I was watching a newborn in a baby carriage at a café. I was startled to realize I’m nearly a half century older than that human. What will life be like for her or him? And what will life be like in two centuries? Sir Martin Rees is happy to help us think ahead. The eminent astronomer is a professor emeritus at the University of Cambridge and Astronomer Royal for the U.K. His new book, On the Future, takes readers on a wide-ranging exploration of what may lie ahead for the human species—as well as what may replace us, including cyber species and artificial intelligence.

We’re deep into the “Anthropocene,” the era when humans are the dominant force shaping earth’s environment, and Rees goes over some of the challenges, such as population growth, climate change—and, well, avoiding extinction. But it’s in the second half of the book that Rees’s intellect and imagination truly take wing. Will the dramatic advances humans have already achieved in technology lead to machines with the same biological-level complexity we have enjoyed? Will the “people” living on Mars be people at all? He’s also at his best discussing aliens and the culture gap we’d face, if we ever were to encounter them. Still, “They may come from planet Zog and have seven tentacles; they may be metallic and electronic. But they would be made of similar atoms to us; they would (if they had eyes) stare out at the same cosmos.” His theme of connection and common origin, not only between life forms on earth but also linking everything in the cosmos, feels reassuring and timely. —KDW