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

by Roger Penrose
Princeton, 2016, 501 pages
reviewed by T. Nelson

oger Penrose's earlier book, The Road to Reality, was didactic: I've recommended some of his chapters as nice introductions to various topics. This one isn't. It's an argument against some of the weird stuff in modern physics. His take: it's not weird enough.

Criticizing string theory might seem pointless; it's been done to death, and the theory could change radically tomorrow. So what we want from Penrose is new ideas. (No more quantum consciousness, please!) New ideas are here, but this book is aimed at a general audience, so they're way in the back.

Part 1 (‘Fashion’) are his arguments against string theory. The main one is those extra useless dimensions that are curled up in every string. He says there's more than enough energy in the solar system to affect a string and disrupt them. But of course that's irrelevant: what we really want is high energy density, not just a lot of it. The cross section of such an interaction would be way too small. Moreover, not just any kind of energy would do; it would have to be gravitational energy. Maybe I'm misunderstanding the argument; not sure what he's getting at here.

Part 2 (‘Faith’) is an elementary nontechnical explanation of quantum mechanics starting with the two-slit experiment and the Mach-Zehnder interferometer. The idea here is that we take QM on faith, but there are problems, the main one being that decoherence might not be something that occurs automatically as everybody assumes; it only happens, he suggests, when a shift in mass occurs. This is wholly described in the last two pages of part 2; people knowledgeable about QM can skip the rest.

In part 3 (‘Fantasy’) he has two main points: first, he favors equating dark matter with Einstein's cosmological constant Λ. Second, he regards the theory of multiverses and cosmological inflation as sheer fantasy. Not, he says, that there's anything wrong with that, but we need to recognize that inflation is purely conjectural. All the ideas so far aren't fantastic enough: “Something more, perhaps with an even greater element of fantasy, is needed!”

Instead of inflation, Penrose favors the ekpyrotic / cyclic cosmology theory. And so it's not until page 328 that the book gets really interesting.

In Part 4 (‘A new physics for the universe?’) we finally find out why Penrose was arguing against fashion: he proposes taking his own invention of twistors, which are about as unfashionable as you can get (which could well mean they're closest to the truth), and applying them to cosmology.

What is the audience for this book? Not scientists, who would already know all this stuff; they should skip the first 327 pages and go straight to the good part. Not people looking for a debunking of ideas of modern physics: Penrose's critiques are pretty darn gentle. I'd say the typical reader would be a layman who wants a basic orientation to QM, QFT and cosmology but has little physics or math background. These readers should start with the math appendices, which are a very light introduction to complex numbers and vectors.

It could be a roller coaster ride. Judging from the reviews on Amazon, many laymen seem to be struggling with even the little math that's here. I'd say, though, that it's really not that bad.

nov 21, 2016