Re: Interested in thoughts on this excerpt from Martin Rees

From: Bruno Marchal <>
Date: Fri, 4 Aug 2006 11:24:40 +0200

Le 04-août-06, à 08:03, W. C. a écrit :

>> From: Bruno Marchal
>> All we need to *reason* for getting consequence of comp is that such
>> substitution is *in principle* possible. Theoreticians does that, in
>> many >
>> fields. I insist that the UDA (Universal Dovetailer Argument) is
>> based on
>> the notion of generalized brain: you could say that your brain in the
>> entire galaxy. By comp this entails the entire galaxy is turing
>> emulable,
>> then, this is enough to say the platonic UD will go through your
>> "generalized" brain soon or later (in term of number of steps), and
>> that is
>> enough to understand that comp makes obligatory that the laws of
>> physics
>> emerge from the relation existing among numbers (that + other steps
>> of the
>> reasoning of course). The impracticality of substitution is just not
>> relevant to throw out the theoretical consequences. Then comp can be
>> tested
>> experimentally due to others consequences (like the observable
>> interference
>> among many computations, etc.). OK?
> I have an idea (or dream) for some time. Let's call it the "perfect
> universe
> argument" (PUA).
> The purpose of PUA is to produce a perfect universe (a perfect world
> without
> any crimes, any bad things, any natural disasters ... etc.).
> It's as follows:
> (1) I teleport myself to the origin of the universe.

Are you sure that this is possible, even just in principle? Actually,
just to show me that it could be possible in principle you have to give
me your fundamental assumptions. Actually it looks like you are
assuming the following:
a) there is a physical universe (well, with comp this is already
b) accepting "a)" you assume that that universe has an origin (this
would be impossible even in principle in case there is no origin)
c) Accepting "a)" and "b)" you assume "physical laws" making time
travel possible (which is of course controversial; this could be in
principle possible with very special assumption, which could also be
false in principle with other assumption).
If you do theoretical reasonings you have to make clear the assumptions
which are making things "possible in principle". Up to here, I can
follow you (I can imagine such fundamental assumptions).

> (2) I adjust some parameters of the universe. (This is like adjusting
> some
> parameters in a modern PC program
> so that you can get the perfect result when running the program.)
> (3) The adjustment changes the whole universe immediately and the
> universe
> becomes perfect.

Your "2" and "3" are unfortunately definitely impossible with comp
without deciding your PU (your Perfect Universe) being trivial. This is
not obvious (but follows from diagonalization similar to those I have
already illustrated). Let me just say that it can be shown that if you
want your PU enough rich for Universal machine to appear, then you
cannot, even in principle, filter those "bad" machines will easily
makes your PU unperfect.

> PUA is possible in principle, right? Does it agree to Comp. and UDA?

So the PUA *is* incompatible with comp. The most basic contradiction is
given by the consequence of the UDA: there is no physical universe:
only computations/dreams some of which "coheres" so as to provides
local first person plural notion supervening on them. But even in the
case those coherence would define "for all practical purposes" a
"physical universe", and even if it has some sort of physical origin
and you can teleport yourself to its origin, the laws of computer
science will eventually prevent you of reprogramming "the universe" to
satisfy your goal of making it perfect.

Now, honestly this is a good news. "Perfection" is a virtue, and comp
makes it impossible to define any virtue from inside the "universe",
and this saves our freeness, and explains why even Gods cannot conceive
"sufficiently rich" universe with build-in perfection.

>> From: Stathis Papaioannou
>> Do you believe that IF you vanished at point A and a copy of you
>> created at
>> point B who was physically and mentally similar to the original to
>> the same
>> extent as if you had walked from A to B you would have survived? If
>> you
>> answer "no" then you are opening yourself up to the possibility that
>> would
>> not survive the walk either. If you argue that the copy might be
>> physiacally the same but mentally different then you are saying there
>> is
>> some non-physical basis to identity which survives walking but not
>> teleportation, which I suppose is possible, but there is no reason to
>> believe that such a strange thing would or could have evolved.
> I can't compare teleportation of human beings with walking since
> teleportation is still a fiction now.

But classical teleportation is possible in principle once we assume
comp. Now I don't want to argue for comp, but there is no contradiction
between comp and any known facts. To be sure I did believe in non-comp
at the time I thought that classical mechanics was valid, but the
quantum kills all the non-comp aspect of physics, until now.

> It's also unknown if there is something non-physical in human (or
> living)

We don't know, it is a theory. And then it is possible to prove in that
theory that IF comp is true then we will never known it "in any third
person communicable ways". Comp is a theological (in the sense of the
greeks, not in the christian sense) belief which forces rationalists to
accept that non-comp could be true. A doctor would be criminal to give
to his/her (non dying) patient an artificial brain without his/her
patient's consent. No computationalist (unless mad or ignorant) would
ever force any-soul to believe in comp. Comp is a provably *personal*


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Received on Fri Aug 04 2006 - 05:26:54 PDT

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