On Fri, Mar 25, 2022 at 7:33 AM smitra <smi...@zonnet.nl> wrote: > On 23-03-2022 02:11, Bruce Kellett wrote: > > > > Well, these results certainly show that some work needs to be done if > > you are to recover a completely local theory. > > > The unitary time evolution in QM is local. There is only an issue with > collapse, as the mechanism for this is usually left unspecified. But > apart form the issues with collapse QM is a local theory.
OK. I see now that your insistence that QM is local is based on dogma, rather than logic. Your claim is that the unitary time evolution in QM is local, therefore QM is a local theory, regardless of anything else. But that position relies on another hidden assumption. The unitary time evolution of QM depends on the Hamiltonian. The Hamiltonian is not given by the theory; it is constructed according to the details of the system one is attempting to model. Generally, one is modelling local systems, so one uses a local Hamiltonian and the time evolution is local. But this is by no means necessary. One could always use a non-local Hamiltonian, then the time evolution would not be local. This is the situation with the entangled spinor case. The state vector is non-separable and does not specify any particular separation for the two entangled particles. If one wants to continue to treat this as a single system even when the particles are far apart, one must use a non-local Hamiltonian. That is, a Hamiltonian that has a component for each of the particles. Since these particles are, in general, spacelike separated, the requisite Hamiltonian is non-local. So your assertion that quantum mechanics is local because unitary time evolution is local is false. Unitary time evolution can be local or non-local, depending on the circumstances. Non-separable entangled states are one of those circumstances in which QM is necessarily non-local. Bell's theorem then serves to prove that these non-local quantum systems cannot have a local hidden variable underpinning. Bruce -- You received this message because you are subscribed to the Google Groups "Everything List" group. To unsubscribe from this group and stop receiving emails from it, send an email to everything-list+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/everything-list/CAFxXSLT-1WKGub%3DoyuXgoMCMXSZg%2Bj9rKO0rftuJHuB5ohH-Yw%40mail.gmail.com.
