From: *smitra* <smi...@zonnet.nl <mailto:smi...@zonnet.nl>>
One can a priori rule out any non-local effects using the fact that the dynamics as described by the Schrödinger equation is local.
That is false. The dynamics in the Schrödinger equation are given by the Hamiltonian. And there is absolutely no reason why the Hamiltonian should describe only local dynamics. It is easy to construct non-local Hamiltonians.
So, in any theory where there is no collapse and everything follows from only the Schrödinger equation, there cannot be non-local effects other than due to common cause effects. Then suppose that in an example where things are simplified to allow for Alice and Bob thought experiments to be discussed without having to rigorously show how Alice, Bob and the experimental apparatus used are to be extracted from the wavefunction one does see non-local effects, then it follows that these non-local effects are artifacts of these simplifications.
That does not follow at all. You forget that in addition to the possibility of non-local dynamics, the wave-function for many-particle systems is defined in configuration space, and things that are local in configuration space can easily be non-local in ordinary 3d space. And we live in 3D space, so have to live with non-local effects. Common cause explanations do not work for space-like separations.
Now, in standard quantum mechanics one does routinely make such simplifying assumptions, this allows for QM to be useful as a practical theory, but we then also know that strictly speaking, it's not how Nature really works.
How do you know how Nature really works? We observe correlations in Bell-type measurements. These indicate non-local effects in the world. Going to another world does not actually help you, because we are stuck in 3D reality.
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