Let us think for a moment about alien, regarding possibility...

Let us think for a moment about alien, regarding possibility of the existence of other civilization beyond our dear planet earth. We probably conclude that it's all just hoax, or some rumors issued by ruling government for some purpose. Now, we can contemplate a bit about it by asking this simple rhetorical question, 'How could possibly people be able to think about something unknown, which have never been popped out in human minds at all?'