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50 of 53 people found the following review helpful:
5.0 out of 5 stars
A rival theory to inflation, 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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42 of 47 people found the following review helpful:
5.0 out of 5 stars
Challenging, to say the least, in every way., July 26, 2007
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.
Jerry
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16 of 16 people found the following review helpful:
5.0 out of 5 stars
Is the universe part of a cyclical Reality?, 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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