Le 26-avr.-07, à 16:31, Juergen Schmidhuber a écrit :

> Hi Max,
> in this particular universe it's going well, thank you!
> As promised, I had a look at your paper. I think
> it is well written and fun to read. I've got a few comments
> though, mostly on the nature of math vs computation,
> and why Goedel is sexy but not an issue
> when it comes to identifying possible mathematical
> structures / universes / formally describable things.
> I think some of the comments are serious enough to affect
> the conclusions. Some come with quotes from papers in
> http://www.idsia.ch/~juergen/computeruniverse.html
> where several of your main issues are addressed.
> Some are marked by "Serious".
> I am making a cc to the everythingers, although it seems
> they are mostly interested in other things now - probably
> nobody is really going to read this tedious response which
> became much longer than I anticipated.

Don't worry, we are used to some long posts in this list. I am not sure 
you follow the list because the "other things" you are mentioning are 
just the follow up of the search of the theory of everything, except 
that since you leave the list, denying the 1-3 distinction, some years 
ago, most people who continue the discussion now are aware of the 
necessity to take into account that distinction between first and third 
person points of view, and more generally they are aware of the mind 
body problem (or of the 1-person/3-person pov relations). I think most 
of them, except new beginners, have no more any trouble with the first 
person indeterminacy in self-duplication experiments, etc.

I have already made this clear: the hypothesis that there is a physical 
computable universe (physicalist-comp) is just untenable.
Let me recall you the reason: obviously physicalist-comp entails what 
we are calling comp in this list, that is, the hypothesis that "we" are 
locally emulable by a digital universal machine. I will call it 
"indexical comp" to insist on the difference. So:


  Then the Universal Dovetailer Argument shows that comp entails that 
the physical appearances have to be justified *exclusively* by a 
self-duplication like first person (plural) indeterminacy: see the pdf:

The main idea is that INDEXICAL-COMP entails that we don't know which 
computations support our local states, and that they are a continuum of 
computational histories (computations + possible "real" oracles) going 
through those states. It can be argued that the first person "physical" 
appearances does emerge from a "sum" on all those computational 
histories, but only *as seen from those 1-person views*. But this 
entails that "apparent physical universe" are not necessarily 
computable objects. Actually, indexical comp entails it exists 
"exploitable" internal indeterminacies. A priori:


It gives to physics a more key role than in Tegmark's idea that the 
physical universe is a mathematical structure of a certain type. Comp 
(indexical comp) relate somehow physics to almost all mathematical 
structures (in a certain sense).

This constitutes the main critic of both your approach and Tegmark's 
one in the search of a TOE.  You still talk like if the mind body 
relation was a one-one relation, when the mind can only be associated 
to infinities of states/worlds. With indexical-comp there is no obvious 
notion of "belonging to an universe". This has been discussed many 
times on the list with different people.

And then, once you realize the fundamental importance, assuming comp, 
of keeping distinct the possible views that a machine has to have about 
arithmetical or mathematical reality, and that physics emerges from one 
such points of view, then it is hard not to take into account the fact 
that any universal machine looking inward cannot not discover those 
points of view; indeed  they appear as inevitable modal or intensional 
variant of the godelian provability predicate. This makes Godel's 
theorems (and Lob's generalization, and then Solovay's one) key tools 
for extracting physicalness from number's extensions and their (lobian) 
intensions. And, and this is a major technical point, it makes this 
form of comp testable, by comparing the comp-physics with the empirical 

Now I have discovered that those modal variant offer a transparent 
arithmetical interpretation of Plotinus hypostases. You are welcome in 
Siena in June where I will present my paper "A purely Arithmetical, yet 
empirically falsifiable, Interpretation of Plotinus' Theory of Matter":


I can send you a copy of the paper later for copyright reason. You can 
also consult my preceding paper:
Marchal, B., Theoretical Computer Science & the Natural Sciences, 
Physics of Life Reviews, Elsevier, Vol 2/4 pp 251-289, 2005. Available 

Max, Juergen, you are still under the Aristotelian physicalist spell, 
and you are still putting the "mind-body" problem under the rug, I'm 
afraid. But I am aware it is a tradition since about 1500 years, when 
scientists, without much choice alas, did abandon theology to 
"politicians" ...
(scientific theology = theology done with the usual doubting procedure 
of the modest interrogating scientist).

Juergen, are you still denying the 1-3 distinction (like in our old 
conversations)?  Are you still thinking  that there is no 1-first 
person indeterminacy, or that such an indeterminacy has no role in the 
emergence of the physical laws?  Could you tell me at which step of the 
UDA you are stuck? (cf the UDA version of the SANE paper, ref above).

I will asap try to explain the arithmetical version of the UDA, the one 
based on Godel and which can be seen as an arithmetical interpretation 
of Plotinus' main "hypostasis" (in case you prefer to read Plotinus 
instead of doing the duplication thought experiment, UDA, ...).
Some people asks me to do this without too much technics and I have to 
think about how to do that. I recall the UDA is already the "non 
technical" (yet rigorous) argument. The interview of the machine is of 
course formal and technical, and its only need (beside illustrating the 
UDA) comes from the desire to *explicitly*extracts the physical from 


PS This list, wisely unmoderated by Wei Dai, welcomes, for obvious 
reason giving the hardness and originality of the subject,  both 
professional and non professional. By professional I just mean people 
submitting theses, papers or books from time to time, even rarely. So, 
don't hesitate to send us "call of paper" related with comp and or 
everything-like or Everett-like TOEs. Thanks. And don't hesitate to 
participate, 'course!


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