Dark Cosmos: In Search of Our Universe’s Missing Mass and Energy , Dan Hooper , Smithsonian Books/HarperCollins, New York, 2006. $24.95 (240 pp.). ISBN 978-0-06-113032-8
Unless you’ve been hiding in a cave, you’ve probably heard about the recent revolution in our understanding of the universe. During the past five decades cosmology has gone from a fringe science, with lots of speculation and woefully insufficient data, to a firmly established field with its own standard model, buttressed by precise measurements and a wealth of data. The dark side of this shift is that we’ve discovered our ignorance of the basic constituents of the universe we live in. In Dark Cosmos: In Search of Our Universe’s Missing Mass and Energy , Dan Hooper concerns himself with the soft underbelly of cosmology—the 95% of the universe that remains mysterious and unaccounted for.
Dark Cosmos tells the story of dark matter and dark energy—why we think they exist, what they might consist of, and how we go about learning more about them. The book, aimed at the general public, is entirely devoid of equations and strikes an informal, accessible tone. Hooper, a theoretical astrophysicist at Fermilab in Batavia, Illinois, is only a few years out of graduate school, and his youthful exuberance for the topic is unmistakable.
Hooper particularly shines when he explains the essentials of particle physics, which is perhaps not surprising because it is his area of expertise. He has thought carefully about the material and has developed effective pedagogical techniques. He provides a thorough introduction to neutrinos, the chapter on symmetry is pitched perfectly, and the discussion of the Higgs boson is a model of clarity. Both lay readers and practicing physicists would benefit from reading the sections on particle theory and detection. Hooper is also quite inventive with his analogies: The curvature of spacetime is compared to the path a taxi takes through traffic; the topology of the universe is like that in the video game Asteroids.
Unfortunately, in his enthusiasm to share the wonders of the universe, Hooper often loses sight of his primary, dark topics. For example, in one short chapter he discusses the life cycle of stars, supernovae, neutron stars, black holes, special relativity, general relativity, primordial black hole formation, black hole evaporation, gravitational lensing, and the search for massive compact halo objects, or MACHOs. Of course, all these topics are fascinating, but a few pages cannot do any of them justice. The author cannot decide whether the goal of his book is to convey some genuine understanding of dark matter and dark energy or instead provide a wide-ranging, superficial description of the subject. Is Hooper chatting with us at a cocktail party, or is he giving a public lecture to a generally informed and attentive audience? The tone of Dark Cosmos shuttles between the informality of a party and the seriousness of a lecture, and although each event is engaging, the inconsistency is disconcerting.
I found myself wishing Hooper had focused the entire book on dark matter, rather than grappling with dark energy as well. By attempting to cover both topics, Hooper dilutes the discussion of dark matter and rushes through the sections on dark energy. For example, the role of supernovae in the discovery of dark energy is hastily sketched out and easily deserves a chapter of its own. Although the chapters on dark matter are strong, the book would benefit from a more detailed historical background, and from an extension of the discussion of particle dark-matter candidates and experiments. Why not discuss axions, which are an important dark-matter candidate and are actively being sought, rather than the considerably more speculative anthropic principle and Kaluza–Klein states?
Hooper also liberally inserts himself into the text. Presumably, the approach is meant to make the scientists—and, by proxy, the science—seem more accessible. At times, however, his personal interjections can be distracting. For instance, a long section discusses one particular paper Hooper co-authored on the possible detection of dark matter through particle annihilation. Given the broad sweep of the book, it isn’t apparent how mention of that specific paper, nor the inclusion of a page-long excerpt from an eccentric response to it, helps his audience appreciate the larger discussion of dark matter. Nevertheless, Dark Cosmos is an informative and accessible introduction to the big questions in cosmology. Hooper’s breadth is impressive.
The study of cosmology has led to a steady diminution of humanity’s importance. We’re not at the center of the solar system. We’re not at the center of the galaxy, and our galaxy isn’t even unique. We’re not at the center of the universe, because there is no center. And now we’re even entertaining the possibility that our universe is only one of many—and a grossly atypical one at that. As if these indignities weren’t enough, cosmologists are now confident that everything we touch, see, or feel is a tiny fraction of what’s out there. All the stars and planets and people are just a minor frosting on the true elements of the universe: dark matter and dark energy. Hooper’s book touches on a large swath of modern physics; laypeople, undergraduates, and even advanced graduates would benefit from it. Dark Cosmos is an entertaining, if uneven, tour through our newfound dark universe.
