Erwin Schrödinger was perhaps the most insightful individual in the development of quantum mechanics.
He produced in 1926 the Schrödinger wave equation, arguably the most important equation in the subject, but he also made key contributions on all levels, even if these are now ignored and forgotten.
He debated the epistemology of physical science, recognising at the outset that there is no ultimate philosophical level at which determinism can be proved. In December 1922, he gave an inaugural address at the University of Zurich, in which he said:
‘It was the experimental physicist, Franz Exner, who for the first time, in 1919, launched a very acute philosophical criticism against the taken-for-granted manner in which the absolute determinism of molecular processes was accepted by everybody. He came to the conclusion that the assertion of determinacy was certainly possible, yet by no means necessary, and when more closely examined not at all very probable.’
By the time of his Nobel Address delivered in Stockholm eleven years later, he felt able to take the discussion further:
‘It is by no means a new demand to claim that, in principle, the ultimate aim of exact science must be restricted to the description of what is really observable. The question is only whether we must henceforth forgo connecting the description, as we did hitherto, with a definite hypothesis as to the real structure of the Universe. Today there is a widespread tendency to insist on this renunciation. But I think that this is taking the matter too lightly.’
This is the position that Schrödinger argued consistently over the following decades.
‘I feel a certain incongruity’, he wrote about the subjective, even solipsistic picture that developed post-Einstein, ‘between the applied means and the problem to be solved.’i
‘Such theoretical controversy is on a different plane. Physics has nothing to do with it. Physics takes its start from everyday experience, which it continues by more subtle means. It remains akin to it, does not transcend it generically, it cannot enter into another realm. Discoveries in physics cannot in themselves – so I believe – have the authority of forcing us to put an end to the habit of picturing the physical world as a reality.’ii
The importance of causal reasoning is discussed here.
Schrödinger’s concern about the unphysical and metaphysical ideas that entered physics after 1905, and especially with the Copenhagen Interpretation of quantum mechanics, led to his creation of Schrödinger’s cat, an apocryphal creature that existed in a state of superposition of life and death. It was a reductio ad absurdum, an absurd consequence of ideas that had become central to quantum theory, intended to show them as flawed. These concerns were a feature of his lectures into the nineteen fifties.
Quantum theory and waves
To quote from Max Jammer in his comprehensive analysis of ‘The Philosophy of Quantum Mechanics’, Erwin Schrödinger consistently ‘interpreted quantum theory as a simple classical theory of waves. In his view, physical reality consists of waves and waves only. He denied categorically the existence of discrete energy levels and quantum jumps, on the grounds that in wave mechanics the discrete eigenvalues are eigenfrequencies of waves rather than energies’.iii
More simply put, standing waves exist only in certain values, and are hence ‘quantised’ in the manner of energy levels.
Schrödinger ‘maintained [that] the wave picture can be extended to account, merely in terms of frequencies and amplitudes, for all known quantum phenomena, including the Franck-Hertz experiment and even the Compton effect, the paradigm of particle physics. As he had shown in a preceding paper, the Compton effect can be described as a Bragg type of reflection of one progressive wave by another; the interference pattern is formed by one wave and its reflected wave’.iv
The use of the Schrödinger equation for problems in quantum theory is commonly referred to as ‘wave mechanics’, exacerbating the tensions created by the particle model. Yet in Schrödinger’s own writing he is cautious about this. He referred in 1952, in ‘Science and Humanism: physics in our time’, to the ‘so-called wave picture’v, and in 1957, in ‘Science Theory and Man’, to ‘so-called wave mechanics’vi. It is possible that he recognised that there were important structural differences between his equation and the wave equation in use for sound and other wave phenomena. There is nevertheless nothing in it to suggest particles either, and, as we saw earlier, Schrödinger strongly resisted such a conclusion.
An analysis of this famous equation, and a possible physical interpretation, are provided here.
There is one quote from Schrödinger that suggests to me that he saw very clearly the dangers of the way that all of theoretical physics was heading, recognising that ‘without an absolutely precise model thinking itself becomes imprecise, and the consequences to be derived from the model become ambiguous.’vii This encapsulates the failure of physics over the past 100 years.
If the analysis of this site is correct, then Schrödinger’s legacy will be much more than his equation. It seems that he did not put a foot wrong, properly understanding and enunciating the epistemology of determinism, providing a cogent critique of careless thinking in physics, and unlocking the stalemate between waves and particles. If he is right, as he appears to be, then physics should have listened to him very much sooner.
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i. E. Schrödinger, Science and Humanism: Physics in our Time (CUP 1952) page 52
ii. E. Schrödinger, Science Theory and Man (Allen & Unwin, 1957) pages 203 to 204
iii. Max Jammer, The Philosophy of Quantum Mechanics (John Wiley, 1974) page 27
iv. Max Jammer, The Philosophy of Quantum Mechanics (John Wiley, 1974) page 29
v. E. Schrödinger, Science and Humanism: Physics in our Time (CUP 1952) page 40
vi. E. Schrödinger, Science Theory and Man (Allen & Unwin, 1957) page 160
vii. E. Schrödinger, Science and Humanism: Physics in our Time (CUP 1952) page 25