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Three Roads To Quantum Gravity

4.14  ·  Rating details ·  4,971 Ratings  ·  74 Reviews
"It would be hard to imagine a better guide to this difficult subject." --Scientific American
In Three Roads to Quantum Gravity, Lee Smolin provides an accessible overview of the attempts to build 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 bla
Paperback, 256 pages
Published July 4th 2002 by Basic Books (first published 2000)
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Dec 01, 2008 rated it really liked it
Shelves: science
Lee Smolin is one of the most interesting and controversial figures in modern physics. Establishment physicists often call him a maverick or worse. I am one of many laypeople who think that he's telling it like it is, and the mainstream people are full of s...trings.

When he wrote this book, around 1999, I think he was more part of the mainstream. He presents several different approaches to the very difficult problem of unifying gravity and quantum mechanics. It's clear that his heart belongs to
Oct 16, 2009 rated it it was ok
a nice, easy intro into quantum gravity for the interested:

This book isn't too bad but I don't think I retain much. the feline analogy and cosmological evolution are cute ideas, and the black hole stuff is fascinating. but much of it is extremely speculative and cryptic rambling. Or maybe I just get more cynical of theoretical physics day by day. That's fine, and at least Lee Smolin acknowledges that it is speculative, but at least don't be so incredibly
James F
Feb 04, 2015 rated it liked it
According to Smolin, there are three "roads" currently leading to a theory of quantum gravity: the first road begins from quantum theory and adds relativity (string theory), the second begins from general relativity and adds quantum theory (loop quantum gravity), and the third rejects both and tries to consider the question from first principles. (This third road is basically not discussed, and later in the book the third road becomes thermodynamics of black holes and the "holographic principle" ...more
Since Lee Smolin has been one of the leading figures both in the string theory and in the theory of loop quantum gravity, I hoped this book would clarify some questions I was left with after reading Carlo Rovelli's Reality Is Not What It Seems: The Journey to Quantum Gravity. I think the main reason both the books failed to do the job is the fact that I lack the adequate background to understand what is really meant by ''strings'' and ''loops'' in the two main approaches to quantum gravity. I fi ...more
this book is so dumbed-down that i seriously considered putting it on the "non-fiction for humans" shelf. the absolute nadir came when he used as his analogy for the superposition principle of quantum mechanics a mouse which, when eaten by a cat, might turn out to be either "tasty" or "yukky". Yukky? Yukky? forget that it's universally spelled "yucky". but he hammers away at his analogy and the reader is subjected to the word "yukky" several times over a few pages.

but thank the lord most of the
Dipanshu Gupta
Apr 11, 2018 rated it really liked it
My professor asked me to starting reading literature for writing my master thesis, so I perused the library for some interesting reads. And oh boy, did I hit gold. Masterfully written by one of the people deeply invested in solving the problem of Quantum Gravity, Smolin takes a broad view of the possibilities. His writing is awkward when trying to do philosophical science but when he gets to the gritty areas, his analogies are beautiful. He talks about Loop Quantum Gravity, String Theory and oth ...more
Bob Nichols
May 05, 2015 rated it liked it
Smolin describes his thinking about how quantum theory (micro level) might be linked to Einstein’s gravitational theory (macro level), to become “a quantum theory of gravity.” His argument is by no means easy for the lay reader to follow, so what follows may not be an accurate rendering.

At the minutest level of reality (spacetime on Planck scale) are strings (“a string is actually made of discrete pieces, called string bits, each of which carries a discrete amount of momentum and energy”). Part
Apr 19, 2008 rated it really liked it
Recommends it for: any young scientist interested in today's fundamental questions in physics
Shelves: popular-physics
Lee Smolin stormed his way onto my fantasy grandfather list the fateful summer of 2008 when I realized physics and I were more than just a fling. His The Trouble with Physics was a fatherly introduction to the current state of the edges of theoretical physics and I was hooked. Needless to see, I was ecstatic to find "Three Roads to Quantum Gravity" under my Christmas tree this year and devoured it on plane ride to Thailand soon after.

"Three Roads to Quantum Gravity" is Smolin's briefing to the p
Oct 12, 2007 rated it really liked it
Recommends it for: Quantum Physics enthusiasts
Either I'm getting progressively dumber, or the books I'm reading are getting progressively harder for me to understand. Hopefully it's the latter of the two. I enjoyed this book in principle, however there was a lot that I had trouble understanding. I think I was able to grasp the basic ideas behind most of the theories mentioned, but some of the finer details may have been lost on me.

Still, Smolin does give very detailed explanations for the different versions of String Theory, Loop Quantum Gr
Excellent book describing how the routes to quantum gravity work in rather precise but laymen terms. The human elements are also very clearly done. However, there is clear "side" taken in making loop quantum gravity sound "better" than string theory, which from what I know on technical level they are both stuck in equally critical stalemate (maybe I am wrong). But otherwise it is a good exposition, especially when Smolin laid clear the "philosophy" behind doing science - what are our biases, etc ...more

I'm sorry. Even from the (relatively) short part I read it's clear Smolin is a brilliant scientist, but a writer he is not. The writing is just painful, rambling at times. Very little is explained, and what is explained is done so in the most simplistic ways by comparing certain concepts in quantum theory with daily life events that might work had Smolin not drawn it out to the max, making me forget what he was trying to explain in the first place. This book and I, unfortunately, must part w
Carl Stevens
Aug 25, 2014 rated it really liked it
Do you know a similar book with a little more technical detail? This was an excellent popular treatment of quantum gravity and related topics but I have read several popular treatments now and find myself wanting to dust off my old math texts and go a little deeper. So if you know something that would challenge someone with a math background comparable to a math major in his junior year, please let me know.
Evan Macbeth
Feb 28, 2012 rated it it was ok
It's a complicated subject, no doubt. And Smolin does his best to make it narratively accessible. That being said, this book is disjointed and a bit impenetrable, not because Smolin doesn't understand the subject matter. He clearly does! But because his explanations of that subject matter don't seem to answer some basic "why?" and "how?" questions.

But then again, I'm not a physicist so I am probably not the best person to judge.
Ami Iida
May 18, 2015 rated it did not like it
Shelves: physics
There is some description of the physics mistakes clearly.
It is a disqualification as a physics manual.
Oct 04, 2012 rated it really liked it
I love Smolin's style of writing. A worthwhile read for those interested in the diversity of the field and the questions being tackled.
Austin Barselau
Jun 11, 2016 rated it it was ok
Writing about complex topics, not to mention quantum theoretical physics, is tremendously challenging. Distilling dense, abstruse, and highly mathematized information down to the comprehension level of the average reader is a feat in itself. This is why good popular science- writing that can be accessed and enjoyed by that layperson- is scarce. Far too many academics fall prey to the so-called “curse of knowledge,” or the inability of the expert to condense and summarize information to novices. ...more
Aug 02, 2018 rated it really liked it  ·  review of another edition
Shelves: phd-studies
Not the typical quantum trip down the garden path leading from Aristotle, Galileo and Newton to Einstein, Bohr and Heisenberg. Instead Smolin waves his hand out the window as he Ferraris by classical and early mechanics gardens to take us for a spin on each of the three roads that will get us to his horizon point, quantum gravity being taught in high school classrooms by the end of the 21st century. To get up to speed, he takes the cat out of the Schrödingerian box and gives them some mice to ea ...more
William Lovas
Jun 10, 2018 rated it liked it
A good intro to the (near) current state of the art, and in particular the idea that string theory and loop quantum gravity are just two ways of unifying general relativity and quantum mechanics starting from different end points — the “third road” starts from neither. I’m especially excited about the idea that maybe, just maybe, intuitionistic logic is the key to quantum gravity, but that’s undoubtedly my personal bias showing through..
Michael Flick
Sketchy—maybe just too soon for a book for the lay reader. For me, the most interesting part was the atomic (quantum) nature of space (and likely time as well). Makes me wonder if we need a quantum theory of time? (For more on this see eg. Rovelli’s “Reality Is Not What It Seems” and others....)
Arno Mosikyan
Oct 09, 2018 rated it it was amazing
Shelves: physics
Always pleasure to read reasonable contrarians.
Matthew Koban
Jul 12, 2018 rated it liked it
Really interesting read, it was great to see a few of the developments that have been made in theories besides string theory. However I would have preferred a bit more in depth treatment.
May 09, 2018 rated it it was amazing
Simply the clearest explanation of the subject I have read.
Jul 03, 2007 rated it it was amazing  ·  review of another edition
Shelves: science
This is one of the small list of books that has forever changed my paradigm. Unlike the other ones, I was aware of the paradigm change as it was happening and I could not put this book down.

"...the first principle of cosmology must be 'There is nothing outside the universe' . . . This first principle means that we take the universe to be, by definition, a closed system. It means that the explanation for anything in the universe can involve only other things that also exist in the universe . . .
May 18, 2018 rated it really liked it  ·  review of another edition

Pretty much all was new to me in this book and consequently there was a massive amount of information to assimilate. The author is a very well known figure in quantum gravity and he not only describes the three roads, but gives the history of their development and the effects on research of having these three approaches to one problem. Very interesting.
The book is written well and with quite a light hand, but I did skip a little of it in the last quarter or so. Probably one for me to
Feb 19, 2014 rated it really liked it
An Introduction to Loop Quantum Gravity

Since the postulation of theory of relativity (theory of cosmos, which describes the structure of space and time), and quantum mechanics (laws of microcosm, which describes atomic structure, nuclear forces, and nature of basic component of matter); physicists until now have struggled to explain gravity (which is a manifestation of spacetime fabric in presence of matter) in terms of quantum mechanics (quantum gravity). In this book the author attempts to exp
Jul 15, 2008 rated it it was amazing
Recommended to Kev by: Clayton Crockett
I cannot adequately express how amazing this book is. If you are at all interested in physics -- and I am! -- this is a very important one to read. If you read "The Evolution of Physics" & "Relativity: The Special & General Theory" by Einstein, "Chaos" & "Genius" by Gleick & "Feynman's Lost Lecture" by the Goodsteins, then, read this one ... you will be in a position to reevaluate all of the known unviverse as we understand it right now.

I think this one is better by far than Gre
Jan 28, 2013 rated it liked it  ·  review of another edition
Shelves: physics, philosophy
Overall this was a good read. That said, I think I liked reading Hawkings better back some 20-odd years ago. Of course the scope and the topic is a little different here, and maybe I was just that much more impressionable back then, who knows.

Smolin starts out string, the first few chapters regarding "why we don't ask what's outside the universe" and "why classical logic is unsuitable for cosmology (and real life)" were really great. As you make it further into the book things fall apart a littl
Vicky Chijwani
Oct 08, 2016 rated it really liked it
Shelves: science
A good way to get up to speed on (almost) the latest physics, after you've worked your way through the thicket of relativity and quantum physics. Although I must say, the sheer abstractness of physics today kinda dampens my enthusiasm for the subject.

What follows below is basically terse notes for my future self:

- Why is quantum gravity important? General relativity and quantum mechanics are simply incompatible. GR does not take into account the role of the observer, while QM accepts Newton's vi
Aug 24, 2015 rated it really liked it
To start this review off, I must say that I was impressed with how well this book was written. Being a high school student with no prior knowledge of quantum gravity or quantum mechanics, I was pleased that this book was written in a way that I could actually understand the content and learn from it. Also, Lee Smolin's "Three Roads to Quantum Gravity" not only taught me about today's groundbreaking physics, but has also sparked my interest in pursuing further knowledge in the fields of theoretic ...more
Nov 26, 2010 rated it really liked it
An amazingly lucid book evenly dealing with different approaches to unify quantum mechanics and general relativity in a theory of quantum gravity. Smolin is very straight-forward and presents his ideas in an interesting, provocative and intelligent manner. I've struggled to understand how space can be quantized for three months, and I think I finally have some solid explanations. Smolin also does well with the Holographic Principle, which is about a difficult subject as you can come by in modern ...more
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Lee Smolin is a theoretical physicist who has made influential contributions to the search for a unification of physics. He is a founding faculty member of the Perimeter Institute for Theoretical Physics. His previous books include The Trouble with Physics, The Life of the Cosmos and Three Roads to Quantum Gravity.
“if physics is much simpler to describe under the assumption that space is discrete, rather than continuous, is not this fact itself a strong argument for space being discrete? If so, then might space look, on some very small scale, something like Wilson's lattice.” 1 likes
“The search for the meaning of temperature and entropy of matter led to the discovery of atoms. The search for the meaning of the temperature and entropy of radiation led to the discovery of quanta. In just the same way, 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.” 1 likes
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