Also, personally I think it is entirely possible that we have been visited by aliens. Why is it so difficult to believe, you think we are the only life in the universe? Of course the idea is mixed up in a whole lot of mythology, it's a magnet for crackpots. But underneath all that, the central position that we may have been visited by aliens and we may have observed them, is not really crazy, when you think about it coolly and logically. I haven't seen any evidence in my life that can convince me either way and I am comfortable with that ambiguity.
There is a vast difference between life out there somewhere and life out there, that's intelligent, can travel in space, is close enough to visit, and can visit without being obvious about it.
Suppose there were 1 trillion intelligent civilizations spanning 2,000,000 light years wide civilizations in the observable universe right now. Observable universe has a radius of ed: ~78 billion light years. 4/3 pi * r ^3 = ~2 * 10 ^ 33 cubic light years. Where those 1 billion civilizations would cover 4/3 * pi * (2,000,000/2) ^3 * 1 trillion = 4.19 * 10 ^ 30 cubic light years. End result we would have (2e33/4.19e30) = less than 1% chance of being in the area of even one of them.
PS: Sure it's a silly example, but space is ridiculously huge. If assume there was 1 billion billion billion civilisations as advanced as us (as in radio at current power levels) and chances are we would not detect any of them.
