Frank Wilczek about Penrose's new book

Frank Wilczek did not allow his first Nobel prize to reduce his activity, and one of the many things he recently did was to read the new book The Road to Reality by Roger Penrose, even though it has about 1100 pages. Wilczek wrote an excellent review of this book for a recent issue of Science. Unfortunately, you need a subscription to access the article, or you need to buy the paper version.



Although I have not read the whole book, it does not seem necessary to determine that I completely agree with Wilczek's comments. First of all, Penrose is a highly original thinker. Among his discoveries, we find

• Various methods and solutions of GR related to dynamics of black holes (which includes his method to gain energy from the Kerr black hole)
• The Penrose (BMN) limit of geometries, a kind of pp-waves
• The Penrose causal diagrams
• The esoteric Insect formalism for GR: tensors are bugs and indices are their legs
• The Penrose tilings and quasicrystals
• The twistors (1967)
• Spin networks that he invented decades before they became fashionable in loop quantum gravity which was another framework that people were proposing as an approach to quantum gravity

If I paraphrase him, Wilczek argues that Penrose's book should rather be called Fifty Sidewalks Around Reality. It is a physics-oriented book, but otherwise another eclectic interdisciplinary work with many layers, different ideas, and viewpoints. Wilczek looks at the book from three different perspectives. Penrose is most successful from the viewpoint of a teenager who is interested in math and physics: the book will make such readers excited about the complex numbers, relativity, and spinors. (Although it is unlikely that they will learn what a line bundle on the twistor space is.)




However, the perspective of a professional physicist is less encouraging. Penrose proposes

• that the wavefunction collapse is a real process that is somewhat connected with quantum gravity and perhaps time-asymmetry of the fundamental physical laws; I guess that Wilczek and I are not the only people who think that these ideas are misguided
• the initial conditions for the Big Bang are, according to Penrose, unlikely - the gravitational field must be very ordered while the matter is in thermal state which is an unlikely state; well, I would say that these things are explained well in Brian Greene's The Fabric of the Cosmos

Penrose also talks about particle physics which is the most problematic part of the book. Wilczek has found several huge errors, for example

• Penrose believes that the Cabibbo angle governs the mixing of K0 and K0bar into K0-short-lived and K0-long-lived.
• Penrose apparently talks about some non-existing alternative directions in electroweak symmetry breaking
• Penrose believes that at this transition, some new kind of disorder arises

Peter Woit loves Penrose's book because it is also critical about string theory: Peter Woit's reaction is more predictable than the Hydrogen atom. Wilczek does not say much about these topics, but according to the available data

• Penrose believes that there is something wrong with the black hole entropy calculations - which must definitely be a misunderstanding on his side (I don't have the book so it's not clear what the misunderstanding is)
• We've been informed that Penrose protested that something had to be wrong with all theories with extra dimensions because the moduli spaces of Calabi-Yau spaces have singularities such as the conifold; Penrose obviously has not been explained that the conifold singularity is exactly one of the physical questions that has been best understood in the 1990s, and physics of string theory around this point is completely non-singular. It's an example of a triumph of string theory. See the paper by Strominger and its 400 citations. ("Conifolds in string theory" is a larger field than "loop quantum gravity", and the former makes sense.) Roger Penrose also does not like higher-dimensional theories because they make his twistor ideas less important.

To summarize with Wilczek: there's much to admire and profit from in this book, but judged by the highest standards The Road to Reality is deeply flawed.