On 16 Jun 2017, at 04:21, Bruce Kellett wrote:
On 15/06/2017 6:01 pm, Bruno Marchal wrote:
On 14 Jun 2017, at 01:06, Bruce Kellett wrote:
You seem to be taking the older view of many worlds that is
favoured by David Deutsch. This approach has serious problems with
the notorious basis problem, and there does not seem to be any
principled way from within the theory to select unambiguosly the
basis in which all of these worlds form. More recent
understandings of MWI take decoherence into account. Decoherence
provides a principled dynamical way to solve the basis problem,
but it means the worlds do not actually form until there is
decoherence -- worlds cannot form until they know what basis is
relevant!
I recommend the paper I suggested to Telmo:
Michael Cuffaro, http://arxiv.org/abs/1110.2514v2
Cuffaro discusses the problems with the older form of MWI and
suggests that although many worlds might be a useful heuristic in
quantum computing, decoherence is required before worlds could be
considered to have any ontological basis. The exponential speedup
with a quantum computer is then seen in the fact that the QC
manipulates the phases inherent in the entanglement of qbits, and
doesn't have to actually calculate the function in question for
all possible inputs, as the older many worlds view requires.
Oh! I see that my explanation that the MW prevents the need of
action at a distance was neo-everettian!
Well, no! Your explanation was not anything at all because you have
not given an explanation, despite my asking many times. The best you
have managed is some general comments and a lot of hand-waving.
Rhetorical trick. The linearity of evolution, and tensor product, and
interaction makes just impossible any action action at a distance. I
might say that you are the one imposing some unclear interpretation of
"world" so that you can extract from the bell's violation some spoky
action at a distance. That does not make sense in special relativity.
I am not sure I understand the paper by Currafo, as I have no
single-world interpretation of entanglement and/or quantum phase.
That must be a considerable disadvantage for you! Entanglement is
universal in quantum mechanics: every time objects interact they
become entangled.
Yes, that is why I consider the Aspect experience as an evidence for
the MW. I agree that Bells violation in one world entails action at a
distance.
Entanglement is at the basis of the emergence of a classical world,
and since we only ever experience just one world, we must have a
single-world understanding of entanglement.
We need only a theory of mind, and Everett use mechanism. Only
problem: with mechanism we have to derive the physics as a first
plural self-referential reality. But it works already rather well at
the propositional level.
I don't know what you mean by no single-world interpretation of a
quantum phase. A quantum phase is just an angle like any other.
But "quantum" is the subject on which we search an interpretation for.
To me, MW is the same as QM-without collapse axioms. I use it
informally and formally to compare with the internal many dreams
interpretation of arithmetic, that the numbers can discuss in
arithmetical forum.
I think the problem you face is always going to be that of finding a
basis that is not ad hoc.
The basis, like the histories in arithmetic, are chosen from inside,
indexically. Consciousness can only differentiate on distinguishable
realities, choosing the bases is a bit like choosing your parents.
If you see every superposition as a matter of multiple worlds, then
you have no interpretation of a pure quantum state. As Brent (and
everyone else) points out, a pure state is not a superposition in
the basis in which that state is one of the basis vectors, and there
are an infinite number of other bases in which it is a
superposition. So what are you going to choose? One world or an
infinity of different incompatible worlds?
Define world.
I assume only 0, s, + x usual sense.
And I agree it is weird. A particle with a precise position is a
particle with an imprecise impulsion, so you have the choice to
partitioned the mutltiverse in different relative way. If you see that
this is an argument against the notion of worlds, OK, it might be a
good new for the mechanist, because we do have a serious measure
problem, and we still not have the "Gleason theorem", but we do have
three quantum logics, so let us see.
I do not defend any theory. I am a logician. I just show that If we
survive a digital brain transplant, then physics has to be retrieved
from the logic of self-reference on the sigma sentence. That works.
At best, it would be a critics of the notion of world (be it single
or not), and this would made QM even closer to the physics
extracted from computationalism, where there is no world at all,
and the differentiation is only a relative differentiation of the
consciousness of a person. I guess mechanism is probably neo-neo-
everettian, if not neo-neo-neo-Everettian. As I said once, despite
Everett seems to disagree, it is better to talk in term of relative
state, or relative dreams, instead of world. The worlds, with
mechanism, are maximal consistent extensions, and exists only in
the mind of the numbers. The FPI are not on the worlds, but on the
first person (hopefully plural, as it seems) experience.
Probably more on this later, I have still a lot of work to do.
Meanwhile, Bruce, or anyone, you might try to explain his cluster
quantum computing in a single world, or with collapse. Cuffaro does
not provide any explanation of this, and when taken literally, his
multi-qubit entanglement requires "MW" (or many minds, many dreams,
many numbers, etc.).
I am not an expert in quantum computing, but I though Cuffaro's
paper was relatively self-explanatory. The basis problem effectively
sinks the many-worlds interpretation of quantum computing.
I cannot even make sense of this.
Of course, if you have difficulty in understanding entanglement in
one world, then you might have trouble with the multiple entangled
qbits involved in cluster QC. But the fact that there is no single
basis in which this entangled cluster can be interpreted -- the
measurement bases are adaptive from one qbit to the next -- makes
any many-worlds interpretation extremely cumbersome and artificial.
Whatever we have, as long as there is no collapse, we will have to eat
the cake, and above all, compared to the arithmetical weirdness.
The bottom line in all of this is the need to have a definite basis
in which one's many-worlds are to be defined.
This Everett refutes at the start. That is a problem for cosmologist
or any one interested in the historico-geographical aspect of reality.
In mechanism, we have a similar situation, we can use any base
(universal system), eventually the physics and the whole theology is
the same, and it involves some special type of universal numbers.
QC does not appear to have any principled way to define such a
basis, whereas what Cuffaro calls neo-Everettian approaches do --
He is not convincing. Given the basis chosen "by nature" by
decoherence, once we realize we can exploit the many worlds, to make
Fourier transform on many parallel computations, or to select or
project complex entangled states, that is partition of the multiverse,
it is obvious, that different universal computing machinery will
partitionned the multiverse differently.
one simply uses the basic dynamics to define a basis that is stable
against environmental decoherence. That give a suitable basis in a
way that is not ad hoc or circular.
But the point of quantum computing is in rotating a bit those base,
and, to prevent decoherence by all means, for a period of times,
exploiting either the many branching and fusing, or the selection from
very complex entangling preparation.
You might convince me to come back to my favorite terming "the
relative state" theory. The notion of world is a semantical, very
complicated notion. It is modeled by a ... model, in mathematical
semantic. To be consistent and to have a model are equivalent (in
reasonable theories) so no reasonable entity can prove the existence
of a model of itself. With mechanism, it is obviously open if the
number dreams cohere enough to get a well defined physical world/
reality, be it a multiverse, or a multi-multiverse.
Keep in mind I am interested in consciousness and reality, not in the
best way to make local predictions, even if this remains useful to
falsify the fundamental theory of consciousness/mind/soul. Church's
thesis rehabilitates the view of Pythagorus, and Gödel's
incompleteness theorem rehabilitates a thread going from Parmenides,
Plato, Moderatus of Gadès, Plotinus, ... Damascius.
Bruno
Bruce
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