On Wednesday, March 03, 1999, Robin Hanson wrote:
>David Blenkinsop <firstname.lastname@example.org> wrote:
>>Since Robin Hanson has been mentioned, maybe this would be a good time to
>>a question about *another* ET article of his, "Burning the Cosmic Commons:
>>Evolutionary Strategies for Interstellar Colonization".
>Thanks for the plug. This paper is now revise & resubmit at Icarus:
> http://hanson.berkeley.edu/filluniv.pdf or .ps
>a selection effect may eventually
>determine frontier behavior
>This colonization model explains several astrophysical
>puzzles, predicting lone oases like ours, amid large quiet regions
>with vast unused resources.
> . . .
>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.
>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.
ET's being such an open field for speculation, I suppose that we ought to appreciate anything that sets out some evolutionary hypothesis as to why none seem to be near. However, I can't help but think that that this is fairly "nebulous" (excuse the pun), if there isn't yet much of a glimpse of what the initial "bottleneck" resource might be (let alone a good idea as to why succeeding settlement waves would be so slow or inefficient as to apparently miss our solar system altogether). Trying to imagine what the "fast travel" resource might be could be entertaining, though; is it naturally ocurring nuggets of antimatter, perhaps, or magnetic monopoles, or mini black holes? Maybe the capturing of this exotic whatever-it-is has helped to sling some of those giant planets into the odd orbits that we keep finding? Come to think of it, maybe neighboring planetary systems are rigged with dangerous booby traps to this day, we could be living on the one relatively safe spot in a vast "anti-competitor" minefield of some kind. That would be double jeopardy for a second or third wave, with the most powerful star travel resources gone *and* maybe you go "kaboom" if you try to make use of the leftovers, the front runners in the Great Race desiring not to be overtaken, you see.
Compared to such grand space-trashing ideas, I still wonder if a relatively mundane idea might be worth thinking about, namely the chance that intelligence might survive preferentially on quite "large" planets as compared to the Earth. If a solid planet with the Earth's density were twice as large in overall dimensions, it would then have eight times the mass of the Earth. Presumably, the atmosphere would then almost have to be much thicker, giving any surface inhabitants much better protection against radiation events than we have. I understand that small, long-lived stars are prone to solar flares, and we've talked about gamma ray bursters, too, so maybe you really *need* the extra shielding if surface dwelling technology builders are to generally have a good chance of evolving.
Now, the "catch" to this large planet business is that actually getting into outer space should be much harder for the ET's involved than it is for us, and, even for us, space travel hasn't been a tremendously easy thing to develop! For a planet that's 2X the size of the Earth, all around, you'd expect the escape velocity to be *twice* that of the Earth, since you have eight times the mass divided by twice the radius, that's an energy gravity well *four times* deeper than *we* have to deal with. Going further, if a planet were 3X the Earth's size dimensions, you'd get a 9X deeper gravity well, meaning that the escape velocity would relate as the square root of 9, so escape would be 3X the speed for a 3X larger, solid, planet. Maybe 3X is going a bit far, that's getting more massive than Neptune, but you get the idea. Even if we're talking only a "2X Earth" planet, it could be tremendously discouraging for even a very sophisticated technology to break out of that kind of gravity well, certainly it would be *enormously* difficult to launch the way we do, with chemically fuelled rockets! Now, could this almost be a SETI searcher's dream come true? Question: where are the ET civilizations? Answer: why, stuck on their respective planets, furiously beaming out high powered radio messages, because that's all they *can* do!
David Blenkinsop <email@example.com>