Neils Bohr (1885-1962), Danish physicist.
Bohr studied at the University of Copenhagen which he entered in 1903. He studied physics as his main subject but took mathematics, astronomy and chemistry as minor subjects.
At university Bohr could not carry out physics experiments since there was no physics laboratory. However his father had a physiology laboratory and his first paper describes experimental work in physics which he carried out in that laboratory. He dictated the paper to his brother Harald. This paper is the only one that Bohr wrote describing experiments which he had carried out. With it he won the Gold Medal for 1906 from the Royal Danish Academy of Sciences for his analysis of vibrations of water jets as a means of determining surface tension. He received his Master's degree from the University of Copenhagen in 1909 and his doctorate in May 1911 for a thesis entitled Studies on the electron theory of metals. It was a thesis based on classical physics and as such necessarily failed to explain certain effects. Bohr wrote in this work: "It does not seem possible at the present stage of the development of the electron theory to explain the magnetic properties of bodies from this theory."
In 1917 Bohr was elected to the Danish Academy of Sciences and he began to plan for an Institute of Theoretical Physics in Copenhagen. This was created for him and, from its opening in 1921, he became its director, a position he held for the rest of his life.
Danish banknote featuring Neils Bohr
Bohr is best known for the investigations of atomic structure referred to above and also for work on radiation, which won him the 1922 Nobel Prize for physics. He gave a lecture on the work for which he was awarded the Prize on 11 December 1922 in Stockholm. He talked of atomic stability and electrodynamic theory giving an account of the origins of quantum theory, the hydrogen spectrum, explaining the relationships between the elements. His explanation covered the absorbsion and excitation of spectral lines and the correspondence principle which he had set out in three papers On the quantum theory of spectra between 1918 and 1922. It was Bohr's view of quantum theory which was eventually to become accepted. Einstein expressed grave doubts about Bohr's interpretation and Bohr, Einstein and Ehrenfest spent many hours in deep discussion, but Bohr's view prevailed. Bohr expressed this view saying: "Evidence obtained under different experimental conditions cannot be comprehended within a single picture, but must be regarded as complementary in the sense that only the totality of the phenomena exhausts the possible information about the objects."
H.B.G. Casimir wrote describing what it was like working with Bohr in his Institute: "Even Bohr who concentrated more intensely and had more staying power than any of us, looked for relaxation in crossword puzzles, in sports, and in facetious discussions."
Bohr's other major contributions, in addition to quantum theory, include his theoretical description of the periodic table of elements around 1920, his theory of the atomic nucleus being a compound structure in 1936, and his understanding of uranium fission in terms of the isotope 235 in 1939.