On 04 Jun 2017, at 14:48, David Nyman wrote:
On 4 Jun 2017 1:05 p.m., "Bruno Marchal" <marc...@ulb.ac.be> wrote:
On 02 Jun 2017, at 03:01, Bruce Kellett wrote:
On 1/06/2017 10:19 pm, Bruno Marchal wrote:
On 01 Jun 2017, at 02:26, Bruce Kellett wrote:
On 1/06/2017 4:43 am, Bruno Marchal wrote:
On 31 May 2017, at 04:01, Bruce Kellett wrote:
On 30/05/2017 9:35 pm, Bruno Marchal wrote:
On 30 May 2017, at 11:28, Telmo Menezes wrote:
I get your point with decoherence.
Again, I would say that it all depends on theories of mind. What does
mind supervene on? Perhaps it is true that every single coupling with
the environment prevents the current observer state to become
compatible with other branches. But can we be sure? I feel that such
certainties come from a strong belief in emergentism (which I cannot
disprove, but find problematic).
It is impossible to recohere the past, FAPP.
But only FAPP. To make the blue T-rex interfereing with the red-T-
rex, we must erase the trace of particle interaction between the T-
rex in its whole light-cone, and this without forgetting the
particles "swallowed" by the black-holes, etc. It is just completely
impossible, but to derive from that the unicity of the past, is, it
seems to me (and you if I understood well) is invalid.
I think the recoherence of paths that have completely decohered is
more than just FAPP impossible, I think it is impossible in
principle. One major problem with recoherence in general is that
information leaks from the paths at the speed of light (as well as
less slowly for other interactions). Since this vital information
goes out along the light cone, it can never be recaptured and
returned to the original interaction.
In QM + special relativity OK. (note that to me QM + special
relativity => no collapse (and even the Many dreams, but we have
agreed to disagree on this if I remember well).
Reasoning in QM without SR is not very profitable. Besides, QM + SR
does not particularly imply MWI -- it is perfectly possible to have
a consistent collapse model of QM+SR. I know you don't agree because
of the non-locality implied by EPR, but this non-locality is not
removed in MWI, regardless of what you might say.
I don't see it, and the mast time we discuss this, we conclude on
some vocabulary problem. When there is no collapse, measurement
tells to people light separated in which branch theiy belongs, but
to exploits that information, they need to come into contact.
Last time we discussed this, no resolution was achieved.
That is not what I remembered, but I will not insist.
In QM, with or without collapse, decoherence and the transition from
the pure state to a mixture gives a definite measurement result.
In particular branches only. When looking at the whole wave
including the observers, decoherence explain why it *looks*, to all
observers in the different branches, that mixed states have been
obtained, but that is not the case in the global description.
Without collapse, different branches get different results, but once
obtained, these results are fixed, and are not affected by whether
Alice and Bob exchange information or not.
I agree. That is used in the fact that in EPR like situation, when
Alice and Bob are space-time separated, what we have is "only" an
infinity of Alices and Bobs, all with their spin correlated, and
when Alice makes her measurement, at any angle, she will know Bob's
possible result, without needing any action at a distance. She just
localize herself, and her corresponding Bob, in which branch they
belong. There is no influence at a distance, although we would need
it to talk of token unique Alice and Bob in case there would be only
one universe.
Consequently, indispensable phase information is lost *in
principle*, so the recoherence is, in general, impossible.
OK. (I was reasoning in naive classical QM)
Of course, with carefully constructed systems, where the loss of
information along the light cone is prevented, recoherence is
possible in special circumstances, but not in general.
From this, the uniqueness of the past of any decoherent history is
assured. So deriving the unicity (if I understand this use of the
word) is by no means invalid -- it is proved.
In QM + SR. OK.
Even if one encounters one of those rare situations in which
recoherence is achieved, that still does not invalidate the
uniqueness of the past history -- recoherence, if it occurs, simply
means that no new branches are formed at that point, so the
decoherent history remains unique.
OK. That might suggest that we identify our indistinguishible past
in arithmetic, if we assume mechanism. I use the Y = II principle,
or the "quantum" linearity of the tensor product "@": we have that
a @ (b + c) = (a @ b) + (a @ c).
That makes sense.
Linearity is the heart of QM. It is linearity that allows
superpositions, and leads to all the "quantum weirdness".
I agree. Both "linearities" (the quantum evolution, and the tensor
products).
.......
But those state difference are accessible to the observers, and
indeed, only this makes the analogy with step 3 working.
In MWI, the differences are not observable by anyone. Any observer
has access to only one branch, so only one copy. They can say
nothing about the other branch.
The difference are not observable, but are very gross, like seeing a
cat dead, or alive. Linearity prevent any direct view of that
difference, but it exists, when we assume QM (and non collapse).
It is not linearity that prevents macro-superpositions
That is what I just said.
-- it is decoherence and the reduction to a mixed state.
In each branch, not in the universal wave. Superposition remains
superposition. Only the collapse of a wave would destroy a
superposition, and indeed, in a non-local way. Without collapse we
get only local appearance of mixed states. D'Espagnat called them
"improper" to distinguish them from a proper mixed state that we
could get with a collapse.
The difference between the measurement outcomes exists whatever
interpretation of QM you impose.
That is what I try to explain to John Clark in the mechanist context
of the WM-duplication. The measurement of self-localization is a
precise outcome, but that does not make the other "branch"
disappearing.
.......
Of course, it assures them in all branches, where indeed Aspect like
experiences can be made. It seems to me that we did agree on this:
that non-locality does not entail any physical influence in the
past. That does happen in the unique universe view though; even if
there is no possible communication of information is done.
Non-locality means that there is no physical transfer of
information, but that there is non-physical(non-local) transfer of
information. But this information transfer cannot be used for
signalling. Signalling is possible only with actual; physical
transfer, a consequence of SR and the fact that 'information' is
physical.
So we agree. Yet, with unicity of outcomes assumed for measurement,
we still cannot signal, but must assume some "reduction of a wave
packet at a distance", or super-deterministic conspiracies.
This non-locality is even more evident in the more recent delayed
choice experiments that use entangled photons to manipulate photon
polarization states non-locally.
I have no problem with one-branch observable, apparent, non-locality.
I have a problem only with the action at a distance that you need in
case you assume one contextually well defined physical reality.
Non-locality is not removed in MWI as you appear to believe.
In the sense above, you are right. I was juste arguing against John
Clarks idea that the Bell's inequality violation introduce physical
action at a distance, even with the MWI.
There are two things:
1) no influence at a distance,
2) no signaling at a distance.
With QM-without collapse, there is no influence at a distance. The
no-locality above is explained without them.
With QM+ collapse, there is no signaling at a distance, but there is
an influence at a distance.
There is no non-local signalling whatever interpretation you adopt.
Yes.
But there is non-locality -- non-local influence -- in all
interpretations since it is inherent in the quantum formalism.
I don't see any non-locality in the MWI. EPR, Bell, assumes always
one Alice and Bob, and as Everett shows, decoherence explains the
manitenance of coherent first person plural description, and the
absence of collapse prevent any non-local influence.
Non-locality is not explained away in MWI.
Indeed, the MWI explains well the appearance of non-locality, and
this without needing a physical influence at speed light.
For me the abandon of the collapse is the solution of the EPR
"paradox", and Aspect experience is somehow the confirmation of our
belonging to macrosuperposition.
The non-local (paradoxical) nature of EPR remains even without
collapse.
I know some claims this, but I have never sen a proof. All proofs
relies on unicity of the outcome of some experiences.
You cannot get away by reversing the onus of proof. Bell's theorem
is independent of whether or not a collapse is assumed,
To interpret the experimental violation, you need to identify the
Alice and Bob you talk about. But EPR and Bell talk of Alice and Bob
like if they were in a definite universe all along the experience,
when that is never the case. They do assume implicitly one physical
universe.
so if you want to argue that MWI removes the non-locality proved by
Bell, then the onus of proof is very much on you: you have to
demonstrate how this can be possible.
It is a trivial consequence of the linear differential shroedinger
equation. Or of the fact that the evolution is a rotation (unitary)
in Hilbert space.
You say that Bell's theorem relies on the unicity of outcomes. By
this, I presume you mean that Bell assumes counterfactual
definiteness (in the usual terminology). If by counterfactual
definiteness you mean that a measurement gives a definite (though
unknown in advance) result, even if that measurement is not performed.
This does not make sense in the MWI. If I measure a alive+dead cat,
it is only a "first person illusion, 1p" that such an experience
gives a definite result. In the 3p picture, both results must be
said to obtained.
Then I accept that counterfactual definiteness is assumed in quantum
mechanics. Without such an assumption, the whole notion of an
expectation value would collapse.
Not in the 1-views. It continues to make sense, and the contagion of
superposition (the linearity of the tensor product) even prolongate
the 1-views into 1-plural views, that gives the siplitting/
differentiation/decoherence, which needs only to propagate at the
speed of light or below.
So if you abandon counterfactual definiteness, you have a different
theory -- you have abandoned standard QM, and you then have to
explain how you can get and use expectation values.
We got them in the memories of the person's involved. Not from
looking at the whole universal wave. It is again like with
computationalism.
Your claim appears to be that Bell's theorem is not valid in MWI.
Bell's theorem is valid. His inequality does not even assume QM, but
just locality. It is violate when we do the experience, like Aspect,
and this shows non-locality in our branch, but when looking at the
big picture, we see that this non-locality has a local origin. It
would need an action at a distance to destroy the alternante
branches alwailable to Bob, but without collapse, non-locality is a
local, branch-owned, phenomenon. I take Bells theorem + Aspect as a
quasi definite proof that if there is one universe, then there are
many universes.
This is nonsense. Bell's theorem is a theorem of quantum mechanics,
and it is therefore valid in all interpretations of that theory.
Yes, in all interpretation of quantum mechanics, the relevant
branches violate the inequality, but they do that without involving
an action at a distance when we look at the entire wave. It is
phenomenological.
Suppose one were to enquire what makes those branches "relevant".
One answer is that other pairings would be in conflict both with the
predictions of QM and with observation, but that is circular. What
then? Perhaps one might speculate that other pairings would somehow
be fundamentally inconsistent with any physics that would permit its
own coherent (or for that matter decoherent) observation.
The branches are just the superposed states, and with singlet or with
simple qubit, the other branches are just the other term of the
superposition which describes ourselves. To get rid of such
superposition, we need to get rid of quantum mechanics, *and* of
mechanism.
This might ultimately be related to the speculation that the
appearance of spacetime itself may emerge as a consequence of
entanglement.
Possibly, although you might elaborate a little bit. I certainly like
the idea that space emerge from entanglement. There are some relation
between "entanglement" in knot theory, and the quantum entanglement,
notably suggested by some work by Louis Kauffman, but that too needs
some elaboration. I expect that the emergence of space in Mechanism
will comes from a more primitive notion of entanglement, but for this
we need to derive the tensor product, and that is not easy at all, and
requires solution of open problems related to the semantics of the
"material hypostases".
Bruno
David
If it is not valid in MWI, then Many-Worlds is a different theory,
and not just an interpretation of standard QM.
It is valid in the MWI, but interpreted differently than in a mono-
universe interpretation which requires non local action at a
distance to get the same non-locality.
(with or without hidden variables).
As on the previous occasion we discussed this, you were unable to
demonstrate where the notion of 'collapse' is used in Bell's theorem
- all Bell requires is that measurements give results, and that is
what the whole of physics is based on: in MWI as well as in any
other interpretation.
We did eventually agree. May be reread those post. Bell's supposed
that when the two measurement are done, Alice and Bob get a precise
answer, which makes no sense without-collapse.
That is what making a measurement means. It is what happens in all
interpretations. It makes no sense to deny counterfactual
definiteness -- that is not QM.
It is QM without collapse, and using the simple mechanist FPI.
Alice and Bob get *all* (always correlated) answers, but when light-
separated, it make no sense to compare them. They can only make
comparison with the person accessible in their light cone, where the
contagious superposition spread out.
I presume you mean "space-like separated". Alice and Bob do their
measurements;
The infinities of Alices and Bobs do their measurements.
they get their results and write them in their lab books. They meet
years later and compare lab books. Are you trying to suggest that
they do not have definite answers in their lab books before then?
The infinities of Alices and Bobs get their infinities of definite
results.
In MWI (with two-outcome experiments), there is a copy of Alice that
writes '+' in her lab book, and a copy who writes '-' (for a given
orientation theta). Similarly for Bob. There are, therefore, only
four possibilities when they meet: '++', '+-', '--', and '-+'. The
non-locality is necessary to set the probabilities for each of these
four possible combinations of results. If you want to eliminate the
non-locality, you have to give a non-magical way of establishing the
necessary probabilities. You have never been able to do this.
QM does that, and without collapse, I don't see how any influence
leaking at the speed of light need to be introduced.
Remember that in a sequence of such experiments, the probabilities
for '+' and '-' are 50/50 for both Alice and Bob.
OK.
The joint probabilities, or correlations, depend on the relative
orientations of their polarizers.
Right.
It is information about this relative orientation that must be
conveyed non-locally for the correlations to come out correctly when
they meet.
Why? That would be the case if you think that it is the same Bob and
Alice all along the experiences, but that cannot be the case.
It is not sufficient for them simply to exchange this information
later, because their results at particular orientations are already
fixed when they meet.
I don't see this. If the angle is some theta different from 0° or
90° they will both split/differentiate, and whoever they will meet
later will be the correspond partner with the correct correlation,
obtained by the decoherence local to their respective branch. In
this case, it is clear that it does not make sense to attribute to
"Alice and Bob" the same identity than the initial one.
Bruno
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.
To post to this group, send email to everything-list@googlegroups.com.
Visit this group at https://groups.google.com/group/everything-list.
For more options, visit https://groups.google.com/d/optout.
http://iridia.ulb.ac.be/~marchal/
--
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.
To post to this group, send email to everything-list@googlegroups.com.
Visit this group at https://groups.google.com/group/everything-list.
For more options, visit https://groups.google.com/d/optout.
--
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.
To post to this group, send email to everything-list@googlegroups.com.
Visit this group at https://groups.google.com/group/everything-list.
For more options, visit https://groups.google.com/d/optout.
http://iridia.ulb.ac.be/~marchal/
--
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.
To post to this group, send email to everything-list@googlegroups.com.
Visit this group at https://groups.google.com/group/everything-list.
For more options, visit https://groups.google.com/d/optout.
