New Twist on Physicist's Role in Nazi BombNew Twist on Physicist's Role in Nazi Bomb

February 7, 2002 


The leader of Hitler's atomic bomb program, Werner
Heisenberg, portrayed himself after World War II as a kind
of scientific resistance hero who sabotaged Hitler's
efforts to build a nuclear weapon. 

But in a series of letters and other documents made public
yesterday, his friend and onetime mentor, the Danish
physicist Niels Bohr, said that is not so. 

Bohr, who died 40 years ago, said that under his beloved
protégé, "everything was being done in Germany to develop
atomic weapons." 

In particular, the documents describe a meeting that
Heisenberg initiated between the two men in occupied
Denmark in September 1941. 

After the war, Heisenberg said he traveled to Copenhagen to
share his qualms about nuclear weapons. But the papers,
released by the Bohr family and posted on the Niels Bohr
Web site,, which is maintained by the Niels
Bohr Archive, tell a different story. 

Heisenberg did not travel to Copenhagen for the 1941
meeting to express moral qualms about building an atomic
weapon in wartime or to suggest that physicists on both
sides of the conflict should refuse to do so, according to
a passage in a letter Bohr wrote to Heisenberg, but never

He was moved to write his letter, the authenticity of which
seems beyond doubt, in 1957 when he read "Brighter Than a
Thousand Suns," a history of the atomic bomb, in which
Heisenberg is quoted offering his defense of his wartime

"You said that there was no need to talk about details,"
Bohr said, "since you were completely familiar with them
and had spent the past two years working more or less
exclusively on such preparations." 

Though historians and scientists agree that Bohr broke off
the meeting in shock, they have debated for decades what
actually happened that day. Did Heisenberg hope to save the
world from the horrors of the bomb, or was he really trying
to pry loose information on the parallel effort by the
Allies, which Bohr later joined? 

The mystery is the center of an award-winning play,
"Copenhagen," by the British playwright Michael Frayn. The
play was inspired by a 1993 book by the journalist Thomas
Powers, "Heisenberg's War," which argues that Heisenberg
destroyed the German project from within. 

The revelation made public yesterday "pretty much knocks
that out of the water," said Dr. David C. Cassidy, a
historian of science at Hofstra University who is the
author of "Uncertainty: The Life and Science of Werner
Heisenberg." "Heisenberg was working full blast on getting
as far as he could on nuclear fission, including a bomb." 

But others say questions about the meeting remain. One of
Heisenberg's sons, Dr. Jochen Heisenberg, who is now a
physicist at the University of New Hampshire, and Mr.
Powers, say the documents show that Bohr never understood
the message Heisenberg meant to convey in Copenhagen. 

Even Dr. Hans Bethe, the Nobel laureate who is one of the
last surviving physicists of the Manhattan Project, said
yesterday he believed that technical misunderstandings
between the physicists on what was then the cutting edge of
science caused them to talk straight past each other. 

"Bohr's letter does not clarify anything about the visit,"
Dr. Bethe said. "One talked with one set of assumptions and
the other with a totally different set of assumptions." 

But theirs is a minority view among historians of science.
"It is in some way appropriate that Frayn's play was
initiated by his reading of Thomas Powers's book," said Dr.
Gerald Holton, an emeritus professor of physics and of
history of science at Harvard. "It is clear that both of
them, now that we know Bohr's report, are essentially

The history of the documents and the physicists they
involve is nearly as interesting as the subject matter they

The two men met when Bohr gave a talk in Göttingen,
Germany, in 1922, by which time he was already known as the
major theorist of the atom. "Suddenly, up jumps a cheeky
pup and tells me that my mathematics is wrong," the
character Bohr recalls in Mr. Frayn's play. 

It was a 20-year-old Heisenberg, asking critical questions
from the audience. Bohr approached him afterward, took him
on as a protégé and together, they all but revolutionized
physics in the 1920's, playing a central role in the
development of quantum mechanics, the science of the very

But after their encounter in Copenhagen, Bohr broke off
nearly all contact with his former protégé. He escaped from
occupied Denmark in 1943 and made his way to England and
then to Los Alamos, N.M. 

No one knows why Bohr never sent the letter that was made
public yesterday. Perhaps the usually soft-spoken Bohr
regretted its strong language. But in characteristic
fashion, he dictated further drafts and notes on the
subject five years later. They appear in the handwriting of
his wife, Margrethe, of various assistants and of his son
Aage Bohr, another Nobel laureate. (In the play, the
character Margrethe complains lovingly about the endless
drafts she types for her husband, a deep thinker who was
known to revise physics papers as many as 100 times before
publishing them.) 

Dr. Finn Aaserud, director of the Niels Bohr Archive in
Copenhagen, said yesterday that the handwriting of all
three had been identified as authentic, leaving little
doubt that the documents are genuine. 

In an interview, Mr. Powers said he wished Bohr had sent
the letter to Heisenberg, so that the German physicist
could have responded to its charges. "My overwhelming
impression was one of sadness that they had never been
sent," Mr. Powers said. 

Bohr died in 1962, and during a conference on his work in
Copenhagen in 1985, Erik Bohr, another of Bohr's sons,
approached Dr. Holton and two others - the physicist Dr.
Abraham Pais and the presidential adviser McGeorge Bundy,
both now dead - with the first letter, asking for advice on
what should be done with it. 

Dr. Holton, who until now has been under a pledge of
secrecy regarding the contents of the letter, said all
three strongly recommended that the letter be preserved.
The family agreed, but because of the nature of the
contents, decided that none of the documents on the meeting
would be released until 2012, 50 years after Bohr's death. 

But in a talk during a conference on Mr. Frayn's play at
the Graduate Center of the City University of New York in
March 2000, Dr. Holton revealed that the letter existed.
And with the play - a hit in London and New York - interest
in the letter mounted, said Dr. Vilhelm A. Bohr, a grandson
of Niels Bohr, and a molecular biologist at the National
Institutes of Health in Baltimore. 

"There was such an active debate about it and we didn't
want to hold up anything that could be of interest to the
historians," Dr. Bohr said. "There's nothing that we need
to hide here." 

Despite the apparent clarity of the recollections in the
letters, said Dr. Jochen Heisenberg, Bohr may have been
confused by the militaristic, pro-German statements he
assumes his grandfather was required to make in public. 

In the letters, Dr. Heisenberg said, Bohr does not
distinguish "between what my father said in official places
and what he said in private." Perhaps Bohr became so
angered by those public statements that he did not listen
clearly when the two men spoke privately, Dr. Heisenberg

Although Dr. Vilhelm Bohr takes exception to Mr. Frayn's
portrayal of his own grandparents in certain respects - he
said that his grandmother Margrethe was not nearly so
outspoken as she is drawn - he still likes the
physics-saturated play. And he said the newly released
documents would do nothing to change that. 

"I still the think the show is very well done," Dr. Bohr
said. "People come away very challenged."

Copyright 2002 The New York Times Company