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Dec25-10, 07:29 PM
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Fredrik's Avatar
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The most useful way to think of QM is not as a description of reality, but as a set of rules that tells us how to calculate probabilities of possible results of experiments.

If "QM" refers to the theory defined by the standard Hilbert space axioms, then there's nothing in QM that tells us unambiguously what the system "is doing" at times between state preparation and measurement.

The "interpretations of QM" are attempts to turn QM into a description of reality. The most straightforward way to do that is to simply add new axioms on top of the ones that define QM, in order to give us a picture of what "actually happens" without changing the theory's predictions. The fact that the predictions are unchanged means that these interpretations are unfalsifiable, so they are strictly speaking not a part of science.

Another approach, which is also considered to be a part of "interpretations of QM", is to find another theory, that makes the same predictions but is defined by a different set of axioms, and see if it suggests a different picture of what "actually happens". A good example is de Broglie-Bohm pilot wave theory.