The Hidden Reality: Parallel Universes and the Deep Laws of the Cosmos Paperback – Illustrated, November 1, 2011

This is an impressive survey of 9 multiverse models by Greene featured in lucid, engaging and effortless prose. This should be a go to book for the public as well as physics students for a conceptual understanding of the multiverse models available.He began with the "Quilted multiverse" model. This model sets up the most basic bare bone structure of the rationale of multiverse theory. Consider our own visible universe's cosmic horizon of a 14 billion year old universe. The cosmic horizon visible to us is only 41 billion light years (distance based on the light coming from objects receding from us). Our cosmic horizon or patch is all there is ever visible to us. The entire universe in the infinite space can contains infinite number of patches each with it's own cosmic horizon, constituting a quilted universe. Each patch is out of reach of the other patches. This is a basic multiverse model showing each multiverse in its own cosmic horizon patch.The "inflationary model" from Alan Guth and Andrei Linde offers further mechanism to account for how the vast expanse of the multiverse can be built out. The idea is an inflation that is triggered by quantum jitter in high energy inflation field level causing it to expand and bubble out into different multiverses. This inflationary mechanism is also commonly used in other multiverse models.Greene, as a String theorist, offers the String Theory model of multiverse by considering our 3 dimensional expanse universe on a 3-brane sheet. Another multiverse would be on another 3-brane sheet, and there can be as many 3-brane sheets on which each multiverse exists. This multiverse model is the "Brane Multiverse" model.Another String Theory model is the "Landscape" model offered by Suskind. In this model, an inflationary mechanism for bubbling into multiverse is augmented with a further feature of quantum tunneling. A multiverse suffused with higher energy level or cosmological constant can expand via repulsion and inflate, but tunnels or drops down to a lower energy level for bubbling into another multiverse. The multitude of landscape with different cosmological constants represented by unique Calabi Yau manifolds can continue and repeat this tunneling process for proliferating further multiverses.Greene also offers a thorough discussion of the Everttian "multiple-world quantum" model. In this model, the Everttian interpretation of quantum mechanics by branching the possible outcomes of quantum state into different worlds is treated as another multiverse model. Instead of collapsing probability amplitudes as in Copenhagen interpretation, Evertt suggested to let probability outcomes to branch out into different worlds such that each outcome constitute its own world. Greene highlighted that Everttian rationale is that multi-world interpretation actually stays faithful to Schrodinger equation and let the equation results speak for itself instead of ad hoc adding probability amplitudes together which are not reflected in the equation. Greene also discussed if such a multi-world interpretation takes quantum probability seriously, which he thinks each multi-world is still a probabilistic outcome.Another model Greene discussed in this work is the conceptually challenging "Holographic multiverse" model. In this model, our universe is a mere holographic phenomena taking place on a distant bounding surface, a physically equivalent parallel universe. In the holographic principle, open strings movement on 3-branes is described by quantum field particle theory in four dimensional space-time. The physics described is the same as the closed loop strings on 10 dimensional black branes as long as the strings at low energy are closed to the event horizon surface. Hence the holographic model reveals universes as holograms of equivalent parallel universes.Three other models discussed are the Cyclic multiverse model and the mathematical models of "Simulated Multiverse" and "Ultimate Multiverse" models which consider mathematical multiverses to be as real as physical multiverses. There is also a chapter devoted to methodological issues such as experimental accessibility, predictions, and the limits of mathematical applicability to physics.

This challenging, but fascinating, book from Brian Greene is another winner. It turns out that there's not just one version of the multiverse proposal but several, ranging from the Quilted and Inflationary Multiverses to the Brane and Quantum Multiverses. If you'r not careful you could get lost on this mathematical road trip. Drawing on everyday analogues to help explain the various examples of the Multiverse, Greene delves into the mysteries of Quantum Mechanics and Relativity searching for some common ground. As always his writing is geared for the well-read layperson but it helps to have a good background in reading this type of book. If you've read his previous books or similar titles by other authors then this one shouldn't be much of a problem. The whole idea of the Multiverse is based on extreme mathematics but you don't have to be a math wizard to enjoy the book. While the approach is non mathematical Greene does provide some equations (in the notes) for anybody so inclined. Some of the information is given as a kind of "refresher course" in String Theory and Quantum Mechanics but the author gives you the opportunity skip ahead if you wish to. Not being a physicists myself I tend to appreciate that kind of approach. The book is presented in 11 chapters with each chapter devoted to one or two kinds of Multiverse so the reader gets an in depth look at each variety. I found that some chapters were easier to read than others and there were some sections that were a little overwhelming in content. It took me two passes to read The Elegant Universe and three attempts on The Hidden Reality but in the end I got through both of them. I liked the section on the Inflationary Multiverse and it's "Swiss Cheese" analogy, it was the easiest to get through while the section on Quantum Mechanics, Probability Waves and Entropy was the most difficult. A good portion of the book is devoted to the history of theoretical physics and multiverse scenarios, giving you a look at the important people and events that made the most impact. To some people things like String Theory and Multiverses are more of a philosophy than a science since proof of their existence lies beyond our currant technology to access. To that end, the book closes with a section of extreme speculation on the future of computer simulation, artificial intelligence and the Multiverse. Read at your own risk. Scientist the world over are pushing the boundaries of knowledge with mathematics and observations, as well as complicated experiments but, so far, have not been unable to come up with any defining answers. And if the answers are not there or they lead in a different direction, then we will have to come up with a whole new set of metaphors to explain the world around us. The Hidden Reality gives you a well written glimpse at this strange landscape. But keep in mind that neither Greene or anyone else know for certain whether or not there are indeed Multiverses out there and he's the first one to admit that. Theoretical Physics is an active, fast changing field and researchers like Greene will continue probing the fringes of the known universe, looking for a way to combine electromagnetism and gravity into one coherent theory and also looking for the back door into other worlds and universes that may be lurking just out of sight, in some hidden reality. I recommend this book to any science reader who has an open, but skeptical, mind. While I had no technical or formatting problems with this Kindle edition it would have been nice if the publisher had saw fit to include the index, from the hard bound edition, to aid in searching the book.LastRanger