During the 1970s Alan Guth helped start a cosmological revolution. Oddly, it has gone largely unnoticed outside professional science, despite the fact that it has scientific, philosophical, and theological implications every bit as mind-boggling as Einstein's revolution of seventy years ago. The idea looks boring, at first. There are certain technical problems with the 'standard' Big Bang theory. So Guth and others develop the idea that the universe underwent 'inflation'-expanding many times faster than the standard theory allows in the first fraction of a fraction of a second of time. This hypothesis, with its fishy, rather ad hoc air, solves the technical problems. But in fact it solves so many problems, and with such spooky neatness, that physicists start to suspect it might be true. As physicists will, they invent an expensive satellite-based experimental test. And the experimental result maps the theory's predictions exactly. By this time, the theory's originators have started to see that this newly confirmed theory has some very, very bizarre consequences. One is that the observable universe (the bubble, radius about 15 billion light years, that we can observe, and which most people confuse with the universe itself) must in fact bear about the same relation to the whole universe as a grain of dust does to the Earth. Another is that this unobserved greater "universe" is, in turn, almost certainly just a "bubble universe" within a creation that is incomprehensibly many orders of magnitude larger and older. Popular science, like liquor, comes in many strengths, and this one is not for the faint of kidney. Although wonderfully lucid (given the subject matter), and charmingly self-deprecating, it tells the recent history of cosmology seriously, carefully, and with a real mission to teach the hard stuff. The result is some long chapters on some very difficult ideas. Magnetic monopoles, false vacuums, and quantum tunnelling in the Higgs field are especially hard on the cranial muscles. But Guth knows what he is doing. One of the best things about the book is the clear explanation of how very speculative theories really are rooted in observation-of how, for example, it's possible to test and judge competing views of what happened 10-to-the-minus-37 seconds after God snapped his fingers. On top of the long, intricate main text, this book has lots of footnotes and four appendices. I guzzled the lot-and I still don't understand energy density in the Higgs field. But if there's a prize for the decade's best science book for the general reader, this should be on the short list.