Summary: The states in which matter can exist is a fascinating area of scientific enquiry. 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, such as glass, gels and liquid crystals - many of them with useful properties. Melyvn Bragg is joined by Andrea Sella, Professor of Chemistry at University College London; Athene Donald, Professor of Experimental Physics at the University of Cambridge and Justin Wark, Professor of Physics and Fellow of Trinity College at the University of Oxford.
