Watch Stephen Hawking's Universe

Still searching for cosmic answers, Professor Hawking says:"Twenty years ago, I said there was a 50/50 chance we would have a complete picture of the universe in the next 20 years.That is still my estimate today, but the 20 years starts now." Where is the search headed now?

Professor Stephen Hawking is sure that the universe began with a Big Bang - but, like other cosmologists, he is much less certain about what will become of it. In order to find out its fate, scientists must discover how much invisible dark matter there is in the universe.

John Wheeler, Professor of Physics at Princeton University, is one of the greatest figures of 20th-century science. Now in his 80s, he recalls how he invented the vivid phrase that went on to capture the imagination of science fiction writers: black holes.

"The world around us is full of variety: different materials, different textures. How did they all arise?" Professor Hawking answers these questions and shows us how the complex universe we live in had its origin in the Big Bang.

For thousands of years, people have wondered about the universe. Did it stretch out forever or was there a limit? And where did it come from? Professor Stephen Hawking examines conflicting arguments about the origin of the universe and traces his own role in The Big Bang theory.

Stephen Hawking begins our journey through cosmology, tracing the history of astronomical theories and technology. In this episode, the Earth shifts from Ptolemy's centre of the universe to what Professor Hawking describes as an orbit around an average-sized sun - one among millions of stars.