The Wraparound Universe

Abstract

I thoroughly enjoyed reading this book. It is written in clear languagesupplemented with many very helpful photographs and drawings. I like the structure ofthe book, which is a collection of 45 rather short chapters that make iteasier for the reader to read it at his/her own speed.The main aim of the author is to interest the reader in cosmology and toconvey to him/her the amazing progress that has been made in recent years in ourunderstanding of the universe, its shape and its future. However, even to formulate this problem and to describesome recent work in this field, the author has to explain to the reader many concepts frommathematics and physics. Jean-Pierre Luminet, in addition to being a well knownastrophysicist, is also a very gifted writer and so he manages to do this very successfully. In fact the bookcontains very few formulae and most of the explanations are given in terms of a written narrativesupplemented by drawings. The author is also extremely skillful in finding and then usingappropriate analogies. The required ideas from mathematics, and topology in particular, present afurther aim of the book—to explain to the interested reader the beautiful world of topology andits relevance to the description of the real world. Here, again, he succeeds very impressively.The central claim of the book is as follows: instead of a simple topology, the Universe may have a multiply-connected topology—hence 'wrapped around'; in consequence, it may be much smaller than is usually assumed. If this is so some of the galaxies we see are not real galaxies, but only images of a smaller number of genuine galaxies. The author then discusses possible topologies, and finally chooses the 'dodecahedral' one. A large part of the book is dedicated to showing how this hypothesis can be tested, and what the most recent data on the cosmic background radiation from the WMAP satellite say about this issue (they are inconclusive). Jean-Pierre Luminet's suggestions disagree with the standard inflationary model, which uses the same data to argue that the Universe is spatially flat, and so infinite.The author is also scrupulous in apportioning priorities. As he explains in detail in several historical sections, the standard cosmological equations (normally called Robertson Walker, or FriedmannRobertson Walker equations) were first written by Lemaitre and Friedmann—hence in the book thecosmological models which use them are always referred to as Friedmann–Lemaitre models. Similarly, the Doppler effect becomes the Doppler–Fizeau effect and Hubble's law is entitled Hubble–Lemaitre.I also liked the sections of the book in which the author shows how the same ideas in different historic or geographic conditions have had different impacts on the development of science; some were ignored, some misunderstood and some considered more seriously than they deserved.All in all, 'The Wraparound Universe' is a great general-audience book and I recommend it unreservedly.