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 universes that make up the "multiverse." In this show, Brian Greene takes us on a tour of this brave new theory at the frontier of physics, 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. Brian 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.

Join Brian Greene on a wild ride into the weird realm of quantum physics, which governs the universe on the tiniest of scales. Greene brings quantum mechanics to life in a nightclub like no other, where objects pop in and out of existence, and things over here can affect others over there, instantaneously and without anything crossing the space between them. A century ago, during the initial shots in the quantum revolution, the best minds of a generation—including Albert Einstein and Niels Bohr—squared off in a battle for the soul of physics. How could the rules of the quantum world, which work so well to describe the behavior of individual atoms and their components, conflict so dramatically with the everyday rules that govern people, planets, and galaxies? Quantum mechanics may be counterintuitive, but it's one of the most successful theories in the history of science, making predictions that have been confirmed to better than one part in a billion, while also launching the technological advances at the heart of modern life, like computers and cell phones. But even today, even with such profound successes, the debate still rages over what quantum mechanics implies for the true nature of reality.

Time. We waste it, save it, kill it, make it. The world runs on it. Yet ask physicists what time actually is, and the answer might shock you: They have no idea. Even more surprising, the deep sense we have of time passing from present to past may be nothing more than an illusion. How can our understanding of something so familiar be so wrong? In search of answers, Brian Greene takes us on the ultimate time-traveling adventure, hurtling 50 years into the future before stepping into a wormhole to travel back to the past. Along the way, he will reveal a new way of thinking about time in which moments past, present, and future—from the reign of T. rex to the birth of your great-great-grandchildren—exist all at once. This journey will bring us all the way back to the Big Bang, where physicists think the ultimate secrets of time may be hidden. You'll never look at your wristwatch the same way again.

Space. It separates you from me, one galaxy from the next, and atoms from one another. It is everywhere in the universe. But to most of us, space is nothing, an empty void. Well, it turns out space is not what it seems. From the passenger seat of a New York cab driving near the speed of light, to a pool hall where billiard tables do fantastical things, Brian Greene reveals space as a dynamic fabric that can stretch, twist, warp, and ripple under the influence of gravity. Stranger still is a newly discovered ingredient of space that actually makes up 70 percent of the universe. Physicists call it dark energy, because while they know it's out there, driving space to expand ever more quickly, they have no idea what it is. Probing space on the smallest scales only makes the mysteries multiply. Down there, things are going on that physicists today can barely fathom—forces powerful enough to generate whole universes. To top it off, some of the strangest places in space, black holes, have led scientists to propose that like the hologram on your credit card, space may just be a projection of a deeper two-dimensional reality taking place on a distant surface that surrounds us. Space, far from being empty, is filled with some of the deepest mysteries of our time.