Biographical note

​Roger A. Freedman is a Lecturer in Physics at the University of California, Santa Barbara, USA. At UCSB, Dr. Freedman has taught in both the Department of Physics and the College of Creative Studies, a branch of the university intended for highly gifted and motivated undergraduates. He has published research in nuclear physics, elementary particle physics, and laser physics. In recent years, he has helped to develop computer-based tools for learning introductory physics and astronomy and helped pioneer the use of classroom response systems and the "flipped" classroom model at UCSB. He is co-author of three introductory textbooks: University Physics (Pearson), Universe (Freeman), and Investigating Astronomy (Freeman).
Robert M. Geller teaches and conducts research in astrophysics at the University of California, Santa Barbara, USA. Using data from the Hubble Space Telescope, he is currently involved in a search for bursts of lights that are predicted to occur when a supermassive black hole consumes a star. Dr. Gellar also has a strong emphasis on education, and he received the Distinguished Teaching Award at UCSB in 2003. 
William J. Kaufman III (deceased) was the author of the first four editions of Universe. During his career he held positions at the Griffith Observatory in Los Angeles, San Diego State University, UCLA, Caltech, and the University of Illinois. A prolific author, his many books include Black Holes and Warped Spacetime, Relativity and Cosmology, The Cosmic Frontiers of General Relativity, Exploration of the Solar System, Planets and Moons, Stars and Nebulas, Galaxies and Quasars, and Supercomputing and the Transformation of Science. Dr. Kaufmann died in 1994.