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I'm curious whether philosophers of quantum mechanics (QM) take the following idea seriously:

The Copenhagen interpretation makes sense when combined with decoherence theory. "Measurements" are defined via decoherence of the wavefunction, and the amplitude of each "decohered branch" determines the probability of that branch becoming the one real, unique outcome.

I suppose objective collapse theories (e.g., GRW) take the above idea seriously in a way, but sometimes I think it is (I think) suggested by physicists that the above idea makes sense even without objective collapse. For example, here is a quote from an answer (by @knzhou) to this past physics.SE question of mine:

We know the process of measurement is intimately tied to decoherence, which is perfectly continuous. Copenhagen and, say, many worlds just differ on how to treat branches of a superposition that have completely decohered.

I've read only a little philosophy of QM (e.g., Tim Maudlin's book, "Philosophy of Physics: Quantum Theory"), and I don't think I've heard anyone even try to defend this idea of "Copenhagen + decoherence" carefully (unless, again, they are really talking about objective collapse). And "Copenhagen + decoherence ≠ objective collapse" doesn't make sense to me, because measurements are absolute (a single branch of the wavefunction is chosen and all others disappear), whereas decoherence is gradual (there is no exact line between coherent/incoherent branches).

So my question is, Does anyone have a serious theory that combines Copenhagen and decoherence (without being an objective collapse theory), and if so, what is it?

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  • My understanding is that Copenhagen + decoherence is the standing formulation of Copenhagen. Indeed, decoherence solves one half of the measurement problem for Copenhagen: how does the eigenbasis for collapsing come up? But the wave function is still interpreted as state of knowledge and collapse as a statistical update with moveable timing, not an objective happening.
    – Conifold
    Jul 21, 2021 at 3:28

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