Watch: Martin Rees - What Would Intelligent Aliens Mean? (
Do intelligent aliens exist? Who knows? But here's what we do know: the potential existence of intelligent aliens probes meaning and purpose in the universe. What would it mean if the universe were teeming with life? What would it mean if we humans were alone?

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Martin John Rees, Baron Rees of Ludlow is a British cosmologist and astrophysicist. He served as Astronomer Royal and Master of Trinity College, Cambridge. Rees was President of the Royal Society.

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