What Did Stephen Hawking Think About Aliens?

Stephen Hawking believed that alien life almost certainly exists, but he was famously cautious, even alarmed, about the idea of humanity actively trying to make contact. His position combined scientific optimism about life with a hard-headed warning about the risks.

Life is probably out there

Given the sheer size of the universe, with its hundreds of billions of galaxies each containing hundreds of billions of stars, Hawking thought it would be surprising if Earth were the only place where life had arisen. He considered the existence of microbial life elsewhere highly likely, and intelligent life entirely possible. He supported the scientific search for it, lending his name to the Breakthrough Listen initiative, which scans the skies for signals.

But contact could be dangerous

Where Hawking diverged from the more hopeful voices was on the question of whether we should try to announce ourselves. He warned repeatedly against broadcasting our location to the cosmos. His reasoning drew on human history: when a technologically advanced civilisation has encountered a less advanced one on Earth, the result has rarely been good for the less advanced party. An alien civilisation capable of reaching us, he argued, would by definition be far ahead of us, and we could not assume it would be friendly. We might, he suggested, be wiser to listen quietly than to shout.

A characteristic balance

Hawking's view on aliens captures something typical of his thinking: a willingness to take a bold, imaginative possibility completely seriously, paired with a sober assessment of the risk. It is closely related to his wider concern for the survival of humanity and his belief that we should be thoughtful about powerful forces, whether alien civilisations or artificial intelligence, before we summon them. Whether his caution was justified remains, of course, untested.