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Bohr’s Exile And The Atomic Bomb

Updated: Oct 8, 2023

Author: Miles Qvale

Teacher: Redha Rubaie


With the critical acclaim and the commercial success of Christopher Nolan’s Oppenheimer, there has been a renewed focus on many of the vibrant characters and moments that were involved. Countless articles have been written about Oppenheimer, the US ‘Red Scare’ of the 1950s, and the morality of the Manhattan Project itself. However, though he does receive some screen time, perhaps the most remarkable character of the whole film is relegated to the background.

Niels Henrik David Bohr

Bohr was arguably one of the most influential physicists in the 20th century. He is credited with proposing the ‘Bohr model’ of the atom, which describes the nucleus being orbited by electrons at discrete energy levels. These energy levels, “quanta”, sparked the quantum revolution that we know today. His experiments measuring the light emitted from ionized materials provided the framework to prove that electrons function with quantized energy levels. He received the Nobel Prize for his work later in 1922. Many have written about his Herculean influence over our understanding of the natural world, and far fewer have understood his decades-long humanitarian efforts before, during, and after the Second World War.

The Rise of Nazi Germany

It was clear to many within Denmark, where Bohr was born and lived for the majority of his life, that the Nazi regime posed a real threat to their sovereignty. Some famous Danes, such as the gymnast and public aesthetician Neils Bukh, chose to embrace the National Socialist dogma as a way of ensuring the continued ethnic homogeneity of Denmark. However, these were generally fringe views, and it became obvious through a string of Danish Parliamentary (Folketing) elections that the Nazis were not going to gain power through democratic means. As a result, April 9th, 1940, saw the Germans cross over the Jutland border and march on Copenhagen. Given the nature of the military mismatch between the two countries, the Germans were able to take the Danish capital in a matter of weeks, and a five-year occupation began.

Bohr, whose mother was Jewish, had managed to evade detection from the local authorities for the first three years of the occupation. Unbeknownst to these occupying authorities, the Niels Bohr Institute was at the center of a concerted effort by Bohr and Max Mason (the head of the US-based Rockefeller Foundation) to provide a number of physicists who were political exiles a means through which they could reach the United States. Dozens of Jewish and dissident researchers escaped Nazi occupation in this way. One of them was Edward Teller - who also featured in Oppenheimer as the main advocate for the hydrogen bomb. As Nazism spread over Europe, the scientific community found itself grappling with deep ethical questions. Bohr was no exception, and he keenly understood the role that physicists could play in shaping the course of history.

Bohr's Escape from Denmark

By September 1943, it became clear to Bohr and his brother that the Nazis had chosen to consider them Jewish based on their maternal heritage. Owing to the symbolic significance that Bohr represented for the Danish resistance movement, they were given a simple choice - stay, and be interred by the Nazis, or escape to non-occupied Europe. Having heard of the conditions in which the Nazis kept prisoners, the decision for Niels and Harold was a simple one, and they would attempt an escape laden with risk. The occupying forces were tipped off about their plans at the last minute and stormed Bohr’s family home. It was only because of the bravery of Danish resistance fighters, who risked their lives shooting at the Nazi officials, that the Bohrs were able to escape on a fishing boat towards Sweden. On one hand, Bohr held his fake travel documents in case they encountered Nazis elsewhere. In the other, a bottle of deuterium, the ‘heavy water’ that would later become central to many of the world’s largest nuclear projects.

Once safely in Sweden, it was clear that Bohr’s role in the war was far from over. Rumors spread to London of a world-leading nuclear physicist who had managed to escape the grip of the Nazi regime. After considerable encouragement, Niels and his son (Aage) agreed to be secretly ferried by a military convoy from Sweden to the UK, in the hope that Niels would support the British Tube Alloys nuclear weapons development team. At this time, he developed a personal correspondence with Prime Minister Winston Churchill, where they shared updates about the progress towards a weapon that would render conventional warfare, in their eyes, redundant. Once the Americans learned of Bohr’s presence in London, they issued a formal invite to the biggest show in town when it came to the development of nuclear weapons - the Manhattan Project. Under the guise of Nicholas Baker, his role as a knowledge consultant for the Allies began…

The Ethical Dilemma

Niels Bohr is primarily accredited with developing the modulated neutron initiator, which is the device responsible for firing the first neutrons and starting the chain reaction in the atomic bomb. According to Oppenheimer, “This device remained a stubborn puzzle, but in early February 1945, Niels Bohr clarified what had to be done.” He acted as a scientific father figure for many of the young boys who took part in the Manhattan Project, including Richard Feynman. Amidst the secrecy of the project, Bohr’s clarity of thought and insightful interventions helped resolve many technical challenges faced by Oppenheimer and the rest of the team.

While working on the Manhattan Project, Bohr was honest about his opinions about secrecy and the sharing of information. He believed that it was a good idea to share ideas about the nuclear bomb with Soviet Russia to speed up the rate of development. However, many political figures disapproved of this approach due to anti-communist sentiment, and he was put under close scrutiny to ensure that no information about the project was leaked to Soviet sources. Throughout the war, Bohr met with prominent historical figures such as Winston Churchill and Theodore Roosevelt to discuss the secrecy of the Manhattan Project. Though his idea to share the details of the project with the Soviets was rejected, he sparked numerous discussions about the importance of an “open-world” viewpoint in scientific discovery. Bohr’s inclination towards sharing information was not just rooted in scientific camaraderie, but also in the aspiration that a collective understanding would prevent aggressive use of nuclear weapons.

Post-War Activities and Legacy

After the war, Bohr was deeply worried about the implications of the technology that he had helped create. He understood that the atomic bomb had catastrophic potential for death and destruction and recognized that, more than ever, there was a need for international cooperation. He spent his remaining years advocating for peaceful ways to utilize nuclear energy. His efforts had many lasting influences on his scientific legacy. He advocated for the numerous benefits of using nuclear energy as a civilian power source. Bohr’s goal was to change the global focus away from the military and toward the development of science and nuclear energy. His dedication to peace after witnessing the destructive potential of his own contributions, combined with his perspective that scientific discoveries can be harnessed for the betterment of mankind, proves his integrity.


Niels Bohr's life is a testament to the remarkable journey of a physicist during one of the most tumultuous periods in history. Having fled from Nazi-occupied Denmark, he continued to make scientific discoveries and even participated in the construction of the atomic bomb. However, his legacy as an individual isn’t limited to his scientific contributions but also to his unwavering commitment to peace and cooperation in an age of atomic energy. He worked to establish international cooperation in the scientific community, which testifies to his vision for a more scientific future. Niels Bohr's multidimensional legacy as a groundbreaking physicist, a beacon of resistance during WWII, and a post-war advocate for peace and collaboration serves as a profound lesson for all of us about the interplay between science and society.


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