Malcolm Longair, CBE, FRS, FRSE is Jacksonian Professor Emeritus of Natural Philosophy and Director of Development, Cavendish Laboratory. He has held many highly respected positions within the fields of physics and astronomy. He was appointed the ninth Astronomer Royal of Scotland in 1980, as well as the Regius Professor of Astronomy, University of Edinburgh, and the Director of the Royal Observatory, Edinburgh. He was head of the Cavendish Laboratory, the Physics Department of Cambridge University, from 1997 to 2005. He has served on and chaired many international committees, boards and panels, working with both NASA, the European Space Agency and the ERC. He has received much recognition for his work over the years. His main research interests are in high energy astrophysics, astrophysical cosmology and the history of physics and astrophysics. He has chaired numerous committees for specific science projects, including the Planck and Euclid missions of ESA. His major books, in addition to the present volume, include Theoretical Concepts in Physics (3rd edition 2020), High Energy Astrophysics (3rd edition 2011), Quantum Concepts in Physics (2013), the Cosmic Century: A History of Astrophysics and Cosmology (2008) and Maxwell's Enduring Legacy: A Scientific History of the Cavendish Laboratory (2016).