David Blenkinsop <blenl@sk.sympatico.ca> wrote:
Thanks for the plug. This paper is now revise & resubmit at Icarus:
>Since Robin Hanson has been mentioned, maybe this would be a good time to ask
>a question about *another* ET article of his, "Burning the Cosmic Commons:
>Evolutionary Strategies for Interstellar Colonization".
Burning The Cosmic Commons:
Evolutionary Strategies For Interstellar Colonization
by Robin Hanson
http://hanson.berkeley.edu/filluniv.pdf or .ps
Attempts to model interstellar colonization may seem hopelessly compromised by uncertainties regarding the technologies and preferences of advanced civilizations. If light speed limits travel speeds, however, then a selection effect may eventually determine frontier behavior. Making weak assumptions about colonization technology, we use this selection effect to predict colonists' behavior, including which oases they colonize, how long they stay there, how many seeds they then launch, how fast and far those seeds fly, and how behavior changes with increasing congestion. This colonization model explains several astrophysical puzzles, predicting lone oases like ours, amid large quiet regions with vast unused resources.
>Supposedly, they've never returned from that great expansion wave
>front, figuring that our locality is used up, or burnt out, so in
>this concept *that's* why no obvious ET settlements!
I think Hal (as always) presented a nice summary of my argument. It's not so much that stuff behind the frontier is "used up" as it is that its just not useful toward jumping ahead of the expanding frontier. Agents tempted to hang behind for a bit to use stuff get selected out of the frontier of the wave.
>... just what could possibly be so important that it would get
>used up, and prevent really expansive ET's from gradually expanding into all
>available niches, including our solar system? For instance, one "life
>essential" resource that comes to my mind is *phosphorus*, but I can't imagine
>why phosphorus atoms would actually be destroyed by ET settlers? Actually, I
>suppose that's two questions: first, any reason why nearby ET's couldn't be
>communicative, but planet-bound, and, second, what's burned in the "Burning
>the Commons" scenario?
The model predicts that what gets used up are resources that support fast growth of a seed into a site capable of launching more seeds. If seeds could grow faster in comets than in asteriods, for example, then we might see systems with lots of asteriods but few comets left. Or maybe there was something even better than comets that we don't see because a wave came through here already.
Hal Finney writes:
>You'd still think that there could be a second wave of colonization,
>replicators evolved and specialized to work with the detritus of the
>hyper-fast expansion wave. The first wave can't have used things up
>_too_ completely - the star is still there, ... big planets
Yes, and then maybe a third and forth wave as well.
>It seems difficulty to come up with an evolutionary scenario in which
>life does not advance into every possible niche, so that we can say that
>our own solar system just happens to have been skipped. At best you
>can argue that we are near enough to the time that life first was able
>to spread through the galaxy that it just hasn't gotten here yet. Maybe
>by combining the "we're relatively early" and "life misses niches"
>ideas you can make the numbers work out to give us a reasonable chance
>of existing.
How about this perspective: a section effect makes it easier to overestimate how fast our colonization wave will spread. The waves that passed this way before make the universe appear to conspire to make fast growth hard. Yes, eventually it all gets filled in with life that hangs around for a long time, but this process may take longer than a naive analysis would suggest.
Robin Hanson
hanson@econ.berkeley.edu http://hanson.berkeley.edu/ RWJF Health Policy Scholar FAX: 510-643-8614140 Warren Hall, UC Berkeley, CA 94720-7360 510-643-1884 after 8/99: Assist. Prof. Economics, George Mason Univ.