On Wed, Oct 9, 2019 at 11:36 AM 'Brent Meeker' via Everything List < [email protected]> wrote:
> On 10/8/2019 5:03 PM, Bruce Kellett wrote: > > On Wed, Oct 9, 2019 at 10:49 AM 'Brent Meeker' via Everything List < > [email protected]> wrote: > >> On 10/8/2019 4:21 PM, Bruce Kellett wrote: >> >> On Wed, Oct 9, 2019 at 9:53 AM 'Brent Meeker' via Everything List < >> [email protected]> wrote: >> >> >>> What additional assumptions do you mean? >>> >> >> What assumptions does he have to make to get a probability >> interpretation? Probability is not an evident property of the SE. Like many >> approaches to probability in Everett, he has to assume decoherence to >> distinguishable branches to get anywhere. But that relies on using the Born >> rule to justify ignoring branches with low amplitude >> >> The low amplitude branches aren't ignored. Do you mean cross-terms in >> the density matrix? >> > > Explain to me how these are functionally different from low amplitude > branches. > > > The branches are projections of the universal Hilbert ray onto > (approximately) orthogonal subspaces corresponding to the preferred basis. > Cross terms are what make them approximate. The cross-terms supposedly go > to zero when you compute the reduced density matrix, but the diagonal terms > don't go to zero...they measure the probability of the branches, including > branches with low probability. > It seems to me that that is what I said. > -- the notorious "trace over environmental degrees of freedom". Sean's >> "self-locating uncertainty" is not well-defined. >> >> >> I tend to agree with you there. But if you assume that the human brain >> is a classical information processor of limited capacity I think you could >> get there. >> > > Only at the price of re-introducing the human observer into your > exposition of QM. I thought that was the cardinal sin of the CI, and here > Sean is bringing it back into Everett!!!! > > > Well, if you're going to explain why we experience a classical world, > you're going to have to say something about experience. To say it's > information processing in the brain sounds pretty good to me. > But that is what he needs in order to introduce probabilities -- and that is just as circular as the Deutsch-Wallace use of decision theory -- both need observers to have a notion of probability. > In the lecture he hints that the observer is uncertain about the fate of >> the cat until he opens the box -- until then he is uncertain of which >> branch he is on. But given the timescale of decoherence, he has branched >> within 10^{-20} sec, so the is no longer any "self-locating uncertainty" -- >> he is definitely on one branch or the other, he just doesn't know which. >> And that is just classical probability due to lack of knowledge -- nothing >> quantum about it. In another interview, he does suggest that the >> "self-locating uncertainty" lasts only until decoherence reaches the >> observer, at which time copies become entangled within each branch. Now if >> you can think relevant thoughts in 10^{-20} sec, then his argument might >> make some sense. But it fails to convince..... >> >> >> So you're faulting him for not calling 1e-20sec zero? >> > > No. I am not faulting him for not calling it zero. I am faulting him for > calling something that is uncertain in any quantum sense for 10^{-20} sec > significant for the interpretation of probabilities. > > But it's relevant to showing MWI is consistent with the experimenter not > knowing which "world" he is in. He might not look at the data for a long > time. > Exactly. So his "uncertainty" is purely classical. That is not an explanation of quantum probabilities. Remember, the Everettian promise is that the concept of "an observer" is irrelevant for understanding the theory -- it is all in the SWE. The theory provides its own explanation...... 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/CAFxXSLQnC%3DA2q2T8dCDbmCkG%3D6AA91u24rN4pPb%2BnGfMKivzEA%40mail.gmail.com.
