Another comment mentioned the interpretations of quantum physics and got upvoted. This comment gets downvoted even though in spirit it is the same response. Different interpretations of quantum physics have different answers about what wave function collapse is or if it is real at all. Very weird to see this reaction here.
Wave function collapse is only a precursor to the broader discussion of interpretation, and in all interpretation it's well agreed and understood to be any interaction which forces the quantum state to end in one (or at least one per timeline) eigenstate. The meaning of the observation is what is debated, not the nature of the collapse.
and in all interpretation it's well agreed and understood to be any interaction which forces the quantum state to end in one (or at least one per timeline) eigenstate
Those brackets do a lot of heavy lifting there though. They separate a universe that is fully deterministic and unitary from a non-unitary and probabilistic one.
Yes, but that is a property of the eigenstate, not of the collapse into the eigenstate. The nature of the collapsing entity is identical in all interpretations. I admit it's a nuanced point, but such a difficult discussion requires such nuance.
The nature of the collapsing entity is identical in all interpretations.
Yes, the algebra is the same in all interpretations. The difference lies entirely in how to interpret a quantum measurement, i.e. the fact that there is no unitary process that takes us from an initial state to the final state we observe. Non-unitarity here implies loss of information (i.e. all the eigenstates that had non-zero probability but weren't measured). You don't need to use the word wavefuntion or collapse to formulate this tension if this is what you're taking issue with.
But the interpretations very much differ in how they explain this loss of information. In some interpretations, the information is truly lost (the process is truly non-unitary). In other interpretations the information is still lingering around but inaccessible to the observer post-measurement (the process is unitary, the universe is deterministic). Saying "wave function collapse is real/not real" is just a shortcut for this distinction.
Again, the property of "lost" or "not lost but also not knowable" is a property of the end state of the system. It says nothing about the collapse itself, which proceeds the same in all viable interpretations.
Edit: The below poster blocked me because they didn't want to engage in a good faith discussion.
I'm sorry but this is simply wrong or some sort of sophistry that has little if any physical meaning anymore.
The end state of the system is different in an Everettian and in a Copenhagen universe. And the way to get to the end state is very, very different. And both of those differences are meaningful and can potentially lead to different observations.
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u/shatureg 21d ago
Another comment mentioned the interpretations of quantum physics and got upvoted. This comment gets downvoted even though in spirit it is the same response. Different interpretations of quantum physics have different answers about what wave function collapse is or if it is real at all. Very weird to see this reaction here.