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May 29, 2023·edited May 29, 2023Liked by Ulrich Mohrhoff

'Falkenburg gets it right: “Quantum physics investigates nothing but phenomena in a classical environment.... [C]urrent physics only supports the belief in the existence of quantum processes within a classical world”'

What a nice quote and a fascinating post overall.

Gunther Ludwig's four volume work on the Foundations of Quantum Theory begins with a derivation of quantum theory as describing the set of effects one classical system can have on another without the assumption that one may objectivate those effects, i.e. reconstruct them as being due to some third object "exchanged" between the two. He then reconstructs all of atomic and molecular physics along these lines.

From this we get a nice explanation of why quantum physics uses universal covers of various groups, i.e. SU(2) rather than SO(3) or SL(2,C) rather than the Lorentz group. Since we must use not the rotation group (e.g. SO(3)) but rather the relative orientation group (SU(2)) describing the relative orientations of the classical systems. Gravitation by Wheeler, Misner and Thorne has a similar explanation of SU(2).

Of course we have the notion of particles being explicitly tied to the Lorentz group and thus not clearly surviving acceleration or curved spacetimes. Even more so quarks describe not even classical processes, but a certain algebraic decomposition of classical processes in terms of fictional processes, hence the negative norm to their states.

The complete failure of the bottom up view of the world in quantum theory should really be driven home to students and it's one of the best parts of your book that you do so.

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