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.

SETTING: 72 million years ago, near present-day Montana. As a young male daspletosaurus, it's Das' job to herd unsuspecting prey towards the rest of the pack. But he's easily distracted and ruins several hunts getting him in deep trouble with his mother, the pack leader. When a volcano threatens, the dinosaurs are unprepared.

It is one of the most unnerving discoveries in space science - that most of the universe is missing. We live in a material world, so instinctively we know what normal matter is - the world around us, the planets, stars and interstellar dust. But scientists currently estimate that 95 per cent of everything in the universe is actually - one way or another - invisible.
Some of this is ordinary matter that we just can't easily see. But there's also stuff that's much more weird. For instance, there's a new kind of matter we think is out there, but whose very existence is still largely hypothetical - dark matter. And most mysteriously of all, scientists think there is an unknown form of energy pervading the universe that we know so little about, all it has so far is a name - dark energy. Embark on a tour of this invisible universe, and shows how its existence - or lack of it - will define the fate of the entire universe.

The documentary is about the effect of fossil fuels on issues such as global warming, the environmental crisis, society and the questionable practices of oil companies. It examines the interconnection of human domination of the planet and the use of petroleum, and offers solutions for how we can stop our progression down this destructive path. Written and directed by James Jandak Wood. The film has several awards and nominations

Zachary Quinto embarks on a journey to understand how artificial intelligence may already be a threat to humanity. He visits Facebook headquarters where he learns about a failed AI experiment where two chat boxes created a language that only they could understand. Zach also gets a firsthand look at the world's latest technology, including life-like dolls programmed with advanced AI, robots that learn and communicate telepathically, highly intelligent drones of war, and Uber self-driving cars.

From small viscous meat eaters to vegetarian giants, dinosaurs came in all shapes and sizes. Remarkable new evidence suggests that one dinosaur did not become extinct but evolved into a new animal species we all know today. Discover the missing link between the velociraptor and modern day birds.