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 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 of view?  I so will different probabilities be calculated if one
takes a different basis?

> 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
different conclusions?  I very much appreciate your helping me to
understand this problem.

>>   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 qubits instead 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 having one of them read a 1 and the other read a 0.
When you do this, you are talking about two different computational states,
(you might as well model them as separate Turing machines/programs at this
point) and hence you are talking about two different minds, not one mind
that is conscious of a superpositional state.


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