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No.Blue Scallop said:In an isolated close system that evolves unitarity, can decoherence occurs inside the isolated close system?
No.Blue Scallop said:In an isolated close system that evolves unitarity, can decoherence occurs inside the isolated close system?
Demystifier said:No.
First, in MWI, it is the multiverse (not the universe) that evolves unitarily. The multiverse is the collection of all universes.Blue Scallop said:In MWI, the universe is a close system and evolves unitarity.. so how can there even be decoherence inside it?
Demystifier said:First, in MWI, it is the multiverse (not the universe) that evolves unitarily. The multiverse is the collection of all universes.
Second, decoherence happens not in the whole universe/multiverse, but in a part of it.
I have misunderstood your question. Decoherence can happen in a subsystem of the closed system, but not in the whole closed system.Blue Scallop said:But you said decoherence couldn't occur inside a close system
Demystifier said:I have misunderstood your question. Decoherence can happen in a subsystem of the closed system, but not in the whole closed system. This is like saying that energy can disappear in a subsystem of the closed system, but not in the whole closed system.
Please do not imply that I said something which I didn't. I never said anything about phase randomization. And she is right.Blue Scallop said:But you said in a close system with unitarity.. decoherence could occur in the subsystem even without a phase randomization.. is she wrong?
Demystifier said:Please do not imply that I said something which I didn't. I never said anything about phase randomization. And she is right.
If there is phase randomization, then there is no unitarity. But let me be clear. I think she is right in her critique of MWI, but I don't think that this problem should be resolved by phase randomization. I think it should be resolved by other means, most likely by introducing new "hidden" variables. In this way the theory remains unitary and the problems of MWI (that she correctly identifies) are avoided without phase randomization.Blue Scallop said:I thought in a close system in unitarity evolution, there is no phase randomization? If there is phase randomization, can it still be called unitarity?
Demystifier said:If there is phase randomization, then there is no unitarity. But let me be clear. I think she is right in her critique of MWI, but I don't think that this problem should be resolved by phase randomization. I think it should be resolved by other means, most likely by introducing new "hidden" variables. In this way the theory remains unitary and the problems of MWI (that she correctly identifies) are avoided without phase randomization.
This is an illusion. Classical statistical mechanics (and hence Bohmian - hidden variable - mechanics) also needs phase randomization to go from the underlying deterministic dynamics to an observed stochastic one.Demystifier said:by introducing new "hidden" variables. In this way the theory remains unitary and the problems of MWI (that she correctly identifies) are avoided without phase randomization.
When it comes to statistics and probability, I disagree with you almost always. What is your opinion about https://www.physicsforums.com/threads/the-sleeping-beauty-problem-any-halfers-here.916459/ ?A. Neumaier said:This is an illusion. Classical statistical mechanics (and hence Bohmian - hidden variable - mechanics) also needs phase randomization to go from the underlying deterministic dynamics to an observed stochastic one.
This is completely unrelated to the problem how to get a stochastic process from a deterministic dynamics. The latter needs some randomization assumption as it introduces irreversibility and hence an arrow of time into a reversible dynamics.Demystifier said:What is your opinion about
Wrong. There is decoherence, but you just can't use pure MWI to explain it. What I'm saying is that pure MWI is an incomplete theory.Blue Scallop said:So in a close system with unitary (or unitarity) evolution, even the subsystem shouldn't have decoherence.. right?
Perhaps, but I am really curious to see how do you think on that.A. Neumaier said:This is completely unrelated
Demystifier said:Wrong. There is decoherence, but you just can't use pure MWI to explain it. What I'm saying is that pure MWI is an incomplete theory.
The "you" which performs the measurement must also be described as a subsystem of quantum particles.Blue Scallop said:you have a three-particle entangled system and you measure just two
Well, whatever she answers is correct, as it is a question about subjective probability. Subjects do not need to act rationally.Demystifier said:Perhaps, but I am really curious to see how do you think on that.
Again, I disagree.A. Neumaier said:Well, whatever she answers is correct, as it is a question about subjective probability. Subjects do not need to act rationally.
Demystifier said:When it comes to statistics and probability, I disagree with you almost always.
Disagreeing doesn't make you correct.Demystifier said:Again, I disagree.
Demystifier said:The "you" which performs the measurement must also be described as a subsystem of quantum particles.
Disagreeing on such basic things makes me unmotivated to discuss more complicated things on probability in physics with you.A. Neumaier said:Disagreeing doesn't make you correct.
Yes.Blue Scallop said:You seemed to be saying that decoherence can occur even without phase randomization inside a subsystem.
I say yes, provided that one uses a better interpretation of QM (e.g. Bohmian).Blue Scallop said:In a natural close quantum system in unitary dynamics without phase randomization.. can einselection of pointer observable occur naturally? She seemed to be saying not. How about you?
Demystifier said:Yes.I say yes, provided that one uses a better interpretation of QM (e.g. Bohmian).
Yes, that's what I think.Blue Scallop said:In pure MWI, it's true systems can't even be defined?
Demystifier said:Yes, that's what I think.
What do you mean by "pure unitarity"?Blue Scallop said:But you said in pure unitarity, decoherence is possible.. isn't it that having system is related to decoherence.. so in pure unitarity, where there is decoherence, system is automatically defined...
or maybe it's about the preferred basis, but pure unitarity has system and basis.. unless you mean there is no basis in pure unitarity? really?
Demystifier said:What do you mean by "pure unitarity"?
It looks as you fail to distinguish a system from a subsystem.Blue Scallop said:pure unitarity = closed system in unitary (or unitarity) evolution
so does pure unitarity automatically have system?
But why did Zurek ask "It is the question of what are the “systems” which play such a crucial role in all the discussions of the emergent classicality"
Was he asking about the preferred basis or the mere existence of systems? If not what was he talking about (since a close quantum system in unitarity dynamics has systems in the first place)?
Demystifier said:It looks as you fail to distinguish a system from a subsystem.
Yes.Blue Scallop said:Or do you need a preferred basis to have a subsystem?
Demystifier said:Yes.
I didn't say that there is no preferred basis at all. There isn't in MWI, but there is in Bohmian interpretation.Blue Scallop said:But in a closed system with unitarity dynamics.. you said decoherence can occur inside.. but how can it have a subsystem when there is no preferred basis at all?
Demystifier said:I didn't say that there is no preferred basis at all. There isn't in MWI, but there is in Bohmian interpretation.
Yes.Blue Scallop said:You mean if there is no preferred basis.. there is no subsystem? Like the two are linked together?