Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.1 6/24/83; site umcp-cs.UUCP Path: utzoo!linus!philabs!cmcl2!seismo!umcp-cs!mangoe From: mangoe@umcp-cs.UUCP (Charley Wingate) Newsgroups: net.sf-lovers Subject: Re: The Great Silence Message-ID: <1190@umcp-cs.UUCP> Date: Sun, 11-Aug-85 12:51:22 EDT Article-I.D.: umcp-cs.1190 Posted: Sun Aug 11 12:51:22 1985 Date-Received: Tue, 13-Aug-85 04:06:53 EDT References: <579@mmintl.UUCP> Organization: U of Maryland, Computer Science Dept., College Park, MD Lines: 66 In article <579@mmintl.UUCP> franka@mmintl.UUCP (Frank Adams) writes: >One more time ... an intelligent race with interstellar flight doesn't go >to just a few places, it goes everywhere. All nearby star systems are >more or less equally attractive, so you colonize all the nearby star systems. >A few dozen generations later, you have filled up all the nearby star >systems, so you colonize the next layer out. In a few hundred thousand >years, you have filled the galaxy. All of it. Really? Isn't this article just a little anthropocentric? To do this, a race needs a whole list of things: lots of energy, lots of technology, and (most importantly) motivation. A race which doesn't have a severe population growth problem doesn't need to colonize. Resources for thousands of years are to be had in one's own solar system. A race which is just starting interstellar travel has enourmous constraints. Generation ships are SLOW. Assuming that FTL travel isn't possible, the energy needed to travel at reasonable speeds is tremendous. Since probes in the EM spectrum are relatively cheap, it makes some sense to pick and choose. If all Bernard's Star has is big gas planets, then it's going to take a lot of energy to make something livable there for a race like us. Detecting terrestrial planets over interstellar distances is enourmously difficult. They emit essentially no thermal radiation, they are too small to occult anything or influence the obvious body's orbits. The only way one could detect Earth from interstellar distances is to detect man-made radio emissions; we've already discussed reasons why these are difficult to detect and have reached only a few stars anyway. This brings us to the question of why one would want to visit a planet which is apparently inhabited. >A race from a planet where life started at the same time as on Earth, which >evolved to a technological civilization one percent faster, has had thirty >million years or so to spread out since. That is time enough to fill the >galaxy about a hundred times over. "They just haven't found us [yet]" is >just not an adequate explanation. This baldly assumes that they have a pressing desire to do so, and the technology to accomplish it. >Most plausible explanations for why they aren't here are variations on >three themes: (1) they aren't there, (2) they are deliberately leaving us >alone, and (3) war prevents permanent settlement of planets. And remember >the time scales involved for (2) -- they have to have decided to leave "us" >alone while "we" were dinosaurs (or perhaps earlier; I'm not quite sure of >the evolutionary time scale (if you don't believe in the evolution of >species, send comments to net.origins where I won't have to read them)). And 4) they haven't looked hard enough or had the time to. Assuming you had the power to search the entire galaxy for life, it's still going to take a long time to find any. Also 5) we aren't very interesting to them. >Now this does not mean that SETI is hopeless. They may be just waiting >for us to contact them to welcome us into the Galactic Federation. But >it seems about equally likely to me that as soon as they detect us, they >will come by to sterilize our planet, before we can do the same to them. >But we should not *expect* SETI to succeed. Likelyhood here is essentially meaningless. We are on an obscure planet whose civilization could only be apparent to those within 20 light years of us. Therefore the only real explanation must be that whatever civilization is on the planets within that range either a) hasn't noticed, b) doesn't care, or c) hasn't had enough time to act. (Remember, only those within 10 lightyears have had time to get back to us.) Or d) has acted, but we didn't notice. C Wingate