Three Roads to Quantum Gravity

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Three Roads to Quantum Gravity: A New Understanding of Space, Time and the Universe
Three Roads to Quantum Gravity - bookcover.JPG
Cover of the hardcover edition
Author Lee Smolin
CountryUnited States
SeriesScience Masters
SubjectsPhysics, quantum gravity
Publisher Basic Books
Publication date
May 30, 2001
Media typePrint
Pages240 pp.
ISBN 978-0465078356
Preceded by The Life of the Cosmos (1999) 
Followed by The Trouble With Physics (2006) 

Three Roads to Quantum Gravity: A New Understanding of Space, Time and the Universe is a non-fiction book by American theoretical physicist Lee Smolin. The book was initially published on May 30, 2001 by Basic Books as a part of the Science Masters series. [1] [2] [3]



Smolin discusses three potential approaches by which a unified theory of quantum gravity, arguably the foremost issue in theoretical physics, may be realized. Approaches discussed include string theory, M-theory, and Smolin's preferred approach, loop quantum gravity. Smolin suggests that these approaches may be approximations of a single, underlying theory.


Divide an inch in two. Now divide each half again, and then repeat the division, over and over. Can you go on for ever, or do the laws of physics eventually get in the way? Is the fabric of space infinitely divisible, or is it ultimately made up of "atoms"—tiny chunks of space that can never be split? This question may seem almost unanswerable. But as physicist Lee Smolin writes in Three Roads to Quantum Gravity, some of the newest ideas in physics are pointing to a surprising answer: space and time do indeed appear to be made out of such atoms. In explaining why, he offers a tour by a skilled teacher through some of the boldest and most beautiful ideas of modern science. Smolin has been one of the leading figures in recent efforts to bring together two of the most far-reaching scientific theories of our age.

The Guardian [4]

See also

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Quantum gravity (QG) is a field of theoretical physics that seeks to describe gravity according to the principles of quantum mechanics, and where quantum effects cannot be ignored, such as in the vicinity of black holes or similar compact astrophysical objects where the effects of gravity are strong, such as neutron stars.

String theory Theoretical framework in physics

In physics, string theory is a theoretical framework in which the point-like particles of particle physics are replaced by one-dimensional objects called strings. String theory describes how these strings propagate through space and interact with each other. On distance scales larger than the string scale, a string looks just like an ordinary particle, with its mass, charge, and other properties determined by the vibrational state of the string. In string theory, one of the many vibrational states of the string corresponds to the graviton, a quantum mechanical particle that carries gravitational force. Thus string theory is a theory of quantum gravity.

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Lee Smolin American theoretical physicist

Lee Smolin is an American theoretical physicist, a faculty member at the Perimeter Institute for Theoretical Physics, an adjunct professor of physics at the University of Waterloo and a member of the graduate faculty of the philosophy department at the University of Toronto. Smolin's 2006 book The Trouble with Physics criticized string theory as a viable scientific theory. He has made contributions to quantum gravity theory, in particular the approach known as loop quantum gravity. He advocates that the two primary approaches to quantum gravity, loop quantum gravity and string theory, can be reconciled as different aspects of the same underlying theory. His research interests also include cosmology, elementary particle theory, the foundations of quantum mechanics, and theoretical biology.

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Carlo Rovelli Italian physicist

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  1. MATTHEWS, ROBERT (3 February 2001). "Three Roads to Quantum Gravity by Lee Smolin". New Scientist . Retrieved 20 December 2019.
  2. Smolin, Lee (19 August 2001). [ "'Three Roads to Quantum Gravity'"] Check |url= value (help). The New York Times . Retrieved 20 December 2019.
  3. "Nonfiction Book Review: THREE ROADS TO QUANTUM GRAVITY by Lee Smolin, Author . Basic $24 (231p) ISBN 978-0-465-07835-6". Publishers Weekly . Retrieved 20 December 2019.
  4. Buchanan, Mark (February 17, 2001). "Three Roads to Quantum Gravity by Lee Smolin". . Retrieved 2015-05-29.