# New Books of Note

By Richard Panek, Houghton Mifflin Harcourt, 2011, illustrated, 297 pp., $26.00 ## The Dark Matter Problem A Historical Perspective By Robert H. Sanders, Cambridge University Press, 2010, illustrated, 206 pp.,$60.00

Reviewed by Robert P. Crease

Certain scientific discoveries develop in a way similar to cities. Scattered research programs —settlements, in this loose analogy— spring up without much interaction at first. They begin to discover linkages with related programs, and interactions as well with clusters of others nearby. These interactions grow more extensive and diverse. Eventually a large research enterprise results, in which the work of any one part is related, directly or indirectly, with those of others. Then, in a visionary and crystallizing moment, a coherent structure emerges unexpectedly from the whole, rejuvenating it in a way that explains many puzzles, reorganizes and unites apparently unrelated research, and points the way to further efforts.

The twin discoveries of dark matter and dark energy—sure to rank as among the most revolutionary developments ever in the history of astrophysics, are classic examples. They became firmly established in the past decade thanks to a complex synthesis of evidence amassed by interdisciplinary teams of researchers studying such diverse phenomena as supernovae, galaxy rotations and spatial distributions, light-element abundances, variations in the cosmic microwave background radiation, gravitational lensing, and models of cosmological behavior.

Equally engrossing as the discoveries themselves is the problem of how to write about such wide-ranging, interdisciplinary events. It is indeed much like writing about a city: how you go about it depends on your audience and goals. You can write for city dwellers who want to improve some municipal feature, or for new inhabitants who need basic information about such things as sanitation, police, and navigating City Hall. You can write for tourists, who have no interest in these functional questions, but want to see the famous buildings, noteworthy museums, and urban movers and shakers. Finally, you can write for historians, who are primarily interested in what light this city’s story sheds on those of other cities and on municipal life more generally.

A spate of new books about dark matter and dark energy—by the time this review appears there will no doubt be more—indeed reveals this range of approaches. Several scientific review articles have already been published on dark energy and dark matter; these are like handbooks for active practitioners. Two textbooks have recently been published: Dark Energy: Theory and Observations, by Luca Amendola and Shinji Tsujikawa (Cambridge University Press, 2010); and Dark Energy, by Yun Wang (Wiley-VCH, 2010); they were reviewed together in the June 2011 issue of Physics Today. These publications discuss the ins and outs of models, methods, and measurements—on the information, instruments, and techniques that future practitioners will need to know.

Two other books—The 4% Universe, by Richard Panek, and The Dark Matter Problem, by Robert H. Sanders—are aimed less at practitioners and more at outsiders interested in what’s been happening in these research areas. They differ dramatically in style and substance, and what they capture (or fail to capture) helps reveal the special achievement a truly historical perspective might be.

Panek’s is a fabulous popular science book written in the form of an evolving drama whose driver is the actions of a small number of individuals. He characterizes their personalities carefully and finely. One protagonist is Princeton theorist Jim Peebles, who is restless and even a daredevil, both physically and intellectually. “He loved identifying the next big problem, solving it, seeing where it led, identifying that big problem, solving it, seeing where it led: a bend-in-the-knees, wind-in-the-face rush into the future” (p. 23). Another protagonist is Carnegie Institution astronomer Vera Rubin, through whose eyes we learn what it’s like to have alcoholic mentors and cope with colleagues who think that having a child disables one professionally. Panek builds his narrative around the feverish competition between the two teams hunting distant “Type 1a” supernovae, the Supernova Cosmology Project (SCP) centered at Berkeley, and the High-Z team centered at Harvard. Covering such intense scientific competition is a sure-fire way to grip your readers and hold their interest. The twists and turns of the story, indeed, provide material that is the envy of any novelist.

Panek keeps the number of players small and selects the most interesting ones. He also ruthlessly pares away all information from this extraordinarily complex and messy tale except for what readers must know to appreciate the denouement: the dark energy discovery itself. He says little, for instance, about the 1984 discovery of cold dark matter, about the 1990s studies of the spatial distribution of galaxies, and indeed about the activities of research programs not directly involved in this discovery. On the last page he quotes SCP leader Saul Perlmutter as follows:

I have the impression that most people don’t realize that what got physicists into physics usually is not the desire to understand what we already know but the desire to catch the universe in the act of doing really bizarre things. We love the fact that our ordinary intuitions about the world can be fooled, and that the world can just act strangely, and you can just go out and make it good over and over again (p. 243).

Panek cannot fully relate just how bizarre physicists find dark energy, but his carefully told tale succeeds in conveying something of their astonishment. His omissions are however the collateral damage necessary for his success in getting a messy story into popular form.

Sanders’ book is quite different. The subtitle contains the word “historical,” the introduction refers to the book as “narrative and personal,” but perhaps the best term he uses is “overview,” as the book is described in the front matter. While written from the perspective of a participant in this research, this book outlines the emerging threads that coalesced into the idea of dark matter. If Panek’s narrative camera rests on the shoulders of a few well-chosen protagonists, Sanders’ is pulled back to such a distance that human beings are all but invisible. The first time Peebles appears, for instance, it is as Jeremiah Ostriker’s collaborator in determining how a rigid spheroidal halo insures the stability of galactic discs. The first time Rubin is mentioned is as a collaborator in the study of spectroscopic observations of rotation curves of spiral galaxies using emission lines of hydrogen and nitrogen molecules. Whenever Rubin is mentioned thereafter, it is usually in the form of “Rubin and collaborators” or “Rubin et al.” You never learn that she’s also a mother, or even a woman.

Sanders does, however, provide a comprehensive map of the background pieces to the discovery of dark matter and how they emerged, the sort of thing almost entirely missing from Panek’s book. Six full chapters describe how the reigning theory of cold dark matter arose, another few detail its difficulties, and one chapter is devoted to an alternative: modified Newtonian dynamics. An appendix takes interested readers through the details of such issues as establishing distance in astronomy, weighing galaxies and clusters, and the growth of cosmological structures.

Thus Panek’s book covers its subject from the close-in perspectives of a few individual observers, while Sanders describes events from a perspective so distant that, while the full extent of the enterprise becomes visible, the individual participants are all but invisible. Neither book provides what purists would deem a true history of its subject.

The audience for such a thorough historical account is neither tourists nor participants; its aim would be to explore what this particular story of science says about other stories of science and about science itself. It would take more of a mid-range perspective, examining the interaction between scientists and the expanding research frontier. Historical research might explore, for instance, how the principal discoveries happened, what constitutes an announcement and a priority claim, and the course of competition and cooperation among the groups involved. It would examine how scientists inherit certain assumptions and behavior patterns, apply them to problems, and in so doing transform their discipline.

At the end of 2009, for example, the Cryogenic Dark Matter Search collaboration circulated a paper announcing the first direct evidence for dark matter. On the day the paper was submitted, the collaboration held two seminars, after signaling the press in a way that generated much publicity and excitement. But the evidence turned out to be substantially weaker than adumbrated —in fact, it was hardly evidence at all. Panek took the initial announcement at face value, and used it to build excitement for his story, but made nothing of the subsequent disappointment. Sanders did not mention these events at all; they were irrelevant to his account. It is understandable why Panek and Sanders made little or nothing of this episode. Yet it is loaded with meanings for the history of astrophysics and cosmology, revealing much about the value of sufficient statistics, announcements and discovery claims, publicity, and the effect of competition. A full-scale history of dark matter and dark energy, yet to be written, would explore such meanings in far more detail.

Robert P. Crease is Chair of the Philosophy Department at Stony Brook University. He is author of World in the Balance: The Historic Quest For an Absolute System of Measurement (Norton, 2011), and The Great Equations: Breakthroughs in Science from Pythagoras to Heisenberg (Norton, 2008)

The articles in this issue represent the views of their authors and are not necessarily those of the Forum or APS.