Tom Kibble is Senior Research Fellow and Emeritus Professor of Theoretical Physics at Imperial College London, and a Fellow of the Royal Society. He has published many articles on theoretical particle physics and cosmology. Frank Berkshire is also at Imperial College London. He is Senior Lecturer and Director of Undergraduate Studies in the Department of Mathematics, and has published on dynamical systems, waves and fluids. He was elected as Imperial College Teaching Fellow in 1996. Both authors have long experience of lecturing to physics and applied mathematics students.