REM@MIT-MC@sri-unix (10/23/82)
From: Robert Elton Maas <REM at MIT-MC> Please specify which of my claims is silly. You seem to be saying the same thing I'm saying, that planets around the galaxy are teeming with life, and that intelligence develops everywhere. The only part you seem to be disputing is that if life somewhere developed the technology to move into space and miagrate to other stars, then after a few billion years it should have occupied every nook and cranny of habitable space in the galaxy, including our very own Solar System, turning every star including our own into a Dyson sphere or better. You cite the many South Pacific islands that weren't even visited until WW-II. Well, 1492 to 1945 is less than 500 years. It takes about that long for the population explosion to get to the point where there are enough people to explore all land on Earth, and a little longer to get to where not only all land but also all underseas locations are inhabited (not just explored). I suspect in another 200 years the Earth will be totaly saturated, every nook and cranny including 7 miles deep in the ocean and the poles and deserts and mountain tops. Now let's assume some advanced civilization can achieve 0.5 C going from one star to the next, say 8 light years away, so the trip takes 16 years. I figure it would take a well-prepared colony about 10 years to get bootstrapped into using asteroids and solar energy to support life and to process materials and build new collecting and processing equipment. Then the population explosion can begin. Let's say due to unlimited energy and resources, each family has 5 children, and a generation is about 25 years. Let's say the initial colony is 1000 people. After 1 century, i.e. 100-(16+10)=74 years from end of bootstraping, we have 120,000 people. After 1 more century we have 75 million people. After 1 more century we have 46E9 people, which is enough to start sending out colonies to nearby stars. Thus every 300 years life expands 8 light years. The galaxy is about 25,000 light years in radius, thus it takes about 25,000*(300/8)=937,000 years for life developing space technology near the center of the galaxy to spread throughout the entire galaxy. That's less than a million years. They may miss a few stars, maybe the initial expansion hits only 10% of the stars. But now there's no room left to expand, except by carefully searching for new stars and missed stars nearby. Another 900 years and each little colony will have located all neighbors within 8*3=24 light years and planted colonies there. This is still less than a million years, and the galaxy is already totally cramped. Now suppose such a population explosion started 8E9 years ago. Well, 7.999E9 years ago the Galaxy was already saturated. Probably they'd find ways to consume stars faster, or they'd have galactic wars, or who knows. I doubt we'd find our Solar System sitting here with most of its hydrogen not yet burned and in fact looking rather virgin like nobody has made use of it yet. Even if they somehow missed our tiny star, I doubt we'd find the whole Galaxy full of hydrogen-burning stars after all this time; rather we'd find ourselves in a burned out galaxy, where virtually all the hydrogen has already been consumed. Enough speculation. Let's go out there and find out what's living on planets of neighboring stars. Let's succeed [at establishing civilization in space] where they all failed, and go find out why they all failed.
POURNE@MIT-MC@sri-unix (10/24/82)
From: Jerry E. Pournelle <POURNE at MIT-MC> I see nothing wrong with REM's analysis. Assume he's off by a factor of 100 and the question remains, Where Are They? did they all discover Zen and stay home? We won't know until we go; but we can sure as hell learn what population pressure is REALLY like if we stay here...