A journey through the cosmos in search of alien life. We seek out planets around distand stars and dive into the oceans of other worlds - seeking an answer to the question: is there anybody out there?

We float along the river of time. But does that river have a source? Where did time come from? Some believe time and space are one thing, and the Big Bang started the cosmic clock. Others believe the universe existed for almost half a million "years" before light could move and time began. Still others say time is older than our universe. But what if time itself is an illusion? Incredible new experiments may hold the answer. One groundbreaking experiment gives us the power to punch holes in time…and another may create a machine that operates outside time’s boundaries!

The final part examines political revolution and how art was at the forefront of throwing out 1,000 years of royal rule, from its earliest revolutionary days of enthusiasm and optimism when painting died, the poster was king and the machine-made triumphed over the handmade to the dead hand of Socialist Realism. Andrew roots out great portraits of Stalin now hidden in museum storerooms and never on public view, looks at the transformation of the Moscow metro into a great public art gallery and visits the most stunning creation of post-war Communist rule, the Space Monument. Finally, he comes to the confusion and chaos of Russia today and how it is producing some of the world's strangest art - from heroic sculptures of Russian leader Vladimir Putin to the insides of a giant erotic apple; from the recreation of the Imperial royal family facing the firing squad to sculpture in liquid oil; from Russia's embrace of the commercial art market to a return to Socialist Realism. Russia seems to stand on another brink of revolution.

We move around in space, but we are stuck in a prison of time moving ever forwards. Einstein said, 'The distinction between past, present and future is only a stubbornly persistent illusion.' Is our experience of the ticking clock merely a trick of the mind? Could science ever make the clock move backwards? Experiments in quantum physics are showing that the future influences the present: what happens later limits the choices we think we have now. The laws of physics say visiting or talking to ourselves in the past is possible – but changing history once we get there is not.

A group of Egyptian revolutionaries battle leaders and regimes, risking their lives to build a new society. The Egyptian Revolution has been an ongoing rollercoaster over the past two and a half years. Through the news, we only get a glimpse of the bloodiest battle, an election, or a million man march. At the beginning of July 2013, we witnessed the second president deposed within the space of three years. The Square is an immersive experience, transporting the viewer deeply into the intense emotional drama and personal stories behind the news. It is the inspirational story of young people claiming their rights, struggling through multiple forces: from a brutal army dictatorship willing to crush protesters with military tanks, to a corrupt Muslim Brotherhood using mosques to manipulate voters. Directed by Jehane Noujaim, the film was nominated for the Academy Award and also won three Emmy Awards.

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.