2017-06-08 12:40 GMT+02:00 Bruce Kellett <[email protected]>:
> On 8/06/2017 7:52 pm, David Nyman wrote: > > On 8 Jun 2017 1:05 a.m., "Bruce Kellett" < <[email protected]> > [email protected]> wrote: > > > The question then, is whether many worlds can provide a fully local > account of this situation. I claim, with most present day physicists, that > MWI does not provide any such local account. > > > I suspect I'm being obtuse in some way here but, rereading the quote > attributed to Bell himself by Wikipedia about superdeterminism, it strikes > me that MWI seems to describe a species of this sort of thing. IOW when > Alice and Bob make their measurements, the consequence in terms of branches > is a spectrum of all the possible outcomes. Indeed one could say that this > is what has been propagating from one to the other, rather than a > 'particle'. Let's say then that the various versions of Alice and Bob that > consequently coexist in MWI terms, however far apart they may have been, > eventually meet to compare notes. Again, the spectrum of possible outcomes > implicit in the global MWI perspective travels with them, as it were. > However, of all the possible pairings of the two, it appears to be > 'superdetermined' that each observed encounter must be consistent with the > predictions of QM. And so it would appear that the paired results of their > joint measurements are somehow inseparable, in Wallace's language, without > there having been any action at a distance. If this depiction were to make > any sense, one might then enquire what common cause, or other explanatory > device, could account for this apparent superdetermination of observed > outcomes? > > > I don't think that superdeterminism and MWI have very much in common. > Although Bell did acknowledge that superdeterminism provides a possible > local loophole to his theorem, Bell always thought that superdeterminism > was sufficiently implausible to be disregarded as a serious contender as an > explanation. > > I tend to agree with the comment from Zeilinger on the same Wiki page, to > the effect that such absolute superdeterminism would render the whole > scientific enterprise otiose. I think that non-locality is a better > approach -- at least then science can still make sense. > > The problem with attempts to find local accounts of the correlations > between Alice and Bob is that their measurements are taken to be > independent. If they are independent, then they cannot be correlated -- > that is in the definition of independence. Superdeterminism circumvents > this, simply by denying that Alice and Bob can freely choose their > measurements, and are consequently not independent. > > As I understand the better attempts to give an account in MWI, it is > accepted that Alice and Bob are independent, so their results are > uncorrelated *when they are made*, but the necessary correlation is built > later when they meet to compare results. I find this unconvincing, and no > satisfactory account of any mechanism whereby this could be achieved has > been given. Accounts along this line seem to depend on multiple worlds > containing all possible results that somehow, miraculously, pair up, > without any outside intervention, in such a way to give the necessary > correlations. This is rendered less plausible if one considers timelike > separations, where Bob, say, is always in Alice's forward light cone, so > any splitting of either observer is communicated to the other by normal > decoherence, long before the other measurement is made, and before they > meet up to compare lab books. > > If I remember David Deutsch explained that the worlds were not "splitting" but differentiating, and thus are all preexisting... so even if their measures are independent, this gives only a self localisation... and so nothing non-local happens ? Quentin > 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 post to this group, send email to [email protected]. > Visit this group at https://groups.google.com/group/everything-list. > For more options, visit https://groups.google.com/d/optout. > -- All those moments will be lost in time, like tears in rain. (Roy Batty/Rutger Hauer) <http://www.avg.com/email-signature?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail> Virus-free. www.avg.com <http://www.avg.com/email-signature?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail> <#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2> -- 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 post to this group, send email to [email protected]. Visit this group at https://groups.google.com/group/everything-list. For more options, visit https://groups.google.com/d/optout.
