On Wed, Dec 18, 2024 at 9:57 AM Russell Standish <[email protected]> wrote:
> On Tue, Dec 17, 2024 at 05:48:02PM +1100, Bruce Kellett wrote: > > > The proof is fairly straightforward. Informally, locality > means > > that if we have two disjoint points, A and B, separated by > some > > distance , either spacelike or timelike, then what happens > at point > > A cannot affect what happens at point B, and what happens at > point > > B cannot affect what happens at point A. This informal > notion can > > be formalized by saying that the joint probability for > outcomes a > > at point A , and b at point B, must factorize, so that the > joint > > probability can be written as a product of two terms, one > dependent > > only on factors local to point A, and the other dependent > only on > > factors local to point B: > > > > Pr(a,b) = p(a)*p(b), > > > > once all common causal factors have been taken into account. > > > - > > > > Thank you. That's what I thought. AG > > > > > > How is non-local defined? Does it imply instantaneous, or faster > than light > > transference of information? AG > > > > > > I defined non-local above: whatever happens at A does not affect B and > vice > > versa. It has nothing to do with faster-than-light transfer of > information. If > > there was some FTL transfer between A and B, then the effect would be > local. > > The idea that non-locality means FTL effects is a common confusion. That > idea > > is totally wrong. > > > > Bruce > > It strikes me that for Bruce, "local" means factorisability of the > joint probability distribution. Which for most other people is what > "locally real" means, IIUC, ie the conjunction of a measurement > outcome depends only on physical things (reality) in the past light > cone (locality). > I thought it had been made clear that the factorization holds after all such common causal factors had been taken into account. Reality does not enter into it. "Reality" is usually taken to refer to Einstein's idea of realism - namely that a state has a definite value before any measurement. That idea of realism plays no role in the Brunner proof of non-locality. I'm not saying Bruce is wrong with his definitions, but he is in > the minority AFAICT. > > BTW - I'm not claiming that MWI is a locally unreal theory, but it has > been claimed by eg Deutsch. But now I see why Bruce would say that any > "locally unreal" theory is "non-local", as his definitions are different. > I think the fact that the CHSH inequality can be derived by assuming only factorizability as Brunner has defined it is sufficient for one to claim that quantum mechanics is non-local in the required sense. So any theory that reproduces the results of quantum mechanics must be non-local. Claims by Deutsch and others that MWI is local are, therefore, spurious. Either MWI is not a full implementation of quantum mechanics, or it, also, is non-local. Bruce -- You received this message because you are subscribed to the Google Groups "Everything List" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion visit https://groups.google.com/d/msgid/everything-list/CAFxXSLTpuCMB8QXo58tVMQqtbD%3DwC1gj%2BThppxthQmLoNM9UmA%40mail.gmail.com.
