On 11 Jul 2011, at 19:56, meekerdb wrote:

On 7/10/2011 8:16 AM, Bruno Marchal wrote:
You confuse perhaps with Schmidhuber's position, or some digital physicist (DP). But as I have explained many times here that this position does not work. Computationalism or digital mechanism (DM) is the idea that "I" am a machine, and by the first person indeterminacy, and the way the laws of physics have to emerge from computations, the physical universe (nor the fundamental reality) cannot be described entirely by a computation. On the contrary it is a sum on an infinity of computations.

If the universe is a computation, then "I" am computable, but then it cannot be a computation (by what I say above, it is not obvious). So with comp, or without comp, the physical universe is not a computation. With comp, the laws of nature are not computable, or have strong non computable components.

DM -> ~DP
DP -> DM,

So DP -> ~DP, so ~DP.



Bruno

This confuses me. When you say the universe is not computable, you mean it is not the process of computing a function. But you think it is generated by a UD. Right? In other words, you are saying what a UD does is *not* a computation.

I think you are forgetting to take into account the first person indeterminacy. Your probable next first person state in indeterminate, and the domain of indetermination is all the third person states equivalent (in the third person doctor sense) with the state of your current body (at the right level or below) generated infinitely often by the UD. The physical laws have to be retrieved from that indeterminacy on that domain, and there is no reason why your statistical experience or physical reality is computable. The UD does (an infinite) computation, but the universe results from an internal and relative statistics on all computations. It remains possible that somehow a computation wins the game, but if that is the case that has to be justify from the statistics on all the computation, and strictly speaking this is rather unplausible.

Instead of the UD, take the simpler case of the iterated WM self- duplication. Let us fix the iteration to 1000. In this case, you can see easily that what you can expect is not computable at all. All 2^1000 histories will be generated, and the computable are rare.

The UD makes dummy similar iteration with all states, so you can guess that physics arise from a subtle mixture of computability and randomness. I think that Bennett depth plays also a role, the self- referential constraints play a role. But it predicts that some randomness is at play in the stabilization/normalisation of the deep computational histories.

You don't need step 8 to understand this. Just imagine the "physical universe" big enough to run a UD. In one instant your futures is determined by an infinity of computations. This shows already that physicists use implicitly an induction principle, by assuming the inexistence of other instantiations of couple <you, the observed electron> other that the one under their consideration. But the UD guarantied (unlike Boltzmann brain) an infinity of them.

Bruno


http://iridia.ulb.ac.be/~marchal/



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