X-Message-Number: 11338
Date: Tue, 02 Mar 1999 01:09:57 -0700
From: Mike Perry <>
Subject: Re: CryoNet #11331

Thomas Donaldson writes,

>... I will point out that discreteness does not imply digitalness.
>Yes, atoms and electrons, when found, occupy DISCRETE positions in space,
>but this does not mean that those positions can be expressed DIGITALLY ie
>in a computer with a fixed length of numbers (if that is what you mean).
No. Not a "fixed length of numbers." Computers are not limited to that.
They can work with a growing length of numbers.
The most general digital system
as I see it is a Turing machine with infinitely inscribed tape, 
and its computational
equivalents. It could work with infinite decimal
expansions. (It is, on
the other hand, not realizable by our finite devices but could
be approximated by them.)
A pretty powerful system, yet the significant events in such a system
are discrete, and describable as simple changes of 
symbols chosen from a finite alphabet. I think such a system 
could handle the major "discrete" models
of reality we have dreamed up that use 
quantum mechanics, and I think this follows from
the Bekenstein bounds, the finite-state-machineness
of bounded subsets of spacetime, etc. Incidentally, 
while I agree that relativity theory
as usually formulated (classical, general relativity theory) is continuous
not discrete, there is an interesting recent development that *seems* to
imply that to harmonize relativity with quantum mechanics will result in
its becoming discrete. See Hans Moravec, *Robot: Mere Machine to 
Transcendent Mind* note 11, p. 214, reporting on work of Abhay 
Ashtekar from 1989.

>As for the possibility of resurrecting all possible creatures able to
>fit into 5 cubic meters, I explained my response to that idea in my
>previous message: I cannot imagine much that is as senseless as that,
>even if the world IS digital. Nor do I see it as having any moral

Well, we disagree on this. I see it, or something similar, suitably
sandwiched into a hopefully infinite future that will also have many
other things to do, and suitably followed through, as having immense
moral and other value.

Mike Perry

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