Three Roads to Quantum Gravity by Lee Smolin

  (out of 5 stars)

I just started Smolin's latest book, The Trouble With Physics, and had gotten about 50 pages into it when my copy of Three Roads to Quantum Gravity arrived, so I decided to dig into it before moving to Trouble. Three Roads is Smolin's excellent overview of the landscape and issues involved in the pursuit of a quantum theory of gravity. A very quick read, filled with useful diagrams, I was able to knock it out in a quick evening.

Rather than giving a hundred pages of history or dozens of 'nifty' side stories, Smolin hits a few brief points needed to understand the book and quickly moves into describing how black holes, loop quantum gravity, and string theory have appeared to lead the way in the search for the elusive gravitational theory.

Smolin is one of the pioneers of loop quantum gravity, but is fairly rare in that he has also worked with string theory during his career. His perspective on the competition of the two theories offers some hope for progress by way of synergy (though of course, this was published in 2001 and the lack of a solid theory of quantum gravity, as well as the title of his latest book, The Trouble With Physics: The Rise of String Theory, the Fall of a Science, and What Comes Next, leads me to believe he has lost his rose-colored glasses).

Unlike string theory books by Brian Greene, Michio Kaku and others, and especially unlike the bitter, sarcastic (and relatively boring) anti-string theory book by Peter Woit (titled Not Even Wrong), Smolin offers a very balanced, complimentary account of physics as it stood in 2001, much of which is still accurate and pertinent today.

The discussions of casuality, black hole horizons and entropy, and the implication that space is quantized offer some well-articulated additions to the discussion of popular physics. Smolin doesn't weigh down this book with math or complex discussions of symmetry (unlike Woit). However, this book is not dumbed down for the average reader. You need some strong interest in science, and a basic understanding of physics in order to enjoy this book, but again, it isn't overwhelming or overly complex.

Later chapters cover loop quantum gravity, string theory, M-Theory (which was still extremely new at the time of publication), the holographic principle, and some meta discussions on the subject of anthropic arguments. I hope to find a more detailed presentation of loop quantum gravity, whether from Smolin or another physicist, because the discussion of the 'knots, links, and kinks' offered here is a summary and skips most of the details in favor of brevity and clarity.

I look forward now to picking up Smolin's latest book (Trouble) again and charging into a more recent offering on the subject. I'm glad I read this one before getting too far into Trouble because it really establishes the dynamics of physics as seen through Smolin's eyes as well as setting Smolin's own mindset for comparison with the latter offering. Four and one-half stars and highly recommended to the science junkie.