From: Glenn Morton (glennmorton@entouch.net)
Date: Wed Jul 09 2003 - 07:27:06 EDT
>On Tue, 8 Jul 2003 19:17:08 -0500 "Glenn Morton"
><glennmorton@entouch.net> writes:
>>
>Glenn,
>I've tried to follow the discussion, which seems to be encapsulated in
>these quotations, with the status of almost complete ignrorance. But I am
>wondering about moving from a quantum computer in which Qbits apparently
>take all values simultaneously, to a digital one with a capacity of 10^80
>or 10^500 bits. There are also analog computers that do not figure on a
>0/1 basis. Depending on how finely they can be set and read, do they not
>have the potential for dealing with larger numbers for the same number of
>active entities (or whatever you call them)? 2^10 is roughly equal to
>10^3, but one may be able to read out more than 10 states. Do not Qbits
>enormously extend the place capacity of normal analog computers?
When I first started in the oil industry, there were still a few analog
computers in use. They were quickly replaced by digital for a variety of
reasons, accuracy and speed among them. There is a fundamental difference
between an analog signal and an quantum qubit. While the superpositional
state of the qubit is like an analog signal, when the measurement is made of
the value in the register the qubit must yield either a 0 or a 1. The analog
computer will yield any value at all. And when one has a two-register
quantum computer (QC) it can represent 0,1,2,and 3 simultaneously; the
analog will represent only it's analog value which is not simultaneously
0,1,2 or 3. This difference is the basis (not the entire explanation) for
why quantum computers are radically different from analog. Other features
are that there is no analogy for coherence, and entanglement with analog.
Superposition exists in both systems but the quantum effects change the
nature of the logic.
>
>Second, if a quantum computer is to require 10^500 bits and so exceed the
>capacity of our universe's 10^80 potential bits, does this not mean that
>the Qbits have to be somehow entangled with the entire collection of
>10^420 extra-universal particles? Is such entanglement possible?
I am not sure exactly the direction you are coming from here. I will try two
tracks. That is what the MWH interpretation of quantum would hold. As well
as the nature of calculation. As I have pointed out, calculation requires
the manipulation of a particle. Information is a property of matter, not the
ether. Deutsch would claim that IF we solve such an intractable problem (by
today's standard), there is no alternative interpretation in the Copenhagen
view of quantum.
As to whether it is possible or not to assess these other universes? (the
second track for this answer). The universes are only partly independent
giving quantum level interference. Penrose raised a couple of objections to
MWH based upon the inaccessibility of them and the supposed fact that the
probabilities of quantum can't be calculated with the MWH view. In 1999,
Deutsch published an article which does calculate the probabilities from
mwh.
It is Deutsch, "Quantum Theory of Probability and Decisions," Proc. royal
Soc. of London A455 (1999): 3129-38
>Entanglement seems to have more restrictions, including the length of
>time that it holds before some interaction ends it. While entanglement
>seems to be instantaneous, can the signal to establish entanglement
>exceed the limit of c?
Your first sentence is why building a QC is going to be technically
difficult (although small ones have already been built). One must protect
the qubit from the environmental interference. If that can't be done
practically, then neither of the tests will ever be carried out (the two
tests being a large calculation or running Deutsch's program for determining
which quantum interp wins).
>
>Are these problems with the proposed test for MWH, or do I have no grasp
>of what is involved?
The test I think there is little problem with is the large calculation test.
I can't concieve of where the resources in our Hubble volume (HV)can come
from to engage 10^500 particles in a calculation. Shoot, even the power
requirement to move that many particles would be overwhelming and out of all
possibility. This is true, even if the particles are electrons. See, this is
another aspect of the large calculation test. Where would the energy come
from to move these particles or switch their spin or whatever you use as the
memory device. Such a calculation should be physically impossible. If it
isn't, and that is still unproven, then I see no way it could be done in our
local neighborhood inside our HV. If such a calculation proves possible,
then the MWH almost certainly has to be true.
The other test, I will leave to the mathematicians, but I haven't heard
serious challenges against that program. But there may be some and I
haven't heard of it..
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