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The holographic principle is an axiom in 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-theory 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.
The heat death of the universe is a hypothesis on the ultimate fate of the universe, which suggests the universe will evolve to a state of no thermodynamic free energy, and will therefore be unable to sustain processes that increase entropy. Heat death does not imply any particular absolute temperature; it only requires that temperature differences or other processes may no longer be exploited to perform work. In the language of physics, this is when the universe reaches thermodynamic equilibrium. The Heat Death theory has become the leading theory in the modern age with the fewest unpredictable factors.
In theoretical physics, the BFSS matrix model or matrix theory is a quantum mechanical model proposed by Tom Banks, Willy Fischler, Stephen Shenker, and Leonard Susskind in 1997.
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, the anti-de Sitter/conformal field theory correspondence, sometimes called Maldacena duality or gauge/gravity duality, is a conjectured relationship between two kinds of physical theories. On one side are anti-de Sitter spaces (AdS) which are used in theories of quantum gravity, formulated in terms of string theory or M-theory. On the other side of the correspondence are conformal field theories (CFT) which are quantum field theories, including theories similar to the Yang–Mills theories that describe elementary particles.
Leonard Susskind is an American physicist, who is a professor of theoretical physics at Stanford University, and founding director of the Stanford Institute for Theoretical Physics. His research interests include 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 black hole information paradox is a puzzle 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 rules of quantum mechanics to such systems and found that an isolated black hole would emit a form of radiation called Hawking radiation. Hawking also argued that the detailed form of the radiation would be independent of the initial state of the black hole and would depend only on its mass, electric charge and angular momentum. The information paradox appears when one considers a process in which a black hole is formed through a physical process and then evaporates away entirely through Hawking radiation. Hawking's calculation suggests that the final state of radiation would retain information only about the total mass, electric charge and angular momentum of the initial state. Since many different states can have the same mass, charge and angular momentum this suggests that many initial physical states could evolve into the same final state. Therefore, information about the details of the initial state would be permanently lost. However, this violates a core precept of both classical and quantum physics—that, in principle, the state of a system at one point in time should determine its value at any other time. Specifically, in quantum mechanics the state of the system is encoded by its wave function. The evolution of the wave function is determined by a unitary operator, and unitarity implies that the wave function at any instant of time can be used to determine the wave function either in the past or the future.
The string theory landscape or landscape of vacua refers to the collection of possible false vacua in string theory, together comprising a collective "landscape" of choices of parameters governing compactifications.
Stephen Hart Shenker is an American theoretical physicist who works on string theory. He is a professor at Stanford University and former director of the Stanford Institute for Theoretical Physics. His brother Scott Shenker is a computer scientist.
The Boltzmann brain thought experiment suggests that it might be more likely for a single brain to spontaneously form in a void rather than for the entire universe to come about in the manner cosmologists think it actually did. Physicists use the Boltzmann brain thought experiment as a reductio ad absurdum argument for evaluating competing scientific theories.
David Elazzar Kaplan is a theoretical particle physicist at the Johns Hopkins University.
The Fischler–Susskind mechanism, first proposed by Willy Fischler and Leonard Susskind in 1998, is a holographic prescription based on the particle horizon.
Black hole complementarity is a conjectured solution to the black hole information paradox, proposed by Leonard Susskind, Larus Thorlacius, and Gerard 't Hooft.
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.
Matthew Benjamin Kleban is an American theoretical physicist who works on string theory and theoretical cosmology. He is the chair of the Department of Physics and a professor at New York University, former director of the Center for Cosmology and Particle Physics, and a former member of the Institute for Advanced Study. His contributions to physics include:
A black hole firewall is a hypothetical phenomenon where an observer falling into a black hole encounters high-energy quanta at the event horizon. The "firewall" phenomenon was proposed in 2012 by physicists Ahmed Almheiri, Donald Marolf, Joseph Polchinski, and James Sully as a possible solution to an apparent inconsistency in black hole complementarity. The proposal is sometimes referred to as the AMPS firewall, an initialism for the names of the authors of the 2012 paper. The potential inconsistency pointed out by AMPS had been pointed out earlier by Samir Mathur who used the argument in favour of the fuzzball proposal. The use of a firewall to resolve this inconsistency remains controversial, with physicists divided as to the solution to the paradox.
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.
Henriette D. Elvang is a Theoretical Particle Physicist and Professor at the University of Michigan. She works on quantum field theory and scattering processes.
References
- ↑ Dyson, Lisa; Kleban, Matthew; Susskind, Leonard (October 2002). "Disturbing Implications of a Cosmological Constant". Journal of High Energy Physics. 2002 (10): 011. arXiv: hep-th/0208013 . Bibcode:2002JHEP...10..011D. doi:10.1088/1126-6708/2002/10/011. S2CID 2344440.
- ↑ Goheer, Naureen; Kleban, Matthew; Susskind, Leonard (July 2003). "The Trouble with de Sitter Space". Journal of High Energy Physics. 2003 (7): 056. arXiv: hep-th/0212209 . Bibcode:2003JHEP...07..056G. doi:10.1088/1126-6708/2003/07/056. S2CID 12766264.
