Our improving understanding of the cosmos points to an early epoch during which the universe expanded at a stupendous rate to create the vast amount of space we can observe. Cosmologist are now coming to believe that this "cosmic inflation" may do much more: in many versions, inflation goes on forever, generating not just our observable universe but also infinitely many such regions with similar or different properties, together forming a staggeringly complex and vast "multiverse". Dr. Anthony Aguirre (University of California at Santa Cruz) traces the genesis of this idea, explores some of its implications, and discusses how scientists are seeking ways to test this idea. Recorded May 18, 2011.