RE: delayed reply

From: Marchal <>
Date: Fri Mar 19 01:09:59 1999

James wrote:
>In answer to Wei dai's question, what is the set of all possible universes,
>I would say, it is the set of all universes which can be rendered by
> mapping
>a subset of the output of "LET A=A+1; GOTO START", however you wish to map
>it. I'm not sure why we want to know if we are living in 'this particular
>turing machine' - as far as I understand it only one machine is running.

OK, although I would say "no machines are running". "Running" is a
dynamical concept, and "dynamics" is an internal modality of arithmeticla
And, if you have go through the PE-omega thought experiment, you know
also that we are not localized at all in any universe, we "belong" to all
(indiscernible) computationnal histories passing by our computationnal
Time AND space are internal modalities.

>generates everything possible as per previous paragraph, so what the
> program
>looks like can only be known if we know the mapping and all that seems
>a fruitless avenue of research.

Indeed. That is why I prefer to think in semantical term (arithmetical
truth) and not in any syntactical or formal specifications. Those
specifications are useful for the thought experiments, and they are
useful for giving hyperbolic shortcuts to convey some point. But we must
never take them too litteraly.

>I'm confused: why do we need to explain anything? If everything possible
>exists then that X exists in our environment can never be very surprising.

The surprising thing is that, although "everything possible exists" some
Y does NOT appear in our environment. We need to explain that, if
"everything possible exists" can be taken as an explanation.

Received on Fri Mar 19 1999 - 01:09:59 PST

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