Melvyn Bragg and guests discuss plasma, the fourth state of matter after solid, liquid and gas. As over ninety-nine percent of all observable matter in the Universe is plasma, planets like ours, with so little plasma and so much solid, liquid and gas, appear all the more remarkable. On the grand scale, plasma is what the Sun is made from and, when we look into the night sky, almost everything we can see with the naked eye is made of plasma. On the smallest scale, here on Earth, scientists make plasma to etch the microchips on which we rely for so much. Plasma is in the fluorescent light bulbs above our heads and, in laboratories around the world, it is the subject of tests to create, one day, an inexhaustible and clean source of energy from nuclear fusion.With Justin Wark Professor of Physics and Fellow of Trinity College at the University of OxfordKate Lancaster Research Fellow for Innovation and Impact at the York Plasma Institute at the University of Yorkand Bill Graham Professor of Physics at Queens University, BelfastProducer: Simon Tillotson.