Niels Bohr: One Scientist's Quiet War Against Hitler

by Martha Hutchens

Niels Bohr, 1935, Public Domain, Wikipedia Commons

No book covering the history of science would ignore Niels Bohr. His concept of atomic structure formed the basis of much of twentieth-century physics and chemistry. But in this blog post, I mention his scientific brilliance mainly because of the platform it gave him.

As early as 1924, Bohr watched events in Germany cautiously. He questioned Werner Heisenberg, one of Germany’s premier scientists, about the ominous anti-Semitic trends “obviously fostered by demagogues.” Heisenberg dismissed them as the work of “some of the old officers embittered by the war.”

As early as 1919, scientists in Germany resented the worldwide attention given to Albert Einstein, who was Jewish. But the Law for the Restoration of the Professional Civil Service, enacted on April 7, 1933, proved Germany had no place for Jewish scientists. The act decreed that civil servants, including university faculty, must be Aryan. A quarter of Germany’s physicists lost their livelihoods. Several either had or would earn the Nobel Prize.

By this time, Bohr led the Institute of Theoretical Physics at the University of Copenhagen. He was one of Denmark’s most respected citizens and had extensive connections throughout the scientific community.

Bohr traveled through Germany to determine who needed help. He met Otto Frisch and told him, “I hope you will come and work with us sometime; we like people who can carry out ‘thought experiments.’”

Bohr was not the only physicist trying to rescue fellow scientists. Leo Szilard and Otto Stern were also finding positions for those displaced by Nazi racial laws. Many fled to England or America, while others found refuge in Copenhagen with Bohr.

Bohr did not merely help displaced scientists find jobs. On the same trip, he met James Franck, a Nobel Laureate. Franck was Jewish, but because he had fought at the front during World War I, he was exempt from the civil service law. Years later, he said a meeting with Bohr gave him the final push to protest publicly. Franck resigned his position on April 17, 1933, and made sure the newspapers knew why.

The rescue effort for Jewish scientists was exhausting and stretched beyond Germany. In October 1933, George Gamow and his wife escaped the increasingly hostile Soviet Union. In 1938, Lise Meitner fled Austria after the Anschluss. Later that same year, Enrico Fermi fled Italy after Mussolini adopted anti-Semitic laws.

Also in 1938, Bohr addressed the International Congress of Anthropological and Ethnological Sciences in Denmark. He publicly challenged Nazi racism before an international audience. It was a brave stand because he believed Germany would eventually invade Denmark. He was putting a target on his own back.

On April 8, 1940, Bohr dined with the King of Norway before returning to Copenhagen. In the early hours of April 9, Germany invaded both Denmark and Norway. Denmark did not resist militarily. The American Embassy offered the Bohr family safe passage to the United States, but Bohr’s first concern was burning the files of the refugees his committee had helped escape.

Laboratory flasks like those used by Niels Bohr to hide two
Nobel Prize medals during World War II.
Depositphotos, @Harmony Video Production.

Even on that chaotic day, he worried about two gold Nobel Prize medals friends had left in his hands for safekeeping. Their names were engraved on the back, and exporting gold from Germany was a serious crime. Bohr and a colleague dissolved the medals in acid and left the flask sitting on a laboratory shelf. After the war, the gold was recovered and the Nobel Foundation recast the medals.

One of the most ambiguous meetings in atomic bomb history took place in Copenhagen in 1941. Heisenberg, now leading Germany’s atomic bomb project, traveled there for a scientific conference. Bohr routinely boycotted joint Danish-German activities, but he agreed to meet privately with his former friend.

Because Bohr was under surveillance, the two men talked while walking together. Historians still debate what happened during that conversation. Heisenberg later claimed he wanted to discuss the moral implications of atomic research. Bohr believed Heisenberg was probing how much the Allies knew about Germany’s progress. Perhaps both were true.

Germany depended heavily on Danish agriculture during the war. Denmark, in turn, cooperated only as long as Danish Jews remained safe. In 1943, the relationship deteriorated. The Nazis disarmed the Danish army and confined the king. Danish Jews were no longer protected.

In September, Bohr learned that his émigré colleagues were slated for arrest. He contacted the underground, which helped them escape. Soon afterward, the Swedish ambassador hinted that Bohr himself was now on the arrest list.

The Bohr family escaped by fishing boat to Sweden. The Swedish government had already offered asylum to Denmark’s Jews, though Germany denied any roundup was underway. In reality, Danish citizens were already hiding their Jewish neighbors. Bohr met with Swedish officials, including the king, to advocate for his fellow Danes. On October 2, Swedish radio publicly announced the asylum offer. Within two months, more than 7,000 Jews escaped to safety in Sweden.

A British Mosquito aircraft, the type used to fly Niels Bohr
 from Sweden to safety in 1943.
Deposit Photos, @Paulspix

The Bohrs later flew to England. To avoid anti-aircraft fire, the plane flew at high altitude and required oxygen masks. Unfortunately, Bohr’s helmet did not fit correctly, and he missed the order to begin oxygen. He passed out during the flight but arrived safely in England. Robert Oppenheimer later joked that “The Royal Air Force was not used to such great heads as Bohr’s.”

Bohr eventually joined the American atomic bomb project. Click here to learn more about his life after he left Denmark and his trips to Los Alamos.

Best-selling author Martha Hutchens is a history nerd who loves nothing more than finding a new place and time to explore. She won the 2019 Golden Heart for Romance with Religious and Spiritual Elements. A former analytical chemist and retired homeschool mom, Martha occasionally finds time for knitting when writing projects allow.

Martha’s debut novel, A Steadfast Heart, is now available. You can learn more about her books and historical research at marthahutchens.com.

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