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.
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 <mailto: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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