On 27-04-2018 00:41, Bruce Kellett wrote:
From: JOHN CLARK <johnkcl...@gmail.com>
On Thu, Apr 26, 2018 at 2:02 PM, <agrayson2...@gmail.com> wrote:
> How many times must I remind you that Feynman explained
that very clearly.
42.
> _Please repeat it. AG_
I originally sent this on December 14 2017:
David Deutsch proposed a test of Many Worlds about 30 years ago in
his book "The Ghost In The Atom", but it would be very difficult to
perform. The reason it's so difficult to test is not the Many
World's theory fault, the reason is that the conventional view says
that 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 the 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 electrons 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 one slit only and the mind has knowledge of
which one. There is a signed document to this effect for every
photon it shot.
Now the mind uses quantum erasure to completely destroy its memory
of which slit any of the photons went through; the only part
remaining 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. 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, 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
indications that the photon went through slot A only and indications
it went through slot B only, and that's what causes interference.
Quantum erasure involves more than just forgetting what happened.
What about Zurek's "many records in the environment". If you know what
happened, many traces of that result remain -- even if your memory is
erased. Deutsch on the wrong track, yet again!
Bruce
Deutsch is right, because your objection is irrelevant for a thought
experiment. Deutsch formulated his thought experiment before the concept
of quantum computers was proposed, and you can now just as well
formulate an equivalent thought experiment where decoherence is
completely contained. E.g. you can use qubits to represent spins and let
some AI generated by a quantum computer measure the x-component of a
spin polarized in the positive z-direction and then play this same game
of erasing the memory of the AI about the measurement result, except the
memory that the measurement was carried out. The transform back to the
state that is the same as the initial state except for the presence of a
record about the measurement having been performed, can be shown to be a
unitary transform.
Saibal
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