Stathis Papaioannou writes:
> 1. Every possible world can be simulated by a computer program.

I'm not sure that this is the best definition of a "possible" world.
I'm concerned that we are hiding a lot of assumptions in this word.
It relates to my earlier comment about ambiguity in which constitutes
the multiverse.

> 4. A computer need not be a box that runs Windows or Linux. Conceivably, a 
> computer could consist of the idle passage of time, or the set of natural 
> numbers, operated on by some hugely complex look-up table. In Greg Egan's 
> 1994 novel "Permutation City", it is pointed out that a simulated being's 
> experiences are the same if the computation is run backwards, forwards, 
> chopped up into individual pieces and randomly dispersed throughout the 
> world-wide network; the computation somehow assembles itself out of "dust" - 
> out of omnipresent, apparently randomly distributed ones and zeroes.

I had a problem with the demonstration in Permutation City.  They claimed
to chop up a simulated consciousness timewise, and then to run the pieces
backwards: first the 10th second, then the 9th second, then the 8th,
and so on.  And of course the consciousness being simulated was not
aware of the chopping.

The problem is that you can't calculate the 10th second without
calculating the 9th second first.  That's a fundamental property of our
laws of physics and I suspect of consciousness as we know it.  This means
that what they actually did was to initially calculate seconds 1, 2,
3... in order, then to re-run them in the order 10, 9, 8....  And of
course the consciousness wasn't aware of the re-runs.  But it's not clear
that from this you can draw Egan's strong conclusions about "dust".
It's possible that the initial, sequential run was necessary for the
consciousness to exist.

> As for the "failure of induction" if all possible worlds exist, I prefer to 
> simply bypass the problem. I predict that in the next few moments the world 
> will most likely continue to behave as it always has in the past... Here I 
> am a few moments later, and I am completely, horribly wrong. A zillion 
> versions of me in other worlds are dying or losing consciousness as they 
> watch fire-breathing dragons materialise out of nothing. So what? Those 
> versions are not continuing to type to the end of this paragraph, while this 
> one-in-a-zillion version manifestly is, and will continue to live life 
> holding the delusional belief that the laws of physics will remain constant.

This works OK to reject worlds where you die, but presumably there are
also more worlds where you survive but see surprising failures of natural
law than worlds where natural law exists.  If you truly believe this,
it should affect your actions, and you should not proceed under the
assumption that everything will be normal.  Most universes where you
survive would probably be so lawless that you would just barely survive,
so perhaps this would point to abandoning moral behavior and striving
for brute survival at all costs.  I.e. go out and steal from people,
rob banks, commit murder without thought of the consequences, because
it's far more likely that the street will turn to molten metal than that
you'll be apprehended and sent to jail.

Hal Finney

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