On 10/19/2013 12:42 AM, Jason Resch wrote:

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On Fri, Oct 18, 2013 at 6:09 PM, meekerdb <meeke...@verizon.net<mailto: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 <mailto: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 the physical - at least not unless he can solve the basis problem. Could you do me a favor and explain what the basis problem is in a way that a 6th grader could understand? I've found all kinds of things said on it, and they all seem to be asking different things.For physicists, it's part of the problem of explaining the emergence of the classical world from the quantum world. Decoherence can diagonalize (approximately) a reduced density matrix 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 a reduced density matrix"?It means to take an average over all the other variables except those of interest (i.e. the ones you measure). If you do this in a particular basis we think it makes the submatrix corresponding to those variables diagonal. Then it can be interpreted as the probabilities of the different values. Note that it is a mathematical operation that depends on choosing a basis, not a physical process.Is this a process to recover the probabilities of some observation from some point ofview? I so will different probabilities be calculated if one takes a different basis?

`There's only one basis in which the reduced matrix is diagonal - i.e. the 'classical`

`basis'. But saying which basis this is from a fundamentally quantum standpoint (not`

`relying on a classical world like Bohr) is part of "the basis problem".`

The MWI view is that this is a physical process - which it could be IF the basis was not an arbitrary choice but was somehow dictated by the 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 to differentconclusions? I very much appreciate your helping me to understand this problem.

`If you choose a basis in which the density matrix is not diagonal, then there's no clear`

`interpretation of it as probabilities. There are complex cross-terms that have not`

`probabilistic interpretation.`

Being diagonal in one basis means it's superposition in some other basis. So for physicists the problem is saying what privileges or picks out the particular bases we see in experiments. Why do our instruments have needles that are in eigen states of position, while some other things (e.g. atoms) are in eigen states of energy or eigen states of momentum. For physicists there are some suggestive, but not fully worked out answers to these questions, e.g. you get position eigenstates because the interaction term of the Hamiltonian is a function of position. But those answers assume the physics. If you want to reconstruct physics from experiences, you can't borrow the physical explanation to say why your experiences are classical. I think the assumption that experiences are classical comes from the classicality of Turing machines (which are the supposed mechanism by which experiences are manifest).I don't think there's anything either classical or quantum about Turing machines.They are just mathematical abstractions. And assuming they read and write qubitsinstead of bits doesn't change the range of things they can compute.But qubits don't exist in normal definitions of information or Turing machines. Sure,they can be modeled, but only by splitting the entire tape and Turing machine and havingone of them read a 1 and the other read a 0. When you do this, you are talking about twodifferent computational states, (you might as well model them as separate Turingmachines/programs at this point) and hence you are talking about two different minds,not one mind that is conscious of a superpositional state.

`I don't think that's right. A universal Turing machine can emulate a quantum Turing`

`machine, it's just less efficient. But that's part of the point of Seth Lloyd's paper and`

`of Scott Aaronson, that maybe efficiency is important. It's not in Bruno's theory,`

`because if your computing the Everything, then time is part of the computation and not`

`some outside measure against which to judge efficiency.`

Brent

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