In MWI, the future state of the universe is uniquely determined by the past state of the universe and the laws of physics. In Copenhagen, the future state of the universe isn’t uniquely determined by those things, but is uniquely determined by those things plus a lot of additional bits that represent how each measurement goes. You could either call those bits part of the state of the universe (in which case Copenhagen is deterministic) or you could call them something else (in which case Copenhagen is nondeterministic), so it seems like a matter of convention. The usual convention is to call the bits something else than part of the state of the universe, making Copenhagen nondeterministic, but I don’t think there’s a fully principled way across theories to decide what to call part of the state of the universe.
In Copenhagen, the future state of the universe isn’t uniquely determined by those things, but is uniquely determined by those things plus a lot of additional bits that represent how each measurement goes.
That’s rather misleading. If the extra bits pop into existence at time T, then the outcome at time T+1 isn’t determined by the conditions at time T-1 as standardly envisaged by determinism. Your kind of redefining determinism.
What does it mean for a bit to pop into existence? As I see it, if I measure a particle’s spin at time t, then it’s either timelessly the case that the result is “up” or timelessly the case that the result is “down”. Maybe this is an issue of A Theory versus B Theory?
In MWI, the future state of the universe is uniquely determined by the past state of the universe and the laws of physics. In Copenhagen, the future state of the universe isn’t uniquely determined by those things, but is uniquely determined by those things plus a lot of additional bits that represent how each measurement goes. You could either call those bits part of the state of the universe (in which case Copenhagen is deterministic) or you could call them something else (in which case Copenhagen is nondeterministic), so it seems like a matter of convention. The usual convention is to call the bits something else than part of the state of the universe, making Copenhagen nondeterministic, but I don’t think there’s a fully principled way across theories to decide what to call part of the state of the universe.
Thanks I think that clarifies everything I’m wondering about. If we had a feature like Stack Overflow’s “accepted answer” this would be it for me :)
That’s rather misleading. If the extra bits pop into existence at time T, then the outcome at time T+1 isn’t determined by the conditions at time T-1 as standardly envisaged by determinism. Your kind of redefining determinism.
What does it mean for a bit to pop into existence? As I see it, if I measure a particle’s spin at time t, then it’s either timelessly the case that the result is “up” or timelessly the case that the result is “down”. Maybe this is an issue of A Theory versus B Theory?
I thought you were referring to collapse in that way.