This is a question I have wondered forever. Of course there is no way to ever know for sure, unless you meet someone in heaven.
I think there is no way that we are the only planet out there with intelligent life. I'm not saying that little green men have came here on space ships but as big and never ending as the universe is, there has to be someone else out there.
Do you think we are god's only experiment?
Does god have a brother or sister that rules other universes? I know he says he is the only one but maybe he means the only one for our planet.
By the way, I am not making fun or being silly. It's something I have always wondered.