Eric writes: < 4. The values of those microscopic observables can evolve jointly with values of more complicated large-actor observables that we describe as apparatus measuring spins etc., and the branches of the large-actor state vector can evolve to have no coherence; but that evolution is still all under the same local Hamiltonian. >
< There is no instantaneous dynamics that “creates” these correlations at the time of the measurement, the presence or absence of correlations was generated as a feature of the state vector, locally, when the EPR pair was produced, and they evolved locally with consequences for the possible correlations among macro-actors since. I guess whether this bothers you depends on whether you view the phases over which one averages to compute the coherence or decoherence as “properties” somehow of degrees of freedom at distinct locations. > Being a gearhead, I look at from the perspective of a distributed computing problem. Classical supercomputers are limited in their effective size by the speed of light. If it takes longer to share a computation result than to do it locally, then there’s no point in scaling out. Here we have new rules where the local Hamiltonian can be copied elsewhere without a cost. It’s like having an infinite dimensional communication fabric. (Assuming it was possible to engineer a system where one could isolate or outrun entanglement with the environment and assuming that measurement could be deferred until the desired evolution had completed.) Marcus
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