Feynman's Interpretation of Quantum Theory

Page 14 of Zeh's Feynman's Interpretation of Quantum Theory:
Feynman then gave a resumé of the conference, adding some "critical comments", from which I would like to quote a remark addressed to mathematical physicists (page 150):
Feynman: "Don't be so rigorous or you will not succeed."
(He explains in detail how he means it.) It is indeed a big question what mathematically rigor-
ous theories can tell us about reality, since their axioms can never be exactly empirically
founded (as emphasized already by Henry Poincaré 20 ). This question is particularly pressing if the formal theory does not even contain the most general axiom of quantum theory: the superposition principle. So towards the end of his resumé (page 154), he said
Feynman: “Even if one believes in exhausting the classical problems first and also
believes in unification, there is some question as to whether the unified theories are the
correct starting point. At the end of the list of classical problems there is the real prob-
lem of the feasibility of separating the strictly classical questions from the quantum
Doesn't this warning perfectly apply to the present search for a unified theory? The important
lesson from decoherence theory was that the superposition principle holds even where it did
not seem to hold, and that classical concepts emerge from a universal quantum theory: their
superpositions cannot be observed locally even if they persist in the global wave function.
Nonetheless, many modern field theorists and cosmologists seem to regard quantization as of
secondary or merely technical importance (just providing certain "quantum corrections") for
their endeavors, which are essentially based on classical terms – such as classical fields – (see
also Ch. 6 of Ref. 16). It is then not surprising that the measurement problem never comes up
to them. How can anybody even argue about unified quantum field theories or cosmology
(which must both include a description of observers) without first defining his interpretation,
14that is, without clarifying whether he/she is using Everett’s interpretation or some kind of col-
lapse mechanism (or something even more speculative than a collapse)?

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