On 12 Jun 2017, at 17:09, John Clark wrote:
On Fri, Jun 9, 2017 at 7:11 PM, Bruce Kellett <bhkell...@optusnet.com.au
> wrote:
> Deutsch is out to lunch on this. He appears to assume that a
quantum computer is just using the same algorithms that a classical
computer would use, only executing them in a massively parallel
manner.
As Deutsch is probably only the second person (after Richard
Feynman) to think long and hard about quantum computers I'm pretty
sure he doesn't believe that just any old algorithm will do, and I'm
even more sure he doesn't believe the classical hardware we use in
our computers today can take advantage of a quantum speedup.
The miniaturisation of the concrete cassical computers of today has
been made possible thanks to quantum mechanics. In fact, the discovery
of the transistor has been made through the solving of Schrodinger
equation. But classical computer, which are quantum object like any
piece of matter, does not exploit the quantum in his way of computing.
We could in principle do that, if we were able to isolated them enough
from their environment, but this is quasi impossible today.
>Scott Aaronson points out:
"The way a quantum algorithms work is that they arrange for wrong
answers to destructively interfere while the desired answer
interferes constructively. Interference requires that they take
place in the same world."
I agree Interference must take place in a single world,
I would say: in a single multiverse. "World" is ambiguous, because in
some context it denote a branch of the universal wave, and sometimes
the universal wave itself.
but where did all the information that produced the interference
come from, where did the computations that produced all those wrong
answers (and a few correct ones) come from? Even the 2-slit
experiment will not produce interference if you remove the
photographic plate and just allow the photons to continue into
infinite space after they pass the slits because then the world
splits but the two never recombine again so no interference.
This is a bit weird. I would say that the interference are still
there, but that we can't see them. Without the photographic plate, we
can still introduce a needle at a position where no photon will ever
go, because of the destructive interference due to the two slits open.
If we accept Einstein reality principle, we know that even without
that needle, no photon can ever appears at such a position.
Interferences occur independently of our decision to observe them.
You need places for things to become different and also a place for
things to come together again for interference to occur.
>Quantum computing does not prove the existence of parallel worlds
-- there is no need for other worlds in which to find the
computational power,
A large Quantum Computer wouldn't prove beyond any logical doubt
that other world's must exist, but then you don't exactly "need"
a heliocentric solar system theory to explain the
movements of the planets either; you could stick with the Earth
centered model if you added enough epicycles of the type used by
Ptolemy 2000 years ago. Then the way the planets moved in
relation to the crystalline celestial sphere, the one
that has the stars painted on it, could be
predicted to the limits of observational accuracy. But
you'd need a awful lot of epicycles and calculations would
literally be astronomically more complex than with the
far simpler heliocentric model.
OK.
In the same way I think when quantum computers become commonplace
programers will take Many Worlds as a given even if they
can't formally prove they exist because it's just easier to
visualize how they work that way, just as it's easier to visualize a
few elliptical orbits around the sun than visualize a
gazilian circles around circles around circles around the Earth.
OK.
I take, like Deutsch, the two slits experiences (with photon or
electrons, in a corresponding set-up, sent one by one) as a strong
evidence of the Many Worlds/Dreams (MW). Then I take Aspect
experience, and Bell's inequality violation testing as an even much
stronger evidence for them. In fact all evidences for literal quantum
mechanics are evidences for MW.
Bruno
John K Clark
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