On 8 Jun 2017 11:40 a.m., "Bruce Kellett" <bhkell...@optusnet.com.au> wrote:
On 8/06/2017 7:52 pm, David Nyman wrote: On 8 Jun 2017 1:05 a.m., "Bruce Kellett" < <bhkell...@optusnet.com.au> bhkell...@optusnet.com.au> 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. Yes, this is also the point where I stumble. I've been trying somewhat inarticulately to characterise a possibly non-miraculous approach from a slightly different perspective. Suppose we think about the matter from the point of view of Hoyle's pigeonholes. Perhaps there are pigeonholes that in some sense correspond to observations that are 'malformed' with respect to the predictions of QM. Now, we are presumably to suppose that the entanglement which leads to well-formed predictions embodies a very fundamental aspect of physical reality and consequently also the possibility of meaningful observation. Hence any such malformed 'observations' should by the same assumption be considered of very low measure, in the sense of any possible contribution to Hoyle's conceptualised sum of well-formed observation. I suppose what I'm suggesting is that something fundamental and highly constraining about the demands of observation of a consistent physical environment itself effectively filters out what is possible but incompatible with those demands. Is this irretrievably circular? David Bruce -- You received this message because you are subscribed to the Google Groups "Everything List" group. 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