# Re: The Computing Spacetime

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On 20 Jan 2012, at 07:17, Joseph Knight wrote:```
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On Wed, Jan 18, 2012 at 1:33 PM, Bruno Marchal <marc...@ulb.ac.be> wrote:
```Stephen, Ronald,

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The paper is very interesting, on physics, but succumbs directly from the argument that any digital physics is bound to be unsuccessful on the mind-body problem by being still physicalist. The body problem is a problem of computer science, that is arithmetic, once we bet that observer are Turing emulable, as they should if the physics is digital.
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If the universe is a computation, then comp is true. But comp implies that the universe cannot be a computation (by UDA).
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Could you explain this a little bit? I didn't get that from my reading of the UDA
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I suppose you grasped well the sixth first steps.

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Consider yourself in front of a running UD, and the "protocol" is that it will never stop. Suppose you drop a pen. To predict what you will feel is determined by *all* computations in the UD's work going through your states. So to predict exactly what you will feel, you cannot use one computation, but an infinity of them. This is a priori non computable. Even if it is computable (like if ONE computation multiplies so much that it get a measure near one), we know that there are other computations, so, this can only be 1 - epsilon, and the exact decimal will still need an infinite computation, even if much shorter computation provides excellent approximations. But in principle, your exact future, even the "physical" first person sharable, is not given by one computation, but, below your substitution level, all of them. You can't compute that. And he phyical laws are just describing your normal histories, and the nomality can only come on the "winning computations" in the limit. Phycics might remain arithmetical, but certainly well above Sigma_1 (the computable).
```Tell me if this helps.

Bruno

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So the universe is a computation implies that the universe is not a computation. So the universe is not a computation, whatever it can be. This defeat Finkelstein, Schmidhuber, Fredkin, and all attempts to conceive the physical universe as a computation, or output of a computation.
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This does not mean that the paper does not have interesting ideas on the unification of known forces in physics, and that "quantum graphity" might be a good idea, but if correct, such idea have to be recovered from the (more ambitious) attempt to get a unification of both qualia and quanta (consciousness and matter). The authors have still not integrate the mind-body problem. We are still much in advance on this list :)
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Bruno

On 18 Jan 2012, at 14:53, ronaldheld wrote:

I found this at arXiv:1201.3398v1 [gr-qc] 17 Jan 2012. Any comments?
I have just started to read it.,
Ronald

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

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