Grujic, P.

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Serb. Astron. J. } 180 (2010), 111 - 112Book reviewTHE UNIVERSE EXPANDSHarry Nussbaumer and Lydia Bieri,"Discovering the Expanding Universe", Cambridge University Press, 2009P. Gruji¶ cInstitute of Physics, Belgrade, SerbiaE{mail: petar.grujic@ipb.ac.rs(Received: March 26, 2010)When Einstein published his theory of gravi-tation in 1915, now known as The General Relativ-ity (GR), cosmology was for the ¯rst time in pos-session of a mathematical formalism which could en-able scientists to make it a hard science. Einsteinwas the ¯rst to realize it and soon he formulatedhis model of our universe (the Universe), now thewell known "Einstein static endless cosmos". Manymathematicians, astrophysicists, theoretical physi-cists, astronomers and others followed the suit andthe last century may well be called the century ofcosmology.Einstein's equations of GR are practically im-possible to solve in the general case, thus furthertheoretical investigations made extensive use of vari-ous approximate cosmological models, whose numberproliferates up to the present. On the other hand, aremarkable advance of the astronomical equipment,¯rst of all telescopes, then the astrophysical science,both theoretical and empirical, have helped our pic-ture of the global structure and dynamics of the Uni-verse to be examined in unprecedented detail andaccuracy. Thus the cosmology has become one ofthe most exciting and fascinating scienti¯c adven-tures of our time. Last years have witnessed an enor-mous proliferation of speculative models concerningthe early phases of our universe, making the scienceof Cosmos more a metaphysics than a standard sci-enti¯c enquiry.Many books have been written about the his-tory of modern cosmology and the present day stateof the art. The monograph by Nussbaumer andBieri stands apart from these attempts to presenta complex and di±cult subject to a broader reader-ship in many respects. Written by an astrophysicistand a cosmologist, the book covers almost all rel-evant aspects necessary for the general readershipto get insight and to appreciate the development ofour knowledge of the global features and behaviourof the universe. The monograph has successfullyblended the historical account, theoretical investi-gations and empirical evidence, making the bookboth self-su±cient and instructive. Theoretical as-pects are covered in two layers. In the main textequations are presented and analyzed with the helpof ¯gures which explain the nature of various theo-retical constructs beyond the usual descriptive level,which allows readers to get a deeper insight into var-ious notions, like the hyperbolic cosmological space,open and closed universe etc. In the mathematicalappendix each relevant chapter has been presentedat a more scrutinized mathematical level, explain-ing what really is calculated by the equations whichgenerally stem from the Einstein's original GR. Thelatter is taken for granted, but very few highly spe-cialized textbooks go further from quoting Einstein'sequation. The book is by no means textbook andthese elaborations just help to appreciate what theauthors (original or of the present book) wanted tosay, rather than aiming at real understanding.The book closely follows main steps in acquir-ing relevant cosmological empirical evidence, withinstructive details concerning exchange and inter-pretation of the astrophysical data. Many authorsare already present in the general outlook of the as-trophysical history, but some, like Milton Humason,111P. GRUJI¶ CHubble's collaborator, emerge as mainly neglected inthe popular accounts of the development of our pic-ture of the universe. The same holds for Tolman,Robertson and other less known but important cos-mologists of the last century.But the principal value of the book is its de-tailed historical account of the merits of the mostprominent ¯gures linked with the last century cos-mology. The authors reveal many misconceptionsand delusions deeply rooted into minds of those notfamiliar with cosmological research history. Thus we¯nd that Hubble did not discover the universal ex-pansion, that it was not Hubble who introduced theso-called Hubble constant, etc. The authors do notbelittle Hubble achievements, but try to do justice toall those whose contributions should be appreciated.From their account another eminent ¯gure emerges,rev. Georges Lemaitre, who should be considered themost (with Einstein, of course) proli¯c researcher inthe last century's cosmology.The book is lavishly illustrated by photos,¯gures, facsimiles of the primary historical sourcesetc. Some of them are amazing, like the photo ofthe postcard Einstein sent to Herman Weyl (anotherauthor rather neglected in the popular literature),where Einstein discusses some controversial currentissues. Another intriguing story appears, that of Ein-stein's cosmological constant, ¤ (originally ¸), whichEinstein called his biggest blunt in cosmology andwhich Lemaitre (and some others) defended vigor-ously from the majority of the cosmological popu-lation (including very Einstein). This cosmologicalbastard disappears and reappears despite almost uni-versal aversion against it, under many disguises andat present turns out the principal player on the cos-mological arena.With brief but instructive prelude of cosmo-logical (pre)history, and preface by Allan Sandage,the book appears self-su±cient, easy to read and fullof unexpected revelations of importance to every-body engaged in cosmology, both at the research andinformational levels. My only remark is the neglectof the so-called hierarchical model, mentioned only inpassing (Einstein himself considered the model, butrejected it). The issue of the accelerating universehas not been exploited as much as one might expect,but with good reason. The ¯nal message of the bookis that scienti¯c enquiry at this level, as illustratedin the monograph, undergoes many changes and onemay not expect de¯nite answers, particularly fromthe cosmologists. (They could be found elsewhere,in the Bible, for instance, anyway). The message(which the authors are cautious not to o®er explic-itly) appears, paradoxically - we don't know yet forsure that our Universe expands. Or, put it di®er-ently, if it does so, why. Though the authors do notinsist on the epistemological issues, the book o®ersa nice illustration of some of the general aspects ofthe scienti¯c methodology. It demonstrates, for in-stance, how risky is to assign a particular scienti¯cachievement to a single author. As the case withother scienti¯c activities, important cosmological re-sults are collective products of many contributors.The target readership are academics with in-terest in cosmology, but to my estimate those whowill bene¯t most are historians of modern cosmol-ogy, many of whom will have to revise their simplis-tic picture of the development of the discipline, fromAntiquity to the present day.Petar Gruji¶ cPrincipal Research Fellow,Institute of Physics, Belgrade112

Book Review: The Universe Expands, Harry Nussbaumer and Lydia Bieri, "Discovering the Expanding Universe", Cambridge University Press, 2009

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