“It takes one to know one”—this schoolyard retort has thus far guided the search for extraterrestrial intelligence (SETI), and the belief is reinforced by countless science-fiction portrayals of aliens as humanoids. Is it possible that cosmic evolution has converged on bipedal, big-headed forms looking somewhat like us and having their run of a bevy of Earth-like planets? If so, where are they? Why haven’t they, like us, broadcast their presence across the electromagnetic spectrum, contacting their brothers across the stars and mitigating our cosmic loneliness?

I ponder these questions and more in my new book, Cosmic Apprentice: Dispatches from the Edges of Science.

SETI is complicated by the fact that intelligence is multiple and the possibility  that the search for extraterrestrial intelligence is a replacement for religion in a secular age. Instead of believing in a god who made us in his image, we are on the lookout for aliens who have evolved an advanced technical civilization on the human model.

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Read an excerpt from Chapter 9 of Cosmic Apprentice.