Ah, but there must be at least some other planets with life. And life starts small, but with proper conditions, it can evolve into more sophisticated beings, and become what we can call 'intelligent'. While we cannot be sure of who is more 'intelligent', we can just about say there has to be other intelligent life forms out there. I don't believe we'll find stuff like Star Wars or Star Trek and stuff, but it's interesting to imagine possibilities. Like- what if other non-humanoid creatures developed larger brains and higher mental capacities? If they became more dexterous with their paws/fins/other appendages, what creatures would we have? It's very interesting. But science is not my thing. Biology sounds like a nightmare. *shudders*
Oh, and to those saying "Then why haven't we seen them yet?" let's just stop thinking in movie terms. They could be on the other side of the freaking universe, literally billions, and trillions, and googolplex light years away!! And since it's physically impossible to travel faster than light (without entering the fourth dimension I believe), it would take trillions of years for those beings to reach us. I highly doubt they can live that long, have enough fuel, navigation, food, air, liquid, to come here. The chances of encountering other intelligent life is very, very, very, very (repeat, oh, I don't know, as many times as you'd like) slim. But once I think about it, they might not be too far away either. We humans have never reached Andromeda, the closest galaxy (I think) to ours. Not with satellites, only with very powerful cameras. But another life form there could be trying to find 'aliens' as well, and not possess the capability to fly out that far. Do not underestimate the distance between stars, galaxies, and galaxy clusters. The distance itself makes the chances about zero. And then there's what Moho said about parallel universes, AKA string theory, where the probability of everything is one because everything has to happen. Therefore, a new universe is formed every time something has different choices, and aliens must exist in infinite universes. Life on earth does not exist in infinite universes. I think that's how the theory works. But my point is, stop thinking movie aliens and think of them as us. Can we travel thousands and thousands of light-years? Is it even possible? Probably not, so it's probably not possible for the aliens either. Face reality. And accept there has to be other intelligent life out there somewhere.