did seem to indicate that sustained fission was not possible. The Americans managed to get a different (and later proven more accurate) measurement, which showed that a chain reaction was possible, this is one of the major reasons the Russians ended up so far behind at first in the atomic race.
The Germans and Russians certainly had a large initial lead in the more theoretical aspects of radiation and atomic physics, however this one incorrect measurement certainly threw the Russians so far off the track that it basically stopped their work in the area for quite a few years.
The Americans for a long time refused to believe how far behind the Russians were, and managed to loose much advantage by following politically 'suitable' beliefs rather than believing their own intelligence information, whcih turned out to be quite accurate with respect to the Russian position.
On the flip side, both of these men were great scientists, I personally feel it is immaterial whos 'side' they were on in a war.
What most people don't seem to know is that Heisenberg didn't visit Bohr alone. Carl Friedrich von Weizsäcker was also there, and he is still alive today.
He gave an interview with the Süddeutsche Zeitung one or two days ago. His recollection of the meeting is rather interesting (the interview is in German, sorry).
Firstly, he says that Heisenberg started an A-bomb project in 1939, in which Weizsäcker took part, but by 1941 they came to the conclusion that they would not be able to succeed before the war was over. The problem was the tremendous effort needed to separate the isotopes. So from 1941 on they were only interested in building a reactor. Once that worked (it never did, as the heavy water production was sabotaged) there might have been the possibility to create Plutonium and build a bomb with that. But they didn't expect this to happen before the war was over by conventional means.
The reason Heisenberg went to see Bohr, according to Weizsäcker, was that they didn't want the Americans or the British to build a bomb either. If they stated publically that they're not working on a bomb, then of course nobody would have believed them. But Heisenberg thought that they might believe Bohr. So he hoped that Bohr could convince the Allies not to build the bomb either. This was not motivated by pure pacifism - he didn't want Germany to get nuked.
In 1941 the war looked pretty good for Germany, they were winning on all fronts. So basically Heisenberg believed that a German victory was inevitable, but with conventional weapons. He tried to explain this to Bohr, who was shocked. Bohr may have understood Heisenberg's "inevitable" to mean that he WAS working on a bomb, and planning to use it. But Weizsäcker suggests that Bohr may well have understood correctly, and didn't want the Germans to win (conventionally), and therefor figured that the Allies would have to build a bomb, to avoid a Nazi victory.
What we can accept as quite reliable, is the following: (a) Heisenberg did lead an A-bomb project from 1939 to 1941. (b) He came to the conclusion that he couldn't build a bomb before the war was over. (c) He continued working on a reactor from 1941 onwards (possibly with the option of producing Plutonium for later weapons use).
And what also seem quite plausible: (d) that he tried to convince Bohr that he was only working on a reactor, not a bomb. This is what he claimed afterwards, and is backed up by Weizsäcker. Many people might not believe these two, so here is another interesting piece of the puzzle:
I read some time ago, either in Physics Today or in Scientific American that when Bohr came to Los Alamos, he brought with him a sketch which Heisenberg had made during his 1941 visit. Bohr claimed it depicted a bomb which Heisenberg was building, but the people at Los Alamos recognised it as a heavy water reactor. As far as I remember, the sketch depicted a large bottle, filled with water (presumably heavy water, but only labelled "H2O"), and some stuff inside. Can anybody dig up this sketch on the net? At any rate, this strongly suggests that Bohr had misunderstood Heisenberg, and mistook Heisenberg's reactor for a bomb.
"...Look on my works, ye mighty, and despair!"