HighPhy
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Sorry, I hadn't grasp that.PeterDonis said:Isn't that what I said?
So saying that
is equivalent to saying thatPeterDonis said:the entangled superposition wave function does not describe a cat that is dead or alive, we just don't know which. It describes a cat which is in some different state that, whatever it is, is not the state of a cat that is dead or a cat that is alive
? Are these two equal concepts that characterize the paradox as Schroedinger designed it?the entangled superposition of states, peculiar to the quantum laws of the microscopic world, is reflected on a sentient being like the cat, which behaves classically, and therefore this would not be possible.
Is this compatible with the fact that a particle (or the cat, in the paradox) can assume sort of two states at the same time? And that, according to the original formulation of the Copenhagen interpretation, the observer looking at the box after opening collapses the wave function into a single state (cat either alive or dead), creating a contradiction and characterizing the paradox?PeterDonis said:the entangled superposition wave function does not describe a cat that is dead or alive, we just don't know which. It describes a cat which is in some different state that, whatever it is, is not the state of a cat that is dead or a cat that is alive.
(Of course, I'm assuming Schroedinger's original formulation without introducing the concept of decoherence that we have already discussed)
OK, this was the step I missed.PeterDonis said:No. Remember that decoherence is not interpretation dependent. So decoherence is compatible with the MWI, in which "the measurement has a result" means that it has a result in all branches of the wave function. In this case, that would be both the "dead" branch and the "alive" branch. So you can't say the cat is "either dead or alive" in the MWI, because both of those results occur, not just one. Or, to put it another way, the MWI says that the entangled superposition wave function is the physically real state of the overall system. Decoherence, in the MWI, explains why each branch of the wave function involves a single result, without any interference between them (i.e., there is a "dead" branch and an "alive" branch in the case of the cat).
So, let me see if I understand.
On a collapse interpretation, after decoherence occurs, the cat is either alive or dead.
On a no collapse interpretation such as MWI, after decoherence occurs, the cat is both alive and dead in two different branches.
But in general, since decoherence is not interpretation dependent, it cannot be said that decoherence collapses the cat into "alive" or "dead" state. Yes?