World renowned scientist Stephen Hawking believes extraterrestrial life almost certainly exists -- and humans should be extremely cautious about interacting with it.
"To my mathematical brain, the numbers alone make thinking about aliens perfectly rational," Hawking says in a new Discovery Channel series called Stephen Hawking's Universe. "The real challenge is to work out what aliens might actually be like."
He suggests that aliens might simply raid Earth for its resources and then move on: "We only have to look at ourselves to see how intelligent life might develop into something we wouldn't want to meet. I imagine they might exist in massive ships, having used up all the resources from their home planet. Such advanced aliens would perhaps become nomads, looking to conquer and colonise whatever planets they can reach."
He concludes that trying to make contact with alien races is "a little too risky". He said: "If aliens ever visit us, I think the outcome would be much as when Christopher Columbus first landed in America, which didn't turn out very well for the Native Americans."
Previously, Hawking has argued that humans must colonize space in order to survive and thrive. "Sooner or later disasters such as an asteroid collision or a nuclear war could wipe us all out," he told Britain's Royal Society in a 2006 speech. "But once we spread out into space and establish independent colonies, our future should be safe."