Luis Walter Alvarez’s career was marked by two explosions. The first was one the physicist enabled: a plutonium bomb, whose design he oversaw, destroyed the Japanese city of Nagasaki in August 1945. The second was one he theorised: the terrestrial impact 65m years ago of an asteroid sufficiently powerful to drive the dinosaurs to extinction. It may be for the asteroid theory—developed alongside his son and widely accepted after his death—that Alvarez is best remembered, rather than his groundbreaking contributions to the Manhattan Project.