Re: Is the universe computable?

From: Jesse Mazer <>
Date: Thu, 08 Jan 2004 01:17:42 -0500

Stephen Paul King wrote:
>Dear Jesse,
> Would it be sufficient to have some kind of "finite" or "approximate"
>measure even if it can not be taken to infinite limits (is degenerative?)
>order to disallow for "white rabbits"? A very simple and very weak version
>of the anthropic principle works for me: Any observation by an observer
>not contradict the existence of that observer.

But there are plenty of observations that would not result in my
destruction, like seeing a talking white rabbit run by me, anxiously
checking its pocket watch. To pick a less fantastical example, it would also
not be incompatible with my existence to observe a completely wrong
distribution of photons hitting the screen in the double-slit experiment.
Why, out of all possible experiences compatible with my existence, do I only
observe the ones that don't violate the assumption that the laws of physics
work the same way in all places and at all times?

> I disagree with David's claim that "The universe doesn't depend on the
>rock for its existence..." since the notion of quantum entanglement, even
>when considering decoherence, implies that the mere presense of a rock has
>contrapositive effects on the whole of the "universe". The various
>discussions of "null measurements" by Penrose and others given a good
>elaboration on this.

I think you're talking about a different issue than David was. You're
talking about a rock that's a component of our physical universe, while I
think David was responding to Chalmers' question about whether random
thermal vibrations in a rock instantiate all possible computer simulations,
including a complete simulation of the entire universe (complete with all
the rocks inside it).

> To me the computational question boils down to the question of how
>Nature solve NP-Hard (or even NP-Complete) problems, such as those involved
>with "protein folding", in *what appears to be* polynomial time.

What do you mean by "the" computational question? Are you addressing the
same question I was, namely how to decide whether some computer simulation
is instantiating a copy of some other program? If we imagine something like
a detailed physical simulation of some computer circuits running program X,
it seems intuitive that this simulation instantiates a copy of program X,
but Chalmers' paper suggests we don't have a general rule for deciding
whether one program is instantiating any other given program. And as I said,
this is relevant to the question of measure, and a measure on
observer-moments is probably key to solving the white rabbit problem.


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Received on Thu Jan 08 2004 - 01:19:20 PST

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