Neils Bohr – a Danish physicist who made foundational contributions to understanding atomic structure and quantum theory, for which he received the Nobel Prize in Physics in 1922.
Bohr developed the Bohr model of the atom, in which he proposed that energy levels of electrons are discrete and that the electrons revolve in stable orbits around the atomic nucleus but can jump from one energy level (or orbit) to another. Although the Bohr model has been supplanted by other models, its underlying principles remain valid. He conceived the principle of complementarity: that items could be separately analysed in terms of contradictory properties, like behaving as a wave or a stream of particles. The notion of complementarity dominated Bohr’s thinking in both science and philosophy.
Bohr founded the Institute of Theoretical Physics at the University of Copenhagen, now known as the Niels Bohr Institute, which opened in 1920. Bohr mentored and collaborated with physicists including Hans Kramers, Oskar Klein, George de Hevesy, and Werner Heisenberg. He predicted the existence of a new zirconium-like element, which was named hafnium, after the Latin name for Copenhagen, where it was discovered. Later, the element bohrium was named after him.
The rise of Nazism in Germany prompted many scholars to flee their countries, either because they were Jewish or because they were political opponents of the Nazi regime. In 1933, the Rockefeller Foundation created a fund to help support refugee academics, and Bohr discussed this programme with the President of the Rockefeller Foundation, Max Mason, in May 1933 during a visit to the United States. Bohr offered the refugees temporary jobs at the Institute, provided them with financial support, arranged for them to be awarded fellowships from the Rockefeller Foundation, and ultimately found them places at institutions around the world. Those that he helped included Guido Beck, Felix Bloch, James Franck, George de Hevesy, Otto Frisch, Hilde Levi, Lise Meitner, George Placzek, Eugene Rabinowitch, Stefan Rozental, Erich Ernst Schneider, Edward Teller, Arthur von Hippel and Victor Weisskopf.
In April 1940, early in the Second World War, Nazi Germany invaded and occupied Denmark. To prevent the Germans from discovering Max von Laue‘s and James Franck’s gold Nobel medals, Bohr had de Hevesy dissolve them in aqua regia. In this form, they were stored on a shelf at the Institute until after the war, when the gold was precipitated and the medals re-struck by the Nobel Foundation. Bohr kept the Institute running, but all the foreign scholars departed.
This broadcast, given on April 5, 1938 features an address by Bohr on the occasion of the 25th anniversary of his announcement of now-famous Quantum Theory. The broadcast was part of a tribute to Niels Bohr as well as the inauguration of a new wing of the Bohr Institute.
