Niels Bohr

Niels BohrNiels Bohr Biography (1885-1962)
The Nobel Prize in Physics 1922

Niels Henrik David Bohr was born in Copenhagen on October 7, 1885, the son of Christian Bohr, Professor of Physiology at Copenhagen University, and his wife Ellen, née Adler. Niels, together with his younger brother Harald (a future Professor of Mathematics), grew up in an atmosphere most favourable to the development of his genius — his father, an eminent physiologist, was largely responsible for awakening his interest in physics while still at school, and his mother came from a family distinguished in the field of education.

After matriculation at the Gammelholm Grammar School in 1903, he entered Copenhagen University where he came under the guidance of Professor C. Christiansen, a profoundly original and highly endowed physicist, and earned his Master’s degree in Physics in 1909 and his Doctor’s degree in 1911.

Bohr’s subsequent studies, however, became more and more theoretical in character, his doctor’s disputation being a purely theoretical piece of work on the explanation of the properties of metals with the aid of the electron theory, which remains to this day a classic on the subject. It was in this work that Bohr was first confronted with the implications of Planck’s quantum theory of radiation.

At Cambridge in the autumn of 1911, he profited by following the experimental work going on in the Cavendish Laboratory under J.J. Thomson‘s guidance, while at the same time pursuing his own theoretical studies. In the spring of 1912 he was at work in Professor Rutherford’s laboratory in Manchester, where, at that time, an intensive scientific life and activity prevailed as a consequence of that investigator’s fundamental inquiries into radioactive phenomena. Having carried out a theoretical piece of work on the absorption of alpha rays which was published in the Philosophical Magazine in 1913, he moved on to study the structure of atoms on the basis of Rutherford’s discovery of the atomic nucleus. By introducing concepts borrowed from Plancks’ Quantum Theory, which had gradually come to occupy a prominent position in the science of theoretical physics, he succeeded in working out and presenting a picture of atomic structure that, with later improvements (mainly as a result of Heisenberg’s ideas in 1925), still serves as an elucidation of the physical and chemical properties of the elements.

In 1913-14 Bohr held a Lectureship in Physics at Copenhagen University followed in 1914-16 by a similar appointment at the Victoria University in Manchester. In 1916 he was appointed Professor of Theoretical Physics at Copenhagen University, and from 1920 until his death in 1962, he was the head of the Institute for Theoretical Physics, established for him at that university.

Recognition of his work on the structure of atoms came with the award of the Nobel Prize for 1922.

After 1930, Bohr’s activities in his Institute were directed more and more to research on the constitution of the atomic nuclei, and of their transmutations and disintegrations. In 1936 he pointed out that in nuclear processes the smallness of the region in which interactions take place, as well as the strength of these interactions, justify the transition processes to be described more in a classical way than in the case of atoms (“Neutron capture and nuclear constitution”, Nature, 137 (1936) 344).

A liquid drop would, according to this view, give a very good picture of the nucleus. This so-called liquid droplet theory permitted the understanding of the mechanism of nuclear fission, when the splitting of uranium was discovered by Otto Hahn and Fritz Strassmann in 1939, and formed the basis of important theoretical studies in this field (among others, by Frisch and Meitner).

Bohr also contributed to the clarification of the problems encountered in quantum physics, in particular by developing the concept of complementarily. Hereby he could show how deeply the changes in the field of physics have affected fundamental features of our scientific outlook and how the consequences of this change of attitude reach far beyond the scope of atomic physics and touch upon all domains of human knowledge. These views are discussed in a number of essays, written during the years 1933-62. They are available in English, collected in two volumes with the title Atomic Physics and Human Knowledge and Essays 1958-1962, edited by John Wiley and Sons, New York and London, in 1958 and 1963, respectively.

During the Nazi occupation of Denmark in World War II, Bohr escaped to Sweden and spent the last two years of the war in England and America, where he became associated with the Atomic Energy Project. In his later years, he devoted his work to the peaceful application of atomic physics and to the political problems arising from the development of atomic weapons. In particular, he advocated a development towards full openness between nations. His views are especially set forth in his Open Letter to the United Nations, June 9, 1950.

Niels Bohr died in Copenhagen on November 18, 1962.