|
Problem Of Time
In theoretical physics, the problem of time is a conceptual conflict between general relativity and quantum mechanics in that quantum mechanics regards the flow of time as universal and absolute, whereas general relativity regards the flow of time as malleable and relative. This problem raises the question of what time really is in a physical sense and whether it is truly a real, distinct phenomenon. It also involves the related question of why time seems to flow in a single direction, despite the fact that no known physical laws at the microscopic level seem to require a single direction. For macroscopic systems the directionality of time is directly linked to first principles such as the second law of thermodynamics. Time in quantum mechanics In classical mechanics, a special status is assigned to time in the sense that it is treated as a classical background parameter, external to the system itself. This special role is seen in the standard formulation of quantum mechanics ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Theoretical Physics
Theoretical physics is a branch of physics that employs mathematical models and abstractions of physical objects and systems to rationalize, explain and predict natural phenomena. This is in contrast to experimental physics, which uses experimental tools to probe these phenomena. The advancement of science generally depends on the interplay between experimental studies and theory. In some cases, theoretical physics adheres to standards of mathematical rigour while giving little weight to experiments and observations.There is some debate as to whether or not theoretical physics uses mathematics to build intuition and illustrativeness to extract physical insight (especially when normal experience fails), rather than as a tool in formalizing theories. This links to the question of it using mathematics in a less formally rigorous, and more intuitive or heuristic way than, say, mathematical physics. For example, while developing special relativity, Albert Einstein was concerned wit ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Diffeomorphism
In mathematics, a diffeomorphism is an isomorphism of smooth manifolds. It is an invertible function that maps one differentiable manifold to another such that both the function and its inverse are differentiable. Definition Given two manifolds M and N, a differentiable map f \colon M \rightarrow N is called a diffeomorphism if it is a bijection and its inverse f^ \colon N \rightarrow M is differentiable as well. If these functions are r times continuously differentiable, f is called a C^r-diffeomorphism. Two manifolds M and N are diffeomorphic (usually denoted M \simeq N) if there is a diffeomorphism f from M to N. They are C^r-diffeomorphic if there is an r times continuously differentiable bijective map between them whose inverse is also r times continuously differentiable. Diffeomorphisms of subsets of manifolds Given a subset X of a manifold M and a subset Y of a manifold N, a function f:X\to Y is said to be smooth if for all p in X there is a neighbor ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lee Smolin
Lee Smolin (; born June 6, 1955) 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. [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Avshalom Elitzur
Avshalom Cyrus Elitzur ( he, אבשלום כורש אליצור; born 30 May 1957) is an Israeli physicist and philosopher. Biography Avshalom Elitzur was born in Kerman, Iran, to a Jewish family. When he was two years old, his family immigrated to Israel and settled in Rehovot. He left school at the age of sixteen and began working as a laboratory technician at the Weizmann Institute of Science in Rehovot. Elitzur received no formal university training before obtaining his PhD. Elitzur was a senior lecturer at the Unit for Interdisciplinary Studies, Bar-Ilan University, Ramat-Gan, Israel. He is noted for the Elitzur–Vaidman bomb-testing problem in quantum mechanics, which was publicised by Roger Penrose in his book '' Shadows of the Mind''. In 1987, he published his book: ''Into the Holy of Holies: Psychoanalytic Insights into the Bible and Judaism''. During that same year, he was invited to present an unpublished manuscript on quantum mechanics at an international conf ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Black Hole Information Paradox
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 m ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Problem Of Measurement
In quantum mechanics, the measurement problem is the problem of how, or whether, wave function collapse occurs. The inability to observe such a collapse directly has given rise to different interpretations of quantum mechanics and poses a key set of questions that each interpretation must answer. The wave function in quantum mechanics evolves deterministically according to the Schrödinger equation as a linear superposition of different states. However, actual measurements always find the physical system in a definite state. Any future evolution of the wave function is based on the state the system was discovered to be in when the measurement was made, meaning that the measurement "did something" to the system that is not obviously a consequence of Schrödinger evolution. The measurement problem is describing what that "something" is, how a superposition of many possible values becomes a single measured value. To express matters differently (paraphrasing Steven Weinberg), the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Minority Interpretations Of Quantum Mechanics
There is a diversity of views that propose interpretations of quantum mechanics. They vary in how many physicists accept or reject them. An interpretation of quantum mechanics is a conceptual scheme that proposes to relate the mathematical formalism to the physical phenomena of interest. The present article is about those interpretations which, independently of their intrinsic value, remain today less known, or are simply less debated by the scientific community, for different reasons. History The historical dichotomy between the "orthodox" Copenhagen interpretation and "unorthodox" minority views developed in the 1950s debate surrounding Bohmian mechanics. During most of the 20th century, collapse theories were clearly the mainstream view, and the question of interpretation of quantum mechanics mostly revolved around how to interpret "collapse". Proponents of either "pilot-wave" (de Broglie-Bohm-like) or "many-worlds" (Everettian) interpretations tend to emphasize how their resp ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Rodolfo Gambini
Rodolfo Gambini (born 11 May 1946) is a physicist and professor of the Universidad de la Republica in Montevideo, Uruguay and a visiting professor at the Horace Hearne Institute for Theoretical Physics at the Louisiana State University. He works on loop quantum gravity. He got his PhD in Université de Paris VI working with Achilles Papapetrou. From there he moved to the Universidad Simón Bolívar in Venezuela where he rose through the professorial ranks. It was there that together with fellow physicist Antoni Trías he invented the loop representation for Yang-Mills theories in 1986. Gambini returned to Uruguay in 1987 after democracy had returned to the country. Gambini has published over 100 scientific articles ranging from philosophy of science and foundations of quantum mechanics to lattice gauge theories to quantum gravity. He was head of the Pedeciba, the main funding agency for basic sciences in Uruguay (2003–2008). He is a fellow of the American Physical Soci ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Jorge Pullin
Jorge Pullin (; born 1963 in Argentina) is an American theoretical physicist known for his work on black hole collisions and quantum gravity. He is the Horace Hearne Chair in theoretical Physics at the Louisiana State University. Biography Jorge Pullin attended the University of Buenos Aires (electrical engineering) for two years before leaving for Instituto Balseiro in Argentina to finish a M.Sc. in Physics (1986). Then he moved to the University of Córdoba to pursue his Ph.D. which was submitted in 1988 to the Instituto Balseiro; his advisor was Reinaldo J. Gleiser. He moved to Syracuse University in 1989 and to the University of Utah in 1991 as a postdoc. He joined the faculty of Penn State University in 1993, where he was promoted to associate professor in 1997 and full professor in 2000. In 2001 he moved to Louisiana State University, where he is the co-director of the Horace Hearne Institute, along with Jonathan Dowling. Pullin's wife Gabriela González is also a gravita ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Wheeler–DeWitt Equation
The Wheeler–DeWitt equation for theoretical physics and applied mathematics, is a field equation attributed to John Archibald Wheeler and Bryce DeWitt. The equation attempts to mathematically combine the ideas of quantum mechanics and general relativity, a step towards a theory of quantum gravity. In this approach, time plays a role different from what it does in non-relativistic quantum mechanics, leading to the so-called 'problem of time'. More specifically, the equation describes the quantum version of the Hamiltonian constraint using metric variables. Its commutation relations with the diffeomorphism constraints generate the Bergman–Komar "group" (which ''is'' the diffeomorphism group on-shell). Quantum gravity All defined and understood descriptions of string/M-theory deal with fixed asymptotic conditions on the background spacetime. At infinity, the "right" choice of the time coordinate "t" is determined (because the space-time is asymptotic to some fixed space-time) ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Quantum Entanglement
Quantum entanglement is the phenomenon that occurs when a group of particles are generated, interact, or share spatial proximity in a way such that the quantum state of each particle of the group cannot be described independently of the state of the others, including when the particles are separated by a large distance. The topic of quantum entanglement is at the heart of the disparity between classical and quantum physics: entanglement is a primary feature of quantum mechanics not present in classical mechanics. Measurements of physical properties such as position, momentum, spin, and polarization performed on entangled particles can, in some cases, be found to be perfectly correlated. For example, if a pair of entangled particles is generated such that their total spin is known to be zero, and one particle is found to have clockwise spin on a first axis, then the spin of the other particle, measured on the same axis, is found to be anticlockwise. However, this behavior gives ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
William Wootters
William "Bill" Kent Wootters () is an American theoretical physicist, and one of the founders of the field of quantum information theory. In a 1982 joint paper with Wojciech H. Zurek, Wootters proved the no cloning theorem, at the same time as Dennis Dieks, and independently of James L. Park who had formulated the no-cloning theorem in 1970. He is known for his contributions to the theory of quantum entanglement including quantitative measures of it, entanglement-assisted communication (notably quantum teleportation, discovered by Wootters and collaborators in 1993) and entanglement distillation. The term ''qubit,'' denoting the basic unit of quantum information, originated in a conversation between Wootters and Benjamin Schumacher in 1992. He earned a B.S. from Stanford University in 1973, and his Ph.D. from the University of Texas at Austin in 1980. His thesis was titled ''The Acquisition of Information from Quantum Measurements,'' and Linda Reichl was his doctoral advisor, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
