on many of the topics in the text; his ex- quantum fluctuations amplified during perience is reflected in the interesting Many Worlds . Those quantum fluctuations and cohesive perspectives related to the later give rise to galaxies. different subjects discussed and in the in One However, a few years after the inven- adaptation of calculations from his own The Search for Other tion of inflationary theory, cosmologists work to new, substantial, and intrigu- realized that the theory may have some ing problems. unforeseen consequences. Like water, Each chapter has two short intro- Alex Vilenkin which can be either solid or liquid in ductions: one to outline its contents and Hill and Wang, New York, 2006. different parts of the ocean, vacuum $24.00 (235 pp.). the other to discuss the exercises at the may have different properties in differ- ISBN 978-0-8090-9523-0 end of the chapter. The introductions ent parts of the . Inflation are most useful for providing context, Alexander Vilenkin’s Many Worlds in makes each of those parts uniform and and they help the flow of the presenta- One: The Search for Other Universes is a exponentially large, so by looking at tion. The one choice made by the author beautifully written story of a new any of those parts, one would think, in- with which I disagree is that he did not worldview that has developed during correctly, that the whole universe looks provide literature recommendations the past 25 years. Cosmologists associ- the same everywhere. when he did not cover a topic in depth. ate this view with the concept The next important step A highlight of the book is the broad of an eternally inflating multi- was made in the mid-1980s array of thoughtful exercises; an answer verse. String theorists, who with the discovery of the eter- key to most of them is available to in- joined in on the discussions a nal chaotic inflation scenario. structors on request. That sensible few years ago, call it the string The scenario emphasized that policy is a tremendous boon to time- theory landscape. The new even if the universe began its crunched instructors who want to make paradigm replaces the idea of evolution in one particular up problem sets that take an appropri- a single uniform universe with vacuum state, quantum fluc- ate amount of time for students to com- that of a consisting tuations produced during in- of many different universes plete. Sethna asks that instructors do flation would exponentially with different properties. divide the universe into many not post the answers to the exercises on Another recently published large parts corresponding to the Web or distribute them electroni- book on multiverse theory is The Cosmic all possible vacuum states. From a local cally. The exercises include a substantial Landscape: String Theory and the Illusion observer’s point of view, this means the number of computational problems; of Intelligent Design by Leonard universe would divide into many uni- software for several of them can be Susskind (Little, Brown and Co, 2006). verses with different laws of low- downloaded from the author’s website. If you are interested in the string theory energy physics operating in each (see Some of the software is prewritten so perspective, the best introduction can my article in PHYSICS TODAY, September that students can easily download and be found in The Cosmic Landscape (see 1987, page 61). run simulations. When I was writing the review of Susskind’s book by Paul But why would any theory have this review, some of the canned exer- Langacker in PHYSICS TODAY, June 2006, many different vacua? A possible an- cises did not work on Macintosh OS X. page 61). If you are interested in the swer is found in the context of string I hope the problem is remedied by the theory of the inflationary multiverse, theory. According to the theory, our time this review is published. Vilenkin’s book should be your first space has many dimensions, but some Some of the exercises in the book choice. But why not read both? of them are extremely small, or “com- guide students to write their own sim- Susskind is a brilliant and prolific pactified”; therefore, we perceive our ulations. They are encouraged to pro- scientist, an expert on string theory and spacetime as four dimensional. The first gram in Python, a computer language cosmology who coined the term string commonly accepted solution to ensure that runs on all standard platforms and theory landscape. Vilenkin is one of the the stability of compactified dimen- is relatively easy to learn. Some of the world’s leading theoretical cosmolo- sions was the KKLT (Kallosh-Kachru- exercises would take a long time to gists. He is the inventor of the theory of Linde-Trivedi) mechanism, proposed in grade, so it is best to assign them in a cosmic strings, the author of several in- 2003. Researchers soon realized that course only when the class is small or fluential works on quantum creation of this mechanism allows an enormously considerable grading assistance is the universe, and one of the architects large number of ways to stabilize the available. of the theory of . Both vacuum. String theory admits 10100, or Sethna’s book provides an important Susskind’s and Vilenkin’s books are maybe even 101000, different vacuum service to students who want to learn wonderful. solutions. Each solution appears in the modern statistical mechanics. The text Cosmological observations tell us context of the same fundamental the- teaches students how to work out prob- that the universe looks the same every- ory, but the laws of interaction of ele- lems by guiding them through the ex- where and that the physical laws in all mentary particles in each of these vacua ercises rather than by presenting them of its parts are the same as they are in look completely different. Combining with worked-out examples. Overall, the vicinity of our solar system. In the this scenario with the theory of eternal Statistical Mechanics is probably more early 1980s when inflationary cosmol- inflation leads to a picture of an infla- appropriate as a textbook than a self- ogy was first proposed, one of its main tionary multiverse consisting of 101000 study guide. Instructors can point out goals was to explain the uniformity of different types of exponentially large to students which material is core and the universe. Inflation is a stage of an universes, the string-theory landscape. central to understanding following exponentially fast expansion of the If that picture is correct, then it is in- chapters, and which is cultural and not early universe. Inflation stretches all sufficient to find the fundamental the- required to comprehend later topics. previously existing inhomogeneities ory. One must also determine in which Susan Coppersmith and makes our part of the universe per- of the 101000 possible universes we live. University of Wisconsin–Madison fectly uniform, except for the small Some people like this newly revealed

66 May 2007 Physics Today www.physicstoday.org freedom of choice; some people hate it, But what I like most about Many New from 4 calling it metaphysics and theology and Worlds in One is its combination of saying that it kills their dreams of a final Vilenkin’s seriousness, intellectual hon- theory. But in his 2005 paper, “Living in esty, and good sense of humor. When I EXPLORING THE QUANTUM opened the book, I did not expect that Atoms, Cavities, and Photons the Multiverse,” Steven Weinberg com- Serge Haroche, Jean-Michel Raimond pared the recent developments with the it would be so much fun to read. If you This volume, which revolution in physics that happened are not sure whether this book is for combines theory and with the invention of the special theory you, I recommend doing something experiments, is of interest of relativity: “Now we may be at a new that goes against the grain: First read to students in quantum the prologue, then the epilogue, and physics, teachers seeking turning point, a radical change in what illustrations for their we accept as a legitimate foundation for then, if you are intrigued, the rest of the lectures and new problem a physical theory.” book. If you are among those who want sets, researchers in quan- Perhaps the most emotional re- to learn about the emerging worldview tum optics and quantum and enjoy intellectual challenges, you information. sponse is related to the anthropic impli- (Oxford Graduate Texts) cations of multiverse theory, which are are in for a real treat. 2006 978-0-19-850914-1 $89.50 actually quite trivial and, I believe, triv- ially correct: We can live and make our Stanford University RANDOM PROCESSES IN observations only in those parts of Stanford, California PHYSICS AND FINANCE the inflationary multiverse where we Melvin Lax, Wei Cai, and Min Xu can live. This respected high-level Vilenkin’s book contains only 200 Experimental text is for students and pages, which is nearly optimal. The first professionals working on Techniques for random processes in part of the book includes a description various areas, including of the Big Bang theory and inflationary Low-Temperature physics and finance. The cosmology. Years ago inflationary the- material is unique as it ory looked like an exciting piece of sci- Measurements presents the theoretical Cryostat Design, framework of Lax’s treat- ence fiction, but it is gradually becom- ment of random processes ing a widely accepted cosmological Material Properties, and and includes diverse paradigm, and many of its predictions Superconductor applications and a critical viewpoint of mathe- matics currently used in the world of finance. have been confirmed by observational Critical-Current Testing (Oxford Finance Series) data. The rest of the book is devoted to Jack W. Ekin 2006 978-0-19-856776-9 $98.50 the theory of eternal inflation, creation Oxford U. Press, New York, 2006. of the universe “from nothing,” the an- $125.00 (673 pp.). QUANTUM LIQUIDS thropic principle, the cosmological con- ISBN 978-0-19-857054-7 Bose Condensation and Cooper Pairing in stant problem, and the string theory Condensed-Matter Systems At last a new book, not a collection of Anthony James Leggett landscape. Many of the problems re- technical papers, has been published on lated to those theories are still unset- Starting from first princi- the techniques of low-temperature ples, this book introduces tled, but the book conveys the sense of measurements. Jack Ekin’s Experimental the closely related wonder and excitement that is known Techniques for Low-Temperature Measure- phenomena of Bose to those who take the risk to work on condensation and Cooper ments: Cryostat Design, Material Proper- pairing, in which a very some of the most fundamental prob- ties, and Superconductor Critical-Current large number of single lems of modern physics. Testing is an encyclopedia of tech- particles or pairs of parti- It is impossible to write about infla- niques, dos and don’ts for anyone cles are forced to behave in tionary theory and quantum cosmology exactly the same way, and starting measurements in the low- explores their conse- without introducing some of the tech- temperature field. The text is also a use- quences in condensed matter systems. The nical details. In less experienced hands, ful reference for old hands at the pro- book is accessible to beginning graduate students in physics or advanced this could easily make such a book dry fession; its appendix provides a current and intimidating. Fortunately, because undergraduates. list of suppliers and services and an up- (Oxford Graduate Texts) of his deep understanding of the sub- to-date list of cryogenic materials and 2006 978-0-19-852643-8 $64.00 ject, Vilenkin successfully presents even material properties. The information in the most complicated parts of the the- the book’s more than 650 pages is con- LASER CONTROL OF ATOMS ory in a simple and intuitive way, and fined to temperatures between 1 K and AND MOLECULES he does it without making any parts of room temperature because, according Vladilen Letokhov his discussion vague or inaccurate—a to Ekin, it is written “with special Rather different problems real achievement. emphasis on superconductor critical- can be lumped together Vilenkin also offers personal recollec- current measurements.” under the general term tions and a well-balanced narrative of the ‘laser control of atoms and Ekin does not cover such topics molecules.’ The book history of the most interesting cosmolog- as adiabatic demagnetization, dilution reviews these topics from a ical ideas of the 20th century. I found refrigeration, and helium-3 coexistence- unified or ‘coherent’ point his discussion of the work of Russian curve pressure cooling. Those tech- of view. It will be useful for many readers in various cosmologists refreshing, particularly con- niques are treated in Olli V. Lounas- fields of laser science and its applications. cerning Alexei Starobinsky and Viatch- maa’s Experimental Principles and 2007 978-0-19-852816-6 $110.00 eslav Mukhanov, whose seminal contri- Methods Below 1K (Academic Press, bution to the development of inflationary 1974). And Ekin’s book would require Visit Oxford in Booth # 2020 at CLEO cosmology is underappreciated by the another 600 pages or more for those English-reading audience. topics. Guy K. White’s Experimental www.oup.com/us 1 At bookstores everywhere www.physicstoday.org May 2007 Physics Today 67 See www.pt.ims.ca/12306-28