When I came across Roger Penrose's new book, Cycles of Time: An Extraordinary New View of the Universe, I just had to read it, having twice heard him speak on the slightly wacky topic of Conformal Cyclical Cosmology (CCC). CCC is the idea that the Universe may have undergone several cycles and proposed the controversial idea that information about the time before the Big Bang may still be present in the Cosmic Microwave Background today. In both of the talks I heard him give - about a year apart - he ended with the tantalising promise that observational evidence testing CCC theory could be just around the corner.
Perhaps the best introduction I can give to this book is to link to a recording of Penrose speaking on the subject. This talk is from 2005, several years earlier than the talks I heard him give in which he promised observational results. Alas, I do not have recordings of either of those.
The book expands upon the ideas that Penrose speaks about and is able to present them at greater length, which makes it easier to follow than the talks. Mathematical details are included, but mostly kept confined to detailed appendices, with references for the reader who desires to pursue the topic in depth.
Penrose's bold idea brings together several topics in physics: entropy, black holes, particle physics and cosmology, all of which are explored in the book. He closes by explaining exactly how cosmological observations could provide a physical test for his theory. As I spend my days in an environment in which people play with toy mathematical models or hammer out the details of string theory without too much concern for the real world, I find it refreshing to see a theorist giving serious thought to the testability of his theory.