Re: A thought on MWI and its alternative(s)

[Bruce Kellett]

On 8/06/2017 11:25 pm, David Nyman wrote:
On 8 Jun 2017 12:50 p.m., "Bruce Kellett" > wrote:


On 8/06/2017 9:06 pm, David Nyman wrote:


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?


I don't think it is so much circular as conspiratorial. If
physical results were to come about in such a conspiratorial way,
rather than straightforwardly from the formalism as in quantum
non-locality, one might wonder what the scientific enterprise is
really all about. (Rather as Zeilinger wondered about
superdeterminism.)


I'm not sure I agree that it would be conspiratorial. Non-locality as 
a consequence of entanglement would be central to the explanation in 
that it would fix the very limits of what it would be possible to 
observe for a deeply physical reason. I'm also not entirely convinced 
that the idea would necessarily be at odds with the scientific 
enterprise per se. That would be a question of the restrictions one 
wished to place on its explanatory approach. Much the same has been 
remarked about cosmological Multiverse theories, or the String 
Landscape, but ISTM that those judgements - whether they turn out to 
be right or wrong -  are based on little more than a long-standing 
presupposition that there must be a unique solution to certain equations.


However I concede that whereas what I've outlined isn't necessarily 
inconsistent with the predictions of the quantum formalism (else it 
would just be wrong) it would depend on a presently rather 
non-standard notion of 'unobservable'. That notion would in turn 
require us to understand the formalism, at a very fundamental level, 
as describing an emergent epistemological phenomenon rather than a 
basic ontological one. To that degree it may be more compatible with 
an explanatory schema such as computationalism, in terms of which 
physics is indeed an epistemological emergent, as distinct from 
physics tout simple.


The idea that the explanation is epistemological rather that ontological 
has been my preferred position for a long time. If the wave-function is 
merely an epistemological device for calculating probabilities and not a 
really existing object, all worries about collapse and 
action-at-a-distance vanish. Of course, multi worlds also vanish, but in 
my opinion that is no bad thing.


Bruce






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Re: A thought on MWI and its alternative(s)

[David Nyman]

On 8 Jun 2017 12:50 p.m., "Bruce Kellett"  wrote:

On 8/06/2017 9:06 pm, David Nyman wrote:

On 8 Jun 2017 11:40 a.m., "Bruce Kellett"  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> 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?


I don't think it is so much circular as conspiratorial. If physical results
were to come about in such a conspiratorial way, rather than
straightforwardly from the formalism as in quantum non-locality, one might
wonder what the scientific enterprise is really all 

Re: A thought on MWI and its alternative(s)

[Bruce Kellett]

On 8/06/2017 9:06 pm, David Nyman wrote:
On 8 Jun 2017 11:40 a.m., "Bruce Kellett" > wrote:


On 8/06/2017 7:52 pm, David Nyman wrote:

On 8 Jun 2017 1:05 a.m., "Bruce Kellett"
> 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?


I don't think it is so much circular as 

Re: A thought on MWI and its alternative(s)

[David Nyman]

On 8 Jun 2017 11:40 a.m., "Bruce Kellett"  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> 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

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Re: A thought on MWI and its alternative(s)

[Quentin Anciaux]

http://mccabism.blogspot.be/2010/10/many-worlds-and-quantum-fungibility.html


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2017-06-08 12:57 GMT+02:00 Quentin Anciaux :

>
>
> 2017-06-08 12:40 GMT+02:00 Bruce Kellett :
>
>> On 8/06/2017 7:52 pm, David Nyman wrote:
>>
>> On 8 Jun 2017 1:05 a.m., "Bruce Kellett" < 
>> 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.
>>
>>
> 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 everything-list+unsubscr...@googlegroups.com.
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>> 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)
>
>
> 

Re: A thought on MWI and its alternative(s)

[Quentin Anciaux]

2017-06-08 12:40 GMT+02:00 Bruce Kellett :

> On 8/06/2017 7:52 pm, David Nyman wrote:
>
> On 8 Jun 2017 1:05 a.m., "Bruce Kellett" < 
> 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.
>
>
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
>
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>



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Re: Carlo Rovelli's critique of Platonism

[David Nyman]

On 8 Jun 2017 2:35 a.m., "Bruce Kellett"  wrote:

I have just come across this paper from a year or so ago. Rovelli
essentially summarizes many of my own negative feelings about mathematical
platonism.


Interesting paper, Bruce. However AFAICS he is in effect making the case
for the computationalist mode of explanation, which is indeed related to
the notion of Michelangello's stone or Borges's library. The crucial
difference is in the definition of the observer and its 'interest' or
interpretation as intrinsic rather than imposed from without. Of course,
the not inconsiderable task of explicating the precise consequences of such
intrinsic perceptual filtering remains. But the mode of explanation relies
on the computationalist Babel as its inferential basis, which is the extent
to which it need be said to 'exist'. It is precisely *eludes* reification
because it is the unique assumptive basis upon which the provenance of
'things' is subsequently to be inferred. It's not a thing in itself; its
role is explanatory, not substantial.

Again in effect Rovelli alludes to the deeper import of this approach to a
'theory of everything'. In essence it 'out-Darwins Darwin' by proposing, in
principle, how the appearance of creativity, from the emergent perspective
of an intrinsic interpretation, could indeed come about without the need to
appeal to a creator.

https://arxiv.org/pdf/1508.1.pdf

Bruce

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Re: A thought on MWI and its alternative(s)

[Bruce Kellett]

On 8/06/2017 7:52 pm, David Nyman wrote:
On 8 Jun 2017 1:05 a.m., "Bruce Kellett" > 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.


Bruce

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Re: A thought on MWI and its alternative(s)

[David Nyman]

On 8 Jun 2017 1:05 a.m., "Bruce Kellett"  wrote:

On 7/06/2017 10:38 pm, Bruno Marchal wrote:

> On 07 Jun 2017, at 11:42, Bruce Kellett wrote:
> On 7/06/2017 7:09 pm, Bruno Marchal wrote:
>
>> On 06 Jun 2017, at 01:23, Bruce Kellett wrote:
>>>
>>> I have been through this before. I looked at Price again this morning
 and was frankly appalled at the stupidity of what I saw.
 Let me summarize briefly what he did. He has a very cumbersome
 notation, but I will attempt to simplify as far as is possible. I will use
 '+' and '-' as spin states, rather than his 'left', 'right'.

 He write the initial wave function as for the case when you and I agree
 in advance to have aligned polarizers:

 |psi_1> = }me, electrons,you> = |me>(|+-> - |-+>)|you>
= |me, +,-,you> - |me,-,+,you>

 He says that at this point no measurements have been made, and neither
 observer is split. But his fundamental mistake is already present.

 A little test for you: what is wrong with the above set of equations
 from a no-collapse pov?

 skipping some tedium, he then gets

 |psi_3> = |me[+],+,-,you[-]> - |me[-],-,+,you[+]>

 where the notation me[+] etc means I have measured '+', you[-] means
 you have measured '-'.

 He then claims that the QM results of perfect anticorrelation in the
 case of parallel polarizers has been recovered without any non-local
 interaction!

 Spoiler -- in order to write the final line for |psi_1> he has already
 assumed collapse, when I measure '+', you are presented *only* with '-', so
 of course you get the right result -- he has built that non-locality in
 from the start.

>>>
>>> ?
>>>
>>> From the start shows that it is local.
>>>
>>
>> Your failure to see the problem here is symptomatic of your complete
>> failure to understand EPR in the MWI.
>>
>
> I could say the same, but emphatic statements are not helping. My feeling
> is that you interpret the singlet state above like if it prepares Alice and
> Bob particles in the respective + and - states, but that is not the case.
> The singlet state describe a multiverse where Alice and Bob have all
> possible states, yet correlated.
>

The singlet state is rotationally invariant, yes, and can be expanded in
any basis of the 2-d complex Hilbert space. That has never been in doubt.


Then in absence of collapse, all interactions, and results are obtained
> locally, and does not need to be correlated until they spread at low speed
> up their partners.
>

That does not follow. Although there are an infinity of possible bases for
the singlet state, these are potential only, and do not exist in any
operative sense until the state interacts with something that sets a
direction. You appear to claim that A and B exist in separate worlds
corresponding to each of this infinity of bases. But that is a
misunderstanding. They are in superpositions in every base, sure, but that
does not mean that there are 'worlds' corresponding to each possible base
until some external interaction occurs. As you yourself have said, a world
is something that is closed to interaction. But superpositions are not
closed to interaction, they can interfere -- as in the two slit experiment,
and essentially every other application of QM.

So there are no separate worlds corresponding to every possible orientation
of the polarizers. Worlds can arise only after interaction and decoherence
has progressed so that the overlap between the branches of the
superposition is zero (FAPP if you like). It is only then that the branches
can no longer interfere (interact) and are closed to interaction, and thus
constitute different worlds.

The standard procedure in quantum mechanics when one is faced with a
superposition that interacts with something external, is to expand the
superposition in a base that corresponds to the external context. That is
what happens when an unpolarized spin meets a polarizer aligned in a
particular direction -- one expands the rotationally symmetric unpolarized
state in the basis matching the external context. That is all that is
happening with the singlet state above; when Alice comes to measure the
symmetric state, it is convenient to expand the singlet state in a basis
that corresponds to the orientation of Alice's polarizer. Then the result
of the interaction is easily calculated. If one use some other basis, in
some other direction, one would end up with a superposition of states after
measurement, and that superposition would be exactly the same as the
eigenstate obtained when one expanded in the aligned basis. So using a
different basis merely complicates the calculation, it doesn't actually
change anything. It is like trying to drive from Melbourne to Sydney using
a map based on an orthographic projection based on Brisbane. You might
manage it, but it would be needlessly difficult.

I am sorry that I have