Dark energy - the mysterious force that is unexpectedly causing the universe's expansion to speed up. The effects of dark energy were discovered in 1998 but physicists still don't know what it is. Worse, its very existence calls into question Albert Einstein's general theory of relativity - the cornerstone of modern physics. The hunt for the identity of dark energy is on". Experiments on earth and in space generate data that might provide a clue, but there are also hopes that another Einstein might emerge - someone who can write a new theory explaining the mystery of the dark energy.

In episode two, Professor Brian Cox is off to India, where he assesses arguably the first evidence of rational thought in literature, the poetry of the Vedic monks. They pondered mankind's origins, realising there must have been a day with no yesterday - a day of creation - prompting the age-old question of where did the universe come from? Brian marvels that the universe seems to follow a set of rules, the laws of physics, allowing space to be considered on the grandest scale, travelling to the most distant, farthest reaches of the cosmos just by using our minds. Brian also visits Japan, and offers viewers the idea that man lives in just one of an infinite number of universes that are being made all the time.

Beginning with the origins of the universe in the Big Bang, Sagan describes the formation of different types of galaxies and anomalies such as galactic collisions and quasars. The episodes moves further into ideas about the structure of the Universe, such as different dimensions (in the imaginary Flatland and four-dimensional hypercubes), an infinite vs. a finite universe, and the idea of an oscillating Universe (similar to that in Hindu cosmology). The search into other ideas such as dark matter and the multiverse is shown, using tools such as the Very Large Array in New Mexico. Cosmos Update shows new information about the odd, irregular surfaces of galaxies and the Milky Way perhaps being a barred spiral galaxy

It is one of the most baffling questions that scientists can ask: how big is the Universe that we live in? Follow the cosmologists who are creating the most ambitious map in history - a map of everything in existence. And it is stranger than anyone had imagined - a Universe without end that stretches far beyond what the eye can ever see. And, if the latest research proves true, our Universe may just be the start of something even bigger. Much bigger.

On a trip to the fortified Moroccan village of Ait-Ben-Haddou in the Atlas Mountains, Professor Brian Cox reveals how by watching the stars' motion across the night sky, it is quite natural for man to think he is at the centre of everything. That view was held for many ages, but innate human curiosity has eventually led to an understanding of mankind's true place in space and time, and an appreciation that Earth is not a focal point but a mere particle of rock in a possibly infinite expanse of space, 13.8 billion years from the beginning of the universe.

Inspired by the Southern Sky as he travels Australia, Brian reveals our very latest understanding about how the Universe began & how it will end.