posted on Jul, 3 2011 @ 06:09 AM
reply to post by Flyer
Who has said in this or any other thread that there is not life elsewhere in the universe -- or even in the Milky Way galaxy? This seems to be an
argument put forward, often, against those skeptical of ET visitation of Earth, even though such skeptics just about never make the claim that we are
the only life or even sentient life in the universe.
That said, just because there are billions of stars (perhaps 100 billion) in our galaxy, it doesn't mean that a high percentage of them have planets
supporting life. First off, the vast majority of the stars are in the central cloud; these are so close that zone is awash in radiation, so only
stars outside of this zone have any chance for harboring life. Then one needs a planet with a magnetic field and likely one with oxygen, and at a
distance from its sun such that water is in liquid form. Then it helps to have outlying gas giants to suck up most of the objects flying into the
solar system. Also, a lot of star systems are binary or trinary, which are believed to cause unstable orbits for lesser bodies in the system; these
systems wouldn't likely have planets that could support life.
So, of those 100 billion stars in our galaxy, I wouldn't be surprised if only one in a hundred -- or even less -- could support life. So that's
still around one billion, which is an awful lot, I admit, but a very small percentage of these are likely to have advanced civilizations, particularly
those capable of interstellar travel -- if such travel is even possible. Also consider the fact that civilizations fall and species die out. Then
there are always cataclysmic disasters that might snuff life out or set it back. Thus the number of possible starfaring ET civilizations in our
galaxy gets whittled down some more. Granted, there are all the other galaxies to consider too; however, intergalactic travel is even less likely and
the chance that any such denizens would ever take notice of Sol and its blue planet is very unlikely.
The bottom line: yes, there must be some advanced civilizations in our galaxy, but there are probably fewer of them than one might infer from the
number of stars in the galaxy. So the argument that "there are 100 billion stars in our galaxy, and there has to be life on a significant portion of
them, and so we have inevitably been visited" doesn't necessarily follow. I certainly don't dismiss the possibility, but the likelihood isn't as
overwhelming as the number of stars might suggest to some.