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 Rate This Message: http://www.cryonet.org/cgi-bin/rate.cgi?msg=8199