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DOCUMENTS just released show unequivocally that the renowned German physicist
Werner Heisenberg was building an atomic bomb for his country during the Second
World War. The revelations, in letters and notes made public last week by the
Niels Bohr Archive in Denmark, lay to rest a controversy that has spanned 60
years.

After the war, Heisenberg said he had done his best to sabotage Germany’s
bomb project so that the Nazi government would not get the deadly weapon. But
the unsent letters, written to Heisenberg by Bohr after the war, reveal that
during a visit to Copenhagen in 1941 Heisenberg confessed to his former mentor
that he was working on a bomb. Furthermore, Heisenberg told Bohr he was
confident of success.

Bohr’s first letter, written in 1957, appears to be a direct response to
Heisenberg’s denial of involvement with the bomb. In the letter, Bohr, states
that during the 1941 meeting, “you spoke in a manner that could only give me the
firm impression that, under your leadership, everything was being done in
Germany to develop atomic weapons”.

He continues: “You said there was no need to talk about details since you
were completely familiar with them and had spent the past two years working more
or less exclusively on such preparations.” Bohr never sent the letter, although
he crafted several drafts that he gave to his wife, Margarethe, and son, Aage,
to type.

Historian Gerald Holton of Harvard University told 91av
that the release of the letters confirms what many historians already suspected.
“We now know the truth has come out,” he says. He adds that there is no question
Bohr’s recollections were accurate. “Bohr was a superb scientist well known for
his caution.”

The Bohr family initially decided to wait until 2012 to release the letters,
but recent interest led them to order the early release of the letters. The
controversy over Heisenberg’s role was the subject of a successful play,
Copenhagen by Michael Frayn.