Re: Tegmark is too "physics-centric"

From: Stephen Paul King <>
Date: Mon, 8 Mar 2004 22:25:49 -0500

Dear Russell and Bruno,


----- Original Message -----
From: "Russell Standish" <>
To: "Bruno Marchal" <>
Cc: <>
Sent: Monday, March 08, 2004 7:50 PM
Subject: Re: Tegmark is too "physics-centric"

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
> 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).


    I think that the key here is something like a 1st person version of a
Turing Test: If you can not tell a difference between one's world of
experience while in a "meat machine" - brain - and a digital machine then it
is not a difference. Substantivalists will try to dispute this but that is a
debate for another day.
    This would seem to require only that there sufficient expressiveness
within the digital machine's n-ary representation to encode all of the
fullness of all 1st person experiences that whatever kind of "machine" -
meat or silicon or whatever - could have.

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.


    It seems to me that COMP is more general that computationalism since it
seems to include certain unfalsifiable postulations that are independent of
computationalism per say, AR, to be specific. My own difficulties with
Bruno's thesis hinges on this postulation. I see it as an avoidance of a
fundamental difficulty in Foundation research, how to account for the 1st
person experience of time if one assumes that Existence in itself is

> >> Computationnalism is really the "modern" digital version of "Mechanism"
> >> a philosophy guessed by early Hindouist, Plato, ... accepted for
> >> by
> >> Descartes, for humans by La Mettrie, Hobbes, etc. With Church
> >> thesis mechanism can leads to pretty mind/matter theories.
> >>
> >[RS]
> >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).
> [BM]
> 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
> 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.


    This is somewhere else that I trip over and fall in my thinking of your
work, Bruno. Is this "mechanism can compute the output of any
self-duplication" a classical version of the "no-cloning" theorem?

> 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


    Does my comment above about how to bridge this gap of emulating a brain
and emulating the entire universe? If it does it would seem to dramatically
increase the computational power requirements of the emulating computation
on top of the exponential slowdown.
    One technical question I have about this is: if we assume that the
emulated universe is finite, what would be the equation showing the required
computational power of the emulator given an estimate of the total
algorithmic and/or information content of the universe?
    Additionally, what are we to make of results such as the Kochen-Specker
theorem that show that given any quantum mechanical system that has more
than two independent degrees of freedom can not be completely represented in
terms of Boolean algebra?

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'.


    Questions like "What is we are "really" pandimensional beings that are
only consciously aware of what they are like as "humans?" suddenly have more
than a literary meaning. ;-P

Kindest regards,

Received on Mon Mar 08 2004 - 22:43:18 PST

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