|
Edited on Fri Dec-03-04 04:23 PM by RandomUser
The crux of the argument is that it doesn't matter how rare the number of alien civilizations (as given from the Drake Equation). Even if you have very few of them, they should have colonized all of the universe by now, even when you incoporate very modest rates of expansion. http://c2.com/cgi/wiki?FermiParadoxLet's look at the second point first: aliens cannot get here. After all, perhaps they come from the other side of the galaxy, or even from another galaxy. Well, Earth is about 32,000 LY removed from the galactic center, so 64,000 LY would be the distance to the other side of the galaxy. That takes 64,000 years when travelling with the speed of light.
OK, let's suppose that one alien civilization actually manages to build a colonization ship; not one like in StarDreck?, but something like we might build ourselves in a couple of centuries: it goes veeery slow compared to the speed of light, so it arrives only at its destination after about 1,000 years. OK, so now we are there, and the next question is: when will the new civilization build its next vessel? Well, we give them time to fall back to stone age a couple of times, so let's say: 9000 years, which has the advantage to add up with the previous number to 10,000 years. OK, so I pull these number from my *ss, but I hope that I'm somewhat convincing that if a civilization is capable of starfaring at all, 10,000 years might be a reasonable time from launch of ship to planet A to launch on A from ship to B. In other words, 10,000 years would be a rough estimate for the time it takes to double the total number of colonized planets. We all know that exponential growth is too optimistic; after a negligible amount of time, all close-by systems have been colonized and expansion happens only at the surface of the sphere containing the colonized star systems. You then launch to a very-close-by system (of course), say 10LY away. So it takes 10,000 years to cover 10LY, in other words: expansion goes at one thousandth of the speed of light. That still means that you can be here from the other side of the galaxy in a mere 64 million years. That means that if the dinosaurs had spacecraft, they would be at the other end of the galaxy by now. If someone else had spacecraft at the time of the dinosaurs, they would be here by now.
So this strongly suggests that we are really alone in the galaxy. Well, it's ours then, isn't it? Just let's see what we have. A run-of-the-mill galaxy like ours is 100,000LY in diameter and has a center of 10,000LY. It contains mostly ordinary stars (about 10e11 or 100 (American) billion stars). In the center is probably a black hole of about a million solar masses. So that's ours! That's 20 star systems for every person in the world. And then we still have the two Clouds of Magellan: they are a mere 169,000 respectively 205,000 LY away, so sufficiently close for a visit. But wait! What about those nasty Andromedians? Andromeda (M31) is slightly more than 2 million LY away: If there were star-faring Andromedians back when the Earth was trying to evolve algae, they would be here by now. So Andromeda is probably either only "recently" colonized or still virgin terrain, so we could take that, too. And the rest of the Local Group: the whole cluster containing the Milky Way, Andromeda, 7 other big spiral galaxies like ours and some 30 small elliptic ones. Total radius: 6.5 million LY. Peanuts for any sufficiently advanced society.
Of course, the Local Group is, unfortunately, one of the tiniest clusters around. Our closest neighbor, the Virgo cluster, is some 60 million LY away, and it contains thousands of galaxies. Definitely worth going there. Another one is in Coma Berenice, and lies 450 million LY away. It contains about 800 galaxies. The Local Group and Virgo, together with some 100 smaller clusters, form a so-called supercluster, with a total radius of 300 million LY. What reason do we have to believe that either our understanding or our observations are perfect and complete? Exactly, as per your statement, there is no reason to believe the Drake Equation as it stands, or the values accorded to the variables, is in any way correct. That is why the Fermi Paradox is used as a way to "disprove" the Drake Equation. (Not really disprove as such, but require the alteration of the equation in such a way as to account for it -- such as the inclusion of extinction level events to prevent the spread of intelligent life. And it most certainly cast doubt on the use of the Drake Equation to prove the existence and abundance of Alien life, as mostly seems to be the case when the Drake Equation is brandied about.) (edited to cut down quoted text to four paragraphs as per DU rules).
|