On 19 Oct 2013, at 09:42, Jason Resch wrote:

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On Fri, Oct 18, 2013 at 6:09 PM, meekerdb <meeke...@verizon.net>wrote:On 10/18/2013 1:45 PM, Jason Resch wrote:On Fri, Oct 18, 2013 at 11:37 AM, meekerdb <meeke...@verizon.net>wrote:On 10/18/2013 12:42 AM, Jason Resch wrote:But that's not compatible with Bruno's idea of eliminating thephysical - at least not unless he can solve the basis problem.Could you do me a favor and explain what the basis problem is in away that a 6th grader could understand? I've found all kinds ofthings said on it, and they all seem to be asking different things.For physicists, it's part of the problem of explaining theemergence of the classical world from the quantum world.Decoherence can diagonalize (approximately) a reduced densitymatrix IN SOME BASIS.Is this the same basis as in "momentum basis" and "position basis",or is it some other usage of the term?Forgive my ignorance, but what does it mean to "diagonalize areduced density matrix"?It means to take an average over all the other variables exceptthose of interest (i.e. the ones you measure). If you do this in aparticular basis we think it makes the submatrix corresponding tothose variables diagonal. Then it can be interpreted as theprobabilities of the different values. Note that it is amathematical operation that depends on choosing a basis, not aphysical process.Is this a process to recover the probabilities of some observationfrom some point of view? I so will different probabilities becalculated if one takes a different basis?The MWI view is that this is a physical process - which it could beIF the basis was not an arbitrary choice but was somehow dictated bythe physics. But so far there are only hand waving arguments that"it must be that way".Can you provide an example of how using a different basis leads todifferent conclusions? I very much appreciate your helping me tounderstand this problem.

Let me try a short attempt.

`May be you are more familiar with vectors than with "density matrices"`

`used by Brent.`

`Definite states (like definite position) define a base in a vector`

`space. QM associates such a base to anything you can observe, and`

`reciprocally, having a base, you can find the corresponding measuring`

`apparatus. (forgetting annoying selection rules for some observable,`

`like charge).`

`The most typical example is position. A system having a definite`

`position will be the same as a system having all possible impulsion in`

`the parallel "universes", and reciprocally. So a superposition`

`correspond to well defined state for a different measuring apparatus.`

`Likewise a state like 1/sqrt(2)(up + down) is a well defined state in`

`the base {1/sqrt(2)(up + down) , 1/sqrt(2)(up - down) }.`

`When you measure 1/sqrt(2)(up + down) in the base {1/sqrt(2)(up +`

`down) , 1/sqrt(2)(up - down) }, you get 1/sqrt(2)(up + down) with`

`probability one.`

`But in the base {up, down}, you will get up or down with probability`

`1/2, and the local system state will seemingly undergo a projection on`

`up or down state.`

`(That projection is the vector equivalent of the wave packet`

`reduction, and in the MW, there is no reduction, as you have seen. It`

`is only a subjective selection).`

`But now, it looks like the choice of the measuring apparatus determine`

`the possible type of parallel universes you can access, so that the`

`notion of parallel universe seems to be non intrinsic, but depending`

`on the choice of the base, or equivalently, the choice of the`

`observable measured (or the corresponding apparatus).`

`Everett was well aware of that problem, and when you do the math, the`

`entire picture does not depend on the choice of the base, despite`

`locally, the choice of the base will determine the type of parallel`

`universe you can access.`

`There is a problem only if we believe in some naive boolean type of`

`universe. It is just that in some terms of the universal Everett`

`superposition, machines can develop, and then they will indeed`

`continue to work in the same bases (if they are classical machines).`

`But the whole quantum state will not depend on that base at all.`

`I thought that this was the reason to use the label "relative states"`

`instead of parallel universes, but apparently Everett has been asked`

`to avoid the label "parallel universe" as it looks too much like sc.`

`fic. IMO: relative states is better, by preventing the belief that`

`some base plays a crucial role right at the start, which is not the`

`case, as the role will be indexical and relative.`

`The base problem disappears when you take 1) the universal wave, and`

`2) accept the idea that all states of the subsystem are relative`

`indexical defined by the base in which some self-aware subparts (local`

`universal machine) can develop and remember personal memories.`

`Hope this can help a little bit. Normally this is explained in`

`Albert's book, which I think you have.`

Bruno

Being diagonal in one basis means it's superposition in someother basis. So for physicists the problem is saying whatprivileges or picks out the particular bases we see inexperiments. Why do our instruments have needles that are in eigenstates of position, while some other things (e.g. atoms) are ineigen states of energy or eigen states of momentum. For physiciststhere are some suggestive, but not fully worked out answers tothese questions, e.g. you get position eigenstates because theinteraction term of the Hamiltonian is a function of position. Butthose answers assume the physics. If you want to reconstructphysics from experiences, you can't borrow the physical explanationto say why your experiences are classical.I think the assumption that experiences are classical comes fromthe classicality of Turing machines (which are the supposedmechanism by which experiences are manifest).I don't think there's anything either classical or quantum aboutTuring machines. They are just mathematical abstractions. Andassuming they read and write qubits instead of bits doesn't changethe range of things they can compute.But qubits don't exist in normal definitions of information orTuring machines. Sure, they can be modeled, but only by splittingthe entire tape and Turing machine and having one of them read a 1and the other read a 0. When you do this, you are talking about twodifferent computational states, (you might as well model them asseparate Turing machines/programs at this point) and hence you aretalking about two different minds, not one mind that is conscious ofa superpositional state.Jason --You received this message because you are subscribed to the GoogleGroups "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 http://groups.google.com/group/everything-list. For more options, visit https://groups.google.com/groups/opt_out.

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