# Re: The Computing Spacetime

`On Fri, Jan 20, 2012 at 2:49 PM, Bruno Marchal <marc...@ulb.ac.be> wrote:`
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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:
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>> Stephen, Ronald,
>>
>> 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.
>>
>> If the universe is a computation, then comp is true. But comp implies
>> that the universe cannot be a computation (by UDA).
>
>
> Could you explain this a little bit? I didn't get that from my reading of
> the UDA
>
>
> I suppose you grasped well the sixth first steps.
>
> 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.
>

Yes - thanks!

>
> 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.
>
>
>> 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 :)
>>
>> 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/ <http://iridia.ulb.ac.be/~marchal/>
>>
>>
>>
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> Joseph Knight
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