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atyy
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Fredrik said:I assume that what you mean by "everything is quantum" is that every physical system is such that a pure state (a mathematical thing) can represent what you previously called the system's "real state" (a real-world thing). Since the universe is a physical system, it follows that we can assign a state to the universe. But to me, "everything is quantum" just means that there's no experiment in which QM will not work, and that doesn't imply that we can assign a state to the universe.
In your minimal interpretation, does the universe have a "real state"?
Fredrik said:If someone who advocates a minimal interpretation disagrees with this, it's not because they're making some huge assumption. It's because they disagree with you about the meaning of concepts like "collapse" or "classical/quantum cut", as I did above.
I was replying to vanhees71 there, not to you, because I am not sure that your and vanhee71's idea of a "minimal interpretation" are the same. For example, I am pretty sure that bhobba's ensemble interpretation is not the same as Ballentine's, and there is no substantial disagreement between his Ensemble interpretation and Copenhagen. So far, I am not sure whether you and I disagree about the meaning of a "classical/quantum cut" and "collapse", maybe just the naming of the concept.
Edit: bhobba's Ensemble interpretation differs from Ballentine's because bhobba explicitly acknowledges as axioms a classical/quantum cut, and the equivalence of proper and improper density matrices. That's why I believe bhobba's interpretation makes sense, while Ballentine's is misleading or wrong.