Three Roads to Quantum Gravity by Lee Smolin

Three Roads to Quantum Gravity


Well this might end up being lengthy… I have a lot of stuff to address. First let me put up a disclaimer here – I have pretty much zero science background except what I’ve been reading in books. I’ve been branching into reading about physics, quantum mechanics, and the hunt for a theory of everything out of my own curiosity. Also, this book was written in 2001 so there have probably been plenty of changes to the scientific fields discussed in this book since there. Still, it seemed like a good starting point for me to learn a bit more about the hunt for a theory of quantum gravity.
So, here is the description from the back of the book:

“The Holy Grail of modern physics is the theory of “quantum gravity.” It is a search for a view of the Universe that unites two seemingly opposed pillars of modern science: Einstein’s theory of general relativity, which deals with large scale phenomena like planets, solar systems and galaxies, and quantum theory, which deals with the world of the very small – molecules, atoms, and electrons. In the last few years physicists have made steps toward their goal of a completely new theory of space, time and the universe, a “theory of everything.” In Three Roads to Quantum Gravity, Lee Smolin, who has spent his career at the forefront of these new discoveries, presents for the first time the main ideas behind the new developments that have brought a quantum theory of gravity in right.

Written with exceptional style and clarity, Three Roads to Quantum Gravity confronts the deepest questions of the nature of the universe and provides a preview of some of the remarkable scientific developments we can look forward to in the twenty-first century.”

Lee Smolin does an excellent job leading into the book, as he discusses some basic things about time and space, the logic needed to think about aspects of quantum gravity, the causal structure of the universe, black holes, and entropy. I thoroughly enjoyed the first 7 chapters, as they were interesting and Smolin made the ideas easy to understand and used helpful analogies and images. I can honestly say that I learned a lot here, and that these chapters made the book worth reading.
I do think that Smolin missed his main mark with this book, which was to explain the three leading theories currently being worked on that might end up leading to a true theory of quantum gravity. Two of the theories promised to be discussed are two I’ve heard about before – loop quantum gravity and string theory, and I was really looking forward to learning more about these theories.* And that is where the book took a dive and I got frustrated. Almost two chapters are spent on loop quantum gravity, and while I suppose that I learned some basics about it, I feel like it wasn’t explained as thoroughly as the concepts he discussed earlier in the book. Instead, he spent a lot of time talking about his own schooling and career, because he is a physicist working on loop quantum gravity and helped to create the theory. While that’s nice, this entire book is only 225 pages long – I would have preferred that he left out the personal stuff and instead spent more time actually discussing loop quantum gravity.
The chapter about string theory was where I really started to get upset. I’m not a scientist or physicist, and haven’t “picked a side” between LQG and string theory, because I don’t know much about either one and this book was supposed to be a nice introduction to both for me. Smolin didn’t even seem like he was trying to be objective here. The first several pages of the string theory chapter was a story about Einstein and how even he made mistakes and “we are all equally prone to error” – basically patting string theorists on the head condescendingly and saying “It’s okay that you’re wrong.” He continues to make snide remarks about string theory and all of its flaws, while here and there throwing in a compliment to the things that string theory has done right. By the end of the chapter, I have no better understanding of string theory than when I started.
He tries to rectify this a bit in later chapters, in which he admits that neither LQG or string theory is 100% correct and in fact the two scientific communities really need to work together, because that’s the only way that a true theory of quantum gravity will be developed. He discusses the ways in which the two theories might be merged, and points out that the problem each group is having is exactly the problem that the other group has solved. He ends the book optimistically, saying that if both groups can try to work together and as long as people stay excited about theoretical physics, a theory of quantum theory is within our grasp.
He also includes a postscript in the book, written a year after the book was published, in which he discusses some of the things that have changed since writing the book and what it means for LQG and string theory. And while this was nice, it was unnecessary unless he intended to add a postscript to the book every year. (Which since the postscript was written in 2002, he has not done.)
I think the next science book I read will be written by a string theorist, to give myself a sense of balance.
Sarah Says: 3 stars (2 stars docked because while I did learn a lot, it was not what the premise of the book promised, and because of his haughty attitude towards string theory.)
*(Honestly, I don’t know what the third theory was supposed to be… I think it was black hole thermodynamics, but that doesn’t seem like it’s a theory that anyone is hoping will be the answer to quantum gravity. Rather, I think that black hole thermodynamics is expected to play a part in a final unified theory of quantum gravity / everything.)




    1. I gave it 3 stars because I did learn some things, even though it wasn’t the things I was hoping to. And he was really only that haughty whenever string theory was mentioned – I was kind of fine with the book up until those chapters.


Talk to me.

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s