The Order of Time

Carlo Rovelli

Riverhead, 2018, 240 pages

Reviewed by T. Nelson

I had tears in my eyes after reading this little book on the physics of time. Not because it is so beautifully written, or because his nontechnical explanations of the latest thinking about what time may be are so clear, but because I became immensely jealous of Rovelli's erudition and his writing skill. And even more so because he gets paid to work on this stuff. More than anything else, what I learned from this book is that I hate Carlo Rovelli.

I can take solace in the fact that he doesn't yet know what time is. Also, on page 117 he has a sentence with no verb.

Rovelli describes entropy and how some physicists think it is the basis for the directionality of time. The universe's entropy increased as space expanded after the Big Bang. But he knows that more than just that is needed, and besides, didn't he say in his last book that entropy is a fiction? Or did he change his mind?

We could suppose that maybe time is an artifact of the three spatial dimensions moving with respect to each other as they expand, or we might take Rovelli's description of time as a type of “blurring”—or more accurately that energy and time are ‘conjugate variables’, which means we have a sort of dualism, two ways of looking at the same thing. The trouble comes in when we say that something changes: just as spatially extended objects like those that make up Rovelli's quantum foam can only have a size if they exist in a pre-existing space, change can only happen if there is a pre-existing thing called time for the change to occur in. This is the problem of the background that physicists are trying to deal with. It's a conceptual problem whereby the concepts with which we think worm their way into our solutions.

The sentences that lack verbs may, therefore, be no accident. We will need a whole new way of thinking before we can answer these questions.

may 12, 2018

Acoustic Metamaterials: Negative Refraction, Imaging, Lensing and Cloaking

R.V. Craster and Sébastien Guenneau, eds.

Springer, 2017, 323 pages

Reviewed by T. Nelson

Negative refraction metamaterials are not just for making flat optical lenses and for cloaking airplanes against radar. They can be used to manipulate any kind of waves, including sound waves. The range of potential uses is astounding: acoustic metamaterials can be used to create acoustic microscopes with a resolution that is a small fraction of a wavelength—something considered impossible only a few years ago. They can create acoustical cloaks, which can make submarines undetectable and invisible to sonar. At even lower frequencies, an acoustic metamaterial could even cloak a building against earthquakes, so the vibrations pass harmlessly around them. This beautifully printed and very expensive multi-author book describes the theory for such materials as well as how they're made and what they can accomplish. Some chapters are almost all mathematical; others supplement the math with interesting colored graphs and diagrams, and some are surveys of the particular field.

dec 29, 2017

Particle Physics, 4e

B.R. Martin and G. Shaw

Wiley, 2017, 456 pages

Reviewed by T. Nelson

Particle physics is one of those fields where everything keeps changing, so everyone has to keep learning it over again. This book is designed to fill the gap between quantum mechanics and quantum field theory. It has the usual stuff about the quark model, QCD, CPT symmetry, and electroweak unification, and has 65 pages of appendices on things like relativistic kinematics and gauge theory. There is a chapter on detectors.

The math isn't too bad, and there are good insights here, though things could perhaps be explained a little more clearly in some places. Answers to all the problems are on the book's website, which helps for self-study. They use Feynman diagrams, but don't tell you how to calculate them.

The real advantage of this book is that it's new enough to have a good discussion of the Higgs mechanism. The last chapter talks about interesting unsolved problems in particle physics, such as double β decay, supersymmetry, and dark matter. The authors love neutrinos and the LHC, and they seem to really, really hate string theory.

dec 31, 2017