Re: To Mars 2

Hal Finney (
Mon, 2 Mar 1998 08:47:17 -0800

Charlie Stross, <>, writes:
> Um ... I disagree with O'Neill on _one_ point. Planets with a working
> ecosystem can be engineered to be reasonably fail-safe, to the extent
> of surviving a collapse (or even extinction) of civilization. A habitat
> could _conceivably_ be built to such a scale (go re-read Ringworld, for
> example), but most designs for space habitats are way too small to be
> stable -- much less to withstand the slings and arrows of existence in
> a planetary system for long periods of time (megayears).
> If you hit an O'Neill cylinder with a rock, it dies. If you hit the
> Earth with a rock -- anything much smaller than Phobos -- well, a few
> species may go extinct, but the whole system will pick itself up and
> carry on as before.

Good point, Charlie, but isn't it largely a matter of size rather than
of design? Suppose you had an earth-mass of O'Neill cylinders. (How
many would that be? A whole lot, you betcha.) Now throwing a rock or
two isn't going to cause much damage either.

Conceivably the system could even withstand collapse of civilization,
if it is self-repairing. The idea of a culture living unknowingly within
a starship is as old as SF.

> Of course, why the hell are we talking about habitats to support an
> agriculture-based society when there's the open question of what kind
> of habitat is appropriate to an uploaded mind to discuss?)

In Greg Egan's Diaspora (now available in the U.S., BTW) a whole
civilization lives uploaded in a featureless blob a foot or so in size.
(Actually it was never clear to me how large the population was; at some
point I had the impression that everyone knew everyone else at least
dimly, and even accounting for large lifespans it would suggest that
there were no more than a few million inhabitants).