I may have been using a technical term too glibly there. Local conservation of momentum is a fundamental property of any translation-invariant model in the fra

I may have been using a technical term too glibly there. Local conservation of momentum is a fundamental property of any translation-invariant model in the framework of quantum field theory. All this means is that the (vector) momentum flowing into any point in space-time must equal the momentum flowing out plus any increase in "stored" momentum at that point (whatever that might mean). Quantum mechanics is a "local" theory in the formal sense, at least in any halfway mainstream formulation (from Copenhagen to many-worlds). Even the "spooky action at a distance" that folks talk about in reference to quantum phenomena is never capable of transmitting information outside of the "cone of causality" in space-time (which is the "light cone" in most relativistic theories: information can't travel faster than light).