From: *Bruno Marchal* <[email protected] <mailto:[email protected]>>
On 18 Apr 2018, at 15:11, Bruce Kellett <[email protected]
<mailto:[email protected]>> wrote:
From: *Bruno Marchal* <[email protected] <mailto:[email protected]>>
On 17 Apr 2018, at 00:58, Bruce Kellett <[email protected]
<mailto:[email protected]>> wrote:
From: *Brent Meeker* <[email protected]
<mailto:[email protected]>>
On 4/15/2018 8:33 PM, Bruce Kellett wrote:
We have discussed this, and I have never agree with this. The
singlet state (in classical non GR QM) describes at all times an
infinity of combinations of experimental result.
This is false. Even in Everettian QM there are only two possible
outcomes for each spin measurement: this leads to two distinct
worlds for each particle of the pair. Hence only 4 possible
parallel universes. Where do you get the idea that there are
infinitely many parallel universes? This is not part of
Everettian QM, or any other model of QM. But even if you can
manufacture an infinity of universes, you still have not shown
how this removes the non-locality inherent in the quantum formalism.
Bruno's ontology is all possible computations, so he's already
assumed (countably) infinite worlds. When there are only four or
two outcomes of an experiment it just means his worlds are divided
into four or two equivalent subsets.
That might very well be the case. But then that has absolutely
nothing to do with Everett or quantum mechanics. Bruno's long-held
claim is that Everett's many worlds obviate the need for
non-locality. But he has never been able to produce a coherent
argument to this effect. It is always this bullshit about an
infinite number of worlds -- as if that made any difference at all.
You are the one making the extra-ordinary claims. I don’t say much
more than maudlin on this issue in his book on Nonon-Locality: it
makes no sense in the many-world.
You seriously misrepresent Maudlin. To make this as clear as
possible, I have taken the third edition (2011) of Maudlin's book
"Quantum Non-Locality and Relativity" and typed out all the sections
under the heading of "many-worlds theory" from the index.
"The many-worlds theory is incoherent for reasons which have been
often pointed out: since there are no frequencies in the theory there
is nothing for the numerical predictions of quantum theory to mean."
(Page 4, Note 1.)
"So we must either abandon locality or abandon the predictions of
quantum theory for events at space-like separation. I have sketched
how some versions of the many-worlds interpretation of quantum theory
appear to do the latter, and considered in some detail how locality
might be abandoned in a technically precise way." (Page 224, Chapter 10)
"Other, more popular approaches, though, are taken quite seriously
even though they offer no clear account of local beables at all. Most
obviously, many-worlds theorists typically do not postulate any local
ontology in the foundations of the theory: all there is is the
wave-function. A lot of attention is paid to "observables" and
"decoherence", but it is not at all clear how to generate a local
ontology if all one has to work with is the wave-function. ... But
since the wave-function is not itself a local beable, nothing about
its dynamics can yield a local ontology." (Page 250.)
Then the most extensive discussion of many-worlds appears in Chapter
10, which was new for the third edition of his book.
"Standard quantum theory asserts that measurements always have
outcomes, and furthermore have unique (albeit unpredictable)
outcomes. It is exactly because such experiments always have outcomes
that we can ask after the predictions of the theory for the
correlations between the outcomes: if I measure the polarization of a
photon in some direction on one wing of an experiment and the
polarization of an entangled photon on the other wing, how like is it
that the polarization outcomes will be the same (both passed or both
absorbed) or different (one passed and the other absorbed)?
"If a many-worlds interpretation insists that there are no local
beables, then this is the situation. It cannot possibly reproduce the
predictions of standard quantum theory about the outcome of
experiments, and so is not relevant to our discussion of theories
that agree with these predictions. But the many-worlds interpretation
is never presented in this way. It is rather presented as if instead
of no local beables, there is a (largely invisible) profusion of
them. That is, instead of nothing happening on either wing of the
experiment, the standard story is that everything happens on both
wings: on both wings, there is "a world" in which the photon passes
its polarizer and "a world" in which it is absorbed, no matter how
the polarizers were oriented.
"... If the wave-function never collapses, then the matter density
evolves into a rather indistinct blob, consisting in all the
"possible" outcomes of the experiment (passed and absorbed, for
example, with all these results being recorded in macroscopic ways)
literally superposed on one another in the same space-time region.
One then tries to argue that different components of the blob are
causally disconnected from one another, and so would be mutually
transparent: many outcomes co-existing but unaware of each other. One
will typically appeal to decoherence of the wave-function and a
functional analysis of how to separate the blob into distinct worlds
to make out this conclusion.
"But two facts must be kept in mind. First, as we have seen, the
matter density ontology is not implied by the existence of the
wave-function /per se/. ... If a many-worldser wants there to be a
local matter density in space-time, then that has to be postulated in
addition to the wave-function. Second, if we produce an account like
this, then there still has to be discussion of what it means to say
that the outcomes on the two wings of the experiment are correlated
to some degree. If whenever a polarization experiment is done, with
any orientation of the polarizers, both outcomes are always produced,
then it is not obvious what it might mean to say that these outcomes
are correlated. If no sense can be made, then again the theory does
not reproduce the predictions of standard quantum theory, which
predicts definite correlations for outcomes at space-like separation.
And if some sense can be made of the existence of correlations, we
have to understand how. In particular, if appeal is made to the
wave-function to explicate the sense in which, say, the "passed"
outcome on the right is paired with the "absorbed" outcome on the
left to form a single "world", then we have to recognize that this is
not a *local* account of the correlations since the wave-function is
not a local object." (Pages 250-252.)
So Maudlin does not support your notion that many-worlds removes the
need for non-locality. In fact, Maudlin is clearly claiming the exact
opposite. He clearly does not like the many-worlds approach, calling
it incoherent. But even if sense can be made of such a theory, there
is still no possibility of a *local* account of the correlations in
polarization measurements of the entangled singlet state.
I have only the first edition. His “critics” on Everett comes from his
missing of the first-person indeterminacy (he choose “materialism”
against mechanism!): he does not look at each diaries of the observer
of the Schroedinger cat.
The 'diaries' you put so much store on add absolutely nothing.
So, indeed, he needs the “many-mind” theory to give sense to Everett,
where, at least im my edition he made clear that the “non locality”
does not apply. I quote ”Since there are no *relevant* correlation
between space-like separated event [in the many-mind theory] there is
no problem of non-locality.
"Many-minds" theory is not many-worlds theory, nor has it any connection
with Everett. Actually, I think Maudlin is too charitable towards
many-minds. As he points out in edition 3 in his extended discussion of
many-worlds, he says:
"In particular, if appeal is made to the wave-function to explicate the
sense in which, say, the "passed" outcome on the right is paired with
the "absorbed" outcome on the left to form a single "world", then we
have to recognize that this is not a *local* account of the correlations
since the wave-function is not a local object."
That is precisely what the many-minds interpretation does. It claims
that there is no non-locality because minds (separated from events) are
not space-like separated. But that relies on the wave-function, which is
itself intrinsically non-local.
As digital mechanism is of the “many-mind” type at the
phenomenological outset, all problems that some Everettian can have is
due to the Aristotelian assumption, which is inconsistent with
computationalism in cognitive science from the start (as I showed).
Digital mechanism ("comp") is not even closely related to QM and
Everett, so this does not eliminate non-locality in an Everettian
approach to quantum theory.
Maudlin’s conclusion: “Or finally, one can both avoid collapses and
retain locality by embracing the Many-Minds ontology, exacting a
rather high price from common sense”.
I think the fact that he sees "many-minds" as "exacting a rather high
price on common sense" expresses Maudlin's opinion of this approach
fairly clearly -- he considers it to be a load of horseshit. And that is
generally the opinion of the wider scientific community. Many-minds has
never gained any traction because it is just too contrived, too baroque.
Maudlin's final comment on "many-minds" is also quite telling:
"Even more radically, one could adopt the many-minds theory and deny
that there are any violations of Bell's inequality by events at
space-like separation: the relevant correlations exist only in
individual minds. All of these options become yet more bizarre when one
shifts from Special to General Relativity." (Page 222.)
And:
"If the world we experience is only in our mind why does the postulation
of mind-independent determinate physical states work so well?" (Page 222.)
It is interesting that Maudlin, in a book of nearly 300 pages on Quantum
Non-Locality, has devoted only a couple of pages to "many-worlds", and
less than one page to "many-minds". This indicates better than anything
else what he really though of these ideas as resolutions of the
non-locality problem.
For this Plato did warn us, and indeed computationalism leads to that
same form of price. Note that with comp the “many-minds” is stilll
only in the phenomenology. The ontology is given by any Turing
universal machinery (combinators, numbers, …). Of course
“counter-intuitive” is not a refutation.
What "comp" says or does not say is irrelevant to this discussion.
Bruce
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