Accompany physicist and acclaimed author Brian Greene on a mind-bending reality check and journey to the frontiers of physics to see how scientists are piecing together the most complete picture yet of space, time and the universe. Hard as it is to swallow, cutting-edge theories are suggesting that our universe may not be the only universe. Instead, it may be just one of an infinite number of worlds that make up the multiverse. Brian Greene takes us on a tour of this brave new theory at the frontier of physics, explaining why scientists believe it's true and showing what some of these alternate realities might be like. Some universes may be almost indistinguishable from our own; others may contain variations of all of us, where we exist but with different families, careers and life stories. In still others, reality may be so radically different from ours as to be unrecognizable. Greene reveals why this radical new picture of the cosmos is getting serious attention from scientists. It won't be easy to prove, but if it's right, our understanding of space, time and our place in the universe will never be the same.