Melvyn Bragg and his guests discuss the science of matter and the states in which it can exist. Most people are familiar with the idea that a substance like water can exist in solid, liquid and gaseous forms. But as much as 99% of the matter in the universe is now believed to exist in a fourth state, plasma. Today scientists recognise a number of other exotic states or phases, such as glasses, gels and liquid crystals - many of them with useful properties that can be exploited. With: Andrea Sella Professor of Chemistry at University College London Athene Donald Professor of Experimental Physics at the University of Cambridge Justin Wark Professor of Physics and Fellow of Trinity College at the University of Oxford Producer: Thomas Morris.