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.

Visit the ghostly villages surrounding Chernobyl (abandoned by humans after the 1986 nuclear disaster), travel to remote islands off the coast of Maine to search for abandoned towns that have vanished from view in only a few decades, then head beneath the streets of New York to see how subway tunnels may become watery canals. A visual journey, LIFE AFTER PEOPLE is a thought provoking adventure that combines movie-quality visual effects with insights from experts in the fields of engineering, botany, ecology, biology, geology, climatology, and archaeology to demonstrate how the very landscape of our planet will change in our absence.

Ron Mann investigates the miraculous, near-secret world of fungi. Visionaries Gary Lincoff and Larry Evans lead us on a hunt for the wild mushroom and the deeper cultural experiences attached to the mysterious fungi. The oldest and largest living organisms recorded on Earth are both fungi. And their use by a new, maverick breed of scientists and thinkers has proven vital in the cleansing of sites despoiled by toxins and as a "clean" pesticide, among many other environmentally friendly applications. Combining material filmed at the Telluride Mushroom Fest with animation and archival footage, along with a neo-psychedelic soundtrack by The Flaming Lips, this film opens the doors to perception, taking the audience on an extraordinary trip where the fungi might well guide humanity to a saner, safer place.

Filmmaker Jonathan Reiss offers a multilingual look at the evolution of graffiti in a documentary that begins by examining ancient rock paintings and traces the trend straight through to the works of Picasso and 1970s-era New York City hip-hop culture. Shot on five continents using guerilla filmmaking techniques, Bomb It aims to give viewers a newfound appreciation of graffiti culture by exploring the origins of street art and interviewing the artists about their tactics and motivations.

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.