On 30/10/2015 3:47 am, Bruno Marchal wrote:
On 27 Oct 2015, at 06:54, Bruce Kellett wrote:
On 27/10/2015 9:37 am, Russell Standish wrote:
The only clarification I would make is that (with computationalism)
the system is formal, but the observer (individual in your
terminology) and environment (universe with its physics in your
terminology) are a non formal partition of the system.
How is that partition into observer and universe made? If it is
purely formal then it doesn't do the necessary work. But then, how
does a purely formal system generate a non-formal division? I think
your division builds in semantic content from the outside by fiat --
not in a principled way.
This is similar to my objection to the many worlds interpretation of
QM. You have to distinguish between the different worlds in some way
-- unitary evolution cannot do this. Decoherence always leaves
residual correlations, and although these may be small, there are a
very large number of them, so the original superposition is, in fact,
still intact. Everett wants to make the world relative to the
particular observer (hence 'relative state' interpretation). But to
make sense of this mathematically you have to get rid of the unwanted
correlations.
I don't see why. We can fuse again by amnesia, and exploit the
unwanted correlation. They disappears only relatively, nothing is
lost, evolution is time symmetric.
No, amnesia does not reconnect the separate worlds -- it merely
indicates a confused individual. The world is not defined by what one
person sees or thinks. Inter-subjective agreement is essential to
understanding what is going on. You confuse the 1p and 3p, yet again.
Most do this by fiat -- the worlds are orthogonal FAPP. But that is
not principled either. Mathematically, we take a partial trace. But
*we *take the trace*,* it is not in Schroedinger's equation.
It is in the relative choice made by our histories (long
computations), relatively to us. Zurek explains this rather well in my
opinion, I mean why our type of brain needs orthogonal positioning,
why position is favored by brain-like structures, for consciousness to
stabilize enough to make prediction in our deep environment(universal
computations).
Zurek does not explain the point that I am making. Zurek's einselection
is designed to explain the preferred basis problem. But he misses the
mark by quite a wide margin. He explains why the position operator is
often relevant, but that merely selects a Hilbert space, it does not
select a basis in that space. The basis has to be robust against
environmental interactions, not just the operator itself. Einselection,
like decoherence, is part of the solution, but it is not the full solution.
But even if you have actually solved the basis problem, you still have
not solved the problem of quantum measurement. In order to get just one
result for an experiment with only probabilistic results, you have to
project a subspace out of the full Hilbert space. The full space might
well still be 'there' (in whatever sense you like), but the fact that
the observer is conscious of only part of that space involves a
projection operator. And projection operators are not time symmetric or
unitary. This is the partial trace problem, and it remains unsolved.
Bruce
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