Re: Tegmark is too "physics-centric"

From: Russell Standish <>
Date: Tue, 9 Mar 2004 11:50:54 +1100

On Fri, Mar 05, 2004 at 02:20:54PM +0100, Bruno Marchal wrote:
> >How does COMP entail that I am a machine? I don't follow that step at all.
> But comp *is* the assumption that I am a machine, even a digital machine.
> My last formulation of it, easy to remember is that comp = YD + CT + RA
> YD = Yes doctor, it means you accept a artificial digital brain.
> (and CT is Church thesis, and RA is some amount of arithmetical realism).
> In "conscience et mecanisme" comp is called MEC-DIG-IND, DIG is for
> digital, and IND is for indexical. It really is the doctrine that I am a
> digital
> machine, or that I can be emulated by a digital machine.

Yes, in your thesis you often talk about survival under replacement of
a digital brain (cerveau digital). Digital simply means "operates with
1s and 0s". Since any analogue value can be represented arbitrarily
accurately by a digital signal, this doesn't seem much of a stretch.

In your chapter 1, you refer to a "machine universelle digitale, c'est
a dire un ordinateur". The English word computer, which is the literal
translation of ordinateur, can refer to an analogue computer, which is
merely a device for performing computations - it needn't even be
Turing complete. The fact that you used the word "universelle"
previous does imply Turing completeness, but not that it is equivalent
to a Turing machine. After all, I might be concerned if there was some
noncomputable part of the brain that was not captured by a Turing
machine, but could be built into a digital machine of some kind (eg by
accurate copying of the physical layout of the brain).

Now I noticed you used the word "indexical". What does this mean? (I
tend to skip over terms I don't understand, in the hope that I
understand the gist of the argument).

Anyway, the upshot of this was that I assumed that COMP was in fact
more general that computationalism. In fact I believe the first half
of your thesis (chapters 1-4) indeed still hold for this more general
interpretation of COMP (namely the necessity for subjective
indeterminism etc). True computationalism is perhaps only required for
the later sections where you invoke Thaetus's (is that the correct
translation of Theetete?) theories of knowledge (connaissance). For
here, you need Goedel's theorem, which is applicable in the case of
Turing machines.

> >> Computationnalism is really the "modern" digital version of "Mechanism"
> >> a philosophy guessed by early Hindouist, Plato, ... accepted for animals
> >by
> >> Descartes, for humans by La Mettrie, Hobbes, etc. With Church
> >> thesis mechanism can leads to pretty mind/matter theories.
> >>
> >
> >If one accepts mechanisms that go beyond the Turing machine, then
> >computationalism is a stricter assumption than mere mechanism (which I
> >basically interpret as "anti-vitalism").
> >
> >I would counter that a Geiger counter hooked up to a radioactive
> >source is a "mechanism", yet the output cannot be computed by a Turing
> >machine. (Of course some people, such as Schmidhuber would disagree
> >with that too, but that's another story).
> But no mechanism can compute the output of any self-duplication.
> With Everett formulation of QM, a Geiger counter is emulable by a turing
> machine, and the QM indeterminacy is just a first person comp indeterminacy.
> You cannot emulate with a turing machine the *first person* knowledge
> he/she gets from looking at the Geiger counts, but no machine can
> predict the first person knowledge of a Washington/Moscow self-duplication
> either.
> Bruno

I agree one can simulate the Schroedinger equation of QM (albeit with
irrelevant exponential slowdown). However, mapping this back to your
"YD" postulate, this involves the doctor swapping the entire universe,
not just your brain. Perhaps you mean that one of the options the
doctor has is to upload you into a well crafted digital simulation (by
a Turing machine even) of you and your complete environment (a la

Reminds me of the option Arthur Dent was presented with by the
pandimensional beings (aka mice) when they wanted to mince his brain
to extract the question for which the answer was '42'.


A/Prof Russell Standish Director
High Performance Computing Support Unit, Phone 9385 6967, 8308 3119 (mobile)
UNSW SYDNEY 2052 Fax 9385 6965, 0425 253119 (")
Room 2075, Red Centre
            International prefix +612, Interstate prefix 02

Received on Mon Mar 08 2004 - 19:59:19 PST

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