Erwin Schrödinger. 21 October 1926

Erwin Schrödinger (1887-1961).

Typed letter signed (‘E. Schrödinger’) to [Wilhelm Wien: ‘Hochverehrter Herr Geheimrat!’], Zürich, 21 October 1926.

In German. Four pages, 280 x 220mm, autograph emendations. Provenance: by descent from the recipient.

The atomic problem and wave mechanics: Schrödinger reports a fascinating conversation on the structure of the atom with that ‘dreamlike visionary’ Niels Bohr, while questioning Heisenberg’s work on the hydrogen atom. Schrödinger apologises for failing to write sooner to thank Wien and his wife for their recent hospitality; he has been in Vienna and Copenhagen, where he greatly enjoyed meeting Niels Bohr for the first time – the two talked for hours. He shares his impression of Bohr, who was not as he had expected: it is a rare man ‘who achieves such enormous internal and external success, who in his field of work is honoured internationally almost as a demi-god, and at the same time remains – I will not say humble and free of presumption – but as shy and timid as a Theology candidate. Incidentally, I do not necessarily mean this in a positive sense: it is not my ideal of a human being, [but] in comparison to the often very plentiful self-regard that one finds especially in the middling stars of our profession, this attitude is deeply sympathetic’. Schrödinger moves on to quantum mechanics: ‘Bohr’s current attitude to the atomic problems […] is really very peculiar. He is completely convinced that an understanding in the ordinary sense of the word is impossible’, which almost always drags the conversation into the realms of philosophy. However, although Schrödinger concedes that the idea of ‘visualisable images’ (anschaulichen Bilder) that he and Louis de Broglie share is still imperfect, he explains why he refuses to accept Bohr’s view, concluding: ‘for me, the comprehensibility of external natural processes is an axiom […] to understand experience means nothing more than producing the best possible order among the various facts of experience. He notes that it is not always easy to be sure of Bohr’s meaning: the latter often speaks as a ‘dreamlike visionary’, hesitates through shyness, and is painfully careful to give equal time to opposing theses. Despite their differences of opinion, Schrödinger speaks warmly of relations between himself, Bohr and Heisenberg; as regards the latter, he discusses as a matter of special interest Heisenberg’s calculation of the decay constants for the first Balmer series. ‘He therefore presumes, with the unshakeable confidence of the theoretician’ to have measured the decay of Hα [the hydrogen atom]. Schrödinger does not know whether these suppositions around the decay constant of Hα are correct.

In January 1926, Schrödinger presented for the first time his celebrated theory on wave mechanics to account for atomic phenomena in the Annalen der Physik, in a paper titled ‘Quantisierung als Eigenwertproblem’: subsequently known as ‘Schrödinger’s equation’, this famous formulation was lauded by the physics community when it was published in 1926 and remains one of his central achievements. Some months after the paper came out, Schrödinger writes to Wilhelm Wien, discussing a meeting with Niels Bohr in Copenhagen; Bohr had already played host to Werner Heisenberg, Max Born and Paul Dirac, all among the group collaborating on the development of mathematical foundations for quantum mechanics, and Schrödinger’s work had caught his attention for its attempt to explain quantum physics in classical terms using wave mechanics. The point of their theoretical divergence during the meeting seems to have been Schrödinger’s insistence that scientific phenomena should be understood by theories that are visualisable in space and time – the notion of ‘Anschaulichkeit’ that he refers to in the present letter – while Bohr believes such an understanding is impossible. Heisenberg’s work on the hydrogen atom was directly relevant to the debate, as the Schrödinger equation took used a hydrogen-like atom as a reference point.

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