NPR: Physicist Brian Greene explains his theory regarding multiple, parallel universes, for National Public Radio, as spelled out in his latest book, The Hidden Reality: Parallel Universes and the Deep Laws of the Cosmos. Recent discoveries in physics and astronomy, he says, point to the idea that our universe may be one of many universes populating a grander multiverse. For the past 25 years, Greene has been studying string theory as a way of understanding those multiverses.