The holographic principle is a property of string theories and a supposed property of quantum gravity that states that the description of a volume of space can be thought of as encoded on a lower-dimensional boundary to the region — such as a light-like boundary like a gravitational horizon. First proposed by Gerard 't Hooft, it was given a precise string theoretic interpretation by Leonard Susskind, who combined his ideas with previous ones of 't Hooft and Charles Thorn. Leonard Susskind said, “The three-dimensional world of ordinary experience––the universe filled with galaxies, stars, planets, houses, boulders, and people––is a hologram, an image of reality coded on a distant two-dimensional surface." As pointed out by Raphael Bousso, Thorn observed in 1978 that string theory admits a lower-dimensional description in which gravity emerges from it in what would now be called a holographic way. The prime example of holography is the AdS/CFT correspondence.
Juan Martín Maldacena is an Argentine theoretical physicist and the Carl P. Feinberg Professor in the School of Natural Sciences at the Institute for Advanced Study, Princeton. He has made significant contributions to the foundations of string theory and quantum gravity. His most famous discovery is the AdS/CFT correspondence, a realization of the holographic principle in string theory.
In theoretical physics, an extremal black hole is a black hole with the minimum possible mass that is compatible with its charge and angular momentum.
In physics, the Bekenstein bound is an upper limit on the thermodynamic entropy S, or Shannon entropy H, that can be contained within a given finite region of space which has a finite amount of energy—or conversely, the maximal amount of information required to perfectly describe a given physical system down to the quantum level. It implies that the information of a physical system, or the information necessary to perfectly describe that system, must be finite if the region of space and the energy are finite. In computer science this implies that non-finite models such as Turing machines are not realizable as finite devices.
Tamiaki Yoneya is a Japanese physicist.
Igor R. Klebanov is an American theoretical physicist. Since 1989, he has been a faculty member at Princeton University where he is currently a Eugene Higgins Professor of Physics and the director of the Princeton Center for Theoretical Science. In 2016, he was elected to the National Academy of Sciences. Since 2022, he is the director of the Simons Collaboration on Confinement and QCD Strings.
In particle physics and string theory (M-theory), the ADD model, also known as the model with large extra dimensions (LED), is a model framework that attempts to solve the hierarchy problem. The model tries to explain this problem by postulating that our universe, with its four dimensions, exists on a membrane in a higher dimensional space. It is then suggested that the other forces of nature operate within this membrane and its four dimensions, while the hypothetical gravity-bearing particle graviton can propagate across the extra dimensions. This would explain why gravity is very weak compared to the other fundamental forces. The size of the dimensions in ADD is around the order of the TeV scale, which results in it being experimentally probeable by current colliders, unlike many exotic extra dimensional hypotheses that have the relevant size around the Planck scale.
In theoretical particle physics, maximally helicity violating amplitudes (MHV) are amplitudes with massless external gauge bosons, where gauge bosons have a particular helicity and the other two have the opposite helicity. These amplitudes are called MHV amplitudes, because at tree level, they violate helicity conservation to the maximum extent possible. The tree amplitudes in which all gauge bosons have the same helicity or all but one have the same helicity vanish.
Thomas Carlos Mehen is an American physicist. His research has consisted of primarily Quantum chromodynamics (QCD) and the application of effective field theory to problems in hadronic physics. He has also worked on effective field theory for non-relativistic particles whose short range interactions are characterized by a large scattering length, as well as novel field theories which arise from unusual limits of string theory.
A causal patch is a region of spacetime connected within the relativistic framework of causality.
In quantum field theory in curved spacetime, there is a whole class of quantum states over a background de Sitter space which are invariant under all the isometries: the alpha-vacua. Among them there is a particular one whose associated Green functions verify a condition consisting to behave on the light-cone as in flat space. This state is usually called the Bunch–Davies vacuum or Euclidean vacuum, actually was first obtained by N.A. Chernikov and E. A. Tagirov, in 1968 and later by C. Schomblond and P. Spindel, in 1976, in the framework of a general discussion about invariant Green functions on de Sitter space. The Bunch–Davies vacuum can also be described as being generated by an infinite time trace from the condition that the scale of quantum fluctuations is much smaller than the Hubble scale. The state possesses no quanta at the asymptotic past infinity.
The Bousso bound captures a fundamental relation between quantum information and the geometry of space and time. It appears to be an imprint of a unified theory that combines quantum mechanics with Einstein's general relativity. The study of black hole thermodynamics and the information paradox led to the idea of the holographic principle: the entropy of matter and radiation in a spatial region cannot exceed the Bekenstein–Hawking entropy of the boundary of the region, which is proportional to the boundary area. However, this "spacelike" entropy bound fails in cosmology; for example, it does not hold true in our universe.
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.
Riccardo Rattazzi is an Italian theoretical physicist and a professor at the École Polytechnique Fédérale de Lausanne. His main research interests are in physics beyond the Standard Model and in cosmology.
Freddy Alexander Cachazo is a Venezuelan-born theoretical physicist who holds the Gluskin Sheff Freeman Dyson Chair in Theoretical Physics at the Perimeter Institute for Theoretical Physics in Waterloo, Ontario, Canada.
Veronika E. Hubeny is an American physicist and academic who specialises in string theory and quantum gravity. Since 2015, she has been a professor in the Department of Physics of University of California, Davis. Previously, Hubeny was Professor of Physics at Durham University, where she had worked from 2005 to 2015. From January to April 2014, she was a member of the Institute for Advanced Study in Princeton, New Jersey. In 2019, she was selected as a fellow of the International Society on General Relativity and Gravitation.
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.
Anna Ceresole is an Italian high energy physicist and Director of Research in Theoretical Physics at the Istituto Nazionale di Fisica Nucleare (INFN). She is interested in quantum field theory, supergravity and string theory.
Olaf Lechtenfeld is a German mathematical physicist, academic and researcher. He is a full professor at the Institute of Theoretical Physics at Leibniz University, where he founded the Riemann Center for Geometry and Physics.
The spectral dimension is a real-valued quantity that characterizes a spacetime geometry and topology. It characterizes a spread into space over time, e.g. a ink drop diffusing in a water glass or the evolution of a pandemic in a population. Its definition is as follow: if a phenomenon spreads as , with the time, then the spectral dimension is . The spectral dimension depends on the topology of the space, e.g., the distribution of neighbors in a population, and the diffusion rate.
