For decades some have suspected that there might be others out there, intelligent beings capable of communicating with us, even visiting our world. It might sound like science fiction, but today scientists from across the globe are scouring the universe for signals from extraterrestrials. Horizon obtained exclusive access to film researchers at the Green Bank Telescope searching for radio signals from Tabby's Star, a star so mysterious that some scientists believe it might be surrounded by a Dyson Sphere, a vast energy collector built by advanced aliens.

On April 20, 2010, the Deepwater Horizon oil rig exploded in the Gulf of Mexico. It killed 11 workers and caused the worst oil spill in American history. The explosion still haunts the lives of those most intimately affected, though the story has long ago faded from the front page.
At once a fascinating corporate thriller, a heartbreaking human drama and a peek inside the walls of the secretive oil industry, 'The Great Invisible' is the first documentary feature to go beyond the media coverage to examine the crisis in depth through the eyes of oil executives, survivors and Gulf Coast residents who experienced it first-hand and then were left to pick up the pieces while the world moved on.

The film explores how artificial intelligence (AI) is catching up to us in ways once thought to be uniquely human: empathy, emotional intelligence and creativity. AI has the potential to reshape every aspect of our world – but most of us are unaware of what looms on the horizon. This documentary shows viewers what they need to know about a field that is advancing at a dizzying pace, often away from the public eye. Have AI the power to disconnect us from fellow humans? What does it mean when AI makes art? Can really AI interpret and understand human emotions? How is it possible that AI creates sophisticated neural networks that mimic the human brain?
The documentary includes interviews with global leaders, commentators and innovators from the AI field, including Geoff Hinton, Yoshua Bengio, Ray Kurzweil and Douglas Coupland, who highlight some of the innovative and cutting-edge AI technologies that are changing our world.

Horizon discovers what your cat really gets up to when it leaves the cat flap. In a groundbreaking experiment, 50 cats from a village in Surrey are tagged with GPS collars and their every movement is recorded, day and night, as they hunt in our backyards and patrol the garden fences and hedgerows. Cats are fitted with specially developed cat-cams which reveal their unique view of our world. You may think you understand your pet, but their secret life is more surprising than we thought.

Fourth episode examines how plants either share environments harmoniously or compete for dominance within them. Attenborough highlights the 1987 hurricane and the devastation it caused. However, for some species, it was that opportunity for which they had lain dormant for many years. The space left by uprooted trees is soon filled by others who move relatively swiftly towards the light. The oak is one of the strongest and longest-lived, and other, lesser plants nearby must wait until the spring to flourish before the light above is extinguished by leaves. Tropical forests are green throughout the year, so brute force is needed for a successful climb to the top of the canopy: the rattan is an example that has the longest stem of any plant. As its name suggests, the strangler fig 'throttles' its host by growing around it and cutting off essential water and light. Some can take advantage of a fallen tree by setting down roots on the now horizontal trunk and getting nutriment from the surrounding moss and the fungi on the dead bark. The mountain ash (eucalyptus regnans) grows so tall, that regeneration becomes a considerable problem. It is easily flammable, so its solution is to shed its seeds during a forest fire and sacrifice itself. It therefore relies on the periodic near-destruction of its surroundings in order to survive. Attenborough observes that catastrophes such as fire and drought, while initially detrimental to wildlife, eventually allow for deserted habitats to be reborn.

The Sky at Night looks back at the last ten years of astronomy and ponders the most significant milestones and revelations. With the help of six distinguished astronomers, Chris and Maggie consider the state of astronomy in 2020 and wonder what new, exciting discoveries await us across the rest of the decade, as a host of new ground and space telescopes come online. Astronomer Royal Lord Martin Rees is among the guests to walk along the Astronomical Wall of Discovery in this one-hour special.