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

[Bruno Marchal]

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 worl

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

[Bruce Kellett]

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.


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. 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. 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.


I think the problem you face is always going to be that of finding a 
basis that is not ad hoc. 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?


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. 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.


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. QC does not appear to have 
any principled way to define such a basis, whereas what Cuffaro calls 
neo-Everettian approaches do -- 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.


Bruce

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