re: delayed reply

From: Gilles HENRI <>
Date: Fri, 12 Mar 1999 09:39:01 +0100

>Sure. The problem here consist in finding the relation between mathematical
>reality and physical reality. You can believe there is a physical universe,
>and that mathematics are *mental* tools build by high mammifers for strugling
>with the physical universe. This is a respectable position.
>What I say is that such a respectable position is incompatible with the
>hypothesis of computationalisme. I am *just* saying that IF we can survive
>with a digital brain, THEN physical reality is NECESSARILY part of
>arithmetical reality "viewed from inside". This gives us a new
>*space* (the space of computationnal histories) which gives clues on the
>logical origin of the (machine-belief in) physical laws.

I'm still not convinced with that. I'd want to precize the idea "we can
survive with a digital brain". In all your thought experiment you seem to
assume that it is possible to reproduce *exactly* the behaviour of a
physical system (the brain) with some detailed computation. I think it is
impossible : the physical reality is not computable exactly, at least in
our present knowledge. A very profound reason for that is that we do not
know how to describe it, independantly of the physical laws that govern it.
That's why you still have room to make any hypothesis on the nature of the
reality! But that forbids to consider systems strictly "equivalent" to
other ones. You can build machines that will "mimic" other machines up to
some level and during some time, but their fate will necessarily diverge at
some point. As I mentioned in another mail, the fact that we are aware of
our position in space and of our physical constitution makes impossible to
build a machine even "grossly" equivalent to ourselves. The idea, already
mentioned, to simulate also the environment is impracticable, because you
will face the problem of simulating the whole Universe with a machine
embedded in this very universe, which is logically impossible. Furthermore,
the chaotic nature of most physical systems would need an infinite
accuracy, which is also impossible to realize.

>>>Have you follow the PE-omega experience ?

I didn't find this precise term in your thesis, may be because it is an
English acronym for the experiment that you describe in French? I suppose
you are speaking of the replacement of a brain by a digital one, with a
possible infinite duplication of one person.

The problem that I see with this experiment is that it poses the problem of
the definition of identity, which is a sand-heap like problem. It is not a
*physical* problem but a *semantic* one. We, high mammifers that have had to
struggle with the physical universe, have developed the notion of identity
in a case where it was rather well defined, because there is no natural
mechanism that duplicates large organisms. (however such a mechanism does
exist for simple cells, as you remark yourselves at the beginning of your
thesis). However, this notion, like all human notions, could become
unappropriate in different conditions. If we were really able to
"duplicate" the brain (which has to be proven), we should more carefully
redefine this notion. We can argue that two realizations based on the same
initial brain should be consider as the same entity, or the contrary. But
again it is a semantic problem, and for me it cannot give you any clue on
the nature of the world (just like asking whether viruses are living
organisms or not doesn't help to know their replication mechanism). Indeed
in our real world, true twins are born from the same cell : in this case
they *are* actually considered as different persons.

So I think that in the case where duplication would be possible, we would
naturally modify our notion of identity. We may for example think us as an
"array" I[1], I[2]...instead of a single person. The I[i] would share the
same history at the beginning,,but differ after some time. All the
questions and paradoxes related to the question "who is "I"?" would
disappear simply because we would be led to adapt our notions to a new
reality, and this question would loose any sense, because "I" would have
lost its property of unicity. (A comparable evolution has already been made
in QM for example, where the question "where is the electron?" has lost its
sense). That's why I call that a "semantic" problem, and not a physical
one. After this mental revolution , we would face the same problem of
understanding the origin of thought!

>> ... Schmidhuber's programms, for example, could most
>>simply interpreted like the generation of classical worlds where "1" means
>>the presence of a classical particle and 0 an absence. There is nothing
>>wrong logically...just that you cannot make good physical laws with this
>I agree with Schmidhuber and James Higgo (and Wei Dai (?), ...)
>ONTOLOGICAL explanation: roughly speaking I agree that the "great
>programmer" is the simplest explanation for everything.

>What those people seem not to understand is the formidable EPISTEMOLOGICAL
>problems which arise with such an ontology. My UD-argument (or PE-omega
>experiment) is build to show the inevitability of these epistemological

I agree, but for this reason, and as a physicist, I wouldn't call it an
"explanation" at all...


Received on Fri Mar 12 1999 - 00:41:14 PST

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