A peek at dark energy between the pages

If you want to know more about the accelerating, expanding universe and the story behind its discovery, which has been cited for the 2011 Nobel Prize in physics, you might consider a handful of books reviewed in Physics Today. The reviews discussed here span the 13 years since the discovery of dark energy, the mysterious force responsible for the cosmic acceleration, and could help you decide whether the books are worth reading.

‘Two teams of astronomers studying distant type Ia supernovae presented evidence in 1998 that the expansion of the universe is speeding up,’ begins the June 2011 review by Joshua Frieman, a Fermilab staff scientist and University of Chicago professor. A few months following Frieman’s review, the Nobel Prize has been awarded to three of the principal scientists from those teams: Saul Perlmutter, who heads the Supernova Cosmology Project at Lawrence Berkeley National Laboratory in California; Brian Schmidt, who heads the international High-z Supernova Search Team from the Australian National University’s Mount Stromlo Observatory in Canberra; and Schmidt’s collaborator, Adam Riess at the Johns Hopkins University and the Space Telescope Science Institute in Baltimore, Maryland.

Frieman’s history lesson essentially ends after that opening sentence. His task, after all, was to review two textbooks meant for advanced university courses: Dark Energy: Theory and Observations (Cambridge U. Press, 2010) by Luca Amendola and Shinji Tsujikawa, and Dark Energy (Wiley, 2010) by Yun Wang. Of the two books, Frieman writes that Dark Energy: Theory and Observations ‘is the more comprehensive,’ with its focus on ‘theoretical models for acceleration, including the cosmological constant, quintessence and its variations, modified-gravity models, and void models.’

Wang’s Dark Energy, writes Frieman, ‘focuses much more on the major observational methods for probing dark energy—supernovae, large-scale structure, weak lensing, and clusters,’ and her book ‘will therefore be of more practical interest to those contemplating or involved in analysis of cosmological data.’ Frieman concludes that the two textbooks will provide a useful introduction to new and proposed experimental techniques that seek to solve the so-called dark energy problem: What is the nature of the dark-energy force, and does its existence suggest that general relativity must be replaced by a new theory of gravity?

If you want the story straight from the horse’s mouth, Robert Kirshner’s The Extravagant Universe: Exploding Stars, Dark Energy, and the Accelerating Cosmos (Princeton U. Press, 2002) might fit the bill. Reviewed by University of Oklahoma astronomer David Branch in October 2003, The Extravagant Universe recounts the discovery of cosmic acceleration from the viewpoint of Kirshner, a senior member of the High-z Supernova Search Team and PhD adviser to both Schmidt and Riess at Harvard University. According to Branch, Kirshner ‘endows The Extravagant Universe with a strong autobiographical component: He relates many ups and downs of his professional odyssey, from winning an essay prize as a Harvard undergraduate to suffering aching gums as a middle-aged astronomical observer on a Chilean mountaintop.’

Kirshner’s writing is ‘brisk and witty—in places, downright funny’ in his explanation of basic cosmology and its history and in ‘conveying the difficulty and excitement of the hunt for remote supernovae,’ writes Branch. But the reviewer warns the reader that Kirshner inaccurately downplays the Supernova Cosmology Project’s role in ‘developing the breakthrough observational strategy that enabled both teams to guarantee the discovery of high-z type Ia supernovae in batches at predetermined times, so that photometric and spectroscopic follow-up with large telescopes could be scheduled in advance.’ For another personal account, read Perlmutter’s article on page 53 of the April 2003 issue of Physics Today.

Aimed at the general public and ‘entirely devoid of equations’ is Dan Hooper’s Dark Cosmos: In Search of Our Universe’s Missing Mass and Energy (Smithsonian Books/HarperCollins, 2006), writes Los Alamos National Laboratory astrophysicist Daniel Holz in his July 2007 review . Dark Cosmos covers both dark energy and dark matter, the ‘missing mass’ in the rotational velocities of galaxies in clusters. Holz considers Hooper’s book to be an ‘informative,’ ‘entertaining,’ and ‘accessible introduction to the big questions in cosmology’ but finds that Hooper seems to ‘dilute the discussion of dark matter and rush through the sections on dark energy.’ Holz writes that ‘Hooper particularly shines when he explains the essentials of particle physics,’ and that ‘lay readers and practicing physicists would benefit from reading the sections on particle theory and detection.’

If you’re looking for a popular book dedicated to dark energy and written by an expert not involved in its discovery, consider Mario Livio’s The Accelerating Universe: Infinite Expansion, the Cosmological Constant, and the Beauty of the Cosmos (Wiley, 2000). The Accelerating Universe, which was reviewed in December 2000 by Sidney Wolff from the National Optical Astronomy Observatory, covers the action—the supernovae observations—as it unfolded. Livio’s book, writes Wolff, ‘was completed before much of the supporting evidence became available.’

Livio’s interest in the concept of beauty helps the nonspecialist to form a ‘mental image of what is implied by various physical theories’ that were being developed, writes Wolff. In some places, though, Wolff states that scientists unfamiliar with art won’t follow Livio’s many references to famous paintings and that nonscientists will get lost by his ‘superficial explanations’ of astronomy topics such as stellar evolution and the Chandrasekhar limit. Nonetheless, Wolff recommends The Accelerating Universe to introductory college astronomy lecturers and students and to scientists with a basic background in astronomy, all of whom ‘would find that Livio’s ‘lively writing . . . makes [for] pleasant reading.’

Jermey N. A. Matthews