One of the world’s leading scientists makes the claim in a new television documentary series, beginning on the Discovery Channel next month.
Hawking says that in a universe with 100 billion galaxies, each containing hundreds of millions of stars, it is unlikely that earth is the only place where life has evolved.
“To my mathematical brain, the numbers alone make thinking about aliens perfectly rational,” he said, according to The Sunday Times.
Hawking says that they could be microbes – basic animals such as worms which have been on Earth for millions of years, but suggests that extraterrestrial life could develop much further.
“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 colonise whatever planets they can reach.”
The scientist, who is paralysed by motor neurone disease, warned that contact with alien life could spell disaster for the human race.
“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 American Indians.”
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