The central premise of this series is that what the human eye can see is only a fraction of the vast amount of matter and energy that exists out in the Universe: our best estimate is that more than 99% of all the stuff that’s out there is hidden in the dark. So how do we know it’s there? 　　E1 Light: Professor Jim Al-Khalili tells the story of how we used light to reveal the cosmos. 　　E2 Dark: Prof Jim Al-Khalili investigates the 99 per cent of the cosmos that is hidden in the dark. 　　via: 　　http://www.jimal-khalili.com/blog/light-and-dark-bbc4.html 　　http://www.bbc.co.uk/programmes/p01k4ykj