Dear Hal

At 1/18/02, you wrote:


>I'm not convinced about the models of computation involving GTMs and
>such in Juergen Schmidhuber's paper.  Basically these kinds of TMs can
>change their mind about the output, and the machine doesn't know when
>it is through changing its mind.  So there is never any time you can
>point to the output or even a prefix and say that part is done.  It is
>questionable to me whether this ought to count as computation.


I am currently somewhat in accord with this view.  My model of the ensemble 
of universes which is just approaching a "finished" condition is not a 
computational one.  However, without regard to the application of 
"computation" to the comprehension of this ensemble I do not see an 
external difference between any of Juergen's machines and the usual 
UTM.  Whenever a prefix is indeed done that is just the same as any 
external output of a UTM with the computation activity spread over a long 
section of tape internally IMO.


As to the discussions of measure and probability re the likelihood of a 
particular sort of universe I do not see the point.  The core idea for a 
founding postulate that seems most appealing is that no information 
exists.  So the entire discussion re measure IMO is just an effort to 
extract a factual(s) from an ensemble of counterfactuals.


Hal Ruhl 

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