I wish that you’d be more specific.
I am almost certain that there is microscopic life out there. I’m pretty sure that they discovered microscopic fossils on Mars. The universe is so large and there are so many planets that meet the requirements for life, that I feel like probability would dictate that basic life exists out there.
If you’re specifically concerned with creatures at least as developed as human beings, then I’m not so sure. I’ve heard a number of arguments about this from individuals at different levels of expertise.
If there is life that has developed enough to reach us here on Earth, either they’re very caring and don’t want to openly interfere with us (Think the Prime Directive), or they just haven’t found us yet. We’re so far away from being able to travel that far, if someone’s out there, and they could reach us, what else would explain us not meeting the same fate as many Native Americans after European colonists started showing up?
Perhaps there’s life that is at the exact same point of development as humans, and we’re both equally incapable of reaching each other. If this is the case, then it really becomes moot.
On a humorous note; I suppose I have to believe in aliens–one used to work on my uncle’s ranch!
~Pax