Product Description
From one of the World’s most distinguished scientsits, an elegant and concise presentation of the controversial ideas behind quantum gravity. The Holy Grail of modern physics is the search for a theory of “quantum gravity.” It is a search for a view 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, … More >>
Three Roads to Quantum Gravity
Tags: concise presentation, controversial ideas, holy grail, modern physics, modern science, quantum gravity, quantum theory, scale phenomena, theory of general relativity, view of the universe
#1 by Tatsuo Tabata on June 26, 2010 - 5:36 pm
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.”
Rating: 4 / 5
#2 by Kenneth L. Graham on June 26, 2010 - 7:01 pm
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.
Rating: 3 / 5
#3 by Bruce Crocker on June 26, 2010 - 9:14 pm
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.
Rating: 5 / 5
#4 by Irfan A. Alvi on June 26, 2010 - 11:33 pm
As my title states, this book is very good, but with the significant caveat that no particular audience is ideally served by it.
If you are truly a layman, you may initially be pleased to find that the book has essentially no formal mathematics and the technical vocabulary isn’t too extensive. Smolin himself says that the book is aimed at the “intelligent layman” and that “the reader who has not read anything previously on these subjects will be able to follow this book.” However, the book tries to convey a meaningful understanding of some rather advanced (some would say speculative) physics in the areas of thermodynamics of black holes, loop quantum gravity, and string theory, and it does this in a manner which is philosophically sophisticated, with many fundamental questions being raised about the nature of space, time, and scientific theories in general. Moreover, despite Smolin’s claim to the contrary, one can’t adequately appreciate what the book is about without a basic (at least popular-level) background in quantum mechanics and relativity, which the book doesn’t provide.
As a result, I anticipate that the true layman would find this book to be difficult going. Instead, a more realistic audience would be the “advanced layman” who has some prior familiarity with this subject matter, particularly the basics of quantum theory, relativity, the standard model, and cosmology. This audience (which includes me) would probably find the book to be quite stimulating and interesting, and would get a sense of what this advanced physics is all about. However, because the presentation lacks the mathematics and technical details needed for anything resembling a rigorous understanding, they will probably also be left wishing the book had 50 more pages of “meat” and some key equations (explained carefully, but without derivations). For the same reason, the advanced reader would probably also wish the book was at least one notch more advanced, but even these readers may still find the book to be a fun and interesting overview of the subject.
Finally, I’d like to suggest that potential readers should be wary of reviewers who strongly favor the book because they agree with it’s thesis, or condemn the book because they disagree. We are dealing with subject matter about which there is no consensus even among eminent physicists, so these reviews are not the place for readers to throw in their two cents about which theories are right and wrong. Instead, this sort of book should be judged mainly on criteria such as whether good questions are asked, whether the context for these questions is well formed, whether the alternative answers proposed for these questions are explained clearly and fairly, and whether the text is well-written. On all of these counts, my judgement is that Smolin does a good job.
Rating: 4 / 5
#5 by Lubos Motl on June 27, 2010 - 12:51 am
Which roads is Lee Smolin talking about? The first road is superstring theory (or M-theory). The mainstream is convinced that string theory is our leading candidate to describe all the particles and all the interactions and to unify quantum mechanics with general relativity. According to string theory, different particle species are loops of string vibrating in different ways. Brian Greene has described string theory in The Elegant Universe beautifully and the reader will probably learn nothing new from this Smolin’s book.
The second road is the so-called Loop Quantum Gravity (LQG). This framework, started by Abhay Ashtekar and his friends, offers a way to reformulate the original equations written down by Einstein using some new variables leading to Wilson loops in the role of the fundamental observables. While most theoretical physicists believe that this approach is marginal and probably inconsistent, Smolin would like to “unify” it with superstring theory although M-theory and LQG contradict each other quite clearly in many aspects. The reader gets disappointed because he or she will not find out what is the relation between the loop of LQG and the string of string theory. There is none. The experts know it but the laymen can become confused.
The third road, according to Smolin, is a fuzzy collection of speculations invented by the philosophers of various kinds who would like to refuse everything that physicists have learned and to base everything on ill-defined “profound” and “deep” philosophical principles. Wolfgang Pauli would certainly say that the third road “is not even wrong”. Unfortunately, Smolin likes to pretend that marginal directions of research are essential and that people like Finkelstein, Isham, Penrose, Sorkin (and Smolin himself) are heroes of physics today. Read the book if you liked the readable and anecdotal style of the Smolin’s previous book “The Life of the Cosmos” or if you like to hear highly idiosyncratic comments about this exciting subject or if you like to speculate about questions as usually asked by laymen and philosophers. However if you want the author to teach you the right questions and the right answers from physics as understood by real physicists or if you want to learn who are the real heroes of the field and what dramatic discoveries have they done – for example Stephen Hawking or today especially Ed Witten – buy The Elegant Universe instead. Smolin’s ideas have always remained outside the mainstream; “Three Roads” are no exception. And the readers should know it.
Rating: 3 / 5