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By local I mean local in the sense of special relativity. Stuff at a point in spacetime only affects stuff at that point and in its causal future. If you want t

By local I mean local in the sense of special relativity. Stuff at a point in spacetime only affects stuff at that point and in its causal future. If you want to affect something somewhere else then you have to fire a light particle or whatever there. Interference between different "branches" of the wavefunction is local if you're comparing the value of the two branches at the same point(s). Edit: I should emphasise that interference is a completely local (in the sense I use it above) process in every interpretation of quantum mechanics I am aware of (even Copenhagen) generally the thing that makes quantum mechanics non-local in various interpretations is measurement.

l33tman 6y ago
Yeah I guess we're thinking similarly in that case :) It IS annoying though that it seems like the "last step" to produce measurable results requires a global integration though even though all the field interactions are local. The path integral QFT approach even makes this explicitly manifest, and modern QFT is the gold standard of reality-matching-predictions no matter the field.. Oh BTW re your edit: I'm not sure what "local interference" would mean. If interference effects could be solved locally, there would be no entanglement, no violated Bell's theorem or EPR experiments etc.
- eigenket 6y ago
  I think maybe we're talking about different things? Could you be more precise about the sort of interference effects you're talking about? I generally wouldn't call entanglement an "interference effect". When I think about interference my mind goes to the patterns emerging from double slit experiments. Consider a quantum teleportation experiment, I start with N (a|0> + b|1>) ( |00> + |11> ) where N fixes the normalisation I do a measurement on qubits 0 and 1 in the basis ( |00> + |11> ), ( |00> - |11> ), ( |10> + |01> ), ( |10> - |10> ) and observe the outcome associated with ( |00> + |11> ), so now my state is N ( |00> + |11> ) (a|0> + b|1>) Now we collect our grant money because we've teleported the state to the other end. I don't see where the interference effect(s) were, from my perspective everything looked local and nice except for the impact of measurement, which is nonlocal in the "standard" picture and unexplained in general. I think my perspective on interference comes from the fact that water waves and sound waves (for example) exhibit interference in pretty much the same way that wavefunctions do, but we can't break Bell inequalities with them since we don't have the same weirdness around measurement.

l33tman 6y ago

Yeah I guess we're thinking similarly in that case :) It IS annoying though that it seems like the "last step" to produce measurable results requires a global integration though even though all the field interactions are local. The path integral QFT approach even makes this explicitly manifest, and modern QFT is the gold standard of reality-matching-predictions no matter the field.. Oh BTW re your edit: I'm not sure what "local interference" would mean. If interference effects could be solved locally, there would be no entanglement, no violated Bell's theorem or EPR experiments etc.

eigenket 6y ago
I think maybe we're talking about different things? Could you be more precise about the sort of interference effects you're talking about? I generally wouldn't call entanglement an "interference effect". When I think about interference my mind goes to the patterns emerging from double slit experiments. Consider a quantum teleportation experiment, I start with N (a|0> + b|1>) ( |00> + |11> ) where N fixes the normalisation I do a measurement on qubits 0 and 1 in the basis ( |00> + |11> ), ( |00> - |11> ), ( |10> + |01> ), ( |10> - |10> ) and observe the outcome associated with ( |00> + |11> ), so now my state is N ( |00> + |11> ) (a|0> + b|1>) Now we collect our grant money because we've teleported the state to the other end. I don't see where the interference effect(s) were, from my perspective everything looked local and nice except for the impact of measurement, which is nonlocal in the "standard" picture and unexplained in general. I think my perspective on interference comes from the fact that water waves and sound waves (for example) exhibit interference in pretty much the same way that wavefunctions do, but we can't break Bell inequalities with them since we don't have the same weirdness around measurement.