“This text examines the myriad challenges of developing quantum gravity theories by considering the conceptual development of time and background dependence. … Recommended. Graduate students, researchers, and faculty.” (E. Kincanon, Choice, Vol. 55 (11), July, 2018)<br />“From a very special perspective, this book presents a well-versed discussion of quantum gravity programs and, respectively, their problems. … the text begins with a ‘largely theory-free conceptual outline of time and clock concepts, alongside notions of space, length-measuring devices, spacetime and frames’. … it has enough room to trace the Problem of Time facets back to more basic and well-known temporal concepts.” (Horst-Heino von Borzeszkowski, zbMATH 1394.81007, 2018)<br />