If you go forward you need that as well. Same thing.
Only in some interpretations of quantum mechanics.
It is not.
It is an assumption as much as the assumption "gravity exists". It is backed by countless experiments.
Unitary evolution is deterministic, sure.
I don't think that question makes sense. The combined state evolves unitarily.
That is not what unitarity means, and no one said classical mechanics with point particles would be deterministic. Our world is not classical.
In response to:
Also, when you "entangle" two systems - does "unitarity" span the "entanglement" or does it apply only to the "space" "between" the "entanglements"?
The referred to paper seems to imply that unitary evolution is not generally assumed across the entanglement process. He is trying to show how it could be.
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