The Universal Force: Gravity, Creator of Worlds

  • Louis A. Girifalco
Oxford University Press: 2007. 288 pp. £19.99 9780199228966 | ISBN: 978-0-1992-2896-6

Gravity, the weakest known force, is the most obvious in our everyday life. The urge to understand it has challenged generations of great physicists, from Galileo and Newton to Einstein and Hawking. Yet gravity remains aloof and mysterious. The attempt to reconcile it with quantum mechanics is one of the most ambitious and urgent programmes of modern physics. Small wonder popular books on the topic — such as Louis Girifalco's addition — have an enduring appeal.

Our understanding of gravitation is encapsulated in Einstein's general theory of relativity. This supposes that space and time together form a dynamical four-dimensional manifold whose curvature influences the motion of matter. Girifalco tackles this well-trodden ground in the time-honoured way: by focusing on the historical development of the concepts and the colourful scientists involved.

Scientists today typically share a distorted and oversimplified view of the development of their subject, passed down through shared anecdotes of a series of brilliant insights and heroic discoveries. The reality is understandably messier and Girifalco weaves an interesting narrative from the complex history of this field. He opens with an extended discussion of Newton before introducing the ancient Greeks and the Copernican revolution.

Girifalco's historical focus allows him to include material rarely covered in other books on gravity. For example, he digresses to contrast the personalities and skills of Michael Faraday and James Clerk Maxwell and the development of modern electromagnetism — the first true field theory that builds a crucial bridge between newtonian gravity and relativity.

Even to Stephen Hawking — here enjoying zero gravity in a jet — the force remains mysterious. Credit: J. CAMPBELL, AERO-NEWS NETWORK/NASA

The Universal Force fills a niche. Many people who might be interested in physics can be turned off by its abstraction, and physicists have an unfortunate predilection for explaining their subject to non-experts by simply watering down the explanations they would give to their students. For anyone interested in the more human side of science, this work is a valuable contribution.

The emphasis on storytelling over concepts, however, creates pedagogical challenges. For instance, the book is free of pictures and diagrams: a puzzling omission. A picture of the patterns made by iron filings in the presence of a magnet would have helped explain Faraday's lines of magnetic force. Referring to the bending of light by curved space-time, the author writes: “There is a picturesque two-dimensional model that can help our understanding.” Shame we don't get to see it.

Modern gravitational physics is not the author's specialty — he is a solid-state theorist — and it shows in the sections on general relativity and curved space-time. Girifalco is correct to emphasize that general relativity is essentially a very simple theory, its intimidating reputation notwithstanding. But it is harder than he makes it out to be in saying, “the laws of physics are the same for everybody, everywhere”. Properly interpreted, this motto could equally well apply to newtonian gravity.

Similarly, many of the most exciting aspects of general relativity get short shrift. Black holes and the Big Bang each get a brief chapter, and there is almost nothing about the thrilling prospects for gravitational waves. Hawking's epochal (if theoretical) discovery that black holes emit radiation is a mere footnote, and no mention of string theory sullies the pages. Yes, these subjects have been thoroughly picked over in other books, but a reader expecting an introduction to some of Einstein's more recent progeny will feel cheated.

Caveats aside, Girifalco is a fluid writer, and his stories are compelling. This book about the force of gravity has its feet firmly on the ground.