For those who were intimidated by Hawking's previous book, A Brief History of Time (famous for being a best-seller that few people actually read), this book may prove easier going. It consists of 13 pieces written between 1976 and 1992, and although most are based on university lectures, they are all written in a concise and very readable style.
Hawking may be the most famous living cosmologist, and much of his fame stems from his physical condition, which he candidly discusses in the first few chapters. As a student at Cambridge, he was diagnosed with the degenerative neural disease amyotrophic lateral sclerosis (also known as Lou Gehrig's disease), and given only a few years to live. That was almost 40 years ago. He is now confined to a wheelchair, communicating by a computerized voice synthesizer operated by the movement of one finger.
Ironically, the fact that Hawking's muscles no longer work has freed his mind to investigate the physics that makes the cosmos work. The remaining chapters take us on a mental journey from the Big Bang (matter appearing from nowhere) to black holes (matter disappearing back into nowhere) -- both being singularities, places where the standard laws of physics break down. Hawking describes how the theory of quantum mechanics led him to realize that black holes actually give off what is now known as Hawking Radiation, and must gradually evaporate. Curiously, as the size and mass of a black hole decrease, its temperature and radiation increase dramatically; the final instant of evaporation would be a "tremendous explosion," producing a "massive outpouring of high-energy gamma rays." I wonder if this could be the source of the mysterious gamma ray bursts that are now being detected.
The book's final chapter is the transcript of a radio interview Hawking did for the BBC's Desert Island Discs. The interviewer makes the insightful comment that Hawking is "already familiar with the isolation of a desert island, cut off from normal physical life and deprived of any natural means of communication." Hawking resists the notion, and perhaps, in the big picture, he is no more isolated than the rest of humanity. We are all castaways on this island Earth.