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Endless Universe: Beyond the Big Bang [Anglais] [Broché]

Paul J. Steinhardt , Neil Turok

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11 décembre 2008

Two world-renowned scientists present an audacious new vision of the cosmos that “steals the thunder from the Big Bang theory.” —Wall Street Journal

The Big Bang theory—widely regarded as the leading explanation for the origin of the universe—posits that space and time sprang into being about 14 billion years ago in a hot, expanding fireball of nearly infinite density. Over the last three decades the theory has been repeatedly revised to address such issues as how galaxies and stars first formed and why the expansion of the universe is speeding up today. Furthermore, an explanation has yet to be found for what caused the Big Bang in the first place.

In Endless Universe, Paul J. Steinhardt and Neil Turok, both distinguished theoretical physicists, present a bold new cosmology. Steinhardt and Turok “contend that what we think of as the moment of creation was simply part of an infinite cycle of titanic collisions between our universe and a parallel world” (Discover). They recount the remarkable developments in astronomy, particle physics, and superstring theory that form the basis for their groundbreaking “Cyclic Universe” theory. According to this theory, the Big Bang was not the beginning of time but the bridge to a past filled with endlessly repeating cycles of evolution, each accompanied by the creation of new matter and the formation of new galaxies, stars, and planets.

Endless Universe provides answers to longstanding problems with the Big Bang model, while offering a provocative new view of both the past and the future of the cosmos.  It is a “theory that could solve the cosmic mystery” (USA Today).

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Chapter One: 2001

He was moving through a new order of creation of which few men ever dreamed. Beyond the realms of sea and land and air and space lay the realms of fire, which he alone had been privileged to glimpse. It was much too much to expect that he would also understand.
—Arthur C. Clarke, 2001: A Space Odyssey

Two boys sit in darkened cinemas, one in London and one in Miami, set to watch Stanley Kubrick's movie 2001: A Space Odyssey. It is 1968, a year of worldwide conflict and turmoil: Vietnam, the arms race, political assassinations, student protests, and rebellions. But all this is forgotten as the film sweeps the boys along in a glorious tale of science, space, and the future.

The boy in Miami witnessed firsthand the awesome power of technology to annihilate or inspire. Six years earlier, from his home near Homestead Air Force Base, he watched missiles being prepared for a strike on Cuba, knowing that his family and community would be obliterated if the looming crisis led to a nuclear exchange. Then, as the crisis subsided, he became galvanized by John F. Kennedy’s promise to send a man to the Moon by the end of the decade. He emerged from these early experiences optimistic about the power of technology to improve the future and fascinated by all things scientific. He kept logbooks of every manned mission and traveled often to Cape Canaveral to observe the launches. He turned the family garage into a laboratory with large stocks of chemicals and biological specimens. And he headed to the Everglades at night, avoiding the city lights and fending off mosquitoes, to take a peek at the heavens through his telescope.

The boy in London was a refugee from South Africa, where his parents had been imprisoned for resisting the oppressive apartheid regime. But he too was optimistic, having seen the determination of people like Nelson Mandela to build a better future. Upon his parents’ release, the family had left South Africa for Kenya and then Tanzania, new countries full of natural wonders—the Serengeti’s wild animals and the Olduvai Gorge, home of the earliest humans. Under the hot African sun the boy had learned mathematics and science from spirited young teachers. He’d built electric motors, made explosions, and watched ant lions for hours. In 1968 his family had moved to England for the sake of the children's education, arriving in time to watch the Apollo moon landings on TV.

As young children, both boys had acquired their passion for science from their fathers. Each night, the father in America told stories to his little boy of Marie Curie, Louis Pasteur, and other great discoverers. The father in Africa patiently explained the Pythagorean theorem and spoke of the great achievements of ancient Greek science. Their words were like water on seeds, feeding insatiable curiosities. How does the world work? How did it start out? Where is it headed? The boys asked the same questions that have gripped people from every society, every culture, every religion, and every continent since civilization began.

Kubrick’s film speaks of a time in the foreseeable future when people will devote their skills and resources to uncovering the secrets of the universe. A space mission is dispatched to investigate a powerful signal emanating from one of Jupiter’s moons. Technology, in the form of the computer HAL, threatens to end the mission, but human ingenuity and adaptability win out. A lone surviving astronaut arrives to find a giant monolith, appearing like a solid rock two thousand feet high. As he approaches, he realizes that it’s actually the opening of an infinite shaft, drawing him into a transdimensional trip through hyperspace and revealing the creation and the future of the universe. Watching the film, neither boy realizes how prophetic this story might be.

A Real Space Odyssey

Fast–forward to the real 2001: rather than a lone astronaut, a worldwide community of cosmologists engaged in an intense effort to understand the beginning of the universe. The two of us, now grown, are thrilled to be among them. The boy in Miami, Paul Steinhardt, is now a professor of mathematical physics at Princeton University. The boy in London, Neil Turok, is a professor of physics at Cambridge University in England. Each of us, following his own path, has pursued his dream of becoming an explorer of the universe, albeit with paper and pencil instead of a rocketship. Three years have passed since the two of us joined forces on a risky venture to investigate a new, transdimensional view of space and time that challenges the conventional history of the universe.

Cosmologists celebrate 2001 as the year the U.S. National Aeronautics and Space Administration (NASA) launched a satellite mission from Cape Canaveral to investigate not the black monolith of Kubrick’s film but a thin, dark layer of space at the outermost edge of the visible universe. The mission is called WMAP (pronounced “W-map,”), which stands for Wilkinson Microwave Anisotropy Probe. On board is a bank of highly sensitive detectors designed to gather some of the ancient light emitted from the dark layer nearly 14 billion years ago, at a time when the first atoms were just beginning to form. Every 2.2 minutes, the satellite spins once around its axis, and every hour the axis itself traces out a circle. From the combination of motions, light from a narrow ring on the sky is collected. Over the course of six months, the entire satellite keeps shifting, until the detectors have covered the entire sky. The sequence will be repeated every six months until enough light has been gathered to make a detailed portrait of the infant universe. (WMAP is a follow–up to the pioneering NASA satellite launched in 1989 called COBE, the Cosmic Background Explorer, which had made an initial low–resolution image of the early universe; in 2006, the leaders of the COBE team, John Mather at the NASA Goddard Space Flight Center and George Smoot at the University of California at Berkeley, were awarded the Nobel Prize in Physics.)

Nineteen months after the WMAP launch, in February 2003, mission head Charles Bennett and his team had collected and analyzed sufficient light to announce their initial findings at NASA’s Washington headquarters, in a press conference broadcast throughout the world. One of us watched in an auditorium at Princeton University, overflowing with what seemed like everyone in town, from mailroom clerks to middle–school students, drawn by rumors of a great new discovery. The other was in a similarly packed lecture room in Cambridge, England. The sense of anticipation was tremendous, each crowd aware that its understanding of the origin and evolution of the universe would hinge on what the WMAP team had found.

At last, Bennett and his team unveiled the image that had emerged after a yearlong exposure. Just like the fictional astronaut peering into the monolith, the WMAP satellite had gazed into the primordial layer and obtained the first clear view of the infant universe. What the greatest thinkers in history—from Plato to Newton to Einstein—could only speculate about was suddenly there for all to see, bringing humanity closer to answering the ultimate question: Where did it all come from?

At the end of the broadcast, world-renowned astrophysicist John Bahcall summarized the sentiments of the scientists watching: “Every astronomer will remember where he or she was when they first heard the WMAP results. For cosmology, the announcement today represents a rite of passage from speculation to precision science.” Bahcall’s point was that not only are the measurements marvelously accurate, but they are also in astonishing agreement with what cosmologists had been expecting.

By the time of the WMAP announcement, most scientists had come to accept a cosmological theory known as the inflationary model of the universe. In scientific discussions, “model” is often used to mean “theory,” especially cases where the idea includes aspects that are qualitative or incomplete. The inflationary model, as the term is used today, refers to a combination of three concepts: the hot big bang model, developed in the early twentieth century; the inflation mechanism, introduced in the 1980s; and the dark energy hypothesis, added in the 1990s.

In this picture, the big bang itself is not explained. It is simply imagined that space and time emerged somehow. Next, it is assumed that just after the bang, a small region of the universe underwent a dramatic process called inflation, during which it expanded a googol (10 raised to the 100) times or more within a billionth of a billionth of a trillionth (10 raised to the negative 30) of a second. Once this period of inflation ended, the energy causing the inflation was transformed into a dense gas of hot radiation. The gas cooled and the expansion slowed, allowing atoms and molecules to clump into galaxies and stars. This picture of an inflationary universe was originally conceived in the 1980s and is now presented in many textbooks. However, recent astronomical discoveries have led to a major amendment to the story—that 9 billion years after the big bang, a mysterious force called dark energy took over and started to accelerate the expansion again. In the standard picture, the expansion of the universe will accelerate forever, turning all of space into a vast and nearly perfect vacuum.

Both of us had been cosmologists for over two decades by the time of the WMAP announcement, and each had played a part in building the case for the leading view of the universe. In the 1980s, Paul was one of the architects of the original inflationary theory. A decade later, he and his Princeton University colleague Jeremiah Ostriker were among the first to incorporate dark energy into the big bang model. They showed that, assuming a particular mixture of matter and dark energy today, it is pos... --Ce texte fait référence à une édition épuisée ou non disponible de ce titre.

Revue de presse

“Two brilliant theorists offer a true-to-life account of their quest to solve one of the deepest mysteries of the cosmos.”
       —Sir Martin Rees, Astronomer Royal and President of the Royal Society, author of Before the Beginning

“Paul Steinhardt and Neil Turok, two architects of modern cosmology, have written an accessible and engaging account of their exciting new theory of cosmic origins. Should their approach someday be confirmed, it would result in a major upheaval to our understanding of how everything—space, time, and matter—came to be.” —Brian Greene, author of The Elegant Universe and The Fabric of the Cosmos

"For the past twenty years, the combination of the big bang theory plus inflation has offered cosmologists an unbeatable one-two knockout punch . . . But the standard model finally has a worthy challenger."
—Robert Naeye, Mercury

“Perhaps you don’t believe in strings, or extra spatial dimensions, or D-branes, or that the universe’s accelerated expansion may someday reverse. But I urge you to suspend such views and read Steinhardt and Turok’s dramatic and very readable account of their cyclic model of the universe. It may well be closer to truth than you think!”
—Sir Roger Penrose, Rouse Ball Professor of Mathematical Physics at Oxford University, author of The Emperor’s New Mind and The Road to Reality: A Complete Guide to the Laws of the Universe

“The authors manage to make complicated concepts such as the cosmic microwave background understandable.”
The Wall Street Journal

“Steinhardt and Turok are eloquent in describing how theoretical physicists puzzle through cosmic problems.”
—Laurence Marschall, Discover
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Amazon.com: 4.6 étoiles sur 5  45 commentaires
71 internautes sur 76 ont trouvé ce commentaire utile 
5.0 étoiles sur 5 A rival theory to inflation 23 juin 2007
Par Jaume Puigbo Vila - Publié sur Amazon.com
Format:Relié|Achat vérifié
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.
29 internautes sur 29 ont trouvé ce commentaire utile 
5.0 étoiles sur 5 Is the universe part of a cyclical Reality? 15 août 2007
Par Jill Malter - Publié sur Amazon.com
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.
48 internautes sur 54 ont trouvé ce commentaire utile 
5.0 étoiles sur 5 Challenging, to say the least, in every way. 26 juillet 2007
Par Jerry Saperstein - Publié sur Amazon.com
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.

16 internautes sur 16 ont trouvé ce commentaire utile 
4.0 étoiles sur 5 A Challenging Ride Through a New Model of the Universe 3 janvier 2008
Par Steve Koss - Publié sur Amazon.com
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.
13 internautes sur 13 ont trouvé ce commentaire utile 
5.0 étoiles sur 5 Major challenge to the big bang theory 25 novembre 2009
Par Donald E. Fulton - Publié sur Amazon.com
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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