10 of 10 people found the following review helpful:
5.0 out of 5 stars
Major challenge to the big bang theory, November 25, 2009
This review is from: Endless Universe: Beyond the Big Bang -- Rewriting Cosmic History (Paperback)
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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2 of 2 people found the following review helpful:
5.0 out of 5 stars
Interesting ideas, February 5, 2010
This review is from: Endless Universe: Beyond the Big Bang -- Rewriting Cosmic History (Paperback)
This book gives the history and details, in everyday language, of what may turn out to be the two leading theories of the universe.
At least so far. For all the hype about getting close to a "Theory Of Everything" over the last 30 or more years, I wouldn`t be
surprised if these were to eventually bite the dust as so many others have before. But still, the ideas presented are interesting.
And who knows, one of them might actually be right, or at least point in the direction of the right anwsers.
The book is well written, easy to understand, and in everyday language. A fun read.
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7 of 11 people found the following review helpful:
4.0 out of 5 stars
A radical new model of the history of the universe, December 4, 2008
This review is from: Endless Universe: Beyond the Big Bang -- Rewriting Cosmic History (Paperback)
The basic idea presented in this book is a cyclic model of the cosmos, in which our universe is a "brane" (short for "membrane") that is constantly colliding with another brane along an extra dimension. Confusing? A simple illustration might be to imagine two sheets of paper, one on top of the other, where the space between them is repeatedly expanding and contracting as the sheets bounce off of each other. This is somewhat like the Big Bounce hypothesis, except the crunch only happens along the extra dimension between the branes, not within the branes themselves. That's why we only see our universe expanding. This model fits well with string theory (or the more refined "M" theory), in which branes can be viewed as much larger and complex string arrangements.
It's a fascinating idea, even if it does entail some exotic concepts like branes, extra dimensions, and a springlike force that cyclically attracts and repels parallel universes. The great thing about the theory is that it is falsifiable. The science was a little over my head, but to summarize, this cyclic model predicts that we will observe gravitational waves behaving differently than what is predicted by the more popular inflation model. Unfortunately, these predictions are too subtle for us to observe at present, but the matter should be settled within the next couple of decades or so as our technology advances.
On a side note, as a theist, I was rather impressed by the charitable tone that the authors used in discussing the relationship between cosmology and religion. But in the final chapters they made it seem as if the only contenders in the field of cosmology were their cyclic brane collision model and the more popular inflationary multiverse. What about a single inflationary universe model? Such a view might have strongly theistic implications, but I don't think it should be ruled out a priori. Sometimes, especially in cosmology, it is impossible to compartmentalize physics and metaphysics.
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