On 5/1/2018 9:01 AM, Bruno Marchal wrote:
On 29 Apr 2018, at 19:59, Brent Meeker <meeke...@verizon.net
<mailto:meeke...@verizon.net>> wrote:
On 4/29/2018 8:53 AM, Bruno Marchal wrote:
But that's my question: Why isn't it the same? And even if it's
not how would be know? The "conscious" quantum computer assures
us that it not only detected that there was a welcher weg photon
but that it's weg was known to the "consciousness" of the quantum
computer, before it was erased. But why would we believe it? We
already have these experiments in which we know the weg was
available and could have been recorded, but was erased. So what
is the "consciousness" that adds a secret-sauce to the experiment?
Good question. I doubt that you can fool quantum mechanics by
calling it "consciousness". I think in this case the interaction
with the welcher weg photon would amount to sufficient decoherence
-- basically information was extracted that was not restored. Also,
of course, if the QC "forgets" what it did, how can it report on
the fact that it did anything. How can we believe that it actually
knew which slit at some point?
Because in Deutsch experiment, not everything has been erased,
notably the memory that he has known the result. He would say
something like: I remember doing the measurement and writing it in
the enveloppe. Now the envelop has been erased, and I can’t remember
its content, but I definitely remember having known the content.
But two questions remain. First, the empirical question of whether
this erasure is enough to restore interference.
I do not see why it would not been enough … in theory. You need only a
computer able to forget a memory, but not some meta-memory that it has
recorded a definite result. It isa bit like remembering we have done a
dream, without being able to remember any of its content.
In practice, that might be very difficult, if not impossible. I am not
sure.
Second, why should we believe the quantum computer.
In Deutsch proposal, it is a human.
No, it's a conscious quantum computer. It it were a human or other
(quasi-) classical instrument decoherence would happen when there was a
detection of welcher weg and erasure would be impossible.
Brent
And we can repeat the experience with many humans. If they have all
that feeling of having done a measurement and have obtained a definite
record without being able to say which one, I think this coule be
taken as making the MWI more plausible than the Mono-W.
It is not like the classical case in which there is a
fact-of-them-matter about which slit I observed and I've simply
forgotten it. But by quantum erasing the information, there is no
fact-of-the-matter as to welcher weg, so what can it mean that the
quantum consciousness once knew it and now remembers something that
didn't happen.
I don’t think we need a quantum consciousness. It is just the usual
“comp consciousness”. The consciousness differentiate into “I see up
in a definite way” + “I see down in a definite way”. Both separates
the memories of up (resp. down) from the meta-memory “What I saw was
definite”, and then we erase only the memories of “up” and “down”,
taking care to not erase the meta-memory, so both consciousness can
fuse again, with the meta-memory of having see an single outcome, but
cannot tell which one, and in principle we can get (back) the
interference of up and down, as the meta-memory is independent of it
(in principle).
The something did happen (well with MW), only the memories of it has
been completely erased, like in the usual quantum erasing experience.
Bruno
Brent
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