Comment by linuxhansl
15 hours ago
FWIW (and it's not worth a lot, since I'm a layperson), I think the interpretation that makes the most sense to me is Quantum Decoherence (https://en.wikipedia.org/wiki/Quantum_decoherence).
My interpretation of the interpretation is that the universe is a giant constraint resolution system. Particles are free to be anywhere randomly as long as they do not randomly interact with other particles. As soon as they interact they have fewer "degrees of freedom", since now they interacted. When they interact with anything macroscopic they have no freedom left. Makes sense to me anyway.
Decoherence isn't an interpretation, but an experimentally established fact. What makes interpretations interpretations is that they cannot be experimentally distinguished (or in some cases, can only be with great difficulty). That said, the study of decoherence has certainly made aspects of the measurement problem easier to come to terms with, which in turn has bearing on the intuitive draw of some interpretations over others. In particular, it helps answer when universes should be said to "split" in MWI (though, as many will rightly tell you, that's not a complete solution to the measurement problem, as decoherence is still unitary--i.e., there's no in-principle irreversibility there).
Decoherence is how you get from "Maybe the wave function never collapses" to "Maybe there are many parallel 'universes' in QM.".
Decoherence gets you a diagonal density matrix description of the world. It doesn't get you a single-state description of the world. Going from "There are many parallel universes" to "and we are in one of them" still takes a lot of handwaving.
But we're not in one of them. We're in all of them. Yours is a misunderstanding of how it feels to be in a quantum superposition. There's no component of the wave function in which Schrodinger's cat experiences anything other than being alive or being dead. There's no component in which it feels like it's in some ghostly combination of both outcomes. Both components of the wave function exist in superposition, and to the extent that they are decoherent, they do not interact and do not even notice that they have company. I don't mean this only as an academic statement; it's also true of you and me, at this very moment.
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Decoherence only hides entanglement by having the entire world go into a complex superposition. It's entirely compatible with MWI. Decoherence does not resolve the measurement problem on its own. It's not a separate interpretation. It only provides us a mathematical reason for why the world appears classical.