Originally Posted by u-Bob

* Statistically it would be almost impossible that there wouldn't any life on other planets.
* If there's life on other planets, it would be highly unlikely that Earth would have been the first planet with an 'advanced' civilization. (certainly given the position of our galaxy within the universe).
* According to the Everett interpretation of quantum physics there's a very large number of (parallel) universes. If this is true, then it is possible that life on Earth in some of those parallel universes has evolved differently from life in 'our' universe. These lifeforms would then appear 'alien' to us.