Bruno Marchal wrote:
> On 07 Nov 2008, at 20:10, Brent Meeker wrote:
>> It's easy enough to agree with "describes", but is describing something
>> the same as creating it?  
> Yes, for effective things like numbers and programs, (machines, or 
> finite pieces of computations).
>> How can we decide these entities (what makes
>> them entities?) are or are not conscious?
> We just cannot decide. 
>> I understand that up to the "map of our personal ignorance" = "physical
>> things"  How does our uncertainity as to which histories we are entail
>> phyisical things?
> Well, this is really the point of the whole reasoning. UDA(1...7) + UDA.8
> I think now that if you have grasped up to step 6. It is really step 7 
> which explain why the laws of physics have to emerge from computer 
> science or number theory. 
> Imagine that in our physical universe (assumed, if only to get the 
> contradiction) a real concrete UD is running. This makes intuitive 
> sense. I have implemented in 1991 a UD, and it has run for two weeks. 
> The UD has no inputs and no outputs. It just runs, and simulate all 
> possible programs on all possible inputs with all possible (piece of) 
> oracles. The existence of this UD is not something obvious, but it does 
> exist, and is even constructible, if we accept Church Thesis. With 
> Church thesis, even a DU written in FORTRAN, and dovetailing only on the 
> fortran programs will generates all the program in LISP, but also in all 
> not yet invented languages, and runs them. OK?
> I assume here also (in step 7) that our physical universe is robust 
> enough to let the UD run forever. If you grasp up to step 6, then you 
> should understand that if you decide here and now to do any "physical 
> experiment", like sending a photon on a mirror, or like observing an 
> apple in a tree", the only real and correct way to predict or evaluate 
> what will happen, is NO MORE to use the physical laws of your universe, 
> but to look at all the computational histories generated through by the 
> UD up to your actual state of mind (this exists because we assume comp). 
> And what will happen is what happen in most of those stories. OK?

No.  That seems to me to be assuming what you want to prove.  It's assuming 
computations instantiate universes and there is a probability measure 
proportional to their number in the UD.  I look at it the other way around. IF 
look at the computational histories generated by the UD and measure 
probabilities by their number and that accurately predicts what I observe - 
that will be evidence that computations instantiate this universe (and all 

> So, even, without the Movie Graph Argument, if such a concrete UD 
> exists, if no white rabbits appears and if the photon bounce, or the 
> apple falls on the ground, you can deduce that the "physical laws' 
> describe those more common histories.

Right - but that's three conditionals.

> At this point a mechanist who want to stay naturalist and keep "a 
> physical lawful universe" can decide that such a universe just cannot 
> run the UD, nor a too big portion of it. This would indeed evacuate the 
> comp white rabbits, and reinstate a sense to "physical law".
> But then MGA, UDA step 8, shows that such a move don't work.

Yes, I think I understand that part.


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