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on June 22, 2007
Not too many people know that there is a theory which is a rival to the inflationary Big Bang and it is, for the time being, completely compatible also with the WAMP satellite findings. This theory is the Cyclic Universe cooked up by Steinhardt and Turok and derived from M theory.

Although the idea of a cyclic universe is already present in some of the ancient philosophies, this approach differs from previous ones in that it conjectures the existence of two disjoint parts of the universe, two so called "branes" which move to and fro each other along a fourth dimension. This new model avoids the problems Tolman's entropy problem with the classical models which leads to longer cycles.

One way to distinguish experimentally inflation and the cyclic universe is to detect primordial gravitational waves, directly (very difficult) or indirectly (effects of gravitational waves on the polarization of the cosmic background radiation pattern). The inflationary scenario predicts more waves. Some new satellites, already planned or in the drawing boards, may give us an answer to this question in the next ten to twenty years.

Although inflation is at present the standard cosmological paradigm, it has some weak points: creation of the universe about 13,7 billion years out of nothing, the strange inflation field, very strong and very short-lived, etc. The cyclic universe, by postulating an ethernal universe solves the problem of creation and only needs dark energy (no inglation field). In a few trillion years dark energy empties the universe and then the two branes collide and create a new cycle. The authors also claim that, although they did not create their model to solve the cosmological constant problem, an added benefit of the cyclic univers is a relaxing mechanism that very slowly decreases the value of this constant and, at each step, the number of cycles grows exponentially, so that most of the cycles are at a very low value such as the one found today.

The theory also avoids having to make use of the controversial anthropic principle since most of the regions of the cyclic universe can be conducive to life.

Although I learnt quite a few new things by reading this relatively easy to read book, I would have liked a more detailed analysis of the moment of the collision of the two branes. It would seem that at that moment a huge empty space already exists. Does the Big Bang occur locally or everywhere? How far apart can the branes be? It would seem they are very near, but they approach each other once every a few trillion years?

What about the brane we don't see? It seems it has some different properties. If this brane has matter , shouldn't we feel its influence? According to some recent results dark matter is real and is not only the gravitational effect of the other brane.

The book leaves us a little hungry for such answers.
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on August 14, 2007
Is Reality, including the visible universe, something which is roughly steady-state, obeying the same physical laws with about the same fundamental constants? Or is it simply expanding, with an initial time around 14 billion years ago? Or is it somehow cyclical? Or is it a "multiverse" in some other manner?

This excellent popular book addresses these sorts of questions. And it is written by a couple of superb theoreticians who have some interesting ideas on the subject. In addition, it takes into account the latest results of WMAP, released just last year.

Steinhardt and Turok start with a funny quote from the silly spoof "The Restaurant at the End of the Universe," in which Douglas Adams quipped that there was a theory that if we ever figured out what the universe were for, it would immediately "disappear and be replaced by something even more bizarre." And that another theory states that this has already happened. And the model of Reality that Steinhardt and Turok propose may be a little closer to this than one might have imagined.

As the authors explain, a century ago, there was no strong evidence against a steady-state universe. And even the Hubble expansion, discovered around eighty years ago, could still have been consistent with such a model. But that expansion also suggested an alternative idea, namely expansion from a very dense and hot initial state. Although the authors do not get into this, the amounts of helium and isotopes of other light elements were shown to be remarkably consistent with the nucleosynthesis expected from that hot and dense initial state. And as the authors do say, the discovery of the cosmic background radiation got most folks to agree that the temperature and density of the universe were indeed very high at some point (probably around 14 billion years ago).

There were some problems associated with this model of the universe. These included the surprising homogeneity and flatness of the universe we observe as well as the lack of magnetic monopoles. The first two of these problems seemed to me even more fundamental than the third. All three can be solved, however, by a concept known as "inflation," in which the universe expands greatly very early in its history, well before the first nanosecond is complete.

That, however, leads to a possible model that rubs some folks the wrong way. It seems to be saying that Time and Space began around 14 billion years ago. There may be many "bubbles" in which there are universes that look very different from ours. But our universe would then expand forever, and that would be it.

The authors point out that some philosophers do not like a universe which originates from nothing (actually, that in a way does not bother me, given that the physical laws we see could well cause such an event to occur, with a quantum fluctuation of the vacuum producing something about the size of the "big bang"). They also point out that Einstein made it clear he would have objected to the hypothesized final state, as the ultra-dilute universe would effectively be perpetually empty, something he felt to conflict with what we know of reality. I can think of another philosophical objection, namely that we would all look like chumps if we said the world was 6000 years old. Do we really want to be similar chumps who claim that All of Reality began less than 14 billion years ago, less than four times the age of Earth? Isn't it awfully provincial of us to think this way?

The authors also indicate that a cyclical universe would make it easier to put in a way to fine tune the fundamental physical constants we observe. And that's a good point. They propose not a single big bang, but a collision of "branes" which occurs somewhat periodically, producing new universes with different physical laws (or at least fundamental constants) each time (I think the ultimate joke would be if it turned out that remnants of an old universe survived the collision, and that some of the stars that look a little older than 14 billion years are really from a previous universe or an earlier part of the brane collision).

Well, is this cyclical theory coherent? Is it self-consistent? Does it agree with known facts? Does it avoid some old problems (four of which are the entropy issue, the threat of a "mixmaster" universe, the observed acceleration of the universe, and the observed flatness of the universe)? Does it make verifiable "predictions?" Are we really starting with facts and picking a theory that fits them or just picking a theory and looking for facts to support it? The authors basically say yes: the old problems are solved by "extra dimensions, branes, dark energy, and dark energy decay."

In 2006, results from WMAP showed a systematic deviation from perfect scale-invariance. Both inflation and the cyclical model predict this! But there is one more big test to go, and we may know the results in as little as a couple of years. That test is the production of cosmic gravitational waves. A big signal of this sort would support a straightforward inflation model and be inconsistent with the cyclical model. First, of course, we might want to make sure that we can observe gravitational waves at all, and we have some binary stars we can observe to try to do that. Then, perhaps Planck or a later mission will detect (or rule out) such waves.

The authors do like the fact that their model may help solve the issue of the size of the "cosmological constant." And they certainly want to have a multiverse of some sort: "it seems far more plausible that our universe was the result of universe reproduction than that it was created by a unique cosmic event."

I recommend this book. It's readable even for a non-scientist.
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Imagine this as a morning eye opener: "If the extra dimensions start out on a high plateau, they can provide the inflationary energy to drive a powerful burst of inflationary expansion as the roll down to a low-energy state. As they do so, their motion is strongly influenced by quantum jitter." It gets better just a few paragraphs down: "There is nothing unique about the laws of physics, and almost any laws are possible. The universe appears smooth and uniform because astronomers can see only a tiny patch of it: its true wild, random structure on ultralarge scales is unobservable. All of the physical properties of the observable universe are essentially an accident whose history can never be unraveled. Instead of Einstein's dream, the universe is Einstein's worst nightmare."

After you read this book, looking at the night sky will never be the same. Our universe, all those billions of stars, isn't the whole universe according to the author's theory, but only a tiny fraction of a cyclic universe that lasts for a trillion years and starts over again.

One fine day, sometime in the future, there will be a flash and all the particles that make up us and everything will rejoin the cosmos and the cycle begins again.

The inventors of the cyclical universe theory do well at explaining in terms the layperson can, for the most part, grasp, but it is still pretty heady stuff. Helpfully, they provide a glossary that explains terms like "adiabaticity" You can both amaze and baffle your friends as you try to work that one into casual conversation.

Overall, this is a fascinating book, even if difficult to understand. Fun for those with an interest in science, but the general reader would probably not find it attractive.

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VINE VOICEon January 3, 2008
Doubtless one of cosmology's greatest mysteries concerns the origins of the universe. What happened at the Big Bang, and how? What precipitated this momentous event? What existed before it, if anything? Was time born at that same instant? Is ours the only universe? Have others existed or exist even now?

Prevailing scientific belief suggests that the universe as we know it began roughly 13 billion years ago with a "point-centered" Big Bang, followed by unimaginably rapid expansion, then enough slowing and cooling to allow the formation of atoms and molecules into planets, stars, and galaxies. In 1997, Lee Smolin's book THE LIFE OF THE COSMOS proposed an alternate theory in which multitudes of universes form at the output ends of black holes, each universe having its own characteristics and unique set of values for its controlling constants. Now, physicists Paul Steinhardt and Neil Turok offer a vastly different theory in THE ENDLESS UNIVERSE.

In a book that challenges its readers' scientific capacity while remaining within a layman's grasp, Steinhardt and Turok eschew the Big Bang singularity for what they term an ekpyrotic or cyclic model. Derived from underlying principles of advanced string theory, they posit our universe as a three-dimensional brane that co-exists with another, mostly parallel brane of more or less equal size. The two branes are separated along an unseen fourth dimension, although the distance of this separation is small and alone among all known physical forces, only gravity can travel this fourth dimension and exert an attractive force between the branes. The authors use this model to posit a trillion-year process in which the branes collide and then separate to their maximum distance apart. During the collision, a birth process for both universes takes place in a manner that looks like the Big Bang. Radiation gradually gives way to matter, allowing stars and galaxies to form, until finally dark matter exerts itself and accelerates the universes' growth and spreads out the galaxies. The branes then become increasingly flat and parallel (as opposed to having been wrinkled but not intersecting as a result of their last collision), allowing the interbrane (gravitational) force between them to begin pulling them back together for another collision.

THE ENDLESS UNIVERSE is loosely divided into three sections. The first section combines a recap of the Big Bang theory and its development during the 20th Century with far less interesting or relevant information about the authors' respective backgrounds, how they met and decided to collaborate, and how their conception of the cyclic model came to pass. Apparently, they failed to see any irony in commingling discussion of the birth of the universe with a full chapter of numbingly trivial personal background and details like, "In August 1981 my wife, Nancy, and I moved with our four-month old baby, Charlie, to Wayne, Pennsylvania, about tweny miles outside of Philadelphia..." Zzzzzzz...Oh, excuse me. What was that baby's name again?

The second section of the book elaborates on the authors' cyclic model, explaining how the branes interact with each other to cause a "big bang" event and how they are influenced by the accelerating expansion of the universe, gravitational effects, and the increasing role of dark matter. Most of the last section of THE ENDLESS UNIVERSE is taken up with discussions of the various technologies being employed to test the Big Bang and cyclic theories. These chapters are some of the most interesting parts of the book, since they offer a fascinating if complicated view of the intersection between cosmological theory and astrophysical oberservation.

Excepting the authors' space-filling personal stories, the bulk of THE ENDLESS UNIVERSE presents an exciting theoretical proposition in one of Science's most exciting fields of theoretical endeavor, the question of what is the universe and where did it come from. Readers will need to make an effort to absorb this material, but they will be rewarded with a fascinating ride through current cosmological thought and experimental efforts at confirmation.
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on November 25, 2009
This is a very interesting and important book on a major new theory on how the world began. Two prominent players in physics and cosmology (Steinhardt of Princeton and Turok of Cambridge) lay out in a very readable popular science book a fundamentally new theory, which started as the Ekpyrotic universe (terrible name) in 2001 and has evolved into the cyclic universe, a theory that challenges the prevailing big bang theory. The big bang theory in its current form envisions a multi-universe with endless space of which our universe is only a tiny part. The cyclic model envisions repeating versions of a single universe spread out over endless time. In a loose sense the new theory is a 'dual'(engineering term) of the big bang with endless time replacing endless space.

If looked at in isolation, the new theory looks quite bizarre (& crazy) because it comes out of a specific string theory model with 'branes' (membranes) living in hidden extra dimensions. A lot of physicists love string theory because of its elegant mathematics and the hope it will merge merging quantum mechanics and gravity, but there is not a shred of experimental evidence supporting it. Roger Penrose (on the dust jacket) advises readers who are skeptical of string theory to "suspend such views" and read this book, adding, "It may well be closer to truth than you think." Also on the dust jacket are praise from Stephan Hawking, Martin Rees, and Brian Greene. Steinhardt admits this theory is a little crazy, but as Roger Penrose says, "Perhaps we need a crazy theory to address these things".

The authors do a good job showing that the prevailing big bang theory has over the last thirty years acquired its own considerable baggage and is now pretty weird too. Some textbook big bang models are in fact now known to be invalid, ruled out by high resolution data on the cosmic background radiation from the WMAP satellite. The current big bang theory implies eternal inflation and a multi-universe in which we just happen to live in a rare bit of space that is livable (anthropic theory). Big bang needs two types of unseen energy, inflation energy and dark energy, that are unrelated and both carefully tuned.

In the cyclic universe theory the horizon, flatness and monopole problems are all solved without the need of inflation, hence no inflation energy, dark energy does both jobs. One indication they might be on the right track, they argue, is that they didn't construct the theory around dark energy; its ability to solve two problems came as a sudden later revelation that is recounted in the book. Each cycle, which they estimate is about a trillion years, starts with a quasi-big bang, but it is not a singularity (temperatures are not infinite), so conditions are in principle calculable. The initial energy of the hot radiation comes from the kinetic energy of branes which moving toward each other and colliding in an unseen dimension.

The authors emphasize that all five experimental tests currently met by the big bang theory are met by their cyclic theory too, but crucially in a future sixth test (involving gravity waves) their theory and the big bang make very different predictions. Information about gravity waves from the big bang is encoded in the 'ripples' of the cosmic background radiation, and the authors suggest that a few more years of data collection by the WMAP (Wilkinson Microwave Anisotropy Probe) satellite might provide hints as to which theory of the universe is right. While the authors don't say so, confirmation of this theory would be a strong indication that string theorists are on the right track. As an aside, the authors throw out the suggestion (p 140) that dark matter at the center of galaxies might be due to gravity being felt from matter in an unseen dimension.

A major theoretical problem today is that calculation of the cosmological constant or dark energy (physically equivalent to vacuum energy) comes out too high by an astounding 107 orders of magnitude relative to experimental limits! The disagreement is so bad (& important) that it's often called the 'Vacuum catastrophe'. Steinhardt and Turok argue the very long time offered by countless earlier cycles might offer a solution to the vacuum catastrophe, because a very slow decay mechanism (via quantum jitter) for vacuum energy density is thought to exist. Essentially over time vacuum energy 'walks' down to a value just above zero and then hovers there, which is where we see it today.

Steinhardt and Turok claim to have a mechanism that after a trillion years of dark energy expansion of the universe causes the branes to be reset to the same initial conditions that began the previous cycle, so the system doesn't run down, each cycle is the same as the one before, the classic entropy problem of cyclic universes is solved, or so they say. But there is still the matter of energy to power each cycle, energy which goes into kinetic energy of the branes as they accelerate toward each other, some of which, when they collide, is converted into the total energy we see in our present universe. So where does this energy to power each cycle come from? I quote, "gravity is a bottomless (energy) pit .... It can decrease by a finite amount with each bounce and continue that way forever." (p 191-192). Forever? Does this pass the smell test?
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on August 2, 2007
As one who has read many of these popularized physics book, I would rate this one at the top. Without one equation, it is written in a semibiographical way that shows how physicists carry out their work. It captures the excitement of the development of the new "Cyclic Universe" theory that the authors cooperatively developed to counter the current favorite Big Bang- Inflation theory. The new theory incorporates the new theories in physics: M theory, extra dimensions, formation of matter and explains all data from the WMAP measurement of the background radiation as well as the Big Bang model. But, the new theory has the advantage of not requiring a beginning nor does it need to bring in the Anthropic principle to explain fine tuned constants. The new theory differs from previous cyclic models in that it doesn't rely on the amount of matter in the universe to shift the expansion to a contraction. It instead posits that dark energy changes over time and dominates the cycles and the bang is due to colliding branes from M theory. The authors emphasise that physicists don't just make these things up, but they come out of the mathematical theories. There is one prediction of the theory that will distinguish it from the Big Bang. They predict different amounts of gravity waves. Future satellite measurements will be able to prove one theory or the other. As with the authors, I hope the Cyclic theory wins.
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on June 23, 2007
This was a wonderful, easy-to-read book, that will be gratifying not only to hard-core cosmologist devotees, but to the layperson who only has a modicum of knowledge regarding cosmology. I would recommend this book to anyone who wants to learn about the latest theories regarding where we are, where we've been, and what will happen to 'everything' in the far future. A great feast for the mind!

Ed Reifman
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on January 11, 2008
No matter how long, deep and hard we dwell on existence of the Universe, it is impossible to avoid concept of infinity. What (or Who) is able to be eternal? If this is God, then not Universe. If Universe is such, then there is no need for God. Interestingly authors briefly muse about it in the middle of the book. Saying this and taking theology/philosophy aside I highly appreciate the huge effort taken by both scientists to present their quite stunning, and as for today, extravagant theory - theory challenging inflation. It was easier for me to comprehend Inflationary models (for example in Vilenkin's "Many Worlds in One"). Endless Cycling model is by far the most difficult one, since it is based on String Theory and assumption of extra dimensions. Part of the book evaluates supersymmetry vs. simple string theory in particle physics. Most of the time we read about advantages of Ekpyrotic (Cycling) Universe theory when compared to Inflationary models. Swinging back and forth (in a bit of chaotic and repetitive manner ) authors drill voraciously in systematic fashion all possible holes in the Guth/Linde's Inflationary as well as in Susskind's Landscape and Vilenkin's Multiverses models. And how dedicated, convinced, passionate, determined and eloquent they are!! Though certain fragments are truly exhausting (for example: how colliding branes convert one type of energy to another), numerous repetitions and attempts to emphasize how things happen, are actually often helpful. What has been planted in my head is that: extra "D" + branes + dark energy + potential energy related "spring-like" force between the branes = ekpyrosis. Be it. The final judge deciding which model represents true reality appears to be gravity. Authors list number of proposed and being in progress projects aiming at DETECTING gravitational waves. Unfortunately we will not be able to do so in the next decades, especially if it comes to very weak inflationary waves. However detection is not a single dilemma. We still cannot EXPLAIN the essence of gravity and I did not find anything related to it in this book. Physicists sometimes talk about a concept known as "Mach's Principle", but that principle has never been successfully developed and fails to explain apparent instantaneous action-at-a-distance. In the end comes the last strong punch: Cyclic Ekpyrotic model is free of Anthropic Principle dilemma!! It is very important to cosmology to have competing models and unanswered lingering questions about their validity. In general: very brave and colorful popular science book, recommended for curious and following "strange" cosmology ideas readers.
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on April 14, 2010
Wow did this book rock my view of the universe. I keep up to date on most of the major scientific findings in regards to Astronomy and I had heard of the cyclic model but I didn't really take the time to learn much about it. I figured if it was truly a legitimate alternative to Inflation then I would have heard more about it and the things that I did hear about it would have been more convincing. That was certainly not the case and is a mystery to me now that I have read this book.

This book explains both the Inflationary view of the Universe and the Cyclic view of the universe and it does so amazingly well. Even people who are new to this subject matter should have no problem understanding the concepts presented in this book. It explains both models, gives an accurate account of each theories strengths and weaknesses, and explains what the next step is in regards to deciding which of these theories should survive and which one should be discarded. What I really like about this book is it gives a overall history of the pursuit for the unified theory so you understand where each theory came from and what it takes to get such a theory recognized by the scientific community. I also really enjoyed the personal touch that this book had as it gives a thorough account of the two scientists who finally came together and put the Cyclic theory down on paper.

The bottom line - The Cyclic theory may be the new kid on the block but its an incredibly intriguing theory with just as much evidence to back it up as Inflation has. In fact its appearing more and more like the Cyclic model may just wind up dethroning Inflation as the more widely accepted model. Then again it could very well be that neither theory winds up surviving. Either way this book brings you up to date with one of the most interesting battles currently taking place on the physics/cosmology front. I cant wait to see what comes next.

Highly recommended!!
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on July 4, 2007
I am not a professional cosmologist or physicts. I found this book is interesting and it is easily understood by layman like me. I must confess that I do not understand the String M-Theory, Braneworld and inflationary theory clearly. I cannot give a fair judgment about Cyclic Theory and Inflation Theory. Since both the universe past and future is far way from us and they are not reliable to justify the validity of inflation theory and cyclic theory. Since there are no empirical data to distinguish the merits of inflations theory and cyclic theory. Both theories is more or less like science fiction. If the extra dimension between 2 branes are as "large" as Paul and Neil suggests in the book. Cyclic theory may have strong experimental data which support Cyclic theory is right. But no matter which theory is correct, Paul Steinhardt and Neil Turok has clearly tell all the reader why cycle theory is possible and excisting, why START and END of time is important. Personally I found the explanation of inflation theory is very excellent and I recommand any reader to read carefully the inflation explanation, cyclic theory explanation, problem on the start and end time.
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