Three Roads to Quantum Gravity (Paperback)

~ Lee Smolin (Author) "We humans are the species that makes things..." (more)
Key Phrases: loop quantum gravity, anthropic question, consistent string theories, Louis Crane, Chris Isham, Carlo Rovelli (more...)

Editorial Reviews

Amazon.com Review

It's difficult, writes Lee Smolin in this lucid overview of modern physics, to talk meaningfully about the big questions of space and time, given the limitations of our technology and perceptions.

It's more difficult still given some of the contradictions and inconsistencies that obtain between quantum theory, which "was invented to explain why atoms are stable and do not instantly fall apart" but has little to say about space and time, and general relatively theory, which has everything to say about the big picture but tends to collapse when describing the behavior of atoms and their even smaller constituents. Whence the hero of Smolin's tale, the as-yet-incomplete quantum theory of gravity, which seeks to unify relativity and quantum theory--and, in the bargain, to move toward a "grand theory of everything." Smolin ably explains concepts that underlie quantum gravity, such as background independence, the superposition principle, and the notion of causal structure, and he traces the development of allied theories that have shaped modern physics and led to this new view of the universe.

Although he allows that "it has not been possible to test any of our new theories of quantum gravity experimentally," Smolin predicts that a solid framework will be established by 2015 at the outside. If he's correct, the years in between promise to be an exciting time for students of the physical sciences, and Smolin's book makes an engaging introduction to some of the big questions they'll be asking. --Gregory McNamee --This text refers to the Hardcover edition.

From Publishers Weekly

The most obvious questions--e.g., "What are time and space?"--are nearly impossible to answer. Smolin (The Life of the Cosmos), professor of physics at Pennsylvania State University, offers "a report from the front" of the current "revolution" in theories of space and time. Aimed at beginners, this careful treatment of the search for a single theory that brings together relativity and quantum theory will draw in potential explorers. Illus.

Copyright 2001 Cahners Business Information, Inc.

--This text refers to the Hardcover edition.

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Product Details

• Paperback: 240 pages
• Publisher: Basic Books; 1st edition (July 2, 2002)
• Language: English
• ISBN-10: 0465078362
• ISBN-13: 978-0465078363
• Product Dimensions: 7.8 x 5.3 x 0.8 inches
• Shipping Weight: 7.2 ounces (View shipping rates and policies)
• Average Customer Review: 4.2 out of 5 stars  See all reviews (50 customer reviews)
• Amazon.com Sales Rank: #249,290 in Books (See Bestsellers in Books)

Customer Reviews

Most Helpful Customer Reviews

95 of 100 people found the following review helpful:

4.0 out of 5 stars Readers get at least a vague picture of a difficult problem, July 27, 2001

By	Tatsuo Tabata "tttabata" (Sakai, Osaka Japan) - See all my reviews (REAL NAME)

This review is from: Three Roads to Quantum Gravity (Hardcover)

The completion of a quantum theory of gravity (quantum gravity for short) is one of the most challenging problems in science in the twenty-first century. This theory aims at unifying Einstein's theory of general relativity for large-scale phenomena with the quantum theory for the micro-world, to get understanding of everything from space and time to matter and the universe. Lee Smolin, Professor of Physics at Pennsylvania State University, tells the story of recent and future research pursuing this theory for the intelligent layperson.

The author writes earlier chapters very understandably. The reader who knew nothing about the quantum gravity learns easily the following interesting things: There are three approaches to quantum gravity, i.e., the route from quantum theory (string theory), the road from the theory of general relativity (loop quantum gravity), and the path from fundamental principles. To do cosmology the classical logic demanding that every statement be either true or false is inadequate. A theory of quantum gravity has to answer about the nature of the information tapped in a quantum black hole. The search for the meaning of the temperature and entropy of a black hole is now leading to the discovery of the atomic structure of space and time. Etc.

In the middle of the book the author states that the style of these chapters will be more narrative than others because he can describe from personal experience some of the episodes in the development of loop quantum gravity. Lessons told are, for example, as follows: Science progresses quickly when people with different backgrounds and educations join forces. Einstein's example teach us that trying to invent new laws of physics requires not only intelligence and hard work but also insight, stubbornness, patience and character. Of course, these are also quite understandable.

In the last three chapters some or most of readers might find it difficult to follow the author's explanation. After reading the whole book, however, all the readers would feel that they have gotten at least a vague picture about the difficult problem of proceeding to quantum gravity. This is an exciting book for those who want to catch a glimpse of theoretical physics at its forefront.

There are some typos. Among them the followings are especially unfortunate, because the meanings of one of the laws of thermodynamics and the Heisenberg uncertainty principle are completely reversed to lead laypersons astray: In chapter 7, "The second law of thermodynamics requires only that the total entropy of the world never increase" should read "The second law . . . never decreases." In two inequalities in chapter 11, the symbol of "less than" should be that of "greater than or equal to."

34 of 35 people found the following review helpful:

3.0 out of 5 stars Nice book on Quantum Gravity, July 19, 2001

By	Kenneth L. Graham (Ann Arbor, MI USA) - See all my reviews (REAL NAME)

This review is from: Three Roads to Quantum Gravity (Hardcover)

I approached this book with great enthusiasm, hoping for a pedestrian treatment of loop quantum gravity (LQG). To be fair, most of this book is pretty good. Smolin writes pretty well, especially about relational quantum mechanics and how it relates to quantum gravity and cosmology. In addition, Smolin clearly points out why many relativists have issue with string/m-theory's lack of background independence.

I was, however, mildly disappointed in his discussion of the physical meaning of spin networks and loops and in his exposition of a possible synthesis of M-theory and LQG. Perhaps I overlooked it, but this book doesn't directly point out how you go from spin networks and spin foams to spacetime. But, you can figure it out... if you know enough general relativity and quantum field theory.

The appendix of this book is excellent! It provides many useful references to the literature.

All things considered though, this book is worth a read, especially to learn about the connection between spacetime, gravity, and quantum mechanics.

I originally rated this three stars. I recently reread the book and now want to give it four stars.

35 of 39 people found the following review helpful:

5.0 out of 5 stars Light Reading On A Heavy Subject, June 28, 2001

By	Bruce Crocker "agnostictrickster" (Whittier, California United States) - See all my reviews (TOP 1000 REVIEWER)    (REAL NAME)

This review is from: Three Roads to Quantum Gravity (Hardcover)

Three Roads To Quantum Gravity by Lee Smolin isn't the easiest highway to travel in the universe, but will be rewarding to anyone taking the journey. Smolin, currently a professor at Penn State [my alma mater :)], writes simply, but smartly about the biggest piece of unfinished physics business leftover from the 20th Century, the resolution of the conflicts between our theory of the large, general relativity, and our theory of the small, quantum mechanics. Smolin assumes an interested and educated reader and simplifies our trip by not doing long introductions to relativity and quantum mechanics. After introducing the idea of a theory of quantum gravity, Smolin spends the rest of the book laying out the 'three roads' of the title, spending slightly more time on loop quantum gravity, the 'road' he's spent the most time on. Although not as elegantly written or as detailed as Brian Greene's The Elegant Universe, Three Roads To Quantum Gravity compliments that earlier book by coming at 'theory of everything' territory from a different direction. Since there is no AAA for physics, layfolks like myself should be glad that we have guides like Lee Smolin to direct us through the hidden regions of our universe.