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Many Worlds in One: the Search for Other Universes on many of the topics in the text; his ex- quantum fluctuations amplified during perience is reflected in the interesting Many Worlds inflation. 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- Universes 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 universe. 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 multiverse 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 eternal inflation. 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- Andrei Linde 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.
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