In the fourth episode, Professor Marcus du Sautoy concludes his investigation into the history of mathematics with a look at some of the great unsolved problems that confronted mathematicians in the 20th century. After exploring Georg Cantor's work on infinity and Henri Poincare's work on chaos theory, he sees how mathematics was itself thrown into chaos by the discoveries of Kurt Godel and Paul Cohen, before completing his journey by considering some unsolved problems of maths today, including the Riemann Hypothesis.

Take an express journey to the edge of the universe as the filmmakers use computer-generated animation to build on images captures by the Hubble Telescope. The animation and story telling absolutely wonderful. Beginning on planet Earth, viewers are hurtled into the deepest reaches of space. There are no stops on this flight, and along the way the mysteries of the universe come alive as we examine the history and science of distant celestial.

Irena Salina's award-winning documentary investigation into what experts label the most important political and environmental issue of the 21st Century - The World Water Crisis. Salina builds a case against the growing privatization of the world's dwindling fresh water supply with an unflinching focus on politics, pollution, human rights, and the emergence of a domineering world water cartel. Interviews with scientists and activists intelligently reveal the rapidly building crisis, at both the global and human scale, and the film introduces many of the governmental and corporate culprits behind the water grab, while begging the question "CAN ANYONE REALLY OWN WATER?" Beyond identifying the problem, FLOW also gives viewers a look at the people and institutions providing practical solutions to the water crisis and those developing new technologies, which are fast becoming blueprints for a successful global and economic turnaround.

To our medieval forebears the world could appear mysterious, even enchanted. Sightings of green men, dog heads and alien beings were commonplace. The world itself was a book written by God. But as the Middle Ages grew to a close, it became a place to be mastered, even exploited.

Leading authority on the Middle Ages, Professor Robert Bartlett, presents a series which examines the way we thought during medieval times. In the second episode, Bartlett unearths remarkable evidence of the complex passions of Medieval men and women. The Church preached hatred of the flesh, promoted the cult of virginity and condemned woman as the sinful heir to Eve. Yet this was the era that gave birth to the idea of romantic love.

David Attenborough reveals the surprising truth about the cold-blooded lives of reptiles and amphibians. These animals are as dramatic in combat, as colourful in their communication and as tender in their parental care as any other animals. Join giant courting crocodiles, jousting tortoises and bright red sumo-wrestling frogs in their sophisticated, solar-powered lives.