My favorite popular physics book happens to be Prof. Zee's own _An Old Man's Toy_. I found that book more enlightening than (the likewise excellent) books by Brian Greene or Michio Kaku, for example. _Toy_ is infused with physical insight and clear writing. This unique textbook from Prof. Zee reads much like _Toy_ but with all the added mathematics. Thus, it imparts that same physical insight but this time backed by the underlying mathematical and scientific details. The result is a textbook that's humorous, playful, and authoritative mixed with equal parts irreverence, verve, and gusto. Learning general relativity has never been so fun.
And funny, I might add. There are lots of excellent textbooks on general relativity. Professor Zee's new offering differs from all of them, however, in that he takes a lighthearted approach to the subject without sacrificing rigor or thoroughness. Passages describing light following a least time principle because light isn't "stupid" enough not to and dutifully informing us that "After Lagrange invented the Lagrangian, Hamilton invented the Hamiltonian" made me break out laughing. The book abounds with dry humor and witticisms. His introduction of the action principle is particularly mirthful.
But for all the comedy, the book is thorough. One example is the treatment of Hawking radiation. It's as complete as I've seen in other relativity textbooks and even Raine and Thomas's textbook on specifically black holes. Another example is the emphasis on the action principle. For that Prof. Zee discusses the background variational calculus and derives in detail the familiar Euler-Lagrange equation; I mention this only because these steps are often omitted in books on more advanced subjects that assume knowledge of the action principle. There's also a discussion on the relativistic relationship between electricity and magnetism. Some electromagnetism texts, such as Purcell, Schwartz, or Ohanian, perform this derivation in one form or another (I happen to think this is how electromagnetism should be taught), but I haven't seen many general relativity texts step outside their usual confines to broach this subject. I suspect Dr. Zee did so because it beautifully illustrates the symmetry and unification of physics that he has eloquently written about previously. And the last 100 pages or so touch on peripheral topics found also in quantum field theory and string theory, such as Kaluza-Klein theory, Yang-Mills theory, branes, and twistors. A discussion on quantum gravity is included as well. A lot of this is speculative, but as Prof. Zee wryly, and funnily, asserts, textbooks "should not consist exclusively of material that has been carved in stone, or even worse, embalmed." Dr. Zee further demonstrates that the theory of gravity extends beyond the merely secular by thoughtfully providing a section that employs gravitational theorems to prove that Hades isn't on (or in) Earth. Or that if it is, it's not how conventional wisdom depicts it. This book truly has something for everyone, even those unfortunate souls doomed to perdition.
Adding immensely to this book's charm are the analogies. That objects of different mass fall at the same rate can be shown easily enough mathematically, but Prof. Zee likens that fact to different airlines following the same flight path between Los Angeles and Taipei. So masterfully simple, yet I'd never thought of it that way before. The book is packed with similar insights and thought experiments that crystallize many of the concepts. Professor Zee also includes numerous interesting anecdotes and personal observations from the world of relativity, many of which are contained in the end-of-chapter notes. Whenever I came across a superscripted number I immediately paged to the chapter end to read that corresponding note. Those are as fascinating as the main text itself. The notes range from literature references to detailed excursions into topics off the beaten path to the just plain funny. They're not to be missed.
Reading this textbook is like being regaled by that friendly, enthusiastic professor during a profound hallway conversation. I gleaned insight after insight, had several forehead-slapping "Of course!" moments, and chuckled heartily at the humor. It was worth the month I had to wait for it to arrive. If you liked Prof. Zee's quantum field theory textbook, you'll enjoy this one even more. The words on the pages come alive, almost as if he were right there in the room lecturing to you. For self-study especially, as I'm doing, this book is ideal; and, likewise, students whose professors assign this textbook will be in for a fun semester. Whatever the occasion, _Einstein Gravity In A Nutshell_ is a wonderful, worthy addition to the canon of general relativity books.