Product Description

From one of the world's most distinguished scientists, the first popular book to present the controversial and exciting ideas behind quantum gravity.

The Holy Grail of modern physics is a theory of the universe that unites two seemingly opposing pillars of modern science: Einstein's theory of general relativity, which deals with large-scale phenomena (planets, solar systems and galaxies), and quantum theory, which deals with the world of the very small (molecules, atoms, electrons).

In Three Roads to Quantum Gravity, Lee Smolin provides the first concise and accessible overview of current attempts to reconcile these two theories in a final "theory of everything." This is the closest anyone has ever come to devising a completely new theory of space, time and the universe to replace the Newtonian ideas that were the foundation of all science until the beginning of the twentieth century.

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 sight. 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. As he does so, he tells the fascinating stories behind these discoveries: the rivalries, epiphanies, and intrigues he witnessed firsthand.

Science Masters Series

Product Details

• Amazon Sales Rank: #101818 in Books
• Published on: 2002-08-15
• Released on: 2002-07-02
• Original language: English
• Number of items: 1
• Binding: Paperback
• 240 pages

Features

• ISBN13: 9780465078363
• Condition: NEW
• Notes: Brand New from Publisher. No Remainder Mark.
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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

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.

From Scientific American
A colleague of mine, an expert on the foundations of quantum mechanics, recently gave a public lecture at our college called "Quantum Mechanics for Everyone." Afterward, another colleague, not a scientist, said of the talk: "I understood, but I'm not sure what I understood." Many readers of Lee Smolin's Three Roads to Quantum Gravity may have the same reaction. Smolin, professor of physics at Pennsylvania State University, succeeds at giving us what reviews of similar books have called "an illusion of understanding." We read his description of the cutting-edge search for an ultimate theory of reality, we take aboard his metaphors, we digest his anecdotes, and we have a feeling that we understand what he is talking about. Even that is a triumph--for us and for Smolin. The subject of this book is so highly abstract, and so far removed from ordinary experience, that an illusion of understanding is perhaps the best we can hope for. Only a few hundred people in the world may understand the intricacies of loop quantum gravity, Smolin's particular line of research, and I will confess that I am not one of them. Nevertheless, I am grateful that he has taken the time from his science to write this engaging popularization, for, as he rightly supposes, there are many of us who want to think we know what's going on. It would be hard to imagine a better guide to this difficult subject. The first half of the 20th century saw the invention of two highly successful theories for describing the world: quantum mechanics and general relativity (gravity). Each theory reigns supreme in its domain of application: quantum theory on the scale of elementary particles, relativity on the cosmic scale. Only occasionally, as in discussions of black holes, do the two theories rub against each other. The rubbing can be abrasive. Quantum theory radicalizes our assumptions about the relationship between observer and observed but pretty much buys into Newton's ideas of space and time. General relativity changes our notions of space and time but accepts Newton's view of observer and observed. This situation is deemed unacceptable by most physicists, and the race is on to find a unifying theory of quantum gravity, sometimes called a Theory of Everything. Smolin describes the three most prom-ising approaches to such a theory, all of which operate on the so-called Planck scale of reality, 20 orders of magnitude smaller than the atomic nucleus. One approach applies thermodynamics and information theory to black holes. Another is string theory, which proposes that the ultimate elements of reality are vibrating linear mathematical entities existing (in one version of the theory) in nine spatial dimensions that give rise in their various states of excitation to the elementary particles. Smolin pushes hard for a third approach, which involves something called quantum loops--quantized elements of spacetime that in their shimmerings evoke everything else, perhaps even strings. Quantum loop theory proposes that spacetime is a kind of "spin foam," a pure geometry of Planck-scale loops and nodes, that in its "knots, links and kinks" spins out a universe. A note in the book led me to a Web site [see illustration on preceding page] where one can view a quantum universe of one space and one time dimension doing its foamy thing. The prospect is exhilarating that behind the world of our senses this ceaseless Planck-scale fandango is going on. All roads to quantum gravity, when they have battered their way to a common vision, will probably suggest that space and time, like matter and energy, come in quantized, indivisible units and that relationships, rather than things, are the fundamental elements of reality. Alas, it is difficult to conceive how any such theory of quantum gravity can be tested with present technology, although Smolin is confident it will happen. Readers will perhaps best enjoy the first chapters of the book, where the author neatly lays out the philosophical principles that guide the search, and the penultimate chapter, where he explores how quantum gravity relates to our understanding of ourselves and God. Are books like this one, which the typical reader will only partly understand, useful? Absolutely. Quantum gravity theorists may be engaged in the modern equivalent of calculating how many angels can dance on the head of a pin, but we shouldn't forget that some of the best minds of our species once pondered the properties of celestial spirits. It may be that practicing with angels helped to prepare our collective imaginations for quantum loops.

Chet Raymo teaches at Stonehill College in Massachusetts and writes a science column for the Boston Globe.

Customer Reviews

Readers get at least a vague picture of a difficult problem
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."

Nice book on Quantum Gravity
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.

Light Reading On A Heavy Subject
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.