Stephen Hawking has advice for avoiding the apocalypse

Stephen Hawking worries that humanity sometimes seems like a bunch of schoolyard bullies ... in a schoolyard littered with loaded machine guns and land mines. "Since civilization began, aggression has been useful inasmuch as it has definite survival advantages," the world's most famous cosmologist told the UK Times. "Now, however, technology has advanced at such a pace that this aggression may destroy us all by nuclear or biological war." Hawking says logic and reason must act as safeties on the triggers of such apocalyptic weapons. Besides catastrophic war, he also worries about climate change, mass extinctions and unchecked artificial intelligence, as he's mentioned before.