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A physicist casts a critical eye on popular ideas in cosmology, quantum mechanics, and string theory

Fashion, Faith, and Fantasy in the New Physics of the Universe

Roger Penrose
Princeton University Press
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In the personal coda to Fashion, Faith, and Fantasy in the New Physics of the Universe, mathematical physicist Roger Penrose describes how, in response to a question by a Dutch journalist, he replied that he does not consider himself to be a “maverick.” He interprets the term to mean someone who deliberately goes against conventional thinking for the sake of standing apart from the crowd. Under this definition, Penrose is indeed not a maverick. He does, however, stand out as an independent thinker, who for years has been critical of a few current trends in theoretical physics and cosmology.

You don’t have to agree with all, or even a part, of Penrose’s criticism to realize that his latest book represents an extremely original, rich, and thoughtful survey of today’s most fashionable attempts to decipher the cosmos on its smallest and largest scales.

The “fashion” in the book’s title refers mostly to the popularity of string theory and the so-called “M-theory”—the efforts to formulate a quantum theory of gravity. “Faith” refers to our persistent belief in the reality underlying quantum mechanics, even when it seems to clash with the reality we experience in the large-scale “classical” world. “Fantasy” targets mainly the inflationary model, which contends that our universe underwent a stupendous expansion when it was only a fraction of a second old. However, Penrose doesn’t spare other theories that he regards as fantasies, such as eternal inflation and the multiverse, from harsh criticism either.

Penrose makes a strong case for the fact that once a physical theory becomes fashionable, students are mainly guided into that direction of research, sometimes at the expense of other, perhaps equally promising ideas. Using string theory as an example, he points out a number of potential difficulties with the theory’s requirement for the existence of extra (unobserved) dimensions. As he has done in previous books, he also emphasizes the fact that string theories, despite their fashionable status, have failed so far to produce any directly testable predictions.

The many-worlds interpretation of quantum mechanics is not, writes Roger Penrose, “a sensible viewpoint with regard to physical reality.”LEE DAVY/FLICKR

The many-worlds interpretation of quantum mechanics is not, writes Roger Penrose, “a sensible viewpoint with regard to physical reality.”

Penrose acknowledges the successes and predictive power of quantum mechanics. He argues, however, that there should be a limit to our quantum faith, such as when the theory’s predictions are in clear conflict with macroscopic reality. (Schrödinger’s proverbial cat could not pass simultaneously through two separate doors in the classical world, for example.) Penrose uses the example of a Geiger counter, which detects energetic particles resulting from radioactive decays, to construct an explanatory bridge between the subatomic and the classical worlds.

When it comes to cosmology, Penrose returns to a topic he has tackled before: the second law of thermodynamics (1, 2). This impactful law states that the entropy in the universe constantly increases. One interpretation of this law argues that just as shaking a box containing a completed LEGO model will result in increased randomness, the universe started from an extraordinarily ordered state. Penrose uses this notion to argue that the inflationary model cannot provide the answer to a number of puzzling observations, such as the “smoothness” (the extreme cosmic uniformity) and “flatness” (the Euclidean geometrical structure) of the universe.

Penrose is not satisfied with merely criticizing fashionable theories. He concludes with a new theory that he calls “conformal cyclic cosmology,” in which each cosmic eon is but one of an infinite succession of such eons. What is remarkable about this proposal is not necessarily its correctness—although he does offer a few potential observational tests—but rather the fact that Penrose has the imagination, creativity, and indeed “chutzpah” to suggest an original model that is entirely outside the mainstream.

As in his previous books, Penrose’s concept of what constitutes a “popular” science book is somewhat different from that of most other science writers. Accordingly, even though much of the mathematics is pushed to appendices, uninitiated readers will probably find this book challenging. Those who put in the required effort, however, will be amply rewarded by the, dare I say, “fantastic” ideas of an original thinker with an unparalleled geometrical intuition.


  1. R. Penrose, The Emperor’s New Mind: Concerning Computers, Minds, and the Laws of Physics (Oxford Univ. Press, Oxford, 1989)

  2. R. Penrose, . The Road to Reality: A Complete Guide to the Laws of the Universe(Knopf, New York, 2004).

About the author

The reviewer is an astrophysicist and the author of Brilliant Blunders (Simon & Schuster, New York, 2013).