The second part, Nothing, explores science at the very limits of human perception, where we now understand the deepest mysteries of the universe lie. Professor Jim Al-Khalili sets out to answer one very simple question - what is nothing? His journey ends with perhaps the most profound insight about reality that humanity has ever made. Everything came from nothing. The quantum world of the super small shaped the vast universe we inhabit today, and Jim can prove it.

Professor Diarmaid MacCulloch - one of the world's leading historians - reveals the origins of Christianity and explores what it means to be a Christian. In the first episode, he overturns the familiar story that it all began when the apostle Paul took Christianity from Jerusalem to Rome. Instead, he shows that the true origins of Christianity lie further east, and that at one point it was poised to triumph in Asia, maybe even in China. The headquarters of Christianity might well have been Baghdad not Rome, and if that had happened then Western Christianity would have been very different.

In the third part of his journey into the history of Christianity, Professor Diarmaid MacCulloch charts Orthodoxy's extraordinary fight for survival. After its glory days in the eastern Roman Empire, it stood right in the path of Muslim expansion, suffered betrayal by crusading Catholics, was seized by the Russian tsars and faced near-extinction under Soviet communism. MacCulloch visits the greatest collection of early icons in the Sinai desert, a surviving relic of the iconoclastic crisis in Istanbul and Ivan the Terrible's cathedral in Moscow to discover the secret of Orthodoxy's endurance.

In the fourth part of the series, Diarmaid MacCulloch makes sense of the Reformation, and of how a faith based on obedience and authority gave birth to one based on individual conscience. He shows how Martin Luther wrote hymns to teach people the message of the Bible, and how a tasty sausage became the rallying cry for Swiss Reformer Ulrich Zwingli to tear down statues of saints, allow married clergy and deny that communion bread and wine were the body and blood of Christ.

Africa's wildest river is home to the most spectacular wildlife. Hippos fight for territory while herds of elephant, water buffalo and zebra depend on it for life. In the wet season the rains burst the riverbanks and everyone, including people, must move whilst fish swim through the villages. In the dry season the creatures fight over the few pools of water while predators prowl. At its heart it plunges over Victoria Falls and into wild ravines before draining into the Indian Ocean, where storm clouds cycle the water back into the heart of Africa.

Documentary-maker David Malone delves into the secrets of ocean waves. In an elegant and original film he finds that waves are not made of water, that some waves travel sideways and that the sound of the ocean comes not from water but from bubbles. Waves are not only beautiful but also profoundly important, and there is a surprising connection between the life cycle of waves and the life of human beings.