Re: Dyson shells are possible

Robin Hanson (
Fri, 17 Sep 1999 12:35:12 -0400

On 9/13/1999 Robert J. Bradbury wrote:
> > ... 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:
> >
>I think I did read this paper quite a while ago (the date on the copy
>I have saved is Sept. 1998). The problem seems to be the 1% argument
>from Jugaku. I did investigate this a bit more completely and it seems
>he got it from Papagiannis from "The Search for Extraterrestrial Life:
>Recent Developments", 1985, pp. 263-270. Jugaku has been doing
>Dyson "searches" for 15+ years based on the 1% assumption and has
>looked at probably the number of stars you quote.

I referred in my paper to:

Jun Jugaku and Shiro Nishimura. A search for dyson spheres around late-type stars in the solar neighborhood ii. pp. 707-710 in Cristiano B. Cosmovici, Stuart Bowyer, and Dan Werthimer, editors. Astronomical and Biochemical Origins and the Search for Life in the Universe, number 161. Editrice Compositori, 1997.

The 1% isn't an assumption, but rather a measured bound on starlight reradiated at IR temps at these stars.

>So then the questions become what is the power the
>star is emitting and how much material do they have? Smaller
>stars or more material make the power dissipation per m^2 by the
>outermost layers lower and therefore the temperature as well.
> From a theoretical standpoint (if you live long enough and grow
>big enough *or* do stellar mining to reduce the power output
>of your star *or* build the MBrain around a Gas Giant and use
>it to fuel thermonuclear reactors) you can make your radiation
>temperature *very* close to that of the background radiation
>of the universe (2.7K). This is the most efficient situation from a
>thermodynamic viewpoint, and therefore a goal advanced civilizations
>would presumably strive for.

Are you suggesting that aliens may in fact be intercepting more than 1% of the starlight from these 100 nearby stars that Jugaku observed, but are reradiating it at near 3K? Or are you suggesting that there are at least hundreds of other stars that have been completely enclosed and are reradiating at near 3K? Under either of these scenarios you have to ask: why these aliens are leaving all these stars to throw their valuable hot photons off to infinity?

It would be very far from efficient to carefully manage the less than 1% of light you did intercept while completely ignoring the 99% you let go by. And it would be far from efficient to so patiently manage one star while completely ignoring others nearby.

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