On 10/15/2019 2:14 PM, John Clark wrote:
On Tue, Oct 15, 2019 at 1:50 PM 'Brent Meeker'
<[email protected]
<mailto:[email protected]>> wrote:
/> Curiously, Deutsch used a quantum computer in a thought
experiment to prove multiple worlds./
He did indeed, I read about it 30 years ago in Deutsch's book "The
Ghost In The Atom" and that was when I started to take the MWI
seriously. Deutsch's test would be very difficult to perform but the
reason it's so difficult is not the Many World's fault, the reason is
that the conventional view says conscious observers obey different
laws of physics, Many Worlds says they do not, so to test who's right
we need a mind that uses quantum properties. Quantum Computers have
advanced enormously over the last 30 years so I wouldn't be surprised
if it or something very much like it is actually performed in a decade
or two.
An intelligent quantum computer shoots photons at a metal plate one at
a time that has 2 small slits in it, and then the photons hit a
photographic plate. Nobody looks at the photographic plate till the
very end of the experiment. The quantum mind has detectors near each
slit so it knows which slit the various photons went through. After
each photon passes the slits but before they hit the photographic
plate the quantum mind signs a document saying that it has observed
each and every photon and knows which slit each photon went through.
It is very important that the document does NOT say which slit any
photon went through, it only says that they went through one slit and
only one slit and the mind has knowledge of which one. There is a
signed document to this effect for every photon it shoots.
Now the mind uses quantum erasure to completely destroy its memory of
which slit any of the photons went through; the only part remaining in
the universe is the document which states that each photon went
through one and only one slit and the mind (at the time) knew which
one. Now develop the photographic plate and look at it. If you see
interference bands then the Many World interpretation is correct.
But as Scott Aaronson noted the interference had to happen in one world.
If you do not see interference bands then there are no worlds but this
one and the conventional quantum interpretation is correct.
This works because in the Copenhagen interpretation when the results
of a measurement enters the consciousness of an observer the wave
function collapses,
That was von Neumann's (and briefly Wigner's) interpretation, but Bohr,
Heisenberg, and others always held that any macroscopic instrument would
collapse the wf. The development of decoherence theory has made that
more well defined.
Brent
in effect all the universes except one disappear without a trace so
you get no interference. In the Many Worlds model all the other worlds
will converge back into one universe because information on which slit
the various photons went through was the only thing that made one
universe different from another, so when that was erased they became
identical again and merged, but their influence will still be felt,
you'll see ambiguous evidence that the photon went through slot A only
and ambiguous evidence it went through slot B only, and that's what
causes the interference pattern.
John K Clark
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