# Three Roads to Quantum Gravity by Lee Smolin

The theory of quantum gravity is often called the holy grail of modern physics, as it would unite the two most important theories in physics — quantum mechanics and general relativity. The great problem that physicists run into when trying to create the theory of quantum gravity is that Einstein’s general relativity and quantum mechanics seem to be incompatible. General relativity is the theory of space-time, which is mostly used in the context of big objects in the universe, for instance galaxies or even the universe itself. Quantum theory, on the other hand, is the theory of small objects, for instance atoms and the constituents of atoms. When these theories are put together, the calculations produce infinities, which is usually a big headache for theoretical physicists. And even though it’s not the first such case in the history of theoretical physics, scientists can’t resolve the infinities using any typical methods.

“Three Roads to Quantum Gravity” by Lee Smolin focuses on the possible ways of joining relativity and quantum theory together. Lee Smolin, who is one of the leading experts in the field, does a great job at explaining the possible ways to quantum gravity in a easy-to-understand and non-technical manner. So here’s a short review of the book.

**Book Details**

**Paperback:**240 pages**Publisher:**Basic Books; 1st edition (July 2, 2002)**Language:**English**ISBN-10:**0465078362**ISBN-13:**978-0465078363**Average Customer Review:**4.1 out of 5 stars (52 customer reviews)**Amazon Best Sellers Rank:**#481,159 in Books (top 100 physics books)

**About the Author**

Lee Smolin earned his Ph.D. in physics at Harvard, then went on to teach at Yale and Pennsylvania State before helping to found the innovative Perimeter Institute. Smolin is best known for devising several different approaches to quantum gravity, in particular loop quantum gravity. He advocates that the two primary approaches to quantum gravity, loop quantum gravity and string theory, can be reconciled as different aspects of the same underlying theory.

**Short Review**

In Three Roads to Quantum Gravity, Lee Smolin provides a concise and accessible overview of current attempts to reconcile two most important theories of physics — quantum theory and general relativity — into a final “theory of everything.” He explains in simple terms what scientists are talking about when they say the world is made from exotic entities such as loops, strings, and black holes and why these concepts are of great importance in the search for quantum gravity.

The book was written with “advanced laymen” readers in mind. There isn’t a lot of mathematics and technical language, however some general knowledge of relativity and quantum theory is necessary to understand the whole book. As, for expert readers, I wouldn’t recommend this book, as it is only an introduction to this hard yet interesting subject.

Lee Smolin has played an important role in the formation of quantum loop gravity, so naturally the book focuses on this approach mostly. The rivalry between string theorists and their opposers is well known in the world of science and it can be felt in this book as well. Lee Smolin believes that both loop quantum gravity and string theory can be unified as there is some kind of underlying theory, which is seen from different perspectives using LQG and string theory. This is all great, but sometimes it feels like the author is ignoring string theory as an inferior one. Nevertheless, for those looking for an introduction to quantum gravity, the coverage of both theories should be good enough.

Overall, I would recommend this book for those looking for a simple-to-read and mostly non-technical introduction to quantum loop theory. In addition, the author has a unique style and offers some personal anecdotes about the rivalries, epiphanies, and intrigues concerning the ongoing search for the theory of quantum gravity. All of this makes this book worthy of your attention.

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