On 5/12/2015 3:25 AM, Bruno Marchal wrote:
On 12 May 2015, at 02:33, Bruce Kellett wrote:
The fact that projecting the film isn't a general purpose computer seems to me to be a
red herring. It was never claimed that projecting the film of the brain substrate
instantiated general consciousness -- the only claim ever made here is that this
projection recreates the conscious moment that was originally filmed. That is all that
is required. General purpose computing and counterfactual correctness are all beside
the point. If the original conscious moment is recreated, then the film is a
computation in any sense that is necessary to produce a conscious moment. This is
sufficient to undermine the claim that consciousness does not supervene on the physical
body.
The matter of whether the physical is primitive or not is also a red herring. No such
assumption is required in order to show that the MGA fails to prove its point.
It is a reductio ad absurdum. If consciousnesss requires the physical activity and only
the physical activity, then the recording is conscious. But anyone knowing what is a
computation should understand that the recording does not compute more than a trivial
sequence of projection, which is not similar to the computation of the boolean graph.
I think there are five concepts of computation in play here:
1. An abstract deterministic computer (TM) or program running with some given external
input. This program is assumed to have well defined behavior over a whole class of
inputs, not just the one considered.
2. A classical (deterministic) physical computer realizing (1) supra. This is what the
doctor proposes to replace part or all of your brain.
3. A recording of (2) supra being played back.
4. An execution of (1) with a classical (deterministic) computer that has all the
branching points disabled so that it realizes (1) but is not counterfactually equivalent
to (1) or (2).
5. A physical (quantum) computer realizing (1) supra, in it's classical limit.
Bruno takes (1) to define computation and takes the hypothesis that consciousness is
realized by a certain kind of computation, an instance of (1). So he says that if you
believe this you will say yes to the doctor who proposes (2) as a prosthesis. This
substitution of a physical deterministic computer will preserve your consciousness. Then
he proceeds to argue via the MGA that this implies your consciousness will not be affected
by using (4) instead of (2) and further that (4) is equivalent to (3) and (3) is absurd.
Having found a reductio, he wants to reject the assumption that your consciousness is
realized by the physics of a deterministic computer as in (2).
Whether (3) preserving consciousness is absurd or not (and I agree with Russell that's to
much of a stretch of intuition to judge); this is not the reversal of physics claimed.
The Democritan physicist (nothing but atoms and the void) will point out that (2) is not
what the doctor can implement. What is possible is realizing a prosthetic computation by
(5). And (5) cannot be truncated like (4); quantum mechanical systems can only be
approximately classical and only when they are interacting with an environment. The
classical deterministic computer (TM) is a platonic ideal which, as far as we know, cannot
be realized.
Now that doesn't invalidate Bruno just developing his theory of the UD and showing that it
realizes QM and the wholistic quasi-classical physical behavior of macroscopic systems in
some limit. But I don't think he can just help himself to the conclusion that there MUST
BE some measure or some way of looking at the UD in which this is so because the MGA has
refuted Democritus.
Brent
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