On Gravity: A Brief Tour of a Weighty Subject, by A. Zee

Gravity, like death, is an indisputable fact of life. Unlike death, it has become a lot more popular recently, particularly with the awe-inspiring discovery of gravitational waves. What better, then, than a guide to the theory that predicted gravitational waves in the first place? This particular one is concise, timely and (in a feat of nominative determinism) written by an author called A. Zee.

Our tour begins by comparing gravity to the other fundamental forces in the universe, and then exploring how theoretical physicists from Newton and Einstein devised alternative explanations for its “spooky action at a distance”. With little let-up in pace, Zee then bends our brains around the ideas of curved space-time, symmetry, action, black holes, dark matter and the aforementioned gravitational waves. Even current state-of-the-art quantum theories of gravity are mentioned. By the end of the book, you will be breathless, but up to date with the latest advances in the science. It’s a tour intended to take the reader a step beyond a popular treatment and give a deeper glimpse of the beautiful and uncompromising structure underlying the theory. Indeed, Zee suggests that the book might bridge the gap between his own popular book and textbook – and in case you forget, he refers to both frequently in the text.

Zee is chatty company but sometimes seems to try too hard to hold your interest. His pen pictures are lively (“Lady Davy was a horrid snob”, “The famous French guy, René ‘I think’ Descartes”), and his descriptions prone to dramatic exclamations (“Common sense fails!”, “Nerd humor in full force here!”). Although he is an expert in the subject, his text is sometimes careless. For example, trilobites did not exist 1.3 billion years ago, as implied in the prologue, and the story of Galileo dropping weights from the Leaning Tower of Pisa is just that, a story, rather than the high school fact implied in chapter 8.

The author’s descriptions of the type of theoretical concepts usually only found lurking in textbooks work better, and can give really welcome insight. However, the simple introductions can sometimes lull readers into a false sense of security before dropping them into a pit of advanced theory. For example, we are introduced to the idea of action through an analogy with the idea of getting the best possible deal. This quickly leads to the idea of the best deal for space-time (“A natural guess would be the curvature of space time. You got it!”), and, while you are mulling this, a confrontation with the equation for Einstein-Hilbert action. Be prepared for your brain to stretch, perhaps more than you bargained for.

Ambitious readers who demand more depth are catered for in an appendix that gives a mathematical treatment of space-time, curvature and gravitational waves. It’s a nice feature for those who want to get up close and personal with some of the equations. It’s also optional, and so can be left out if you prefer your gravitational insights in verbal form. There is plenty to profit from in Zee’s whistle-stop tour, with or without the maths.

Tara Shears is professor of physics at the University of Liverpool.

On Gravity: A Brief Tour of a Weighty Subject
By A. Zee
Princeton University Press
192pp, £14.99
ISBN 9780691174389
Published 25 April 2018