Re: reasoning under computational limitations

Nick Bostrom (
Sun, 4 Apr 1999 20:13:17 +0000

Wei Dai wrote:

> My version of SIA (let's call it SIA-1) does have that property when the
> measures of all observers are equal.

I have another question before we can go into that. You wrote:

>The "total measure of observer-instants" can be thought of as the
>fraction of the universe (the entire history of the universe, not
>just its current state) that consist of observers.

How do you define this "fraction" when both the number of observers and the size of the universe may be infinite? If you think of density, note that (1) The distribution need not be uniform, so there can be different densities for different regions, and (2) It seems strange if it would matter where in the universe the observers happen to be, how they are grouped.

Nick Bostrom Department of Philosophy, Logic and Scientific Method London School of Economics