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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. He also advocates an alternative view on space and time he calls temporal naturalism. His research interests also include cosmology, elementary particle theory, the foundations of quantum mechanics, and theoretical biology.
Abhay Vasant Ashtekar is an Indian theoretical physicist. He is the Eberly Professor of Physics and the Director of the Institute for Gravitational Physics and Geometry at Pennsylvania State University. As the creator of Ashtekar variables, he is one of the founders of loop quantum gravity and its subfield loop quantum cosmology. He has also written a number of descriptions of loop quantum gravity that are accessible to non-physicists. In 1999, Ashtekar and his colleagues were able to calculate the entropy for a black hole, matching a legendary 1974 prediction by Hawking. Oxford mathematical physicist Roger Penrose has described Ashtekar's approach to quantum gravity as "The most important of all the attempts at 'quantizing' general relativity." Ashtekar was elected as Member to National Academy of Sciences in May 2016.
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Loop quantum cosmology (LQC) is a finite, symmetry-reduced model of loop quantum gravity (LQG) that predicts a "quantum bridge" between contracting and expanding cosmological branches.
Martin Bojowald is a German physicist who now works on the faculty of the Penn State Physics Department, where he is a member of the Institute for Gravitation and the Cosmos. Prior to joining Penn State he spent several years at the Max Planck Institute for Gravitational Physics in Potsdam, Germany. He works on loop quantum gravity and physical cosmology and is credited with establishing the sub-field of loop quantum cosmology.
A quantum field theory of general relativity provides operators that measure the geometry of spacetime. The volume operator of a region is defined as the operator that yields the expectation value of a volume measurement of the region , given a state of quantum General Relativity. I.e. is the expectation value for the volume of . Loop Quantum Gravity, for example, provides volume operators, area operators and length operators for regions, surfaces and path respectively.
In the ADM formulation of general relativity one splits spacetime into spatial slices and time, the basic variables are taken to be the induced metric, , on the spatial slice, and its conjugate momentum variable related to the extrinsic curvature, ,. These are the metric canonical coordinates.
Hermann Nicolai is a German theoretical physicist and director emeritus at the Max Planck Institute for Gravitational Physics in Potsdam-Golm.
References
- ↑ "Jerzy Lewandowski". scholar.google.com. Retrieved 2021-03-05.
- ↑ Domagała, Marcin; Giesel, Kristina; Kamiński, Wojciech; Lewandowski, Jerzy (2010-11-18). "Gravity quantized: Loop quantum gravity with a scalar field". Physical Review D. 82 (10). arXiv: 1009.2445 . doi:10.1103/physrevd.82.104038. ISSN 1550-7998.
- ↑ "The birth of time: Quantum loops describe the evolution of the Universe". ScienceDaily. Retrieved 2021-03-05.
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