As a side note: Do you believe in other life forms? If yes, do you believe there are more intelligent life forms then human beings?
There was a line in a Jodie Foster movie that explains it the best:
"It's a waste of space, if we are the only ones in the universe" Or something alongs those lines, can't recall exactly. (Contact)
I dont think we are the only sentient beings in our universe, though wether they are more intelligent or not would be on my part speculative. However I don't think that we ever had have aliens of another planet visit ours yet. I dont believe in UFO's or alien abductions and nonsence like that either. There's basically no evidence that shows we have been visited by space aliens.