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# Three Roads To Quantum Gravity

by

**"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 ...more

Paperback, 256 pages

Published
July 4th 2002
by Basic Books
(first published 2000)

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## Community Reviews

(showing 1-30)

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 ...more

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 ...more

but thank the lord most of the ...more

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 ...more

Apr 19, 2008
DJ
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 ...more

"Three Roads to Quantum Gravity" is Smolin's briefing to the p ...more

Still, Smolin does give very detailed explanations for the different versions of String Theory, Loop Quantum Gr ...more

**DNF!**

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 ...more

But then again, I'm not a physicist so I am probably not the best person to judge.

"...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 . . . ...more

**Fascinating**.

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 ...more

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 ...more

I think this one is better by far than Gre ...more

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 ...more

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 ...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.

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“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.”
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“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.”
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