Hi David,

This is a nice post, but you are still putting the horse before the  
Now I can see that you have not yet grasp the main UDA point. Hope you  
have no problem with being frank, and a bit undiplomatical, OK?

On 13 Aug 2009, at 23:01, David Nyman wrote:

> Colin's recent interesting (not to say impassioned!) posts have - yet
> again - made me realise the fundamental weakness of my grasp of some
> of the discussions that involve Turing emulation - or emulability - on
> the list.  So I offer myself once more as lead ignoramus in
> stimulating some feedback on this issue .  Anyway, here's what I think
> I know already (and I beg you patience in advance for the
> inaccuracies):
> 1) A Turing machine is an idealised digital computer,

No, Turing tried to capture the notion of a human computer, working  
with a pencil and paper.
He tried to define mathematically what is human computable, and he is,  
with Post, and some other are the discoverer of a purely mathematical  
notion of computation, and this before the appearance of concrete  
computers. Computers have appeared after. Turing has played a role in  
that later appearance.  A platonist could say those concrete beings  
are just pale approximation of the real thing. Later this statement  
will be made precise, but with the step 8, we just cannot invoke any  
physical things or physical reality.
To be sure, the fact that computer have been discovered in math,  
before "in nature" is not an argument, yet it helps a lot to see that,  
especially for the grasp of the comp supervenience thesis. And that is  
the reason why I explain that absolutely fundamental mathematical  
discovery. Computation has nothing to do with physics at the start.
Note that I abstract myself from the pioneer building of a computer by  

> based on a tape
> (memory device) of potentially infinite length,

The human computer can use as many papers, or even the wall of its  
cavern, or of its living room, ... He is a finite being embedded in a  
non finite available memory-time space.

> that has been shown to
> be capable of emulating any type of digital computer,

This has not been shown. But this follows from Church Thesis.

> and hence any
> other TM.

What Turing has shown, is that there is a universal Turing machine,  
capable of simulating all Turing machines. Then that Universal machine  
can be shown to emulate all existing universal machine, and by Church  
Thesis: all universal (and particular) machines.

> The meaning of 'emulation' here entails transforming
> precisely the same inputs into the precisely same outputs, given
> sufficient time.

OK. But there is an intensional Church thesis, which can be deduced  
from Church thesis, saying that not only two universal systems can  
compute the same functions, but they can compute them in the same way  
(same algorithm).

> In effect, digitally 'emulating' a computation is
> conceptually indistinguishable from the computation itself; or to put
> it another way, computation is deemed to be invariant under emulation.

... at some level. OK.

> 2) Insofar as the causal processes of physics are specifiable in the
> form of decidable (i.e. definitely stopping) functions, they are
> capable of finite computation on a TM - i.e. they are TM emulable.
> What this amounts to is that we can in principle use a TM to compute
> the evolution of any physical process given the appropriate
> transformation algorithm.  Since we're dealing with QM this must
> entail various probabilistic aspects and I don't know what else: help
> here please.  But the general sense is that the mathematics of physics
> could in principle be fully Turing-emulable.

Step 8 forbids us to introduce anything physical. The reversal is done  
at that step. I guess you are right that it could be a better idea to  
do the step 8 before, but it is more difficult for most. Any way,  
computational supervenience is defined after step 8.
Then we will discover that "Colin is right" no piece of matter should  
be Turing emulable. The mathematics of physics will have to escape the  
turing emulable. The apparent turing emulability of the world around  
us, is a threat to indexical comp (the idea that "I am machine").
Of course I disagree with Colin's reasoning where he deduce the non  
Turing emulability of nature from the non emulability of mind. UDA  
deduces the non Turing-emulability of matter from the non Turing- 
emulability of the mind. And the proof is constructive. It redefines  
precisely what "matter" consists in.

> 3)  Now we get into more controversial territory.

Really? I don't think so. Difficult, not yet very well known, and  
rather subtle, no doubt.
But I don't think there is anything controversial. Nobody told me that.

>  Bruno has shown (at
> least I agree with him on this) that for the mind to be regarded as a
> computation,

The wording is a bit dangerous. All I know after UDA is that my state  
of mind at time and place (x,t) has to be linked to an infinity of  
computations going through that state, and that my next state, from my  
first person point of view is indeterminate on the set of all those  

> essentially everything else must also be regarded in the
> same light: IOW our ontology is to be understood entirely from the
> perspective of numbers and their relations.

True, but this excludes quickly that it can be conceived a priori as  
computations. Immaterial relation between numbers, sure, but not  
necessarily computable relation. Cf the first person indeterminacy.

> This is not universally
> accepted, but more on this in the next section.

This is not universally understood, nor really studied. But it is  
understood quickly or slowly when studied. To my knowledge.

> Suffice it to say
> that on this basis we would appear to have a situation where the
> appropriate set of computations could be regarded not as mere
> 'emulation', but in fact *as real as it gets*.  But this of course
> also renders 'stuffy matter' irrelevant to the case: it's got to be
> numbers all the way down.

No. With the first person indeterminacy it would be more correct to  
say that it's got to be number all the way up. It makes the comp  
immaterial appearance of "stuffy matter" infinitely complex and non  
turing emulable, a priori. I suspect you have not yet really see the  
role of UDA1-6 in the step-7.

> 4) If we don't accept 3) then we can keep stuffy matter,

We can't by step 8; but by the whole UDA 'stuffy matter" does no more  
make sense at all. The comp "stuffy" matter has to be made by a  
infinite sum of infinite computations including infinities of white  
rabbits-computations. The apparent computability of the physical laws  
*is* a problem for the indexical computationalist.

> but at the
> cost of losing the digital computational model of both mind and body.

Most want introduce a stuffy matter because they believe they can save  
computation for both mind and body. Colin is correct for saying bodies  
cannot be computable, but this follows from the mind being  
"computable", in the "yes doctor" sense, not from the scientist mind  
being non computable.

> Not everyone agrees with that radical assessment, I know;

Who disagree? It is not a question to agree or not. It is a question  
of understanding or not (or to find a mistake).

> but even
> those who don't concur presumably do hold that everything that happens
> finally supervenes on something stuffy as its ontological and causal
> basis, and that numbers and their relations serve merely to model
> this.

That is comp, before UDA, before the necessary reversal.

> The stuffiness doesn't of course mean that the evolution of
> physical systems can't in principle be specified algorithmically,

Comp-stuffiness *is* a priori not algorithmic.

> and
> 'emulated' on a TM if that is possible; we still have mathematics as a
> model of stuff and its relations.

UDA entails there is no stuff at all. No stuff capable of justifying  
in any way the observation of stuff.

> But it does entail that no digital
> emulation of a physical system can - as a mere structure of numbers -
> be considered the 'real thing': it's got to be stuffy all the way
> down.

Well, with comp+physicalism. But this is inconsistent, at the  
epistemological level.

> 5) We might call 3 the numerical (necessary) model, and 4 the stuffy
> (contingent) model of reality -

Hmm... The "numerical model", but non-computational model,  is  
necessary by reasoning. The contingent realities are well explained,  
and the stuffy model is not contingent but impossible.

> but of course I don't insist on this.
> Rather, it seems to me that in our various discussions on the
> emulability or otherwise of physics, we may sometimes lose sight of
> whether we are interpreting in terms of numerical or stuffy
> ontologies.

But "stuffy" or just primitively physical, after UDA has no more any  

> And I think this has something to do with what Colin is
> getting at: if your model is stuffy, then no amount of
> digital-numerical emulation is ever going to get you anything stuffy
> that you didn't have before.  A physical-stuffy TM doing any amount of
> whatever kind of computation-emulation remains just a physical-stuffy
> TM, and a fortiori *not* transmogrified into the stuff whose causal
> structure it happens to be computing.
> Now of course this stricture wouldn't necessarily apply to model 3).
> But the 'comp' that Colin claims to refute is, I suspect, not this but
> stuffy-comp - i.e. the comp based on stuff rather than numbers, that
> Olympia, in her lazy but decisive way, dismisses as ephemeral.  This
> is also the comp that I have argued against, but I don't intend this
> merely to be a re-statement of my prejudices.  I know that Colin isn't
> precisely a proponent of model 3) nor model 4), arguing strenuously
> for a distinctive alternative; so it would be interesting (certainly
> for me) if he'd care to characterise precisely how it diverges from or
> extends the foregoing stuffy-numerical dichotomy.
> Be that as it may, the punchline is: do we find this analysis of the
> distinction between numerical 3) and stuffy 4) to be cogent with
> *specific* respect to the significance and possible application of the
> concept of 'emulation' in each case?

You don't yet have grasped the UDA yet. It makes the stuffy things not  
just useless for having computations and relative emulation, but it  
makes, it is the big hard point, any notion of stuffiness, irrelevant  
for physical objects too.
There is just no stuff available. Even if we introduce it, it makes no  
change in consciousness, and can't have any relation with what we  
observe in nature. We will come back on this.



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