Relativity: An Introduction to Space-time Physics

Abstract

Steve Adams' Relativity is a comprehensive and highly readable introduction to a subject of broad interest and enduring popularity. It is pitched at just the right level for serious sixth-formers or for undergraduates striving to understand the physics that underpins more mathematical treatments of relativity, and will also be of interest to their teachers. The book richly deserves a place in school and college libraries, but the present edition is marred by so many minor misprints that I would be reluctant to make it required reading for novice students, despite its many attractive features. Relativity has an admirably straightforward structure: an introductory chapter outlining classical physics is followed by two substantial chapters on special relativity and a single chapter on general relativity and cosmology. The first of the two special relativity chapters is pivotal since it establishes the `physics-led' rather than `mathematics-led' approach of the book. It achieves this by basing many of its arguments on the behaviour of `light clocks' that measure time by counting the successive reflections of a light pulse as it bounces back and forth between two parallel mirrors separated by a fixed distance. Judicious use of these idealized clocks enables the author to expose all the well known phenomena of special relativity without having to call on the Lorentz transformations at all. The Lorentz transformations are included, but they don't make their first appearance until page 111, and even then their main function is to prepare the way for Chapter 3, which takes the reader deeper into the structure of (Minkowski) space-time and revisits, in a more mathematical way, many of the topics introduced physically in Chapter 2. This double approach to issues such as time dilation and length contraction has been well thought-out and well executed, and seems certain to aid effective learning on the part of students, even those who are reading the book on their own, without the guidance of a teacher or lecturer. The survey of general relativity and cosmology that occupies the book's fourth chapter is much less detailed than that of special relativity, but equally engaging. The treatment of Einstein's geometric theory of gravity is again primarily physical, though the use of elementary calculus is more evident than in the earlier chapters. Only a small proportion of the chapter is devoted to cosmology as such, but the basics are well explained and the chapter is neatly rounded off by 20 pages on black holes and gravitational waves. Students can sometimes lose their way in lengthy chapters, so a book of 280 pages with only three major chapters may seem a somewhat daunting prospect to some. However, each of those chapters starts with a very helpful block diagram showing the relationship between key ideas, and there are plenty of subheadings to help guide and orient the reader. These signposting devices, together with the summaries and problem sets that end each chapter, make Relativity a useful and effective guide to the endlessly fascinating world of space-time. Unfortunately, as indicated earlier, this potentially very valuable text is marred by a number of small but irritating errors. The most prevalent of these concerns the gamma factor that appears in the Lorentz transformations and in many of the results that follow from them. In several different places (pages 118/9, 121, 159) gamma makes an unannounced transformation to g, presumably as a result of some kind of font problem in the production process. Similar problems beset Figure 3.25 and one or two of the other figures. Another kind of gremlin seems to have been at work in some of the summaries; what should have been neatly stacked equations and uniformly indented paragraphs have somehow become misaligned or disarrayed. Other problems, more clearly of the author's own making, result from the decision to use the symbol p4 to indicate an energy-momentum four-vector, and from the rather old fashioned practice of using ict, rather than ct, as the zeroth component of the position four-vector. All of these problems are quite minor, but they are of just the sort that might confuse algebraically timorous students who half expect that relativity will be incomprehensible. Despite its production problems, Relativity is a well planned and well written book which I am pleased to own. I will recommend it to those who will not be confused by its misprints, and I hope that a corrected edition will eventually be published so that the book can achieve the full readership it deserves.