The Cosmic Cocktail: Three Parts Dark Matter, Katherine Freese, Princeton U. Press, 2014. $29.95 (272 pp.). ISBN 978-0-691-15335-3
In her first popular science book, The Cosmic Cocktail: Three Parts Dark Matter, theoretical astrophysicist Katherine Freese lays out the current evidence for dark matter and dark energy and the status of the relevant experiments. Along the way to the most recent developments, she introduces the reader to the concepts necessary to understand the physics and relevance of the matter composition of the universe. Freese adds some historical facts, but the history of the field is not the main theme.
The Cosmic Cocktail is a relevant update to such well-known but now somewhat out-of-date books as Evalyn Gates’s Einstein’s Telescope: The Hunt for Dark Matter and Dark Energy in the Universe (W. W. Norton, 2009) and Dan Hooper’s Dark Cosmos: In Search of Our Universe’s Missing Mass and Energy (HarperCollins, 2006). Gates’s and Hooper’s books are more accessible than Freese’s; she demands more of the reader but also gets across more scientific facts.
Not surprisingly, her chapter on WIMPs (weakly interacting massive particles) is excellent. Freese, a specialist in astroparticle physics, explains clearly the experimental status, and the subtleties of the data interpretation for detecting the class of particles that constitute the presently best motivated and most popular dark-matter candidates. The Cosmic Cocktail also treats dark energy. That discussion is informative and covers the basics, but it is nowhere near as detailed as the presentation on dark-matter detection. Throughout the book, Freese appropriately integrates her own contributions and those of others.
The topics covered in the book are timely, even though some are inadequately discussed and others do not contribute to the title’s “cosmic cocktail.” For example, Freese narrates the relevance and discovery of the Higgs boson and even includes construction details of the Large Hadron Collider’s four detectors. But the topic of inflation gets just two sentences in the text and two more in an endnote. She covers the OPERA anomaly of faster-than-light neutrinos—including the joke about the neutrino entering a bar. But her statement that faster-than-light travel implies violations of causality will confuse readers not familiar with special relativity. Also, she does not even name the Tully–Fisher relation, and she dedicates only half a sentence to baryon acoustic oscillations.
Freese’s writing style interweaves anecdotes from her personal life with the scientific explanations. Some anecdotes document academic life, others seem to serve no purpose other than to break up the text. In the first chapters, occasional abrupt changes of narrative direction take some getting used to; the later chapters are smoother. The book comes with a light dose of humor that shows mostly in the figures, such as a skull to illustrate the “Death of MACHOs” (massive compact halo objects), a penguin postcard from Antarctica, and a blurry photo of a potted plant.
Freese follows the common advice to first say what you want to tell them, then tell them, then tell them what you just told them. She regularly reminds the reader of what was explained in earlier chapters, and repeats explanations frequently throughout the book. Although that repeating material makes it easy to follow the explanations, the alert reader might find the assumed inattention somewhat annoying. The electron volt, for example, is explained at least four times. Several phrases are repeated almost verbatim in various places—for example, “eventually galaxies formed … these galaxies then merged to make clusters and superclusters” (page 31) reappears as “eventually this merger led to the formation of galaxies and clusters of galaxies” (page 51).
The book contains some factual errors: 3 kilometers is not 5 miles (5 kilometers is 3 miles); the radius of the Sun is not 10 000 kilometers (it’s closer to 700 000); and the High Energy Spectroscopic System for measuring gamma rays is not in Europe (it’s in Namibia). Some explanations and comments are vague or even misleading, such as the statement that “only with a flat geometry can the universe grow old enough to create the conditions for life to exist.” One has to read carefully, including the endnotes, to find out that Freese means the spatial geometry has to be almost flat. And, although redshift at a black hole horizon is usually illustrated with somebody sending light signals while falling through the horizon, Freese instead uses sound waves; that adds confusion because sound needs a medium in which to travel. These are minor shortcomings, but they will cause readers with no knowledge of cosmology and particle physics to stumble.
We live in exciting times for cosmology and astroparticle physics—The Cosmic Cocktail mentions that word, “exciting,” more than a dozen times. Especially on the topic of dark-matter detection, the book provides a valuable, nontechnical, and up-to-date overview.
Sabine Hossenfelder is an assistant professor of high-energy physics at Nordita, the Nordic Institute for Theoretical Physics, in Stockholm, Sweden. She works on physics beyond the standard model and on quantum-gravity phenomenology, and she blogs at http://backreaction.blogspot.com.
