Einstein on Observerspace

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Einstein on Observerspace


Einstein repeatedly used Ernst Mach's "positivist" approach as a tool for attacking and overturning older paradigms, but found that while "observer-centric" arguments were useful in a "revolutionary" approach to physics, they were not so useful in more "evolutionary" research. Although he would later publicly describe general relativity as being a theoretical implementation of Mach's ideas about mass and inertia (Princeton lectures, 1921), in private he was already expressing frustration at the "positivist" emphasis on "observables" in 1917 (Jeremy Bernstein, Einstein pp.109):

" I do not inveigh against Mach's little horse; but you know what I think about it. It cannot give birth to anything living, it can only exterminate harmful vermin."

At least some of this frustration seems to have been due to the growing popularity of the view that quantum mechanics, having used observer-centric arguments to overturn earlier classical models, was now being regarded as an "end product" rather than as a stepping stone to new and better classical descriptions. What was "seen" to happen according to QM was now increasingly being described as physical reality.

Einstein discussed his view, that observed reality was secondary to "real" physics, with Werner Heisenberg in 1926: (Bernstein, pp.155 ):

… 1926. Heisenberg still had the notion that Einstein then held the kind of Machian positivistic views - the idea that all quantities that entered a physical theory must have "operational definitions" in terms of measuring instruments - which characterised the analysis leading to the special theory. He did not realise that Einstein had abandoned this position many years earlier when he was seeking his final formulation of the theory of gravitation. Hence Heisenberg was astounded when Einstein asked, "But you don’t seriously believe that none but observable magnitudes must go into a physical theory?" To which Heisenberg replied, with some surprise, isn't that precisely what you have done with relativity? … " ... As Heisenberg recalls, Einstein replied, "Possibly I did use this kind of reasoning but it is nonsense all the same. Perhaps I could put it more diplomatically by saying that it may be heuristically useful to keep in mind what one has actually observed. But on principle, it is quite wrong to try founding a theory on observable magnitudes alone. In reality the very opposite happens. It is the theory which decides what we can observe …"

Heisenberg relates this story in his book Encounters with Einstein and cites Einstein's statement "the theory determines what can be observed" as the inspiration of his famous uncertainty principle.