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Cycles of Time: An Extraordinary New View of the Universe, by Roger Penrose
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This groundbreaking book presents a new perspective on three of cosmology’s essential questions: What came before the Big Bang? What is the source of order in our universe? And what cosmic future awaits us?
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Penrose shows how the expected fate of our ever-accelerating and expanding universe—heat death or ultimate entropy—can actually be reinterpreted as the conditions that will begin a new “Big Bang.” He details the basic principles beneath our universe, explaining various standard and non-standard cosmological models, the fundamental role of the cosmic microwave background, the paramount significance of black holes, and other basic building blocks of contemporary physics. Intellectually thrilling and widely accessible, Cycles of Time is a welcome new contribution to our understanding of the universe from one of our greatest mathematicians and thinkers.
- Sales Rank: #213812 in Books
- Brand: Brand: Vintage
- Published on: 2012-05-01
- Released on: 2012-05-01
- Original language: English
- Number of items: 1
- Dimensions: 8.00" h x .65" w x 5.17" l, .53 pounds
- Binding: Paperback
- 304 pages
- Used Book in Good Condition
Review
“A surprising and unorthodox work. . . . Deeply enlightening.”
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“The hyper-density of this book made my brain feel simultaneously wiped out and dazzled.”
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“An intellectual thrill ride. . . . There’s no science fiction here, no imaginative filling in the gaps. There is, however, a very strong scientific case for expanding the boundaries of our thinking.” —Washington Independent Book Review
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“Science needs more people like Penrose, willing and able to point out the flaws in fashionable models from a position of authority and to signpost alternative roads to follow.” —The Independent
“If you’ll forgive a skiing metaphor, Cycles of Time is a black diamond of a book. But like all steep slopes, sometimes you take a moment from your struggles and look up, and in front of you is an utterly gorgeous view.” —The Boston Globe
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“Truly extraordinary. . . . This fascinating book will surely become a classic in the history of cosmology.” —Choice
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�“Of interest to anyone who is interested in the world, how it works, and how it got here. . . . The best thing to do is to take a deep breath, grab a copy of this fascinating book, and plunge right in.” —New York Journal of Books
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�“We must understand why the universe began in an incredibly special state, so well ordered that 14 billion years later, the universe still has not reached maximum disorder. Penrose is at his best when he explains this deep and beautiful mystery, and the book may be worth reading for this chapter alone.” —Science
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“A genuinely new idea about the origins of the universe . . . [which] must be taken seriously.” —The Scotsman
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�“As uncondescending in style . . . as his previous books. . . . [There are] many pleasures to be had.” —The Sunday Times (London)
About the Author
Roger Penrose is Emeritus Rouse Ball Professor of Mathematics at the University of Oxford. He has received numerous prizes and awards, most notably the Wolf Foundation Prize in physics, which he shared with Stephen Hawking,�and The Royal Society's Copley Medal. He is the author of three previous books, including The Emperor’s New Mind. He lives in Oxford, England.
Excerpt. � Reprinted by permission. All rights reserved.
PREFACE
One of the deepest mysteries of our universe is the puzzle of whence it came.
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When I entered Cambridge University as a mathematics graduate student, in the early 1950s, a fascinating cosmological theory was in the ascendant, known as the steady-state model. According to this scheme, the universe had no beginning, and it remained more-or-less the same, overall, for all time. The steady-state universe was able to achieve this, despite its expansion, because the continual depletion of material arising from the universe’s expansion is taken to be compensated by the continual creation of new material, in the form of an extremely diffuse hydrogen gas. My friend and mentor at Cambridge, the cosmologist Dennis Sciama, from whom I learnt the thrill of so much new physics, was at that time a strong proponent of steady-state cosmology, and he impressed upon me the beauty and power of that remarkable scheme of things.
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Yet this theory has not stood the test of time. About 10 years after I had first entered Cambridge, and had become well acquainted with the theory, Arno Penzias and Robert Wilson discovered, to their own surprise, an all-pervading electromagnetic radiation, coming in from all directions, now referred to as the cosmic microwave background or CMB. This was soon identified, by Robert Dicke, as a predicted implication of the ‘flash’ of a Big-Bang origin to the universe, now presumed to have taken place some 14 thousand million years ago—an event that had been first seriously envisaged by Monsignor Georges Lema�tre in 1927, as an implication of his work on Einstein’s 1915 equations of general relativity and early observational indications of an expansion of the universe. With great courage and scientific honesty (when the CMB data became better established), Dennis Sciama publicly repudiated his earlier views and strongly supported the idea of the Big Bang origin to the universe from then on.
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Since that time, cosmology has matured from a speculative pursuit into an exact science, and intense analysis of the CMB—coming from highly detailed data, generated by numerous superb experiments—has formed a major part of this revolution. However, many mysteries remain, and much speculation continues to be part of this endeavour. In this book, I provide descriptions not only of the main models of classical relativistic cosmology but also of various developments and puzzling issues that have arisen since then. Most particularly, there is a profound oddness underlying the Second Law of thermodynamics and the very nature of the Big Bang. In relation to this, I am putting forward a body of speculation of my own, which brings together many strands of different aspects of the universe we know.
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My own unorthodox approach dates from the summer of 2005, though much of the detail is more recent. This account goes seriously into some of the geometry, but I have refrained from including, in the main body of the text, anything serious in the way of equations or other technicalities, all these being banished to the Appendices. The experts, only, are referred to those parts of the book. The scheme that I am now arguing for here is indeed unorthodox, yet it is based on geometrical and physical ideas which are very soundly based. Although something entirely different, this proposal turns out to have strong echoes of the old steady-state model!
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I wonder what Dennis Sciama would have made of it.
Most helpful customer reviews
249 of 255 people found the following review helpful.
A Mathematical Origin to the Universe?
By Dr. Roy Simpson
Many who wish to buy this book will be familiar with the other works of Professor Roger Penrose (such as The Road to Reality). Some will be curious to learn about a new theory of the origin of the Universe. This book presents a radical new idea which Penrose has been developing in the past few years on the Big Bang: essentially the idea is that there was a pre-Big Bang era and there will be a post-Big Crunch era too.
So one could review both the book and the idea itself. Firstly some will worry about the level of mathematics presented in this book. In the main chapters there are equations such as S = k log V - Boltzmann's Equation. If you are not comfortable with this, then maybe you will not get the most from the book. However if you are comfortable with this and similar physics equations and numbers then the first section of the book is readable. Of course there are plenty of diagrams too. There is some hard maths however and this has been relegated to the Appendix (30 pages). This maths is very advanced and another of Penrose's technical books (Penrose and Rindler Volume 2) would be needed to understand it fully - so that is only for the experts. Given that the reader wont be learning this material in the present book it shows that there is some more complex machinery behind the scenes needed to comprehend the full idea.
In the first section the book returns to an old concern of Penrose namely the entropy present in the early universe: less than today - but why so much less? The chapter then focusses in on the Big Bang described using "Conformal Diagrams". The key on page 115 is important for reading these diagrams.
Part 3 introduces the new idea called Conformal Cyclic Cosmology (CCC). Here we learn something about the idea that the Big Bang is merely a transition in the longer history of the universe. To get the most out of the mathematics in this section one needs to understand the idea of the conformal metrics introduced. Fortunately there are no calculations about it in the main text, but the idea needs to be understood. In order to develop the CCC hypothesis Penrose then needs to consider various physics issues: entropy, black hole information loss, the presence of mass in elementary particles. A novel use of other work in these areas provides for an interesting basis for the CCC hypothesis as we also study the far future of the Universe. Finally we close with some observational details from the Cosmic Background Data being gathered by satellites. So CCC is a physically testable theory!
If you are interested in another theory being presented at the forefront of Cosmology and Physics then this is for you. Also it provides another view of Penrose's approach to these subjects which is different from the mainstream. But beware that some of the mathematical ideas (of conformal infinity) go quite deep indeed - easily the subject of another book if this idea is successful!
175 of 185 people found the following review helpful.
Seduced by Math
By Patrick J. Sullivan
Roger Penrose's latest book is an exposition of his latest cosmological speculations. As usual Penrose cheerfully overestimates the mathematical capabilities and accomplishments of the typical scientifically educated lay person his books are ostensibly aimed at. He presents what he sees as a baffling fact, the unusually low entropy state of the early universe, and gradually leads the reader up to his explanation of the nature of our universe. Though Penrose is coy throughout the book's first two sections about the details of his conjecture, the title gives it away and indeed this book is ultimately a speculation about cyclical universes. There are definitely some points of interest, and readers who enjoyed Penrose's earlier works such as The Emperor's New Mind will likely be intrigued by parts of the book. But while less overambitious than the author's sweeping Road to Reality, Cycles of Time is far denser than more accessible popular science works such as Stephen Hawking's A Brief History of Time, so those who found that bestseller to be of use mostly as bookcase filler might want to give Penrose a pass here.
The book is divided into three main sections: entropy and the Second Law of Thermodynamics; the Big Bang and the puzzling low-entropy state of the early universe; then the largest and most detailed concluding section. This section details Penrose's Conformal Cyclic Cosmology (CCC) model, a scheme whereby a tiny portion of a late-stage universe in its Big Rip phase becomes the seed of the next universe's Big Bang, and so on ad infinitum.
Also as the book progresses, the author goes through at least three voices: first the definite, lecturing one in which entropy and Big bang cosmology are presented. Then the speculative, theorizing one in which CCC is detailed. Finally he concludes on a tentative note with overtones of self-doubt. Here Penrose frankly muses aloud. He makes vague moves toward linking (A) the explosive late-stage expansion of the universe as the expansive cosmological constant lambda overwhelms the dwindling effects of gravity and (B) the similarly explosive growth of the very early-stage universe in its hypothetical inflationary phase. But up until that point, Penrose has expressed nothing but skepticism regarding inflation, and in fact one of the self-described strengths of his CCC proposal is that it obviates the need for inflation altogether!
Penrose raises up CCC as the latest rival to the plain linear time Big Bang. He admits to a youthful fondness for the old Continuous Creation (CC) model, and CCC is admittedly negatively motivated by an authorial distaste for the unadorned Big Bang. On the positive motivation side, Penrose has been so captivated by a mathematical model developed by his colleague Paul Tod that he has developed it into his CCC idea. There seems to be no direct evidence for CCC, it offers no possibility for experiment, and it is probably non-falsifiable. In other words, on its merits it has a great deal in common with string theory, which Penrose has always been openly skeptical of. I refer to his seduction by math because reading Penrose enthuse over Tod's conformal map and its implication of a pre-Big Bang universe is a little like reading about Edward Witten championing string theory on the grounds of its mathematical beauty.
The author is of course not the first to speculate about earlier and later Big Bangs, cyclical Big Bangs, infinite Big Bangs, Big Bounces, etc. He acknowledges as much and even devotes a brief chapter to previous pre-Big Bang theories. Oddly though, he is quite unsympathetic to rival ideas that on the surface have a great deal in common with his CCC; I am referring specifically to Andre Linde's infinite inflation model. Penrose is skeptical of inflation and the need for it and is no champion of string theory or any string-based ideas. But strings aside, anyone familiar with infinite inflation will be right at home with CCC.
So although I am left completely unconvinced by book's end about the usefulness of or the need for CCC, the foregoing thoughts should serve to demonstrate that the book has succeeded at least in getting one reader to consider Penrose's arguments and to ponder the issues he raises. If Cycles of Time can do as much for some key young physics and math students, then the author may be content.
I should mention that although the appendices are mostly repositories of even more advanced math than Penrose believed most of his readers would be comfortable with, the endnotes are of significant use while reading the text. Chore though it may be, it is a more rewarding read to keep one finger open to the notes while reading the text and flip between the two as needed. The notes explain and clarify points Penrose makes throughout the text; they are mostly not simply page references to cited works. I wish (American) publishers would realize that in many cases such as this one footnotes serve the purpose far better than endnotes; they are not just irrelevant distractions cluttering up the page margin. But this seems to be a losing battle, and Penrose's publisher, Knopf, has joined the majority in considering notes to be best tucked tidily into the back of the book, 200 pages away from the text they apply to.
59 of 62 people found the following review helpful.
Beautiful but very speculative
By Light Pebble
Penrose puts forth an old idea, that the end of our universe is the start of a new one, in a beautiful new way. That is, eventually the universe will lose track of the scale of space and time. So the whole giant universe turns into a Big Bang of about zero size!
Astronomers have recently found out that the expansion of the universe is accelerating, so it doesn't look like it will ever recollapse in the ordinary way. But in Penrose's theory, this apparently depressing reality is essential for a cyclic universe, because it means that the universe at the end of time is a spacelike surface, so its geometry can match the geometry of the Big Bang singularity in the next eon.
He offers a partial answer for an old puzzle: why did the Big Bang have such incredibly low entropy? The second law of thermodynamics tells us that entropy never decreases. The low entropy of the Big Bang defines the arrow of time, since entropy has been increasing since then, and life wouldn't be possible without a low-entropy state to start from. But where did the very low-entropy Big Bang come from?
Penrose's answer (or part of it) is that black holes destroy the information that goes into them (whether black holes destroy information is a big controversy in physics). That means that when the black hole eventually evaporates by Hawking radiation, the entropy that was in the matter that fell in has been permanently destroyed. I don't know if this can destroy enough entropy to explain the next very low entropy Big Bang.
Penrose doesn't believe the inflation theory, which is that space expanded incredibly rapidly right after the Big Bang. He says his conformal cyclic cosmology theory explains the things that inflation was invented to explain: it explains correlations in temperature in the cosmic microwave background between areas that are separated by large angles, and the scale invariance in the temperature fluctuations. The CCC theory also requires Weyl curvature to be zero at the Big Bang. This apparently explains why we don't see magnetic monopoles, another thing that inflation is invoked to explain, although Penrose doesn't discuss this in his book.
The CCC theory seems much more appealing than the inflation theory. It's more parsimonious, not requiring extra fields or an incredibly rapid expansion of spacetime. The universe would have expanded at the normal rate, only over a very very long time before the Big Bang.
The big hole in Penrose's theory is that our universe can only lose track of the scale of space and time if rest mass disappears. Rest mass gives a scale to spacetime. So it's necessary that all particles should eventually decay into massless particles like photons, or lose their rest-mass some other way. He hasn't come up with any good explanation for how this would happen. His best attempt at a theoretical framework for the decay of rest mass is:
"A standard procedure for addressing the idea of an 'elementary particle' is to look for what are termed the 'irreducible representations of the Poincare' group'. Any elementary particle is supposed to be described according to such an irreducible representation. The Poincare' group is the mathematical structure describing the symmetries of the Minkowski space M, and this procedure is a natural one in the context of special relativity and quantum mechanics. The Poincare' group possesses two quantities referred to as Casimir operators, these being rest-mass and intrinsic spin, and accordingly the rest-mass and spin are deemed to be 'good quantum numbers', which remain constant so long as the particle is a stable one and does not interact with anything. However, this role of M appears to be less fundamental when there is a positive cosmological constant L (Greek letter Lambda in the book) present in physical laws (as L=0 for M), and it would seem that, when we are concerned with matters related to cosmology, it should be the symmetry group of de Sitter space-time D, rather than of M, that should ultimately be our concern. However, it turns out that rest-mass is not exactly a Casimir operator of the de Sitter group (there being a small additional term involving L), so that its ultimate status is more questionable in this case, and a very slow decay of rest mass seems to me to be not out of the question."
I don't know how convincing this is. Does rest mass need to be a Casimir operator of the spacetime, to be a good quantum number, so that it's conserved for a particle as long as it exists? Apparently nobody's worked out what becomes of quantum mechanics and the Standard Model of particle physics in de Sitter spacetime. Until they do, and rest mass really does turn out to fade away in the expanding universe, Penrose's theory will limp badly.
Perhaps the above quote will tell you whether you'll find Cycles of Time to be readable, or whether it'll make your eyes glaze over. I found it readable, but I'm somewhere between the "intelligent layman" and a real expert. I loved Penrose's earlier book The Road to Reality, and worked all the exercises in it that looked challenging, except for one.
In Cycles of Time, unlike in Road to Reality, Penrose relegates almost all equations and mathematics to a couple of appendices, where he explains the transition from the scale free geometry at the end of the previous eon, to the Big Bang. The dynamics of the earlier universe propagate through the Big Bang. There's a loose end: unwanted freedom in the spacetime metric right after the Big Bang, so it isn't fully determined by the universe before the Big Bang. Penrose proposes various ways of eliminating this freedom.
Penrose tends to throw around technical language without much explanation. Road to Reality might be a good reference; or Google it. He mentions "gravitational degrees of freedom" early in the book. What concretely ARE gravitational degrees of freedom, I wondered? I asked online, then noticed he defines them later in the book!
Even though he uses technical language, he's very good at making advanced physics accessible. I found Road to Reality to be intellectually nurturing. It stimulated me to learn multivariable complex analysis, which he uses in his work.
Penrose is a maverick who disagrees with much of the contemporary physics consensus. He dislikes many contemporary physics theories that are science-fictiony or kludgish, like string theory with its extra dimensions, and inflation. But as Mark Twain said, "Whenever you find yourself on the side of the majority, it is time to reform (or pause and reflect)." Penrose has done it again in this book: come up with a wonderful and beautiful idea for Penroseland, his mirror of reality. Perhaps his mirror focuses better than the consensus mirror.
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