On 13 May 2015, at 21:04, meekerdb wrote:
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.
I use a dream to make it simpler, but you can do the MGA with an
interactive environment. There are two ways for doing that: either you
put the digital approximation of the environnment, in the graph,
or ... you don't. You will need different kind of magic for preventing
the physical supervenience (assumed for the reduction ad absurdum) to
be inherited by the filmed graph. That's why you can' avoid comp2,
when you have comp1.
Bruno
Brent
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