Quantum gravity (QG) is a field of theoretical physics that seeks to describe gravity according to the principles of quantum mechanics. It deals with environments in which neither gravitational nor quantum effects can be ignored,such as in the vicinity of black holes or similar compact astrophysical objects,such as neutron stars as well as in the early stages of the universe moments after the Big Bang.
In physics,string theory is a theory that attempts to merge quantum mechanics with Einstein’s general theory of relativity. The theory puts forth the premise of the material universe being made of tiny one-dimensional “strings”,rather than the more conventional approach in which they are modeled as zero-dimensional point particles. String theory envisions that a string undergoing a particular mode of vibration corresponds to a particle with definite properties such as mass and charge.
Edward Witten is an American mathematical and theoretical physicist. He is a professor emeritus in the school of natural sciences at the Institute for Advanced Study in Princeton. Witten is a researcher in string theory,quantum gravity,supersymmetric quantum field theories,and other areas of mathematical physics. Witten's work has also significantly impacted pure mathematics. In 1990,he became the first physicist to be awarded a Fields Medal by the International Mathematical Union,for his mathematical insights in physics,such as his 1981 proof of the positive energy theorem in general relativity,and his interpretation of the Jones invariants of knots as Feynman integrals. He is considered the practical founder of M-theory.
Hawking radiation is the theoretical thermal black-body radiation released outside a black hole's event horizon. This is counterintuitive because once ordinary electromagnetic radiation is inside the event horizon,it cannot escape. It is named after the physicist Stephen Hawking,who developed a theoretical argument for its existence in 1974. Hawking radiation is predicted to be extremely faint and is many orders of magnitude below the current best telescopes' detecting ability.
Doubly special relativity (DSR) –also called deformed special relativity or,by some,extra-special relativity –is a modified theory of special relativity in which there is not only an observer-independent maximum velocity,but also,an observer-independent maximum energy scale and/or a minimum length scale. This contrasts with other Lorentz-violating theories,such as the Standard-Model Extension,where Lorentz invariance is instead broken by the presence of a preferred frame. The main motivation for this theory is that the Planck energy should be the scale where as yet unknown quantum gravity effects become important and,due to invariance of physical laws,this scale should remain fixed in all inertial frames.
Supersymmetry is a theoretical framework in physics that suggests the existence of a symmetry between particles with integer spin (bosons) and particles with half-integer spin (fermions). It proposes that for every known particle,there exists a partner particle with different spin properties. There have been multiple experiments on supersymmetry that have failed to provide evidence that it exists in nature. If evidence is found,supersymmetry could help explain certain phenomena,such as the nature of dark matter and the hierarchy problem in particle physics.
Leonard Susskind is an American theoretical physicist,Professor of theoretical physics in Stanford University and founding director of the Stanford Institute for Theoretical Physics. His research interests are string theory,quantum field theory,quantum statistical mechanics and quantum cosmology. He is a member of the US National Academy of Sciences,and the American Academy of Arts and Sciences,an associate member of the faculty of Canada's Perimeter Institute for Theoretical Physics,and a distinguished professor of the Korea Institute for Advanced Study.
The chronology protection conjecture is a hypothesis first proposed by Stephen Hawking that laws of physics beyond those of standard general relativity prevent time travel on all but microscopic scales - even when the latter theory states that it should be possible. The permissibility of time travel is represented mathematically by the existence of closed timelike curves in some solutions to the field equations of general relativity. The chronology protection conjecture should be distinguished from chronological censorship under which every closed timelike curve passes through an event horizon,which might prevent an observer from detecting the causal violation.
In theoretical physics,the hierarchy problem is the problem concerning the large discrepancy between aspects of the weak force and gravity. There is no scientific consensus on why,for example,the weak force is 1024 times stronger than gravity.
The black hole information paradox is a paradox that appears when the predictions of quantum mechanics and general relativity are combined. The theory of general relativity predicts the existence of black holes that are regions of spacetime from which nothing—not even light—can escape. In the 1970s,Stephen Hawking applied the semi-classical approach of quantum field theory in curved spacetime to such systems and found that an isolated black hole would emit a form of radiation called Hawking radiation. He also argued that the detailed form of the radiation would be independent of the initial state of the black hole,and depend only on its mass,electric charge and angular momentum.
Mark Brian Wise is a Canadian-American theoretical physicist. He has conducted research in elementary particle physics and cosmology. He is best known for his role in the development of heavy quark effective theory (HQET),a mathematical formalism that has allowed physicists to make predictions about otherwise intractable problems in the theory of the strong nuclear interactions. He has also published work on mathematical models for finance and risk assessment.
In quantum electrodynamics,the anomalous magnetic moment of a particle is a contribution of effects of quantum mechanics,expressed by Feynman diagrams with loops,to the magnetic moment of that particle. The magnetic moment,also called magnetic dipole moment,is a measure of the strength of a magnetic source.
Physics beyond the Standard Model (BSM) refers to the theoretical developments needed to explain the deficiencies of the Standard Model,such as the inability to explain the fundamental parameters of the standard model,the strong CP problem,neutrino oscillations,matter–antimatter asymmetry,and the nature of dark matter and dark energy. Another problem lies within the mathematical framework of the Standard Model itself:the Standard Model is inconsistent with that of general relativity,and one or both theories break down under certain conditions,such as spacetime singularities like the Big Bang and black hole event horizons.
Helen Fay Dowker is a British physicist who is a current professor of theoretical physics at Imperial College London.
In cosmology,the cosmological constant problem or vacuum catastrophe is the substantial disagreement between the observed values of vacuum energy density and the much larger theoretical value of zero-point energy suggested by quantum field theory.
Sergei D. Odintsov is a Russian astrophysicist active in the fields of cosmology,quantum field theory and quantum gravity. Odintsov is an ICREA Research Professor at the Institut de Ciències de l'Espai (Barcelona) since 2003. He also collaborates as group leader at research projects of the Tomsk State Pedagogical University. He is editor-in-chief of Symmetry,and is a member of the editorial boards of Gravitation and Cosmology,International Journal of Geometric Methods in Modern Physics,International Journal of Modern Physics D,Journal of Gravity,Universe,and the Tomsk State Pedagogical University Bulletin. Odintsov also is an advisory panel member of Classical and Quantum Gravity.
Alejandro Jenkins is a Costa Rican theoretical physicist. He is currently a professor at the University of Costa Rica and a member of Costa Rica's National Academy of Sciences. He has worked on applications of quantum field theory to particle physics and cosmology,as well as on self-oscillating dynamical systems and quantum thermodynamics.
Raphael Bousso is a theoretical physicist and cosmologist. He is a professor at the Berkeley Center for Theoretical Physics in the Department of Physics,UC Berkeley. He is known for the Bousso bound on the information content of the universe. With Joseph Polchinski,Bousso proposed the string theory landscape as a solution to the cosmological constant problem.
Augusto Sagnotti is an Italian theoretical physicist at Scuola Normale.
A. W. Peet is a professor of physics at the University of Toronto. Peet's research interests include string theory as a quantum theory of gravity,quantum field theory and applications of string theory to black holes,gauge theories,cosmology,and the correspondence between anti-de Sitter space and conformal field theories.
