Einstein's Mirror

Abstract

Einstein's Mirror is a companion to the authors' highly successful book, The Quantum Universe. In it Hey and Walters have adopted a similar approach with the clear intention of providing a broadly accessible survey of relativistic physics. The book is well illustrated with photographs and line drawings and covers the development, experimental tests and implications of both the special and general theories. The book divides roughly into three parts: the first four chapters deal with the relativity of space-time and motion (time dilation, length contraction, velocity addition etc); the next three explore the consequences of mass - energy equivalence (E = mc2, fission and fusion etc) with a lengthy digression on how Dirac's relativistic quantum theory of the electron led to the prediction of antimatter and the theoretical description of spin; and the next three chapters discuss the equivalence principle, the development of general relativity and its implications for cosmology. There is also a final chapter on 'Relativity and Science Fiction' which is interesting, but to my mind slightly uncomfortable in the context of the rest of the book. The appendix includes simple derivations of time dilation, velocity addition and mass increase with velocity and there is also a chronology and useful glossary. This book differs from The Quantum Universe in two major ways: whereas quantum theory was developed by the pantheon of twentieth century physicists, relativity (especially the general theory) was created almost single-handedly by Einstein; and where quantum theory is directly relevant to our everyday lives through electronic technology, relativity has few applications outside the rather esoteric worlds of particle physics and cosmology. Einstein's central role means that the book is partly biographical although every opportunity is taken to link Einstein's own ideas to those of his predecessors and contemporaries. This works well, although sometimes the historical context is developed to such an extent that you could forget you are reading a book about relativity. The chapter on E = mc2, for example, begins by discussing caloric, phlogiston and the early development of thermodynamics before considering mass - energy equivalence through an interesting thought experiment that is analysed more carefully in the appendix. The lack of everyday examples of relativistic effects is more of a problem because it was the emphasis on applications that helped distinguish The Quantum Universe from other popular books about quantum mechanics. For this reason Einstein's Mirror is not so distinct, reminding me of earlier books like Einstein's Universe by Nigel Calder, although it is better illustrated and includes an excellent selection of quotes and anecdotes. There are also some informative 'boxes' explaining particular topics such as the Michelson - Morley experiment, the Global Positioning System and radio astronomy. Most of the quotes used were already familiar but it is good to see so many of the best ones collected here. The book is aimed at final-year students in school, undergraduates in science subjects and general readers with an interest in science, and it is certainly accessible to them. It is well-paced, logically structured and an easy and interesting read, although there are a few passages where rather a lot is assumed on behalf of the reader - for example, I doubt whether the following passage, about the Higgs mechanism, will mean a great deal to most sixth formers: 'The key to understanding these interactions was a symmetry known as 'gauge invariance'. A better name for this symmetry would be 'phase invariance', since the symmetry arises because of the freedom for all the matter fields in these theories to be multiplied by an arbitrary space-time dependent phase with no change in the resulting physics.' Einstein's Mirror gives an excellent background to Einstein's life and ideas, and special and general relativity are set in a human and historical context. It will certainly appeal to its intended readers but will be of most value to those who already have some idea about the concepts involved.