In this eccentric collection of essays, edited by the theoretical physicist Jim Al-Khalili, scientists consider our search for extraterrestrial life. … cosmologist Martin Rees notes that our best hope for interstellar travel isn’t as humans, who don’t live very long and require far too much fuel to get very far, but as post-humans, who will have made the Kurzweilian transition from organic to inorganic, from decaying mortals to silicon-based, eminently portable machines. He adds that alien intelligence, if we ever detect it, will also be in this form.