Stephen Hawking, Smartest Man Alive, Says We're Screwed

Renowned British astrophysicist Stephen Hawking says intelligent alien life-forms almost certainly exist, but trying to communicate with them is "too risky."

Their arrival, he says, would be like Columbus landing in the Americas, "which didn't turn out out very well for the Native Americans."

The 68-year-old Hawking speculates on alien life in a new documentary on the Discovery Channel in which says advance life-forms may be "nomads, looking to conquer and colonize."