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. Second, why should we
believe the quantum computer. 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.
Brent
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