On 5/13/2015 5:33 AM, Bruno Marchal wrote:
On 12 May 2015, at 22:27, meekerdb wrote:
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.
OK. That is the standard concept (although the computation does not have to be
deterministic, but that is a detail here).
2. A classical (deterministic) physical computer realizing (1) supra. This is what the
doctor proposes to replace part or all of your brain.
Yes, and this involves physics. But this is no more a computation in the sense of
Church-Turing, which does not refer to physics at all.
3. A recording of (2) supra being played back.
Nobody would call that a computation, except to evade comp's consequences.
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).
This computes one epsilon more than the movie. That is, not a lot.
5. A physical (quantum) computer realizing (1) supra, in it's classical limit.
That is the solution we hope for (as it would make comp and QM ally and very
plausible).
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);
There is no stretch of intuition, the MGA shows that you need to put magic in the
primitive matter to make it playing a role in the consciousness of physical events.
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.
But then comp is false, as comp is a bet of surviving some digital truncation.
That's why you need to distinguish comp1 from comp2. Comp1, which almost everyone agrees
to, assumes the doctor will implant a real quantum mechanical, approximately digital
device. But the reasoning of leading to the MGA assumes and ideal, abstract digital
device which has no interaction with its environment except the TM I/O.
Brent
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