Niels Bohr (Denmark, 1885-1962)

Figure 1.-- Here is Bohr and hos wife with three of the boys at Tisvilde in 1928. Notice that Christain and Hans have very long arrows.

Danish Nobel lauriate nuclear physicist Neils Bohr was born and lived his life in Copenhagen. He grew up in a sophisticated and loving family. He studies physics at University of Copenhagen and worked under J.J. Thomson, who had discovered the electron, in England. Bohr played a major role in understanding the structure of the atom after it was conceptualized by Ernest Rutherford as a dense miniature, nucleus surrounded by a cloud of virtually weightless electrons.


Niels' father was Christian Bohr who earned a doctorate in physiology from the University of Copenhagen (1880). Afterwards he was appointed a Privatdozent at the University (1881). Niels' mother was Ellen Adler. the daughter of David Adler, a notable Jewish politician and businessman.


Neils parents had three children. Christian Bohr married Ellen after he received an appointmaent at the University of Copenhagen (1881). He and Ellen, who was Christian, had three children. Jenny was born in the mansion owned by David Adler located opposite Christiansborg Castle, the seat of the Danish Parliament (1883) Ellen's mother had continued to live there when her husband David died (1878). Ellen went back to her home so her mother could care for her when she had her first child. Noels was also born there (1885). Harald was also born there (1885). Soccer by the early 20th century had already become an important international sport. Harald was a talented athlete and who was at the University of Copenhagen with his older brother later played on the 1908 Danish Olympic soccer team which won a silver medal. Harald went on to become a notable mathematican. Niels and Harald were close throughout their lives.


Neils Bohr was born and and grew up in Copenhagen. He grew up in a sophisticated and loving family. One biographer writes, "Niels, Harald, and their older sister, Jenny, grew up in a cultured and stimulating home. From their earliest days they were exposed to a world of ideas and discussion, of conflicting views rationally and good-temperedly examined, and they developed a respect for all who seek deeper knowledge and understanding." [Kennedy]

Childhood Clothing

We do not have details of the clothes Neils and Harald wore as boys. We see one image with their nurse and the boys are wearing sailor suits. The boys even as teenafers seem to have been dressed alike.


Neils was educated in Copenhagen. At 10 years of age Niels entered the Grammelholms school (1891). This would be comparable to a German Gymnasium which students enered at 9-10 years of age. We do not yet have details on Danish education, but interested readers may want to consult information collected on German education. Both Niels and his brother attended and graduated from the Grammelholms school. Interestingly even some of the older boys at the Grammelholms wore sailor suits in a photograph of Neils class (1901). The boys would be 15-16 years old. He did his Studenterexamen (1903). He was a good student, but not at the top of his classes. In most classes he would finish about third or fourth in classes of about 20 students. Neils in his final 2 years at Grammelholms specialised in mathematics and physics. His father appears to have help spark his son's interest in both physics and mathematics. In these classes Neils began studying texts beyond what his classmaters were working on, and finding mistakes in them. Neils in school was most notable among his school mates for his soccer exploits. Neils next studied physics at University of Copenhagen (1903). He also enjoyed playing soccer, although he was not as talented as his brother. Bohr was awarded his Ph.D (1911).

Atomic Physics

Bohr received a study grant and went to Britain to worked under J.J. Thomson, who had earlier discovered the electron. Bohr's primary interest was the structure of the atom. Ernest Rutherford copnceptualized the atom as a dense miniature, nucleus surrounded by a cloud of virtually weightless electrons. Not all physicists accepted Rutherford's theory. There were problems with classical physics. (This and other issues was why Einstein addressed a unified theory to recocile nuclear and classical physics. Classical physics pctualted that electrons orbiting a nucleus would gradually lose energy until they spiraled into the nucleus, much as a satellite with a decaying orbit. Bohr suggested that Max Planck work on quanta (1901) provided the answer. Bohr maintained that electrons existed at set energy levels and fixed distances from the nucleus. His elaboration of process involved is known as quantum mecahnics and his his chief contribution to science.

Figure 2.-- Here Bohr and Margrethe are on a mottorbike surrounded by the boys. Note Christian is wearing knickers.


Bohr married Margrethe Nørlund (1912). It was a loving marriage and the couple had six sons. Two of the boys died in childhood. The other four survived and carved out sucessful careers of their owm. These four boys included: Hans Henrik (doctor), Erik (chemical engineer), Aage (Ph.D., theoretical physicist), and Ernest (lawyer). We have little information on how the boys were dressed as children. They always wore short pants. We note sailor caps and assumed thdey must have worn sailor suits like their father and uncle. Some images show the boys wearing smocks. Several family photographs show them wearing winter coats with shorts and kneesocks. Aage following his father as Director of the Institute for Theoretical Physics and also won a Nobel Prize. Bohr's sons left him with quite a number of grand children in which he deligted.

Institute of Theoretical Physics

Bohr returned frpm Britain to teach at the University of Copenhagen. He founded founded the Institute for Theoretical Physics (1920). The Carlsberg brewery provided much of the finds. Bohr continued as director of the Institute for his entire life, except for the time he spent in America as a refugee grom the NAZIs during World War II. After his pioneering work on electrons, Bohr continued to work on atomic structure. He conceptualized the nucleus as a liquid drop and the idea of "complementarity". He believed that nuclear particles may have a dual nature. He was an electron as both particle and wave. The Institute still operates and is now named after Bohr.

Nobel Prize

Bohr's basic ideas a bout atomic structure were gardually accepted. He and others worked on refining the basic concept. At the age of only 37 he was awarded the Nobel Pfrize for Physics (1922).


Adolf Hitler and the NAZIs seized power in Germany (1933). Many Jewsish phsicists were Jewish, some colleagues with which he had personal relations. NAZI policy was at first to drive Jews out of Germany, usually after stripping them of their prperty. No real consideration was given to their academic credentials are possible use during a future War. Hitler saw atomic physsics as "Jewish science" and had no real appreciation of the potential milatary potential. Bohr accomodated Jewish scientists who fled to Denmark, finding places for them to live and work. The presence of some of the greatest minds on physics made the Institute for Theoretical Physics one of the most excitig places in the world for discussions of nuclar physics. In many cases, however, Denmark was only a way station for Jews trying to get further away from the NAZIs.

World War II

World War II began with the NAZI invasion of Poland. Soon after the Soviet Union invaded Finland. Bohr donated his gold Nobel medal for the Finnish war effort. The Finns fough valiantly, but in the end were overwealmed by the Red Army. After returning from a trip to the United States, NAZI Germany invaded and occupied Denmark as part of a larger operation to seize Norway (1940). The years that followed are interesting. It was no secret that Bohr was anti-NAZI and had sheltered Jews. He himself was half Jewish as his mother was a Chritianized Jew. The NAZIs as long as a person was descrete and not active in the Resistance apparently did not carry out a roundup of anti-NAZIs as they had done in Germany itself. (We assume Communists here were an exception.) Of course Bohr as a half-Jew was in great danger.

The Institute

Even more interestingly, there was no effort to use the Institute, one of the most prestigious facilities for nuclear research, for war work. One of the fears that Churchill and Roosevelt had was that the NAZIs would organize the industrial and scientific capacity of occupied Europe to support the War. We know that factories were converted for war work, although not as extensively as one might think. As far as we can tell, the scientific potential of the occupied countries was not used. Bohr and the Institute is just one example. We are not prescisely sure why this was. At first the NAZIs believed that they had essentially won the War and thus saw no need to copt the scientific community of defeated nations. There were also security concerns. (Compare this with the hunt for scientists and the hnology that the Americans, British, and Soviets persued in occupied Germay after the War.) The Germans after Bohr escaped to Sweden did seize the Institute, charging that Bohr and the staff had secretly been working for the Allies (December 1943).


Werner Heisenberg and Bohr were colleagues and friends. They socialized on a family basis. Heisenberg had made many visits to the Institute and had been hosted by Bohr. After the NAZI invasion there was a notable meeting betweem Heisenberg and Bohr. Heisenberh had been put in charge of the NAZI atom bomb project. He traveled to Copenhagen to see Bohr (October 1941), but very different accounts of that meeting exist. One account suggests Heisenberg came to see Bohr to offer a tsacit agreement with the Allies that the two sides should refrain from building such a horrendous weapon. [Jungk] This account is based primarily on Heisenberg's claims after the War. Other authors maintain that this is a German effort to whitewash their War effort. Bohhr and his son claimn that no such feeler was made by Heisenberg and that Bohr was uncomfortable with some technical questions that the German physicist posed. There relationship was never the same again. It is notable that Heisenberh after the NAZIs seized the Institute was instrumental in ending the occupstion of the facilities (February 1944). [Blaedel, p. 235-236.]

Escape from the NAZIs

Despite the danger, Bohr did not want to leave Denmark. Not only did he not want to desert his homeland, he feared repercussions on the staff at the Institute and on Danish Jews if he left Denmark. British sciehntists were pleading with him through secret channels to come to England. [Blaedel, p. 213.] Bohr passed on information he acquired about German activities (both scientific and industrial) related to nuclear physics. Bohr at this stage did not believe that it was possible to build a bomb before the War ended because of the massivev industrial requirements. Bohr's Jewish origins meant that he and his family were affected by the deterirating condition in Denmark. The NAZIs arrested many Danish intellectuals (August 29, 1943). The NAZIs had considered arresting Bohr at this time, but then decided that it would cause less notice if he was picked up with the impending deportment of all Danish Jews.[Blaedel, p. 215.] Danish Jews learned of plans for a NAZI roundup on Rosh HaShannah, the Jewish New Year. Nohr was personally informed by the Sedish Ambassador Bohr and his his brother that the NAZIs were preparing to arrest them as part of the impending deportation of Danish Jews. That night the Danish Resistance got them to Sweden abnd the rest of the family the next few days. [Blaedel, p. 215.] The miraculous rescue of Danish Jews is one of the great stories of the Holocaust. The people of Denmark managed tp spirit their Jews away to Sweden--one of the most notable examples of resistance to the NAZI Holocaust (1943). Bohr stayed in Sweden to do what he could to help the Danish Jews get to Sweden. He advised the Swedish Government which acted on many of his suggestions. [Blaedel, p. 215.] Given the number of German agents in Sweden, it was decided that Bohr needed to get to London as soon as posdsible. Bohr and his son Aage, also a noted phyicist, left Sweden for London in the empty bomb rack of a RAF Mosquito bomber. They made their way to the United States where they joined the scientists working on the Manhattan Project.

Manhattan Project

Bohr visited the United States (1939). An Austrian scientist he helped in Copenhagen informed him that German scientists were attempting to split the atom. This was a factor in launching the Manhattan Project. This was the largest weapons development program in history. It was initiated by President Roosevelt when work done by German physicists led to concern that the NAZIs might build an atomic bomb. Important scientists in 1939 concluded that German scienbtists had begun to develop an atomic bomb for the NAZIs. These scientists enduced President Roosevelt to launch an American atomic bomb project. The project was, however, given serious attention only after the Japanese attack on Pearl Harbor bringing America into the war. General Leslie R. Groves (1896-1970), Deputy Chief of Construction of the U.S. Army Corps of Engineers, was assigned to oversee the project. The Manhattan Project us named after the New York borough where the first office headquarters was located and began June 1942. Groves had just completed another rush project, the construction of the Pentagon. He considered himself an astute judge of men and chose Robert J. Oppenheimer (1904-67) to lead the scientific team. Oppenhimer was a respected, but reatively unknown theoretical physicist. Enrico Fermi and Leo Salard working in a converted squash court beneath the University of Chicago's carried out the first controlled nuclear reaction occurred confirming that nuclear fission could unleash huge amounts of energy. The major difficulty in building an atomic bomb was in obtaining the required quanity of fissionable material. A huge facility was built an Oak Ridge, Tennessee to separated the U-235 isotope needed for the bomb from the more common U-238 isotope. The Hanford Engineer Works was built in washington to produce plutonium. Groves chose Los Alamos, New Mexico as a location to acually develop and assemble the bomb or "gadget" a it was called. This ioslated town had by March 1943 been turned into a high-technology boomtown. The Y-12 Plant at Oak Ridge provided the bomb-grade U-235 used for the Little Boy bomb. The Harford plant provided the Plutonium used in the Fat Man bomb.

Post-War Life

As with several other scientists, Bohr had concerns about the consequences of the bomb. He had worked on the Manhattan Project to ensure that the NAZIs would not develop a bomb first. He was surprised when the bomb was used against Japan. He upset Winston Churchill when he advocated sharing information with the Soviet Union. As with many at the time, he was not fully aware of the extent of the crimes committed by Stalin and the Soviet Union. Nor did he ever address the problem that of the Soviets were given American and British nuclear secrets that it would free up resources to build bigger and better bombs. He strongly supported postwar arms control. He organized the Atoms for Peace Conference in Geneva (1955). He participated in setting up Europe's great particle accelerator and research station (CERN). He died in his home after a stroke (1962).


Blaedel, Niels. Harmony and Unity: The Life of Niels Bohr (Science Tech, 1988), 323p.

French, A.P. and P.J. Kennedy (eds.), Niels Bohr : A Centenary Volume (Cambridge, Mass., London, 1985).

Jungk, Robert. Stronger than a Thousand Guns.


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Created: May 5, 2004
Last updated: May 13, 2004