On 1/9/2012 19:54, Craig Weinberg wrote:

On Jan 9, 12:00 pm, Bruno Marchal<marc...@ulb.ac.be> wrote:On 09 Jan 2012, at 14:50, Craig Weinberg wrote:## Advertising

On Jan 9, 6:06 am, Bruno Marchal<marc...@ulb.ac.be> wrote:I agree with your general reply to Craig, but I disagree that computations are physical. That's the revisionist conception of computation, defended by Deustch, Landauer, etc. Computations have been discovered by mathematicians when trying to expalin some foundational difficulties in pure mathematics.Mathematicians aren't physical? Computations are discovered through a living nervous system, one that has been highly developed and conditioned specifically for that purpose.Computation and mechanism have been discovered by many people since humans are there. It is related to the understanding of the difference between "finite" and "infinite". The modern notion has been discovered independently by many mathematicians, notably Emil Post, Alan Turing, Alonzo Church, Andrzei Markov, etc. With the comp. hyp., this is easily explainable, given that we are somehow "made of" (in some not completely Aristotelian sense to be sure) computations.They are making those discoveries by using their physical brain though.

`Sure, but that requires one to better understand what a physical brain`

`is. In the case of COMP(given some basic assumptions), matter is`

`explained as appearing from simpler abstract mathematical relations, in`

`which case, a brain would be an inevitable consequence of such relations.`

We can implement computation in the physical worlds, but that means only that the physical reality is (at least) Turing universal. Theoretical computer science is a branch of pure mathematics, even completely embeddable in arithmetical truth.And pure mathematics is a branch of anthropology.I thought you already agreed that the arithmetical truth are independent of the existence of humans, from old posts you write. Explain me, please, how the truth or falsity of the Riemann hypothesis, or of Goldbach conjecture depend(s) on anthropology. Please, explain me how the convergence or divergence of phi_(j) depends on the existence of humans (with phi_i = the ith computable function in an enumeration based on some universal system).The whole idea of truth or falsity in the first place depends on humans capacities to interpret experiences in those terms. We can read this quality of truth or falsity into many aspects of our direct and indirect experience, but that doesn't mean that the quality itself is external to us. If you look at a starfish, you can see it has five arms, but the starfish doesn't necessarily know it had five arms.

`Yet that the fact the starfish has 5 arms is a fact, regardless of the`

`starfish's awareness of it. It will have many consequences with regards`

`of how the starfish interacts with the rest of the world or how any`

`other system perceives it.`

`If you see something colored red, you will know that you saw red and`

`that is 'true', and that it will be false that you didn't see 'red',`

`assuming you recognize 'red' the same as everyone else and that your`

`nervous system isn't wired too strangely or if your sensory systems`

`aren't defective or function differently than average.`

`Consequences of mathematical truths will be everywhere, regardless if`

`you understand them or not. A circle's length will depend on its radius`

`regardless if you understand the relation or not.`

`Any system, be they human, computer or alien, regardless of the laws of`

`physics in play should also be able to compute (Church-Turing Thesis`

`shows that computation comes very cheap and all it takes is ability of`

`some simple abstract finite rules being followed and always yielding the`

`same result, although specific proofs for showing Turing-universality`

`would depend on each system - some may be too simple to have such a`

`property, but then, it's questionable if they would be powerful enough`

`to support intelligence or even more trivial behavior such as`

`life/replicators or evolution), and if they can, they will always get`

`the same results if they asked the same computational or mathematical`

`question (in this case, mathematical truths, or even yet unknown truths`

`such as Riemann hypothesis, Goldbach conjecture, and so on). Most`

`physics should support computation, and I conjecture that any physics`

`that isn't strong enough to at least support computation isn't strong`

`enough to support intelligence or consciousness (and computation comes`

`very cheap!). Support computation and you get any mathematical truth`

`that humans can reach/talk about. Don't support it, and you probably`

`won't have any intelligence in it.`

`To put it more simply: if Church Turing Thesis(CTT) is correct,`

`mathematics is the same for any system or being you can imagine. If it's`

`wrong, maybe stuff like concrete infinities, hypercomputation and`

`infinite minds could exist and that would falsify COMP, however there is`

`zero evidence for any of that being possible.`

`If any intelligent system capable of interpreting the same idea will`

`always reach the same conclusions about it (if they followed the same`

`steps), I'd call that an external truth, it's about as external as it`

`can get. If your consciousness or physics were a direct result of such`

`abstract relations, it would also be both an internal and external truth.`

What about arabic numerals? Seeing how popular their spread has been on Earth after humans, shouldn't we ask why those numerals, given an arithmetic universal primitive, are not present in nature independently of literate humans? If indeed all qualia, feeling, color, sounds, etc are a consequence of arithmetic, why not the numerals themselves? Why should they be limited to human minds and writings?

`I think you're confusing numerals with numbers. Numeral systems are just`

`an encoding we have for talking about numbers. Numeral encodings are a`

`matter of history, which is a matter of physics, and in case of COMP, is`

`a matter of arithmetic (or any other universal computational system -`

`they're all equivalent by the Church Turing Thesis). In that sense,`

`numeral systems(encodings) are a consequence of arithmetic.`

`The encoding itself is irrelevant, you could use tally notation (such as`

`||| + || = |||||) and it wouldn't matter. Nor is the choice of the`

`universal system - all that matters is the ability of following simple`

`finite rules and getting the same result each time you do.`

`Us finding about the CTT or any other mathematical truth is also such a`

`consequence of arithmetic. In a less serious way, you could say: "It's`

`turtles all the way down!". In a more serious way, you could think of`

`quines and Kleene's recursion theorems about fixed points.`

Craig

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