The will to live and evolve is universal. Therefor, where conditions permit, life will develop. I believe that the universe is infinate. Disagree? then try to imagine what in theory would be the end, or edge of the universe. You can't can you! If life is simply limited to planets with the same or similar envoronment to our own, then in an infinate universe there will still be infinate planets on which life will develop. The possibility of 'aliens' reaching our solar system is slim to nil. Not because they have not tried, but because of the distances involved. There will be alien races somewhere infinately more advanced than ourselves, but technology will only go so far. And if they were here already, we would know for sure. no one would travel the distances involved just to hover around.