Re: Our rocky solar system may be rare

Robin Hanson (
Mon, 13 Sep 1999 10:27:51 -0400

Hal Finney wrote:
>Robert J. Bradbury, <>, writes:
> > The only statements that can be made with putting yourself squarely
> > in the swamp is: "We don't see aliens that are our size nearby
> > (literally walking around on earth)" and "Aliens do not appear
> > to have restructured or consumed *all* of the stars in the galaxy".
>I think you can make some stronger statements than this. ...
>You can probably also put some limits on the amount of energy
>any hiding aliens on earth are using. ... if aliens do
>restructure/consume stars, they appear to prefer small stars and
>avoid large ones ... do it to virtually all the galaxies we can see
>clearly ... and all aliens follow the same policies in this regard. ...
>Overall you can say that intentionally or accidentally, the aliens are
>creating a universe which looks a lot like one which could have evolved

Right. Obviously the universe is very big, and we couldn't expect to see a single nano-alien half-way to the horizon. But we *can* say things about the aggregation of all aliens in a region. For example, aliens aren't intercepting more than 1% of the starlight from the nearest 100 stars, at least if they re-radiate it at obvious IR temps. (For more examples like this, see:

Robin Hanson Asst. Prof. Economics, George Mason University MSN 1D3, Carow Hall, Fairfax VA 22030
703-993-2326 FAX: 703-993-2323