RE: Interested in thoughts on this excerpt from Martin Rees

From: Stathis Papaioannou <>
Date: Sun, 13 Aug 2006 20:57:28 +1000

Bruno Marchal writes:

> >> I know it looks counterintuitive, but an AI can know which computer is
> >> running and how many they are. It is a consequence of comp, and the
> >> UDA
> >> shows why. The answer is:
> >> the computer which is running are the relative universal number which
> >> exist in arithmetical platonia (arithmetical truth is already a
> >> universal video game, if you want, and it is the simplest). How many
> >> are they? 2^aleph_zero.
> >> I have already explain it here:
> >>
> >>
> >> It is a key point and we can come back on it if you have some
> >> difficulties.
> >
> > Well now I'm confused! I thought the whole point of the earlier part
> > of the UDA
> > as discussed in the cited post (and many others of yours) is that you
> > *can't*
> > know the details of your implementation, such as what type of computer
> > you are
> > being run on, how fast it is running, if there are arbitrary delays in
> > the program,
> > and so on. Are you now saying that if I am being run on the 3rd of 100
> > PC's in
> > the basement of the local university computer science department, but
> > everyone
> > is keeping this a secret from me, there is a way I can figure out
> > what's going on
> > all by myself?!
> Did you read my old post to Brett Hall:
> >
> Perhaps you could comment it and tell me what does not convince you. It
> is indeed correct that the earlier parts of the UD Argument show that a
> machine cannot know about comp-delays, or about the real/virtual nature
> of a computer which would support the machine's computation until ...
> you realize that for exactly those reasons the machine first person
> expectations can only be computed (exactly and in principle) through a
> measure on all possible computations (reducing physics to searching
> such a measure). But then the first person can no more be associated
> with *any* particular computations. Read the Brett Hall post where I
> explain more, again in a "steppy" fashion (but the point is different
> from the UDA).
> To sum up that point:
> 1) comp shows we cannot know which computations supported us.
> 2) digging deeper in comp, this means eventually we are supported by
> *all* (relative) computations (relative to some actual state; the
> "actuality" itself is handled in the traditional indexical way, and
> eventually "indexicality" is treated through the logic of
> self-reference (G and G*).
I did read the cited post. I can see that given step 7 - from the inside, we
cannot tell if we are in a physical world emulation or a Platonia emulation -
we could say that we are emulated by all appropriate computations. [I think
it is still logically possible that we are emulated at any instant by one
computation in the ensemble, and that there might still be a separate
physical world, at this point at least.] I can see that step 8 is right:
if we are simulated in a massive real world computer, to make a prediction
about the future we must take into account all the computations passing
through our present state and define a measure on them. I will accept step
9 on your authority, although this seems amazing: we can derive the laws of
physics from a measure on first person computational histories. Now, step 10
is my problem: if the laws of physics as per step 9 turn out to match our
experimentally verifiable reality, then we are no more simulated by the physical
computer than by any of the non-physical ones in Platonia.

Why does it mean that we are no more simulated by the physical computer
than one of the non-physical ones if the laws of physics match the prediction
from the assumption that we are being simulated? Surely all that it suggests is
that we are indeed being simulated - somewhere.

You also state in step 10 that " say we belong to the massive computer has
no real meaning: if it stops, nothing can happen to "us" for example...". That is
true, but it does not mean that we are not actually being simulated in a
particular computer, just that we cannot *know* which computer it is unless
we have external knowledge. But in any case, this is just what I was saying
before: you can't know which computer you are being simulated on. Are you
disagreeing with this statement because you believe you *can* narrow it down
to knowing that you are not being simulated on a physical computer?

Stathis Papaioannou
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Received on Sun Aug 13 2006 - 06:59:29 PDT

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