- Paperback: 288 pages
- Publisher: Basic Books; 3 edition (Aug. 8 2017)
- Language: English
- ISBN-10: 0465094546
- ISBN-13: 978-0465094547
- Product Dimensions: 14.1 x 2.7 x 21 cm
- Shipping Weight: 249 g
- Average Customer Review: 27 customer reviews
- Amazon Bestsellers Rank: #184,756 in Books (See Top 100 in Books)
Three Roads to Quantum Gravity Paperback – Aug 8 2017
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"Lee [Smolin] is a brilliant, original thinker."―Roger Penrose
"[Smolin] argues lucidly and effectively that physicists should pause to reevaluate exactly what they mean when they use the words 'space' and 'time.' This is a deeply philosophical work."―New York Times Books Review
"A mix of science, philosophy, and science fiction, [this] is at once entertaining, thought-provoking, fabulously ambitious, and fabulously speculative."―New York Times
"This is real twenty-first century science."―Allen Lane, Independent
About the Author
Lee Smolin is a theoretical physicist who has been since 2001 a founding and senior faculty member at Perimeter Institute for Theoretical Physics. Fellow of the American Physical Society and of the Royal Society of Canada, Smolin was awarded the 2009 Klopsteg Memorial Award from the American Association of Physics Teachers and in 2008 was voted 21st on a list of the 100 most influential public intellectuals by Prospect and Foreign Policy Magazines. He is again on that list in 2015. This year Marina Cortes and he were also awarded the Inaugural Buchalter Cosmology Prize. He is the author of more than 150 scientific papers and numerous essays and writings for the public on science, as well as four books.
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The author gives us several interesting accounts of physicists working in these fields are in a climate of mutual ignorance and complacency with the belief that their theory is correct and others are wrong. There are instances when one group can't solve certain problems, and they seek the help from the other camp. The author also briefly explains other theories such as Twister theory, and Non-Commutative Geometry. This is one of the few books I have read which describes LQG in some detail, although there are several books in literature, which describes S.-M theory. The author is very honest in comparing the three approaches to offer the best explanation for quantum gravity. Anyone who wants to understand LQG must have this book.
His first book 'The Life of the Cosmos' contained already the simplest and brightest explanations of the basic elements, processes and principles of modern physics. Here he does it again with the latest progress in the search for a theory of quantum gravity: loop quantum gravity, string theory and black hole thermodynamics.
He dissects the strenghts and weaknesses of the different approaches and shows how they culminate into the holographic principle, where one set of events receives information about other parts of the world.
Lee Smolin explains in a very comprehensible vocabulary that space and time are not continuous, but discrete; that the world is made of processes, not things; and that the world is nothing more than an evolving network of relationships, of which causality is the most important.
These characteristics have important philosophical implications; e.g. they refute the belief that observer dependence rules out objectivity.
This book contains some mind-boggling propositions. One from Lee Smolin himself, where he admits that he doesn't belief in the uncertainty principle, although he continues to work with it. Another one is the use of the whole universe as an instrument.
In the end, the author is very optimistic and predicts that a theory of quantum gravity will be found in the first decades of the 21st century.
This book is a fascinating tale about the real nature of the universe. A must read.
But how about space? Is it continuous? Can it be subdivided to any arbitrary level? Is there a minimum increment in space? And how about time? Is there a smallest increment of time? According to Smolin (and quite a few other scientists) the answer is yes to both questions, and such quantization is fundamental to the concept of quantum gravity. To me, it seems at once both strange and common sense.
When I took physics in High School, Mr. Lewis once asked (philosophically); "what is time?" I replied that it's what defines motion. The answer came across, I'm afraid, somewhat flippantly, but I've considered it more seriously over the years and wondered what a universe without motion would really look like. Would there be time in such a universe? Would it even make sense to talk about time if there was no motion - no events - taking place? I've wondered if, at some level, we can understand the motion of particles in their zero state as a requirement that time cannot stop. Of course, this motion is also understood as a consequence of the Heisenberg uncertainty principle. Is there a relationship?
Smolin takes the point of view that time and space are sequences. Processes, in his words. Linkages. He introduces the concepts found in general relativity and quantum theory that there is no "space" that is independent of the observer, but only observers that are an integral part of space. Thus, we cannot talk about a separate space and time, but only of a universe in which we are part of the process. Consider the following, from his book:
"time and causality are synonymous. There is no meaning to the past of an event except the set of events it will influence."
"One cannot talk meaningfully about the existence of any object or the truth of any statement without completely specifying the questions that are to be asked."
".... Our world cannot be understood as a collection of independent entities living in a fixed, static background of space and time. Instead, it is a network of relationships the properties of every part of which are determined by its relationships to the other parts."
"if we look finely enough at our world the continuity of space and time will dissolve as surely as the smoothness of materials gives way to the discrete world of molecules and atoms."
As you can see, the book takes a high-level, qualitative, and philosophical approach. This makes it a bit difficult to make the mental bridge to understanding specific issues with the different theories Smolin discusses. Part of the problem is an unspoken understanding among Physicists that a theory is essentially a mathematical construct, and that even though you might write the equations of the theory, you may have no idea what they say. This is a concept that's probably new for many non-physicists, and I think it would be a good idea in a book such as Smolin's to discuss the situation a little bit. This might involve writing a few equations, like the Lagrangian for a four-body system. I know publishers don't like to use equations (and I disagree strongly with them over this point) but the theories of quantum gravity are mathematical, and the problems with understanding them cannot really be approached without explaining some of these characteristics. Otherwise, the author runs the hazard of saying things like "we don't really understand what the theory is telling us" and someone from the life sciences wondering why on earth a scientist does not understand her own theory.
The book's high-level discussion includes M-theory (string theory), loop quantum gravity, and the holographic principle, complete with Smolin's conjectures (at the end of the book) about how the story will unfold.
Smolin made me sit up and think, and I like that in a book. But the book is also written at the 50,000-foot level, and that made it somewhat frustrating. I'd like to understand Smolin's concepts at a more quantitative level, but don't really want to invest the time required to comprehend the full mathematical theory. I kept wishing there was some middle ground, but never found it.
Those issues aside, Smolin's book is worth reading. I'm glad I did.