David,
As I try to see if we disagree, or if it is just a problem of
vocabulary, I will make comment which might, or not be like I am
nitpicking, and that *might* be the case, and then I apologize.
On 23 Jul 2014, at 15:38, David Nyman wrote:
Recent discussions, mainly with Brent and Bruno, have really got me
thinking again about the issues raised by CTM and the UDA. I'll try
to summarise some of my thoughts in this post. The first thing to
say, I think, is that the assumption of CTM is equivalent to
accepting the existence of an effectively self-contained
"computationally-observable regime" (COR).
My problem here is that COR is ambiguous. I don't know what you mean
by "sef-contained "computationally-observable regime".
It seems to me that UD* *is* such a self-contained computable/
computational structure, and the existence of both the UD and UD* are
*theorem* of arithmetic, which means that such a COR does not need to
assume CTM (comp).
By its very definition, the COR sets the limits of possible physical
observation or empirical discovery. In principle, any physical
phenomenon, whatever its scale, could be brought under observation
if only we had a big enough collider. But by the same token, no
matter how big the collider, no such observable could escape its
confinement within the limits of the COR.
I agree, but why? here a Peter Jones can say: not at all, to have
something "observable", you need consciousness, and to have
consciousness you need a physical primitive reality.
If we accept that the existence of a COR is entailed by assuming
CTM, we come naturally to the question of what might be "doing the
computation".
How could that not be answered by the existence of COR, or by
arithmetic. We know that both the programs and their execution can be
proved to exist in elementary arithmetic. The problem comes
exclusively from the people who say that *a priori* the computation
are not enough, and that they need to be implemented in the primitive
physical reality (that they can't define, but the point is logically
meaningful until step 8).
In terms of the UDA, by the time we get to Step 7, it should be
obvious that, in principle, we could build a computer from
"primitive" physical components that would effectively implement the
infinite trace of the UD (UD*). Furthermore, if such a computer were
indeed to be implemented, the COR would necessarily exist in its
entirety somewhere within the infinite redundancy of that trace.
It would exist physically, and lead to the same measure problem,
forcing the physicalist to bring up an hypothesis that the primitive
physical universe is "small" to avoid the measure problem.
This realisation alone might well persuade us, on grounds of
explanatory parsimony and the avoidance of somewhat strained or ad
hoc reservations, to accept FAPP that UD*->COR. Should we be so
persuaded, any putative underlying "physical computer" would have
already become effectively redundant to further explanation.
Yes. At step seven, we can already use Occam, and abandon physicalism.
At step 8, the move can still be done logically, but it is shown to be
a god-of-the-gap move.
Notwithstanding this, we may still feel the need to retain
reservations of practicability. Perhaps the physical universe isn't
actually sufficiently "robust" to permit the building of such a
computer?
To build it is not a problem, (I did it), but to run it for a
sufficiently long time so that we have a measure problem is different.
Or, even if that were granted, could it not just be the case that no
such computer actually exists?
Well, it exists like prime numbers exists. Same for his execution.
Now, I doubt that in a physical universe we can run it *forever*.
Reservations of this sort can indeed be articulated, although
worryingly, they may still seem to leave us rather vulnerable to
being "captured" by Bostrom-type simulation scenarios.
This assume also the existence of computers, and physical computers.
The bottom line however seems to be this: Under CTM, can we justify
the "singularisation", or confinement, of a computation, and hence
whatever is deemed to be observable in terms of that computation, to
some particular physical computer (e.g. a brain)? More generally,
can we limit all possibility of observation to a particular class of
computations wholly delimited by the activity of a corresponding sub-
class of physical objects (uniquely characterisable as "physical
computers") within the limits of a definitively "physical" universe?
That problem appears once we agree that a non physical computation can
be as conscious as us, and that problems appears at step seven,
including its solutions. It is because we will take all computations
(going through our mental states) into account that we have a measure
problem, which is the stabilization of physical laws problem. Of
course after that we need to formulate and solve that problem
mathematically, and that is what is done in AUDA.
This is where Step 8 comes in. Step 7 seeks to destabilise our naive
intuition about an exclusive 1-to-1 relationship between
computations and particular physical objects by pointing to the
consequences of a physical implementation of UD*. Step 8 however is
a change of tactic. First, it postulates a scenario where physical
tokens have been contrived to represent a "conscious
computation" (either in terms of a brain or in terms of a substitute
"computer"). Then it sets out to shows how all putatively
"computational" relations between such tokens could in principle be
disrupted without change in the net physical action or environmental
relations of the system that embodies them. Step 8 differs from Step
7 in that it seeks in the first instance to undermine the very
notion that physical activity can robustly embody
I agree up to here.
*any* second-order relations above and beyond those of net physical
action.
Here I disagree. I would say instead "Step 8 differs from Step 7 in
that it seeks in the first instance to undermine the very notion that
physical activity can robustly embody consciousness or the first
person subjectivity". I don't see why it would undermine the second or
higher order relation. The problem is only for the higher order *first
person* relation with the physical activity of the device, ISTM (It
seems to me).
Accepting such a stringent conclusion would then seem to rule out
CTM prima facie. The only possibility of salvaging it would lie in
an explanatory strategy in terms of which computational relations
take logical precedence over physical ones.
But this somehow, we already know. "Computation" is prima facie a
notion of pure arithmetic. the difficulty is already in the phsyicist
hands, to explain how it implements a computation in physics, but that
is not to hard, as the physical lwas, and many different subparts are
Turing universal. What they cannot solve (and ignore) is that they
lost the usual 1p-3p link. Here, what saves us, is incompleteness
which will explains that the 1-self is not isomorphic to the 3p-self,
and lives in some different semantical space, incompatible with a
primitive physics.
Given that computational relations are effectively arithmetical,
this in turn leads to the conclusion that CTM->UD*->COR (or more
generally, that each implies the others).
Notwithstanding this it would seem that Step 8 is not wholly
persuasive to everybody, so is there yet another tack? The line of
argument that I've been pursuing with Brent has led me to consider
the following analogy, which I'm sure you'll recognise. Consider
something like an LCD screen as constituting the "universe of all
possible movie-dramas". In terms of this analogy, what are the
referents of any "physical observations" on the part of the dramatis
personae featured in such presentations? IOW what are we to suppose
Joe Friday to be referring to when he asks for "Just the facts,
ma'am"? Well, the one thing we can be sure of is that NO such
reference can allude to the "underlying physics" (i.e. the pixels
and their relations) of the LCD display. If this analogy holds, at
least in general outline, what justification, under CTM, could
remain for any assumption that our own observations and references
might "accidentally" allude to some "LCD-physics" postulated,
mutatis mutandis, as underlying the COR? Would it not seem
extraordinary that any such underlying physics could contrive to
"refer to itself" through the medium of its merely computational
derivatives?
Not sure. If arithmetic can do that, why not physics? Well, because
the MGA explains you need to put infinite magic to singularize
consciousness, and still surivive the comp substitution qua computatio
(and not the will of a God-of-the-gap).
This last point might seem determinative, but might there not still
be a last-ditch redemption, of a physics underlying computation, in
terms of "evolution"? IOW, might it not be argued that the
acquisition of internal "computational" models of their physical
environment confers a survival advantage on the physical creatures
that embody them? But any such argument would, of course, be
completely circular; assuming CTM, it begins and ends in the COR.
IOW, arguing in this way would be to ignore the fact that the
history of such creatures, their survival, and the environment in
which this is supposed to take place, all lie within the COR, not
the putative regime of any "underlying physics". THAT "physics"
would necessarily be entirely inscrutable and inaccessible for
reference at the level of the COR (think of the LCD analogy). And
hence we simply would have no a priori justification for assuming
the observational physics of the COR to be isomorphic with some
notional underlying "LCD-physics". In fact, once having assumed CTM,
we would have no further basis for assigning THAT physics any role
whatsoever in our explanatory strategy.
At first sight I agree here.
Bruno
David
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