Sagan's team created the greatest puzzle of all time, which you can only solve if your species understands the basic nature of the universe.

“I believe extraterrestrial intelligence (in AI form) could be concealed under the lunar surface," Alex Ellery told Newsweek.

Avi Loeb has suggested that humans themselves may be 'intelligent, self-replicating and self-repairing autonomous probes' built by an advanced alien civilisation, arguing in a new essay published ...