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The Uncertainty Principle
A UNH professor speaks about his famous father

In the fall of 1941, German physicist Werner Heisenberg paid a visit to Niels Bohr, his longtime friend and mentor, in Copenhagen, Denmark, which was under German occupation. Exactly what happened during their brief meeting has been the subject of speculation ever since. It's also the subject of the Tony Award-winning play "Copenhagen," which has reopened a heated debate about Heisenberg's presumed role in the German effort to build an atom bomb during World War II.

Werner Heisenberg at chalkboard - Photo courtesy of Jochen Heisenberg
Werner Heisenberg - courtey of Jochen Heisenberg

In the '20s and '30s Heisenberg, working closely with Bohr and others in Copenhagen, laid the foundation for quantum mechanics. He was awarded the Nobel Prize in 1933 and is best known for the Uncertainty Principle, which states that it is impossible to measure both the exact position and the exact momentum of any subatomic particle at any given time. The more precisely one of the quantities is measured, the less precisely the other is known. "Copenhagen" makes an artistic use of this principle by applying it to human motivation and memories, which are similarly difficult to determine accurately.

Werner Heisenberg in Leipzig - Photo courtesy of Jochen Heisenberg
Heisenberg in Leipzig, circa 1929 - courtesy of Jochen Heisenberg

The play, written by Michael Frayn, re-enacts the meeting between Bohr and Heisenberg several times from different perspectives, reflecting different interpretations of what was said and what it meant. At the center of the confusion is Heisenberg's stated knowledge of atomic bombs and the question of whether he would use his knowledge to Hitler's advantage. What was he trying to tell Bohr about his intent?

When "Copenhagen" opened on Broadway, the glare of the footlights reflected all the way to UNH, where Heisenberg's son, Jochen, has been a professor of physics for almost 25 years. He has since become an outspoken public voice on his father's behalf, maintaining that Werner Heisenberg convinced the Hitler regime of the enormous difficulties in building an atomic bomb, persuading it to forgo such a program in favor of quicker weapons and rockets. Heisenberg's own research remained focused on nuclear reactor development until the end of the war.

Jochen Heisenberg sitting - Photo by Perry Smith
UNH physics professor Jochen Heisenberg believes his father tried to prevent Hitler from building an atomic bomb. Photo by Perry Smith/UNH Photographic Services

In February, responding to the public interest generated by "Copenhagen," the Niels Bohr Archive released drafts of letters that Bohr wrote to Werner Heisenberg in 1958 and rewrote several times over the next few years. In one letter, which was never sent, Bohr recalled 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 wrote.

Copenhagen playbill - Photo courtesy of Jochen Heisenberg
Michael Frayn's play "Copenhagen" explores the uncertainty surrounding Werner Heisenberg's role during the war years. - courtesy of Jochen Heisenberg

But Bohr misunderstood what was going on that night, according to Jochen Heisenberg, who points out that in Hitler's Germany and especially on trips abroad, his father could not talk openly due to constant surveillance. "My father said that when he started to talk [to Bohr] about nuclear weapons, he was extremely guarded and tried to say everything between the lines,"Jochen Heisenberg recalls. "My father hated the Nazis with a passion." If Werner Heisenberg had told Bohr or anyone else what he really believed or what he was really doing, he would have risked execution for treason.

Elizabeth and Werner Heisenberg standing with Neils Bohr in Copenhagen, 1937 - Photo courtesy of Jochen Heisenberg
Elisabeth Heisenberg, Niels Bohr, and Werner Heisenberg together in Copenhagen, 193. - courtesy of Jochen Heisenberg

After the war, Bohr and Werner Heisenberg met on a couple of occasions, but they never discussed their wartime experiences or cleared up the questions surrounding what had been said in Copenhagen. Bohr's letter, written so many years later, records his impression of the meeting, but it does not prove that this impression was correct, Jochen Heisenberg points out. ~

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