Where did everything in our universe come from? How did it all begin? For nearly a hundred years, we thought we had the answer: a big bang some 14 billion years ago. But now some scientists believe that was not really the beginning; our universe may have had a life before this violent moment of creation. Take the ultimate trip into the unknown, to explore a dizzying world of cosmic bounces, rips and multiple universes, and finds out what happened before the big bang. Horizon takes the ultimate trip into the unknown, to explore a dizzying world of cosmic bounces, rips and multiple universes, and finds out what happened before the big bang.

The Pythagorian philosopher Plato hinted enigmatically that there was a golden key that unified all of the mysteries of the universe. It is this golden key that we will return to time and again throughout our exploration. The golden key is the intelligence of the logos, the source of the primordial om. One could say that it is the mind of God. With our limited senses we are observing only the outer manifestation of the hidden mechanics of self similarity. The source of this divine symmetry is the greatest mystery of our existence.

Particle physicist Prof. Brian Cox asks, 'What time is it?' It's a simple question and it sounds like it has a simple answer. But do we really know what it is that we're asking? Brian visits the ancient Mayan pyramids in Mexico where the Maya built temples to time. He finds out that a day is never 24 hours and meets Earth's very own Director of Time. He journeys to the beginning of time, and goes beyond within the realms of string theory, and explores the very limit of time. He discovers that we not only travel through time at the speed of light, but the experience we feel as the passing of time could be an illusion.

Professor Brian Cox travels from the fossils of the Burgess Shale to the sands of the oldest desert in the world to show how light holds the key to our understanding of the whole universe, including our own deepest origins. To understand how light holds the key to the story of the universe; you first have to understand its peculiar properties. Brian considers how the properties of light that lend colour to desert sands and the spectrum of a rainbow can lead to profound insights into the history and evolution of our universe. Finally, with some of the world's most fascinating fossils in hand, Brian considers how but for an apparently obscure moment in the early evolutionary history of life, all the secrets of light may have remained hidden. Because although the universe is bathed in light that carries extraordinary amounts of information about where we come from, it would have remained invisible without a crucial evolutionary development that allowed us to see. Only because of that development can we now observe, capture and contemplate the incredible wonders of the universe that we inhabit.

Do dolphins think the way we do or are their brains wired in a very different way from ours? Will we communicate with them one day? Dolphins have been a source of curiosity to humans and have appeared in our stories and myths for thousands of years. What is the link between our two species? Why do we seem to be so interested and curious about each other?

Blowing your mind, that's what Doctor Who's all about. What makes it all so fun is that while all this crazy science fiction is going on, there's actual facts. You've got space travel, you've got time travel, you've got regeneration. These are all the powerful themes of Doctor Who. And they're also the things that drive science forward.