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Loop quantum gravity (LQG) is a theory of quantum gravity that incorporates matter of the Standard Model into the framework established for the intrinsic quantum gravity case. It is an attempt to develop a quantum theory of gravity based directly on Albert Einstein 's geometric formulation rather than the treatment of gravity as a mysterious ...
(Later, loop quantum gravity inherited this geometric interpretation of gravity, and posits that a quantum theory of gravity is fundamentally a quantum theory of spacetime.) In the 1920s, the French mathematician Élie Cartan formulated Einstein's theory in the language of bundles and connections, [ 1 ] a generalization of Riemannian geometry ...
Loop quantum gravity is the fruit of an effort to formulate a background-independent quantum theory. Topological quantum field theory provided an example of background-independent quantum theory, but with no local degrees of freedom, and only finitely many degrees of freedom globally.
The loop representation also provides a natural solution of the spatial diffeomorphism constraint, making a connection between canonical quantum gravity and knot theory. Surprisingly there were a class of loop states that provided exact (if only formal) solutions to Ashtekar's original (ill-defined) Wheeler–DeWitt equation .
In 1988, Rovelli, Lee Smolin and Abhay Ashtekar introduced a theory of quantum gravity called loop quantum gravity.In 1995, Rovelli and Smolin obtained a basis of states of quantum gravity, labelled by Penrose's spin networks, and using this basis they were able to show that the theory predicts that area and volume are quantized.
In loop quantum gravity (LQG), a spin network represents a "quantum state" of the gravitational field on a 3-dimensional hypersurface. The set of all possible spin networks (or, more accurately, "s-knots" – that is, equivalence classes of spin networks under diffeomorphisms) is countable; it constitutes a basis of LQG Hilbert space.
The distinguishing feature of LQC is the prominent role played by the quantum geometry effects of loop quantum gravity (LQG). In particular, quantum geometry creates a brand new repulsive force which is totally negligible at low space-time curvature but rises very rapidly in the Planck regime , overwhelming the classical gravitational ...
Abhay Vasant Ashtekar (born 5 July 1949) is an Indian theoretical physicist who created Ashtekar variables and is one of the founders of loop quantum gravity and its subfield loop quantum cosmology. [2] Ashtekar has also written a number of descriptions of loop quantum gravity that are accessible to non-physicists.