On Tue, Oct 1, 2019 at 9:38 PM Bruno Marchal <[email protected]> wrote:
> > On 1 Oct 2019, at 07:37, 'Brent Meeker' via Everything List < > [email protected]> wrote: > > > > On 9/30/2019 9:52 PM, Bruce Kellett wrote: > >> > >> I haven't read Carroll's book, it isn't released in Australia until > November. I would be interested to see if he has a better account of Bell > non-locality than Wallace. About the spread of "splitting": decoherence is > a local physical interaction -- photons interacting with walls and the > like. This clearly spreads at the speed of light (or less). But splitting > is not really just decoherence. The trouble with Bell non-locality is that > the splitting of worlds is not a physical interaction like decoherence. > Bruno and others speak about a "spread of entanglement" as being associated > with the splitting. But again, entanglement is the result of physical > interaction, and the interaction of looking at a pointer to see a result is > not really an entanglement interaction. I think that there is a lot of > loose thinking about this "splitting" process. > >> > >> The absence of disallowed branches (Alice and Bob both seeing spin-up > with aligned polarisers) is not a matter of worlds (branches) cancelling by > destructive interference, because there is no interaction -- the light > carrying information from the space like separated measurements is not > coherent, so it can't interfere. If it were coherent, allowing > interference, then that coherence itself would indicate non-locality. > > > > But the copying of information as to the measurement result, quantum > Darwinism, is a physical interaction that writes the information into the > environment. So that we can imagine that both UP and DOWN information > spreads from Alice and also separately from Bob. Where they overlap in the > future they must correlate per QM. Why can't we suppose that the > inconsistent worlds cancel out. You say the light carrying the information > isn't coherent, but it's not just the light that carries the information; > it's information encoded in the wave function of the environment. So no > small part of the environment (like the light) is going to appear coherent, > but it's still going to be inconsistent with the opposite result and zero > out cross terms in the density matrix. That's essentially what the > mathematical process of taking the reduced trace does. > > Right. Then the non locality has disappeared from the wave equation at the > start. How? The wave function itself is non-local. > The Wave act locally in the Hilbert space (or the von Neumann algebra, and > we see non locality only from a branch/term perspective. But every branch in the Everettian picture shows non-locality. Where do the other branches make each branch actually local? You are still not explaining anything. > But without collapse, the non locality does not involved neither FTL > communication, nor any FTL influence (which, for a realist on a unique > world would be as much embarrassing). Neither collapse nor FTL are the issue. We can agree that there is no FTL action because that would amount to a local explanation -- the FTL exchange would interact locally at each end. The effect is non-local because the non-separable wave function is intrinsically non-local. Lorentz invariance is intact because of the no signalling theorems. That is why the violation of Bell’s inequality is a quasi-confimartion of > the “other histories” being as real as our’s. > As I said, the thought that Bell might be local in many worlds was really the last hope for MWI being of any use. But all attempts to demonstrate this have failed. The sort of mumbo jumbo you offer here is no better than Wallace's obscurantism. 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 on the web visit https://groups.google.com/d/msgid/everything-list/CAFxXSLSPvk7vU6VHVx2ghaYPL%3Dpg1Vz4xhsccRfRxgOvyfNvwA%40mail.gmail.com.
