The central premise of this series is that what the human eye can see is only a small part of the vast amount of matter and energy present in the universe: our best estimate is that over 99% of the matter in the universe is hidden in darkness. So how do we know where it is? E1 Light: Professor Jim Al Khalili taught us how to use light to reveal the story of the universe. E2 Darkness: Professor Jim Al Khalili studied 99% of the universe hidden in darkness. By: http://www.jimal-khalili.com/blog/light-and-dark-bbc4.html http://www.bbc.co.uk/programmes/p01k4ykj