On 03 May 2009, at 09:00, Stathis Papaioannou wrote:

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> > 2009/5/3 Bruno Marchal <marc...@ulb.ac.be>: > >> 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). > > But you can interpret *any* behaviour as a NAND gate, in an ad hoc > fashion. It doesn't even need to be consistent from moment. On a > Tuesday 3 birds landing could stand for "1" while on a Wednesday 3 > birds landing could stand for "0", and on a Saturday it could stand > for "1" again. But this makes sense only relatively to a "stable universal" machine in which you can encode what you are telling me. > In this way you could take the physical activity > carried out by a store-bought computer calculating factorial(5) and > map it onto the forest with the birds. All right, I see your point, you take any physical activity, and then an ad hoc sequence of universal machine which interpret each piece of birds behavior into a computation of fact(24). That sequence should be capable to be infinite and the birds behavior have to resume more and more complex problem dues to the adhocness of the representations. The complexity of the sequence of universal machine will grow exponentially. Hmm. perhaps. Again this will change nothing, After all, the UD does generate *all* implementation of all computations including your very complex (to encode) interpretation of rocks and forest. > Of course, this won't give you > the answer to factorial(5) unless you already have the answer, but > that just means that the computation is obscured, It is obscured and blurred relatively to its most probable histories. In normal physics (normal in the Gauss meaning) you cannot count on those computations. It would be like saying you win the lottery given that you have the right numbers, in disorder, but after all you can read them in the right order, and someone in Platonia does read them in that different order. I could still disagree because, as you seem to accept, such "physical implementation" can reduce to zero the needed amount of physical activity, and an interpretation of your computation of the factorial of 4, in the rock, will be made by an actual computation of 24 by a "real universal machine" which does not need to be physical, in platonia, and which has a lot of imagination in front of the rock. You need something like this, for your argument to go through, but this *is* mainly the comp supervenience. So what you show is that indeed, we don't need, or cannot use in any genuine sense a primitive notion of physical activity to build a notion of supervenience. Yet I think that the notion of interpretation is more constrained that just invoking some ad hoc sequence of platonist universal interpreters. At some level, we must bet on "just one", if only to be able to talk (even to talk to oneself). > in the same way a > message is obscured if encoded with a one-time pad that is > subsequently destroyed and forgotten. In fact, even with the > store-bought computer the computation is obscured if there are no > intelligent beings around who can understand it. Not at all. If the computer evaluate fact(4), even alone in a room, the probability it gives 24 is one, in a verifiable way by a third person. With or without physicalism we accept the idea that the physical neighborhood is locally Turing universal, and does interpret the computation of 4. If I put a computer evaluating Stathis here and now, under your substitution level, then, despite the computer being alone in the room, the probability that you are where you feel you are (here and now) or in that "room" is 1/2 (accepting the usual probability). Cf step 5. You will not say "yes doctor", but only if you take a permanent look on my working artificial brain". The point of comp is that some program can observe themselves (at some level). And this can be made mathematically precise (by Kleene second recursion theorem). Accpeting your "interpretation of the rock", The probability that you are in the rocks, relatively to you here and now, is 0,00000000000000........1, given that you have to wait the UD generates that immensely long sequences of more and more complex "ad hoc" universal interpreters. > So, if the > computation supervenes on the activity of the store-bought computer > without regard for whether any external observer is around to > understand, then it also supervenes on the activity of the forest with > the birds. You illustrate well that the only question which makes sense is the question of which most probable computation bears us, or which more probable universal machine or number "executes" us. What you say is that the UD will generate stupid program interpreting the empty input like if it was a code for fact(4). > Other possibilities are that the computation supervenes on > physical activity only when an external observer understands it (which > poses difficulties for a closed virtual reality with its own conscious > observers), And leads also to an infinite regression, unless you postulate an absolute external witness with cognitive abilities based on ... nothing (which makes not much sense). > or that the computation does not supervene on physical > activity at all. It seems to me that we agree that physical supervenience leads to many absurdities. Is your argument purely academical, or do you think it can be used to prevent the conclusion that physics has to be explained by the purely mathematical notion of "most probable computation as seen from inside", among the 2^aleph_0 computations going through the current states, in UD* or in arithmetic? With you argument, the movie-graph is conscious. But is all consciousness at once, not just the consciousness corresponding to the filmed boolean graph. This not change the problem measure in any way. It makes the primitive physicalness idea even more absurd. It seems to me that your point just recall that in Platonia, there are complex sequence of universal machine which can interpret any computation, including the empty one, as being any other computations. But this is akin to white rabbits (from the probability pov) and akin to the fact that, with its terrible redundancy and "free imagination", the UD generates also conspirator interpretations. With just arithmetic, when we stop to postulate a primitive or ontological material world, all primitive ad-hocness is removed, given that the existing internal interpretations are all determined, with their relative frequency, by addition and multiplication rules, and physics will be defined by the (absolute) probability of relative computations (here = probability of relative number theoretical relations. "to be a finite piece of computation" is decidable even in very tiny fragment of arithmetic, and this can be used to avoid any starting ambiguity. This is made possible through Church thesis, and it eventually forces us to realize that a rock is the result of an infinity of computation, and the rock "we see" a crude local average, but comp makes it possible that a rock implements all computations to, but only by an explicit call to a sequence of universal machine in Platonia. Meaning; there is no room for providing an explanative power (both for mind and matter) to the notion of primitive substance and primitive substancial incarnated laws. Due to the failure of logicism we need numbers or combinators and primitive immaterial laws to agree on, like addition and multiplication, or lambda abstraction and application, etc. The measure does not depend on which first universal system you choose, by non completely trivial application of computer science. And to use a primitive quantum computer for a primitive physics is treachery with respect to the comp mind body problem. OK? Bruno http://iridia.ulb.ac.be/~marchal/ --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Everything List" group. 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