On 14 Jun 2017, at 01:06, Bruce Kellett wrote:
You seem to be taking the older view of many worlds that is favoured
by David Deutsch. This approach has serious problems with the
notorious basis problem, and there does not seem to be any
principled way from within the theory to select unambiguosly the
basis in which all of these worlds form. More recent understandings
of MWI take decoherence into account. Decoherence provides a
principled dynamical way to solve the basis problem, but it means
the worlds do not actually form until there is decoherence -- worlds
cannot form until they know what basis is relevant!
I recommend the paper I suggested to Telmo:
Michael Cuffaro, http://arxiv.org/abs/1110.2514v2
Cuffaro discusses the problems with the older form of MWI and
suggests that although many worlds might be a useful heuristic in
quantum computing, decoherence is required before worlds could be
considered to have any ontological basis. The exponential speedup
with a quantum computer is then seen in the fact that the QC
manipulates the phases inherent in the entanglement of qbits, and
doesn't have to actually calculate the function in question for all
possible inputs, as the older many worlds view requires.
Oh! I see that my explanation that the MW prevents the need of action
at a distance was neo-everettian!
I am not sure I understand the paper by Currafo, as I have no single-
world interpretation of entanglement and/or quantum phase. At best, it
would be a critics of the notion of world (be it single or not), and
this would made QM even closer to the physics extracted from
computationalism, where there is no world at all, and the
differentiation is only a relative differentiation of the
consciousness of a person. I guess mechanism is probably neo-neo-
everettian, if not neo-neo-neo-Everettian. As I said once, despite
Everett seems to disagree, it is better to talk in term of relative
state, or relative dreams, instead of world. The worlds, with
mechanism, are maximal consistent extensions, and exists only in the
mind of the numbers. The FPI are not on the worlds, but on the first
person (hopefully plural, as it seems) experience.
Probably more on this later, I have still a lot of work to do.
Meanwhile, Bruce, or anyone, you might try to explain his cluster
quantum computing in a single world, or with collapse. Cuffaro does
not provide any explanation of this, and when taken literally, his
multi-qubit entanglement requires "MW" (or many minds, many dreams,
many numbers, etc.).
Bruno
Bruce
On 14/06/2017 4:09 am, John Clark wrote:
On Mon, Jun 12, 2017 at 8:32 PM, Bruce Kellett <bhkell...@optusnet.com.au
> wrote:
>> I agree Interference must take place in a single
world, 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?
> What calculations are performed in these parallel worlds?
Whatever algorithm you and your doppelgangers decided to run
on their quantum computer.
> And what performs those calculations?
Computers made of matter that obey the laws of physics.
> You are the one who insists that calculation is possible
only on a physical computer.
Yes, but you almost make that sound as if it were a contradiction
of some sort.
> Who constructed all these physical computers in the
parallel worlds?
If the MWI is correct and if you're a computer engineer then
you and your doppelganger s made the quantum
computer, made lots and lots of them actually.
>> 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.
> Of course the interference continues -- for ever if
necessary. The screen or photographic plate is only there to enable
you to see it.
No, in the Many World's theory it doesn't matter if anybody
sees the results, in fact a brick wall would work just as well as a
screen or a photographic plate, the only thing the MWI is
interested in is that all of those things destroy the photon.
After the photon passed the slits that photon was the only
difference between those 2 universes, when it is destroyed in both
universes by a screen or photographic plate or brick wall there is
no longer a difference between universes so they merge back
together, but indications it went through slot A and indications it
went through slot B remain. And that produces the interference
pattern. We don't usually see this weird quantum effect in our
everyday macro-world because when a large change is made between
universes it's hard to arrange things so they evolve together
toward the same point, become the identical again, and thus merge
back together. That's why making a quantum computer is hard.
> Of course the interference continues -- for ever if
necessary. [...] Try moving the position of the screen,
what happens?
What happens is if you remove the screen or photographic
plate or brick wall and just let the photon continue on into
infinite space then NON-interference will continue forever because
the 2 universes will always remain different and thus never
recombine.
In the MWI the rules are crystal clear about when things split
and when things merge back together. And In MWI everything
that can happen does happen, so when a photon approaches 2 slits
the universe splits and one photon goes through the right
slit and one goes through the left slit. After those
2 photon s hit a photographic plate or
screen or a brick wall the photons no longer exist in
either universe and so they merge back together into one
universe , and this merger causes the interference lines. If
instead , after passing the slits there is no photographic
plate or screen or brick wall and the photons are
allowed to continue on into infinite space then the 2 universes
remain different and remain separated forever. And so no
interference between them ever occurs.
> Superpositions occur everywhere, and no new worlds are
split off until there is decoherence.
But we don't ALWAYS see a superposition of states. You can place a
detector next to one of the slits so you you know which slit
each photon went through, but if you do that the interference
pattern disappears because interference needs at least 2 different
things to interferer with and with this modified experiment
the universe doesn't split so it can't recombine so you see no
interference pattern. In the unmodified experiment
after the photon makes its decision on which of the 2 slits
to go through i t then hits a screen or
photographic plate or brick wall. When that happens the
photons in both universes are destroyed and thus there is no
longer any difference between the two, so the universes will
merge back together. T hen you will see a
superposition of states. Then you will see indications that you
live in a universe where the photon went through slot A only
and indications you live in a universe where the photon went
through slot B only, and that is why you see an interference
effect even if you only send one photon at a time at the
slits. If you got rid of the film (or the brick wall) and
let the photon head out into infinite space after it passed
the slits then the universes, and you, will split and never
recombine, and so of course you will see no interference
effect.
The beautiful part of the Many World Interpretation
is that unlike its rivals it doesn't have to explain
what an observer is or what consciousness is all about
because whether a universe splits or not has nothing to do
with any of that , a brick wall will work just as well
as a screen or a photographic plate. All of them will
destroy the photon and that is the only difference between one
universe and the other.
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