Bohr, Niels, 1885-1962

Niels Bohr was a Danish physicist who made tremendous contributions to his field, transforming accepted notions of atomic structure, helping to develop nuclear fission, and advocating for international cooperation in crafting responsible nuclear policy.

Bohr was born in Copenhagen in 1885 into a family that encouraged his academic pursuits. Christian Bohr, his father, was professor of physiology at the University of Copenhagen. Bohr credited his father for awakening his interest in physics at a young age. His mother, Ellen Adler Bohr, came from a wealthy Jewish family that was prominent in the field of education. Bohr's brother Harald was a mathematician and Olympic soccer player for the Danish national team.

Bohr graduated from Gammelholm Grammar School in 1903. He then entered Copenhagen University where he earned a Master's degree in Physics in 1909 and a doctorate in 1911. His mentor there, Professor C. Christiansen, was an innovative and well-respected physicist. During graduate school, Bohr won a gold medal from the Academy of Sciences in Copenhagen for his experimental and theoretical exploration of liquids' surface tensions using oscillating fluid jets. He performed the experiments in his father's laboratory, the results of which were published in 1908 in the Transactions of the Royal Society. Following the receipt of this award, however, his work became increasingly theoretical in character. His doctor's disputation, a theoretical explanation of the properties of metals that relied upon electron theory, remains a classic meditation on this subject.

Upon earning his doctorate, Bohr moved to Cambridge, where he pursued his own theoretical work while simultaneously observing the experimental work directed by Sir J.J. Thompson in the Cavendish Laboratory. In 1912 he moved to Manchester, where he worked in Professor Ernest Rutherford's laboratory. Rutherford's discovery of the atomic nucleus became the basis of Bohr's investigation of atomic structure. In 1913, Bohr developed his model of atomic structure, which held that electrons travel in orbits around an atom's nucleus. The chemical properties of the element, his theory held, were determined by the number of electrons in orbit. When an electron dropped from a high-energy orbit to a lower-energy orbit, it emitted a photon of discrete energy. This discovery was central to the development of quantum theory.

Bohr held the position of Lecturer in Physics at Copenhagen University from 1913-1914, and at Victoria University in Manchester from 1914-1916. In 1916, Bohr was appointed Professor of Theoretical Physics at Copenhagen University. From 1920 until his death in 1962, he led the Institute for Theoretical Physics, which was established for him and eventually named for him. In the 1920s and 1930s, Bohr's laboratory hosted most of the world's leading theoretical physicists.

In 1922, Bohr received the Nobel Prize in physics "for his services in the investigation of the structure of atoms and of the radiation emanating from them." Following his receipt of the Nobel Prize, Bohr increasingly investigated the constitution of atomic nuclei, including their transformations and declensions. Bohr also invented the principle of complementarity, the notion that items could be understood as having contradictory properties. Albert Einstein was a vocal opponent of this principle, and he and Bohr had several famous arguments over its feasibility.

While the Nazis occupied Denmark during World War II, Werner Karl Heisenberg, a top German physicist and Director of the Kaiser Wilhelm Institute for Physics, visited Bohr. In 1943, just before he was to be arrested by Nazi police, Bohr escaped to Sweden. He spent the remaining years of the war in England and the United States. In America, Bohr worked at the secret Los Alamos Laboratory on the Manhattan Project, where his assumed name was Nicholas Baker. The younger scientists on the project valued Bohr's contribution as a mentor and consultant. His concern about a nuclear arms race, he explained, was "why I went to America. They didn't need my help in making the atom bomb."

Bohr believed that atomic secrets should be shared by all in the international scientific community. Bohr visited President Roosevelt to convince him to share the Manhattan Project with the Russians for the purpose of speeding its progress. Upon Roosevelt's suggestion, Bohr took this idea to England, where Prime Minister Churchill completely opposed the idea. After the war, Bohr returned to Copenhagen. He spent his last decades developing and promoting the peaceful applications of atomic physics. His Open Letter to the United Nations, published on June 9, 1950, sets forth his views. In his lifetime, Bohr authored or co-authored more than 115 published works.

Bohr married Margrethe Norlund in 1912. They had six sons, of whom two died in childhood. The other four led successful lives