I think that it is almost statistically impossible for Earth to be the only planet that has life on it. Now there may not be other life forms in our galaxy, but there are sure to be some somewhere at some other infinitesimal part of the universe. On the second slide from
this powerpoint presentation given by my astronomy professor for next semester really shows how large the universe is when compared to the Earth. Really, the universe is beyond HUGE, and contains billions and billions (if not more) stars, and with many of those stars come planets, however the vast amount of these cannot be seen from Earth.
And I'd also like to bring up another point to add to the discussion. In every case that I have seen, scientists look for signs of water that would be able to sustain alien life. But who says that these life forms are dependent on water? Given a completely different planet with a completely different set of environments, I think it would be possible that the life on that planet would develop so that it actually lives off some completely different natural resources. It could be that a planet is inhabited by life that lives off of Helium in the air and some kind of Jello for food. Then we have a nice planet of squeaky-voiced Bill Cosby aliens.
Also, it may be that alien life forms
have or
will exist. Given the great amount of time that the universe has been around and probably will be around, all life forms on a planet may have already died out, or are just coming into existence. The possibilities truly are endless.
However, given the size and scope of the universe, I believe it to be very unlikely that we will ever come in contact with any such civilization, because it would take nothing short of science fiction to allow for such beings to travel the great distances of space to just-so-happen to pass by our planet.
My 2.5 cents
