Re: Tough questions

John Clark (
Tue, 7 Sep 1999 01:48:50 -0400

Matt Gingell <> Wrote:

>It seems to me that there must be some smallest unit of matter capable of doing
>computation, some sort of computational 'atom', in the ancient Greek sense of
>the word. This would impose an upper bound on the amount of number crunching you
>could possibly do with a finite amount of mass.

Size is as important as mass. If the Beckenstein bound is true ( it probably is but has never been rigorously proven) then the amount of information inside a sphere of radius R that contains energy E is less than or equal to 2*PI*E*R/(h *ln2), h is really h bar. For meters (R) and kilograms (M) that works out to 2.577 *10^43* M*R bits.

A proton has a radius of 10^-15 meters and a mass of 1.67 *10^-27 kilograms, plug that in and you get 44 bits. You'd do a lot better with a Hydrogen atom. The mass is almost the same but it's a lot bigger, about 10^-10 meters, so a hydrogen atom can store 4*10^6 bits.

> if we are being simulated by a computer built in a world whose
>physics match our own, and we are being simulated in real time, then the
>computer simulating us must be at least as big as our entire universe.

No reason to think the physics would be anything like ours and no reason to think it's in anything close to real time and no reason to think that any part of our universe exists (is being simulated) when nobody is looking at it.

John K Clark