I got to thinking a bit more about an assumption I (and I bet most of us) have held, that surely there is "intelligent" life on other planets, one capable of technology .. thus SETI's radio search. Surely it is hubris to claim humanity is somehow unique, just look at the diversity of our own world! Thus there's got to be lots of intelligent life out there, right?
(Yes, I know, this is pretty vague, and we're intelligent only for very small values of intelligent.) But listening to a TED by Hawking, I was impressed with his somewhat measured approach: that we have not found a radio source within 200-400 light years. I believe his choice of distance had to do with our own development of radio a couple of centuries ago. That got me reading up on just how long we've been around, and how long other civilizations could have existed. Very roughly speaking, the big bang was 14 billion years ago, our sun is 4.5 billion years old, and the earth is 4 billion years old. Well, that sounds like we're late to the game: 4 billion years old in a universe 14 billion years old. But wait a minute, we know we're the result of star-stuff, the heavy elements. The big bang was only able to muster nuclei of fairly low weight, lithium say .. possibly a bit more. The first generation of stars, therefor were fairly odd, huge and short lived. And the second generation of stars were less heavy element rich than our sun, which makes it at best third generation. http://goo.gl/gV54S So given only 14BY for building solar systems, and assuming the requirement for an at least third generation sun, we may be as young as likely a life form possible. So SETI is likely playing a loosing game, we're young enough that the statistics may be that, yes there is life out there, but it's pretty young too and maybe is no more advanced than we are. (Maybe that is Hawking's couple of centuries limit) Of course we're talking about a few centuries, which would make a huge difference in technology, but still. Hawking does end with a grim comment others have made: maybe civilizations are short lived .. they self destruct or fall prey to destructive events (meteors, comets). -- Owen
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