In late 2017, scientists at a Hawaiian observatory glimpsed an object soaring through our inner solar system, moving too fast along a strange orbit to be an asteroid. Could it have been a piece of advanced technology created by a distant alien civilization? Quite possibly, suggests Harvard astronomer Avi Loeb, who outlines his controversial theory and its profound implications: for science, for religion, and for the future of our species and our planet.

"Loeb is one of the more imaginative and articulate scientists around…. Half memoir, half soaring monologue."—New York Times