On Wed, Oct 9, 2019 at 10:49 AM 'Brent Meeker' via Everything List <
everything-list@googlegroups.com> 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 <
> everything-list@googlegroups.com> 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 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!!!!
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.
> Seems nit-picky. I see the problem as sloppy introduction of "the
> observer" harking back to CI.
>
Yes, that is a point I have made.
> If observers are quasi-classical (no funny stuff in microtubles) then it
> should be enough to talk about uncertainty in the location of the geiger
> counter or the environment, but I understand Sean is trying to explain why,
> according to Everett, people don't see the superposition.
>
That is achieved by decoherence and the preferred pointer basis. No need to
introduce observers and self-locating uncertainty.
Bruce
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