British physicist Stephen Hawking says aliens are out there, but it could be too dangerous for humans to interact with extraterrestrial life.
Hawking claims in a new documentary titled "Into the Universe With Stephen Hawking" that intelligent alien life forms almost certainly exist — but warns that communicating with them could be "too risky."
"We only have to look at ourselves to see how intelligent life might develop into something we wouldn’t want to meet," Hawking said. "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 colonize whatever planets they can reach.”
The 68-year-old scientist said a visit by extraterrestrials to Earth might well be like Christopher Columbus arriving in the Americas, "which didn't turn out very well for the Native Americans."
He speculated that most extraterrestrial life would be similar to microbes, or small animals. Microbial life might exist far beneath the Martian surface, where liquid water is thought to trickle through the rock. Marine creatures might also conceivably live in huge oceans of water beneath a miles-thick layer of ice on Europa, a moon of Jupiter.
But if a scientific census could be extended beyond our solar system to the rest of the Milky Way and beyond, the odds in favor of life's existence rise dramatically, Hawking said.
"To my mathematical brain, the numbers alone make thinking about aliens perfectly rational," he said. “The real challenge is to work out what aliens might actually be like."
Hawking said an attack by interstellar predators is just one of the dismaying possibilities in the search for intelligent life beyond Earth. Another possibility is that intelligence itself might be inimical to life. Hawking pointed out that humanity has put itself on the edge of its own destruction by creating nuclear bombs and other weapons of mass destruction.
"If the same holds for intelligent aliens, then they might not last long," he said. "Perhaps they all blow themselves up soon after they discover that E=mc2. If civilizations take billions of years to evolve, only to vanish virtually overnight, then sadly we've next to no chance of hearing from them."
Hawking has become one of the world's best-known scientists — not just because of his theoretical work on cosmology and black holes, but also because he has achieved so much while coping with a paralyzing neural disease for most of his life. In recent years he has become a prominent advocate for space travel, contending that humans must journey into the heavens and going through zero-gravity training himself.
"Into the Universe With Stephen Hawking" had its television premiere in the United States on the Discovery Channel on Sunday, and is due for broadcast in Britain next month.
This report includes information from The Associated Press and msnbc.com.