Niels Bohr

73

Niels Bohr : biography

07 October 1885 – 18 November 1962

In 1914 Bohr managed to explain partially the splitting of spectral lines in Stark and Zeeman’s effect but he couldn’t get splitting on more than two components. It revealed the limitedness of circular orbits which were examined in the theory. It could be surmounted only after at the beginning of 1916 Arnold Zommerfeld formulated generic quantum conditions, imposed three quantum numbers for electron’s orbit and explained thin structure of spectral lines taking into consideration relativistic corrections. Bohr immediately started to reconsider his results in the light of new approach.

Further development of the theory. Correspondence principle (1916-1923)

In summer of 1916 Bohr returned to his native country and headed a chair of theoretical physics in the Copenhagen University. In April of 1917 he addressed to Danish authorities with the request to give money for building the new institute for him and his workers. On the 3d of March in 1921 after overcoming many organizational and administrative difficulties the Institute of theoretical physics was opened in Copenhagen. Now it is named after its first head (The Institute of Niels Bohr).

In spite of being very busy with administrative proceedings Bohr continued to develop his theory and tried to generalize it for more complicated atoms, for example helium. In 1918 Bohr formulated in terms of quantity the so-called correspondence principle in his article “About quantum theory of linear spectrums”, the principle united the quantum theory with the classical physics. Firstly the idea of correspondence appeared in 1913 when Bohr used the idea that passages between stationary orbits with big quantum numbers should give radiation with frequency which coincides with frequency of electron’s circulation. Since 1918 correspondence principle became a powerful means to get new results: it allowed to define probability of passages according to idea of Einstein’s coefficients and therefore define intensity of spectral lines, receive laws of selection (particularly for harmonious oscillator), give interpretation to the number and polarization of Stark and Zeeman’s splitting components.

Establishment of quantum mechanics. Complementarity (1924-1930)

The new theory became quantum mechanics, which was created in 1925-1927 in the works of Werner Heisenberg, Erwin Schrodinger, Max Born, Paul Dirac. But at the same time the main ideas of quantum mechanics, in spite of its formal success remained mainly unclear in first years. In order to understand physic basis of quantum mechanics it was necessary to link it with experience, to reveal the meaning of conception that were used in it (because using the classical terminology wasn’t rightful), to give the interpretation of its formalism.

At tat time Bohr was thinking over these questions of physic interpretation of quantum mechanics. The result of his work was complementarity principle which was represented on the congress of memory to Alessandro Volta in Como in Septenber of 1927. The initial point in evolution of Bohr’s views was his reception in 1925 of dualism wave-particle. Before Bohr refused to admit the reality of Einstein’s quantа of light (photons) which were difficult to coordinate with correspondence principle. It resulted in the article with Cramser and John Slater in which a sudden supposition about nonconservation of energy and impulse in individual microscopic processes was made (laws of conservation became statistical). But these ideas were soon disproved by experiences of Walther Bothe and Hans Geiger.

It was wave-particle duality that Bohr used as a basis of theory interpretation. The idea of complementarity which was developed at the beginning of 1927 during the vacation in Norway reflects logical correlation between two methods of description or sets of conceptions which, although they except each other, both are necessary for exhaustive description of situation. The main point of uncertainty principle is that such physic situation in which both additional aspects of phenomena reflect simultaneously and equally distinctly can’t happen. In other words, there is no conditions in microcosm in which an object has simultaneously exact dynamic characteristics belonged to two definite classes which are mutually excepting each other – that is reflected in correlation of Heizenberg’s uncertainties. It should be noticed that formation of Bohr’s ideas as he admitted influenced on philosophic and psychological investigations of Soren Kierkegaard, Harald Hoffding and William James.