On 01 May 2009, at 17:02, Stathis Papaioannou wrote:

> 2009/5/1 Bruno Marchal <marc...@ulb.ac.be>:
>>> That is, you can't say that the rock
>>> implements one computation but not another.
>> I don't think it implements any computations. I could accept some  
>> tiny
>> apparition of tiny pieces of of tiny automata, but nothing big or
>> sophisticated. Some very special crystals perhaps, no doubt, but  
>> those
>> are, then, computer.
> If your computer has to interact with the external world then that
> imposes some constraints on what counts as an implementation of a
> computation.

OK. Although you could say: "if your computer has to interact with  
another computer then ...". But OK. It is important, not for the rise  
of consciousness, but for its relative stability with respect to some  
notion of first person splral. It is important for having local measure.

> But without this constraint you are free to interpret any
> activity as any computation.

I don't see why. Simple activity could correspond to simple  
computation (I can agree with this). But any complex computation will  
require some gobal connectness among the many simple activity.  
Especially the long and deep (in Bennett sense) computations.

> You could pick three trees and, observing
> the movement of birds on and off the trees, interpret this as  a logic
> gate. Three birds land on the first tree, and that's a "zero" input.
> Two birds alight from the second tree, that's a "zero" input also.
> Three birds land on the third tree, that's a "one" output. A minute
> later, five birds alight from the first tree, one bird lands on the
> second tree and two birds land on the third tree, which is interpreted
> as two "one" inputs giving a "zero" output. Looks like it might be a a
> NAND gate! Not very useful, of course, but is there any reason why my
> interpretation is wrong, or why the birds flying around won't give
> rise to whatever consciousness is associated with the operation of the
> logic gate?

Somehow you make my point, because I am willing to say that you are  
right, ONCE assuming the supervenience thesis. But your conclusion,  
that anything computation supervenes on any physical activity,  
including the empty one, is what I definitely consider as an  
absurdity, and is the reason why, keeping comp, I abandon the physical  
supervenience thesis, and eventually the very idea of primitive  
physical stuff.
A computation is just like they are defined in mathematical books on  
computation: it is a global logical relation capable of sustaining non  
trivial relations among abstract items.

Consider Ned Block's Chinese People Computer. You can (logically, not  
ethically of course) program the people of China so that each chinese,  
just by doing very simple mails, participate into a giant computation  
emulating Einstein' brain, say. The consciousness of Einstein will  
rely on the global organization of the information handled by all  
chineses, not on the physical activity of such or such particular  
person. Of course, this line ends up accepting that from the point of  
view of Einstein it is just undecidable if he is a brain in a vat, a  
body in a hospital, or an abstract (but relatively rare and  
sophisticate) pattern in Platonia, and then the comp 1 person  
indeterminacy leads to a rich non trivial relative state  
interpretation of Arithmetic.

I think that if you take a real forest with birds, here and there, you  
can interpret some behavior as NAND or NOR, but you will not succeed  
ever in finding the computation of factorial(5). Even the universal  
dovetailer has to wait (in its own step-time) billions of billions of  
"steps" before getting something as interesting as the factorial  
functions. For Einstein's brain the UD will already take a  
ridiculously long time (well beyond anything physically observable)  
before getting its simulation.

Even if you decide to no more interact with the "external world", you  
will not say yes to a doctor who propose you a rock in place of your  
brain. This is beacuse the probability, ven and especially from your  
first person point of view, that the many NAND (that the rock could  
perhaps emulates indeed) arrange themselves into a Papaioannou healthy  
mind's state is null? You could survive in some possible world, but  
not through the rock computational power. If ever you survive with the  
rock, the probability that you will be dumb or disable will be far  

But you are right, those who believes in both comp and physical  
supervenience have to attach all consciousness to all physical  
activity, and then they does not need comp anymore and everything  
become trivial. You get a Kelly sort of physics which predict  
everything. I prefer to keep the mathematically coherent and sound  
comp, and forget physical supervenience. Even more so when you realize  
that the math for comp will explain the appearance of rocks and  
particles without assuming any metaphysical naturalism.



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