Early Years of Quantum Mechanics: Some Reminiscences

Abstract

In 1925 Heisenberg published his famous article ‘Über quantentheoretische Umdeutung kinematischer und mechanischer Beziehungen’, giving the fundamentals of what later has been called quantum mechanics. For the participants of the Symposium on the Physicist’s Conception of Nature, no emphasizing of the singular character of that article is necessary; it may be more interesting to say that the ideas of this overwhelmingly fruitful publication were in close accord with the endeavours of many physicists who in those years tried to develop from Bohr’s correspondence principle consequences giving little bits of quantitative knowledge about special cases of exact laws of quantum physics. Van Vleck gave a derivation of Einstein’s laws of the relation between the probabilities of spontaneous emission and positive and negative absorption. This result of Einstein’s had been looked upon for a long time in a sceptical manner by Niels Bohr; now it was highly interesting to see, just how from Bohr’s preferred way of thinking, a derivation of Einstein’s law could be given. Born and I performed a simplified mathematical derivation of the results of Van Vleck. Our article on this topic did not contain anything new apart from our simpler form of calculation, but by studying this topic we both came to a more intimate understanding of Bohr’s leading idea.

At the request of Jagdish Mehra, I take great pleasure in writing some of my reminiscences of the early years in the development of quantum mechanics, as they are still vivid in my memory.