Hi Brent,

On 09 Nov 2008, at 20:29, Brent Meeker wrote:

> Bruno Marchal wrote:

>> You don't get the point. Mechanism is incompatible with naturalism.  
>> To
>> solve the mind body problem, keeping mechanism, the laws of physicist
>> have to be explained from computer science, even from the gap between
>> computer science and computer's computer science ...
>> Physics is the fixed point of universal machine self observation.
> That would be a very impressive result if you could prove it - and  
> you could
> prove that there is no other empirically equivalent model.

I will try to explain, as simply as possible, that this has been  
proved. Indeed by UDA[1...8].

>  I've long been of
> the opinion that space and time are constructs.  I also think the  
> integers and
> arithmetic are constructs.  But so far I understand your thesis to  
> be that
> physics consists of certain relations among experiences regarded as  
> mental
> events.

You can say so, although this is already a simplification. Useful to  
give an idea to the layman, but also capable of making rise to non  
genuine objection for the expert. I will not try to un-simplify your  
point, if I can say, and I will interpret it favorably.

>  This solves the mind-body problem by making the body a construct of  
> the
> mind.  So far, so good.

OK. OK. (well, to be sure, consciousness remains to be explained, but  
consciousness will be explained by the gap between G and G*, but this  
is locally out of the current topic).

> Further, you hold that these relations are Turing
> computable and so exist in Platonia as a subset of all arithmetic.

If by "these relations" you mean those related to my mind, then I am OK.

>  I like this
> better than Tegmark's idea of our physics as a subset of all  
> mathematics because
> your idea is more specific and leads to questions that may be  
> answerable.

I don't think it is a question of "liking", but ... I share your liking.

Remember that I pretend that all what I say is a direct consequence of  
the (digital) mechanist assumption. And then it is Church thesis which  
makes such an approach so robust.

Nobody can know my opinion on the matter. (Except that once I said "I  
don't know").

> But I
> still see some problems:
> First, it doesn't eliminate the possibility that some other subset  
> of Platonia,
> e.g. geometry or topology, might also provide a representation of  
> our physics.
> In fact, given that our knowledge of physics is imprecise, it seems  
> likely that
> there are infinitely many subsets of Platonia that are models of our  
> physics.

No. To predict first person experiences, we have to integrate (sum on,  
taking into account of) ALL the representations occurring in the  
universal deployment.
Ontologically, we have all computations. The UD generates, by  
dovetailing all those computations. Your next state is determined by a  
measure of uncertainty bearing on all computations going through your  
present state.
What is obvious for the naturalist, i.e. the fact that your next state  
is determined by your present state by a simple computational equation  
(like SWE), is NOT obvious for the digital mechanist. There is already  
a continuum of (infinite) computations---involving white rabbits,  
white noise, and all computational and non computational beings--- 
going through your current state. If a physics emerges from that, it  
is just an open problem if that physics is computational or not,  
actually we just don't know yet if that physics even exists or not  
(with comp). What we know, is that IF a physics emerges THEN it takes  
into account, and sum up, infinities of computations.
This follows by taking steps 5, 6 and 7, and 8 (when not executing the  

>  Of course you can argue that even a non-computable model of physics  
> may be
> approximated by a computable model to an adequate degree.  But this  
> just pushes
> the question off to what is "adequate" and it does not warrant  
> rejecting
> materialism as explicated by Peter.

The "rejection of materialism" is really step 8 (the movie graph). It  
explains why we don't have to run the UD, and why we can rely on the  
"natural" UD determined by all true (and provable, here) sentence of  
even just Robinson Arithmetic.

Your current state of mind, and indeed the state of mind of all  
possible Loebian machines (far richer than Robinson Arithmetic) occurs  
in all finite or enumerable approximations of any possible "model" of  
physics rich enough to generate your states. But, mainly because you  
cannot be aware of the delay done by the UD, you, from your first  
person point of view, are living in the infinite union of all those  
finite approximations. Again: there is no reason a priori why they  
have to be computable (and giving the subdovetailing on the reals,  
they have to posses uncomputable aspects when we look at ourself below  
our level of substitution.

> Second, is the problem of finding the fixed point, or distinguishing  
> the measure
> on all the Turing computations that picks out our physics.  I  
> understand you
> have some results, such as "no computation can know which  
> computation it is",
> which are interesting, but do not pick out any particular physics.

All right. But I don't derive physics there. Physics is just shown to  
be given by the science which pick your more probable "next first  
person state" or OM, which exists in aleph_0 exemplars in the  
Universal Deployment, and belongs to 2^aleph_0 histories. This is the  
conclusion of UDA. We see here that comp predicts already something  
"physical": the many worlds", or the many consistent histories.
Then to extract physics more precisely is very difficult, but that  
should have been expected, giving the non constructive top-down  
approach. We are just pushing the comp hyp to its ultimate consequences.
But then I recover a part of physics: the logic of the observable  
propositions with probability/credibility one. For technical reason  
they are modelized by the provability-and-consistency(-and-truth) of  
the sigma_1 propositions. (four and fifth hypostases). And this gives  
a quantum logic, and the shadow of measure on the computations as seen  
by a universal machine embedded in the universal deployment. But this  
is already AUDA. (arithmetical UDA).

> There's a
> general problem here in that the current best theories of physics  
> are based on
> continuous variables.

This should be expected when we assume mechanism. Keep in mind the  
step 7, physics should predict your next state of mind, and it depends  
on 2^aleph_0 histories. If you look at yourself or at your  
neighborhood close enough (below your substitution level) you can  
expect to "see" the white rabbits somehow, you have to expect a  
blurring of an infinity of computations, a bit like a cloud of  
histories. The border of that cloud could be called the white rabbit  
cloud: it is the extremely rare histories, like the border of an  
electronic orbital describes very rare events (an electron far away  
from the nucleus for example.

> Many physicists think that an ultimate theory would be
> discrete,

This is highly implausible, assuming comp. I know that if we want  
quantize gravitation, then space and time should be quantized, but  
then I hope other things will remain continuous, like the statistics  
(hoping it is enough).
But for the reason above, the first persons cannot escape the  
"feeling" or the "appearances" of continua (assuming mech.).

You really have to process carefully the step seven, and remember that  
your first person point of view are determined by all the third person  
describable computations going through your actual comp state (the  
comp supervenience).

> but nobody knows how to make a discrete theory from which our
> continuous theories would emerge.

The comp hypothesis provides such a theory. Physics being a first  
person (plural) construct, it has to rely on the infinite union of all  
the finite piece of all computations accessing your state.

>> Let me know at which step (1?, ... 8?) you have a problem? The only
>> one not discussed thoroughly is the 8th one.
>> To be sure, do you understand the nuance between the following  
>> theses:
>> WEAK AI: some machines can behave as if their were conscious (but
>> could as well be zombies)
>> STRONG AI: some machines can be conscious
>> COMP: I am a machine
>> We have
>> WEAK does not imply STRONG AI which does not imply COMP. (it is not
>> because machine can be conscious that we are necessarily machine
>> ourself, of course with occam razor, STRONG AI go in the direction of
>> COMP).
>> Does those nuances make sense? If not (1...8) does not, indeed, make
>> sense. You just don't believe in consciousness and/or person like in
>> the eliminative materialism of neuro-philosophers ( the Churchland,
>> amost Dennett in "consciousness explained").
> As my lawyer friend says, "I'm not in the belief business."

Scientists have beliefs.
Mystics have knowledge.
Beliefs are refutable and revisable. Science evolves and grow.
Knowledge is not refutable and not revisable, and, in its pure  
platonic form, is invariant.

>> Or you make us very special infinite analogical machines, but then  
>> you
>> drop the digital mechanist thesis (even the naturalist one, which has
>> been shown inconsistent by 1...8.)
> I think it might be that the universe is not computable.

But, after step 1...8, what do you mean by universe?
If I am a (correct) machine, whatever supports me cannot be a machine.

Unless, to be complete, I am the entire universe. I say "yes" to the  
doctor if the artificial brain simulates the entire cosmos and the  
entire cosmological history. In that case there is only one universe,  
only one "bruno marchal", and it can be a computational object  
because, although the UD generates it an infinity of time, there are  
no variations among the genuine computations. No white rabbits here.  
But a big "others mind problem". I think I have to explain this to  
Jason, so I will not insist here. I could also suggest to really  
revised the seven and height steps, keeping cautiously in mind the  
first and third person distinction.

> But I think it is very
> likely that one's consciousness is computable, at least for a finite  
> time period.

That's the comp hyp. It entails my consciousness is "processed" in a  
denumerable but infinite part of the deployment, and the measure is  
determined by the continuum of computations which exists as domain of  
comp indeterminacy. By step 5 (and 8) we are always under the fate of  
that indeterminacy.
A set of computable things is not necessarily computable, and the comp  
hyp makes the computability of the universe, or any big whole, very  

The mind body problem is that tricky!
If mind is computable, then the body is not.
If the body is computable, then the mind is not.

And if the body is computable, and if we still assume comp, then the  
mind is computable (by comp) and the body is not, so we get that the  
body is computable and the body is not computable. Contradiction.  
Meaning, if comp is true, the body, or the universe is NOT computable.  
The UD never generate a physical universe, it always generate set of  
histories from inside which observers categorize into a universe, from  
their points of view. The brain or more generally the lobian machine,  
act as a filter or a selector of a reality from an uncomputable set of  
computable histories.

I would be pleased if you could be kind enough to tell me  if I have  
been able to justify why the first person universe (be it physical or  
mathematical, or whatever) cannot be computable.

Bruno Marchal


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