Dear Heisenberg
I hereby send a reprint of a Rutherford Lecture in which I have
tried to tell a little about my memories of the developments prompted by the
discovery of the atomic nucleus. As you have seen from the small article I
wrote for your 60th birthday and from my lecture at the opening of the 50-year
anniversary Solvay Meeting, I have been much occupied in recent years with
historical studies of physics, which incidentally have now been taken up by an
American committee established by the Washington Academy and the Carnegie
Foundation, and the intention is that in the coming years Kuhn, who is to lead
the project, will have a fixed base in Copenhagen for a secretariat and an
archive.
While occupying myself with such matters I have, of course, many
times felt the difficulty of giving an accurate account of developments in
which many different people have taken part, and I have felt this most strongly
in describing what took place during the war in connection with the atomic
energy projects. In the latter case there has been very keen interest from
various quarters, and the governments of several countries have even begun
investigations using existing archives.
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Similarly, committees have been established in various countries
in order to shed light on the discussions and preparations during the war that
preceded the application of the results of atomic physics for military
purposes, and from many quarters I have been asked in particular about the
arrangement for and the purpose of the visit by you and Weizsäcker to
Copenhagen in 1941.
This has been very difficult for me to answer since, as you know
from our conversations after the war, I have a completely different perception
of what took place during the visit than that you have expressed in your
contribution to Jungk’s book.
For us in Copenhagen, who found ourselves in such a difficult and
dangerous position during the German occupation, the visit was an event that
had to make a quite extraordinary impression on us all, and I therefore
carefully noted every word uttered in our conversation, during which,
constantly threatened as we were by the surveillance of the German police, I
had to assume a very cautious position. I am thinking not only of the strong
conviction that you and Weizsäcker expressed concerning German victory, which
did not correspond to our
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hopes, but
more of how, during the course of the war, your conviction had to become less
strong and finally end with the certainty of Germany’s defeat. Therefore it
would not be incomprehensible if it were difficult for you to keep track of
how, against the background of changing circumstances, statements on the part
of the Germans changed from year to year. On the other hand I remember quite
clearly the impression it made on me when, at the beginning of the
conversation, you told me without preparation that you were certain that the
war, if it lasted long enough, would be decided with atomic weapons. I did not
respond to this at all, but as you perhaps regarded this as an expression of
doubt, you related how in the preceding years you had devoted yourself almost
exclusively to the question and were quite certain that it could be done,
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but you
gave no hint about efforts on the part of German scientists to prevent such a
development.
It is true that, during his visits to Copenhagen in 1943 on his
journeys to Norway to participate in the efforts to increase the production of
heavy water, Jensen did make hints in such a direction, but because of his own
mission and the constantly growing rumours of new German weapons, I necessarily
had to be very sceptical and extremely cautious in my ever more dangerous
existence. It was only a few months later when, in order to avoid imminent
arrest by the German police, I escaped to Sweden and arrived in England that I
heard about the great preparations that were under way there and in the USA and
how far they had come. The question of how far Germany had come occupied not
only the physicists but especially the govern-
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ment and
the secret intelligence service, and naturally I had to tell the latter and
some members of the government about all the experiences we had had in
Copenhagen and in particular about the visits by you and Weizsäcker and Jensen,
which gave rise to thorough discussions about the conclusions which could be
drawn about the information given during the conversations and their comparison
with everything that the intelligence service had been able to obtain. The
point which was put forward during these discussions, and with which all later
enquiries have been particularly concerned, was how the visit had been arranged
and what purpose lay behind it, as one has wondered in particular how and with
what authorization such a dangerous matter, of such great political importance,
could be taken up with someone in an occupied and hostile country.