There are more than 400 Billion stars( http://ask.yahoo.com/20010810.html) in our Milkyway Galaxy and over 500 Billion galaxies in the universe (http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/021127a.html ). How can we believe that we are the only intelligent life in this vast universe. If we are the only one then I would say that there is a lot of space that is wasted? I cant say for sure that alienz have visited earth but we cant disbelieve it totally either.