Atla wrote: ↑Sat Jan 04, 2025 8:23 pm
where you aren't a solipsist or a (dimensionally?) superior observer compared to other people
None of the local interpretations have anything whatever to do with humans, consciousness, philosophy of mind, or anything not part of natural physics. So if it helps, put simple devices doing each of the measurement points since that's what's there anyway. No people, who's only role in any of the experiments is to say, "yea, that's what the gadget says", and also to put a name tag on a worldline or a frame. I know this is the philosophy of mind (PoM) forum, but we've diverged from that from the start. Locality has zero to do with PoM.
One local interpretation (Copenhagen) is epistemological instead of metaphysical. Still not philosophy since machines can infer a remote state as much as any human can, and we've gotten rid of the humans that so many people seem to think are so special.
I will try to frame the description from a relational view RQM and also an MWI view, both of which I understand better than the other local ones.
Remember, no people. Spin-entangled particles are measured at events X and Y, each of which sends a signal to a third event Z has both events X and Y in its past light cone.
RQM: Event X does not exist relative to Y, and Y does not exist relative to X since neither is in the past light cone of the other. Both X & Y events exist relative to Z.
MWI: Both spin up and down are measured at events X and Y causing effectively a 'split' in their respective future light cones. Any events no in these future light cones is unaffected by the measurement and the split. Event Z is in both future light cones, resulting in 4 permutations of possible measurements, except two of those (the uncorrelated ones) are not a valid solution to the Schrodinger equation, so in no world are these two permutations measured by Z.
Of course it matter not if event Z has any object that takes notice of what happened at X & Y.
In both RQM and MWI, from say event X, it would be a counterfactual statement to describe what is going on at unmeasured (by X) event Y.
Everett doesn't actually say any of what I described. He only says that the one wave function describing both states containing X and Y evolves according to the schrodinger equation, which has nothing non-local in it. My wording is more the popular MWI wording as popularized by DeWitt which is a nice, if not intuitive visual, but it is the premise of the interpretation that counts in the end.
Atla wrote: ↑Sat Jan 04, 2025 8:23 pm
Imo for it not to be a counterfactual statement ... , you would have to be in superposition and the other person would have to be in superposition exactly until the moment you two meet.
What? No, meeting is not necessary. I speak of events and measurements that take place at them and signals that pass between them. The sun does not need to meet Earth in order for it to provide energy. In the above example, Z needs to measure X and Y, and by measure, I mean the state of Z needs to be a function of X and Y, in any way. No actual recording, knowledge, or deliberate action is involved.
The word superposition isn't correctly used there, but something like that, yes. From any event, the state of any system outside that event's past light cone is not meaningfully in a defined state. That's sort of like superposition, but without some of the criteria to call it that. it very much means that there is no objective state to the universe since there's nothing to measure the universe in an objective way. Hence not realism. The universe cannot be locally real. It can be local. It can be real. It can't be both. So says Bell in '64, and those other guys who said it more precisely 55 years later.
And even if that WAS the case, you would still both find that you both seem to share a nonlocal world where your two superpositions were somehow nonlocally correlated.
Can't be. No two events can measure each other unless they're the same event. Notice that I speak of events instead of objects. Objects are not entirely defined in an unreal universe, especially in MWI where there is no meaningful identity that persists over time. All the usual pragmatic language people use presumes classical reality, as you are doing. As I am doing as well. One cannot not do it. But while classical assumptions work very well, it can be demonstrated that they're wrong.