Niels Bohr, Werner Heisenberg, and the Atomic Bomb
In September 1941, Germany had occupied much of Europe and was advancing across the Soviet Union toward Moscow. Under this shadow, long-time friends and physicists, Dane Niels Bohr and German Werner Heisenberg, met in Copenhagen. There is no contemporary account of what the two men discussed, but the outcome of their exchange was to have a profound effect on how World War II played out.
In 1938, three scientists in Berlin, Germany showed that the atom could be split. If the atom was of a radioactive element such as uranium there was a immediate and extremely powerful release of energy. A nuclear bomb was possible, at least in theory.
This was a matter of great interest to Niels Bohr. The Dane had won the Nobel Prize for Physics in 1922 for his theories about the structure of atoms and the emission of radiation.
Meanwhile, Werner Heisenberg was demonstrating a brilliant understanding of advanced mathematics and was studying physics at the University of Munich. With his doctorate completed, he spent much of 1925 studying and researching at Niels Bohr’s Institute of Theoretical Physics at the University of Copenhagen.
Bohr was 16 years older than Heisenberg and their friendship has been described as similar to that of the affection between a father and son.
Heisenberg returned to Germany to the post of professor of theoretical physics at the University of Leipzig. His work would lead to a Nobel Prize for physics in 1932.
Later, he became head of the Nazi program to develop an atomic bomb called the Uranverein, or Uranium Club. Bohr was also working in the same field. The race to develop a nuclear bomb was on; who got to the finish line first would win the war.
The 1941 Meeting
In September 1941, Werner Heisenberg was invited to give a speech in German-occupied Denmark and he took the opportunity to catch up with his colleague Niels Bohr.
What they talked about has been a matter of conjecture ever since.
Did Heisenberg try to get information from Bohr to help the Nazi nuclear program? Or, was he seeking advice from his mentor about the morality of developing a weapon of mass destruction to ensure victory for his beloved country?
In later years, both men had different recollections of what they talked about. They couldn’t even agree on where their meeting took place.
The very fact of the meeting placed both men in extreme danger. If it was known that Heisenberg revealed the existence of the secret German nuclear program he would almost certainly have been shot. If Bohr possessed knowledge of the research he would suffer the same fate. As a result, what was said between them, stayed between them – for a while.
Werner Heisenberg expressed his belief that German victory was preferable to German defeat and that scientists such as Bohr should get on board. Niels Bohr, a man of Jewish descent and living under Nazi occupation, would certainly have disagreed. This seems to be the basis of a conflict between the two men that was never resolved.
The second guessing about the meeting has continued to this day and Heisenberg usually comes out of it looking not so good. As a German nationalist, though not a Nazi Party member, he inevitably carries some of the stain on his character associated with the Holocaust. And, as it’s the victors who write the history of wars, he starts off at a disadvantage.
In 1956, the Swiss journalist Robert Jungk published his book Brighter than a Thousand Suns. In it, he quotes from a letter Heisenberg gave him about his recollections of the Copenhagen meeting.
According to the German scientist, he told Bohr he knew how to stall the Nazi nuclear program and called on the Dane to lobby Allied scientists to do the same. In Heisenberg’s version, he was making a gesture that could cost him his life to rally scientists behind an effort never to create such horrendous weapons.
When, Niels Bohr read Robert Jungk’s book he wrote a letter to his old friend in which he outlined a very different remembrance of the talks with his one-time colleague. However, he never sent the letter, and it was archived and sealed by his family after his death in 1962.
The matter lay fallow for years with historians left to speculate on what the two great scientists had discussed in 1941. Then, in 1998, playwright Michael Frayn wrote a drama entitled Copenhagen in which he imagines the two scientists, now dead, meeting and reviewing what they said in 1941.
The play’s success renewed the debate about how pivotal the meeting might have been to the outcome of the war and prompted the Bohr family to release the long-secret letter to Heisenberg.
Niels Bohr wrote that “you … expressed your definite conviction that Germany would win and that it was therefore quite foolish for us to maintain the hope of a different outcome of the war and to be reticent as regards all German offers of cooperation.
“… 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 …”
Bohr interpreted the 1941 discussion as an attempt to recruit him to the German war effort. His expertise would have proved an invaluable asset.
The Meeting’s Aftermath
In 1943, Niels Bohr was tipped off that the Gestapo planned to arrest him. With help from British intelligence he was spirited out of Denmark and joined the Manhattan Project, the Allied attempt to build an atomic bomb.
As we know, the Allied program was successful, if that’s the right word. By 1944, Germany’s industrial capacity was being crippled by Allied bombing and the nuclear program sputtered to a halt. There is speculation, helped along by Heisenberg's insinuations, that he deliberately sabotaged his country’s nuclear program. He never admitted to this because to do so would be confessing to betraying his own country.
Niels Bohr returned to Denmark and, in addition to continuing his work in theoretical physics, campaigned for what he called an “open world.” By this he meant that scientists should be able to travel without restrictions and to share their knowledge with one another. There would be full disclosure of all research and this would lead to a peaceful world.
One of the three scientists who showed, in theory, in 1938 that uranium could be split was Lise Meitner. However, as a woman, she was not admitted to the University of Berlin so she and her colleagues were forced to work on their groundbreaking research in a carpenter’s shop.
Some of the world’s most prominent scientists in the 1920s and ‘30s were German Jews who were driven into exile by the anti-Semitism of the Nazis. It is a great irony that had those brilliant minds stayed in Germany they might have made Hitler’s acquisition of an atomic bomb possible.
Niels Bohr was flown to England in 1943 in the converted bomb bay of an RAF De Havilland Mosquito bomber. However, the great scientist did not put on his oxygen mask properly and fell unconscious. The pilot realized something was amiss when his passenger did not respond to intercom chatter, so he dropped to a lower altitude. Bohr commented that he enjoyed the flight because he slept like a baby the whole way. Had the plane stayed at its planned altitude it's likely Bohr would have died of oxygen deprivation.
“The release of atom power has changed everything except our way of thinking…the solution to this problem lies in the heart of mankind. If only I had known, I should have become a watchmaker.”
- “Otto Hahn, Lise Meitner, and Fritz Strassmann.” Science History Institute, undated.
- “Atomic Bomb History.” History.com, April 15, 2019.
- “The Mysterious Meeting Between Niels Bohr and Werner Heisenberg.” The National WWII Museum, September 15, 2011.
- “Friends and Mortal Enemies.” Michael Frayn, The Guardian, March 23, 2002.
- “The Copenhagen Meeting of Heisenberg and Bohr.” Dwight Jon Zimmerman, Defense Media Network, September 8, 2011.
© 2019 Rupert Taylor