Niels Henrik David Bohr was born in Copenhagen on October 7, 1885, as
the son of Christian Bohr, Professor of Physiology at Copenhagen University,
and his wife Ellen, née Adler. Niels, together with his younger
brother Harald (the future Professor in Mathematics), grew up in an
atmosphere most favourable to the development of his genius - his father was
an eminent physiologist and was largely responsible for awakening his
interest in physics while still at school, 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 took
his Master's degree in Physics in 1909 and his Doctor's degree in 1911.
While still a student, the announcement by the Academy of Sciences in
Copenhagen of a prize to be awarded for the solution of a certain scientific
problem, caused him to take up an experimental and theoretical investigation
of the surface tension by means of oscillating fluid jets. This work, which
he carried out in his father's laboratory and for which he received the
prize offered (a gold medal), was published in the Transactions of the Royal
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 the 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.
In the autumn of 1911 he made a stay at Cambridge, where he profited by
following the experimental work going on in the Cavendish Laboratory under
Thomson's guidance, at the same time as he pursued own theoretical
studies. In the spring of 1912 he was at work in
Professor Rutherford's laboratory in Manchester, where just in those
years such an intensive scientific life and activity prevailed as a
consequence of that investigator's fundamental inquiries into the
radioactive phenomena. Having there carried out a theoretical piece of work
on the absorption of alpha rays which was published in the Philosophical
Magazine, 1913, he passed on to a study of the structure of atoms on the
basis of Rutherford's discovery of the atomic nucleus. By introducing
conceptions borrowed from the Quantum Theory as established by Planck, 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 fitly serves as an elucidation of the
physical and chemical properties of the elements.
In 1913-1914 Bohr held a Lectureship in Physics at Copenhagen University and
in 1914-1916 a similar appointment at the Victoria University in Manchester.
In 1916 he was appointed Professor of Theoretical Physics at Copenhagen
University, and since 1920 (until his death in 1962) he was at the head of
the Institute for Theoretical Physics, established for him at that
Recognition of his work on the structure of atoms came with the award of the
Nobel Prize for 1922.
Bohr's activities in his Institute were since 1930 more and more directed 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 (Cf.
»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 Hahn and Strassmann, in 1939, and formed the basis
of important theoretical studies in this field (among others, by Frisch and
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
1933-1962. They are available in English, collected in two volumes with the
title Atomic Physics and Human Knowledge and Essays 1958-1962 on Atomic
Physics and Human Knowledge, edited by John Wiley and Sons, New York and
London, in 1958 and 1963, respectively.
Among Professor Bohr's numerous writings (some 115 publications), three
appearing as books in the English language may be mentioned here as
embodying his principal thoughts: The Theory of Spectra and Atomic
Constitution, University Press, Cambridge, 1922/2nd. ed., 1924;
Atomic Theory and the Description of Nature, University Press,
Cambridge, 1934/reprint 1961; The Unity of Knowledge, Doubleday &
Co., New York, 1955.
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
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.
Until the end, Bohr's mind remained alert as ever; during the last few years
of his life he had shown keen interest in the new developments of molecular
biology. The latest formulation of his thoughts on the problem of Life
appeared in his final (unfinished) article, published after his death:
"Licht und Leben-noch einmal", Naturwiss., 50 (1963) 72: (in English:
"Light and Life revisited", ICSU Rev., 5 ( 1963) 194).
Niels Bohr was President of the Royal Danish Academy of Sciences, of the
Danish Cancer Committee, and Chairman of the Danish Atomic Energy
Commission. He was a Foreign Member of the Royal Society (London ), the
Royal Institution, and Academies in Amsterdam, Berlin, Bologna, Boston,
Göttingen, Helsingfors, Budapest, München, Oslo, Paris, Rome,
Stockholm, Uppsala, Vienna, Washington, Harlem, Moscow, Trondhjem,
Halle, Dublin, Liege, and Cracow. He was Doctor, honoris causa, of
the following universities, colleges, and institutes: (1923-1939) -
Cambridge, Liverpool, Manchester, Oxford, Copenhagen, Edinburgh, Kiel,
Providence, California, Oslo, Birmingham, London; (1945-1962) -
Sorbonne (Paris), Princeton, Mc. Gill (Montreal), Glasgow, Aberdeen, Athens,
Lund, New York, Basel, Aarhus, Macalester (St. Paul), Minnesota, Roosevek
(Chicago, Ill.), Zagreb, Technion (Haifa), Bombay, Calcutta, Warsaw,
Brussels, Harvard, Cambridge (Mass.), and Rockefeller (New York).
Professor Bohr was married, in 1912, to Margrethe Nřrlund, who was for him
an ideal companion. They had six sons, of whom they lost two; the other four
have made distinguished careers in various professions - Hans Henrik (M.D.),
Erik (chemical engineer),
theoretical physicist, following his father as Director of the Institute for
Theoretical Physics), Ernest (lawyer).
Niels Bohr died in Copenhagen on November 18, 1962