X-Message-Number: 8199
From:  (Thomas Donaldson)
Subject: Re: CryoNet #8196 - #8197
Date: Sat, 10 May 1997 12:59:27 -0700 (PDT)

Hi!

Only some astronomers claim that the universe is finite --- in one parameter
or another. 

As for making a simulation of the entire universe, the biggest problem I can
see (if you really want to do this) is the amount of memory it would require.

I mean here THE ENTIRE UNIVERSE, every atom and photon etc, all the way down.
It's not fair to ignore some things because you believe they won't affect
anything important. OK, so suppose that you store each bit in a single atom:
that won't be enough. You might do it with a quantum computer, but just how
I can't say right now (we're dealing with memory size, not computation).

If the universe is infinite, even just in time, then we may have a doable
problem, but the simulation may turn out very slow compared to our clock time.

And as someone who will accept, certainly, the usefulness of simulations, but
does not believe we are now or will ever be able to understand the universe
COMPLETELY, I wonder just what use such a simulation will be. To point out to
us just what we DON'T understand? that is, when the simulation doesn't 
coincide with the universe itself? 

And of course we also have to deal with the infinite regress 
problem: since the simulation is simulating the entire universe, and the
device on which is running is in the universe, it must simulate itself, and
so on ad infinitum. Perhaps we've stumbled on yet another barber problem:
the barber who shaves all those who do not shave themselves (we do have to
say that he is a man with the proper hormones, though). Is the construction
of such a simulation then impossible for logical reasons? In order to compute
what it will next compute it must first compute what it will next compute it
must first compute what it will next compute it must first compute what it
will next compute ..... hmmm. After all, if we run a simulation to tell us
about the universe, then what it tells us will affect how we behave, and thus
affect the universe itself, yes?

As for memory, I like the Borges story best, the short one about the country
that so prided itself on its mapping ability that it made a larger and 
larger map of itself, until the map covered the entire country in such detail
that it caught everything --- but the country itself then fell apart, was
invaded by barbarians, and now we only see scraps of the map caught on bushes
or trees and blowing in the wind. 

			Long long life,

				Thomas Donaldson

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