X-Message-Number: 11560
Date: Thu, 15 Apr 1999 20:52:35 -0700
From: Mike Perry <>
Subject: Simulations and "Cantgotu" environments

John de Rivaz, #11554, writes:
>
>In article: <>  writes:
>> there IS in 
>> principle the possibility of determining by experiment whether we are 
>> simulations. 
>
>I would add
>
>The Fabric of Reality by David Deutsch
>Is worth reading in this context, and it is also highly entertaining and 
>readable. Do you know that it is physically impossible simulate certain 
>things in virtual reality? So those of you who think this world is a computer 
>simulation, should read on. 
>
Deutsch uses a Cantor diagonal-type argument to show that (1) inasmuch as
the environments simulable by a universal virtual reality generator should
form a denumerable set, (2) therefore, there are *other* logically possible
environments besides the ones that are simulable. However, "logically
possible" is not the same as "physically possible," and Deutsch notes that,
in regard to the unsimulable, Cantgotu environments, "the laws of physics do
not permit us to be in one" (*The Fabric of Reality* p. 129). Another thing
about a Cantgotu environment, if we could experience one, is that for any
*finite* amount of time and experiencing we did, there *would* exist an
indistinguishable, simulable environment. It is only in the limit of time
(assuming we are immortal of course) that our Cantgotu environment would
reveal itself as *different* from every simulable environment. Not a very
practical test. So the logical possibility of Cantgotu environments, as
described by Deutsch, does not shoot down the possibility that we are in a
simulation, nor does it provide any practical way of determining whether we
are in one or not.

Yes, the Deutsch book *is* a good read..

Mike Perry 

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