October 7, 1885, is the birthdate of the Danish physicist Niels Bohr, who had a part in nearly every advance in nuclear physics in the first half of the 19th century; played an important role as both educator and public intellectual, one who understood early on the dangers of nuclear weapons to humanity; and who was involved in encouraging King Gustav V of Sweden to offer asylum to Denmark’s more than 7,000 Jews during World War II.
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Niels Henrik David Bohr was born in Copenhagen, the second of three children of Christian Bohr, a physiologist, and Ellen Adler Bohr, who came from a wealthy and influential Jewish family. Both Niels and his younger brother, Harald, were skilled and enthusiastic soccer players; Harald, who later became an accomplished mathematician, played with the Danish team at the 1908 Olympics.
Bohr earned his undergraduate, master’s and, in 1911, doctoral degrees in physics, all at the University of Copenhagen, which, when he started out, had only one physics professor and no lab. (Niels used his father’s physiology lab for some of his experimental work.)
Bohr’s graduate work concerned the structure of the atom, and, specifically, a theory regarding the magnetism of metal atoms and their electrons. Following a months-long visit in the United Kingdom – where he worked with J.J. Thomson and Ernest Rutherford, who became an important mentor – Bohr returned to Denmark. In 1912, he married Margrethe Norlund, with whom he had six sons (four of whom survived to adulthood), and began teaching. In 1913, he published his celebrated trilogy of papers on atomic structure. His theory on the connection between the changing orbit levels of the electrons circumnavigating the nucleus and the electromagnetic radiation emitted during those shifts formed the basis of “old” quantum mechanics theory, and led to Bohr’s being awarded the Nobel Prize in Physics in 1922.
A Nobel and beer on tap
In the meantime, Bohr had succeeded in convincing the University of Copenhagen to establish an institute of physics. It opened its doors in 1921, with Bohr as its director (today it bears his name), and he and his family settled into an apartment on the first floor of its building. Soon after, when Bohr won the Nobel Prize, the Carlsberg Brewery invited the family to move into a house next door to its plant. One notable feature was the line that ran from the brewery to the residence, making beer available on-tap at all times.
The work being done in the 1920s and '30s by Bohr, Werner Heisenberg, Wolfgang Pauli and many others – and the cooperation between the scientists, much of its facilitated by the Bohr’s graciousness and openness – was responsible for the quantum leap made during this period in understanding atomic behavior. It was Bohr who immediately understood the importance of the discovery of nuclear fission by Lise Meitner and Otto Hahn, and who explained why it was that only the uranium-235 isotope, as opposed to most uranium, was fissile – an important step in the race that soon began toward the development of nuclear weapons.
Nazi Germany occupied Denmark in April 1940. During the 1930s, Bohr had offered German refugee scientists places at the institute in Copenhagen, and later worked with the Rockefeller Foundation to bring a number of them, many among them Jews, to the United States, and support them and their work there. Bohr himself had been christened in the Lutheran Church, but having a Jewish mother meant he would not be safe when the Germans turned to deport Denmark’s Jews, in late 1943.
He fled to Sweden via fishing boat in September of that year. Although the Swedes had been requested by the United States to get him out of the country immediately, and send him to the U.S. to work on the Manhattan Project, Bohr refused to leave Sweden until he had had an opportunity to meet with King Gustav V, whom he helped persuade to make public Sweden’s willingness to provide a refuge to Danish Jews. Soon after, in early October 1943, the great exodus of 7,800 Jews across the Oresund Sea took place.
After a flight in a Mosquito bomber to England, in which he had to lie in the plane’s bomb bay, and during which he lost consciousness from lack of oxygen, Bohr soon traveled on to Washington. He remained in the U.S. until the end of World War II, serving as an advisor to the Manhattan Project, some of that time in Los Alamos, New Mexico.
An early opponent of nukes
Early on, Bohr recognized that nuclear weapons would change the face of international power relations. (The topic had been broached in a long-mysterious meeting with Werner Heisenberg in Copenhagen in September 1941. Heisenberg was then overseeing the Nazi nuclear-research program, and he apparently wanted to discuss the future of nuclear energy after a German victory in the war. There is also evidence that Heisenberg tried to enlist Bohr in efforts to mediate a truce between Germany and the United Kingdom. Bohr ended the conversation very quickly.) He met with both Winston Churchill and Franklin D. Roosevelt, in an attempt to persuade them to publicly announce that science had mastered the use of nuclear fission, and to cooperate with the Soviet Union in the field, so as to prevent proliferation. Both leaders rejected Bohr’s suggestions, and even ordered their security services to keep an eye on him. Churchill, for example, wrote: "It seems to me Bohr ought to be confined or at any rate made to see that he is very near the edge of mortal crimes."
Bohr returned to Denmark in August 1945, where he resumed his work at the Institute of Physics. He was a key player in the creation of CERN, the European scientific research agency, and he continued his efforts to foster international cooperation on nuclear controls. In 1950, he wrote to the United Nations of his conviction that, “Humanity will be confronted with dangers of unprecedented character unless, in due time, measures can be taken to forestall a disastrous competition in such formidable armaments and to establish an international control of the manufacture and use of powerful materials.” For his efforts, he was the recipient of the first U.S. Atoms for Peace Award, in 1957.
Niels Bohr died on November 18, 1962, at the age of 77.