Re: Doomsday Example

Nick Bostrom (
Fri, 28 Aug 1998 17:08:34 +0000

Robin Hanson wrote:

> Consider an exponential model of the time to evolve life on a planet,
> where the probability of life evolving t years after the planet forms
> is proportional to exp(-t/h) within the window [0,T]. The average
> number of planets with life is then proportinal to 1 - exp(-T/h).
> The observation that t ~ T/2 exponentially suppresses the posterior,
> relative to the prior, for h << T. Values of h >> T are only linearly
> suppressed if one expects one is more likely to appear in a universe
> that has more life. In my paper I was focusing on the exponential,
> not the linear, suppression, but I admit both effects are there.

Could you elaborate a little on how this linearly suppression comes about?

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