Sir Roger Penrose, Emeritus Rouse Ball Professor of Mathematics in the University of Oxford, has written another marvellous book. Once again, he manages to discuss topics in modern physics in a way that will educate and enthuse the intelligent layman while retaining enough substance to engage the more sophisticated reader. This time, the topic is (in Penrose's words) "an extraordinary new view of the universe," a theory that he calls "Conformal Cyclic Cosmology (CCC)."
As in his previous efforts, Penrose's success derives from his ability to actually teach some fundamental concepts before entering the more speculative domains. Hence, the first third of the book is devoted to an informative explanation of entropy and the second law of thermodynamics, and their place in describing the evolution of the universe. In the second third, Penrose emphasises the unique character of the low entropy state of the early universe before gravitational degrees of freedom had been activated. In this part, he also introduces the notion of "strict conformal diagrams" that provide a graphical description of the rather involved maths.
The final portion of the book is devoted to an intriguing summary of CCC. This is based largely on Penrose's earlier introduction of the Weyl Curvature Hypothesis that requires the Weyl curvature tensor to vanish at the conformal hypersurface of the Big Bang. CCC proposes that beyond the distant future of the current universe lies another Big Bang and, conversely, before the Big Bang of the current universe lies the future infinity of a previous one, with space-time being merged at the boundary of each "aeon" by a conformal rescaling of the metric tensor. How this is reconciled with the continuing increase in entropy, consistent with the second law, is quite interesting and I won't spoil the surprise by revealing it here. The book concludes with a mathematical appendix that more fully describes some of the basic notions. This, in conjunction with the notes and cited references, will help the student on his way.
To be sure, this book will challenge even the brightest and most motivated layman. Understanding just the elementary exposition of the basic ideas requires some serious thinking. And Penrose cannot help dropping terms like "tensor field" and "tangent space" that will baffle the novice. There are even a few equations. In addition to thinking, one should be prepared to consult additional references and ask many questions. But, after all, that is what learning is all about.
Enthusiastically recommended!
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Top reviews from other countries
LRoyz
Penrose is a genius but not the best writer
Reviewed in the Netherlands on March 27, 2024R. Pedrosa
Wonderful little book on deep issues regarding our way of understanding the universe.
Reviewed in Brazil on December 16, 2020
Edoardo Angeloni
A great expert talks about the contexts of the physics.
Reviewed in Italy on September 15, 2021
