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Measurement Problem
In quantum mechanics, the measurement problem is the ''problem of definite outcomes:'' quantum systems have superpositions but quantum measurements only give one definite result. 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 Schrödinger equation determines the wave function at any later time. If observers and their measuring apparatus are t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Quantum Mechanics
Quantum mechanics is the fundamental physical Scientific theory, theory that describes the behavior of matter and of light; its unusual characteristics typically occur at and below the scale of atoms. Reprinted, Addison-Wesley, 1989, It is the foundation of all quantum physics, which includes quantum chemistry, quantum field theory, quantum technology, and quantum information science. Quantum mechanics can describe many systems that classical physics cannot. Classical physics can describe many aspects of nature at an ordinary (macroscopic and Microscopic scale, (optical) microscopic) scale, but is not sufficient for describing them at very small submicroscopic (atomic and subatomic) scales. Classical mechanics can be derived from quantum mechanics as an approximation that is valid at ordinary scales. Quantum systems have Bound state, bound states that are Quantization (physics), quantized to Discrete mathematics, discrete values of energy, momentum, angular momentum, and ot ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Wave Function Collapse
In various interpretations of quantum mechanics, wave function collapse, also called reduction of the state vector, occurs when a wave function—initially in a superposition of several eigenstates—reduces to a single eigenstate due to interaction with the external world. This interaction is called an ''observation'' and is the essence of a measurement in quantum mechanics, which connects the wave function with classical observables such as position and momentum. Collapse is one of the two processes by which quantum systems evolve in time; the other is the continuous evolution governed by the Schrödinger equation. : In the Copenhagen interpretation, wave function collapse connects quantum to classical models, with a special role for the observer. By contrast, objective-collapse proposes an origin in physical processes. In the many-worlds interpretation, collapse does not exist; all wave function outcomes occur while quantum decoherence accounts for the appearance of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Objective-collapse Theory
Objective-collapse theories, also known spontaneous collapse models or dynamical reduction models, are proposed solutions to the measurement problem in quantum mechanics. As with other interpretations of quantum mechanics, they are possible explanations of why and how quantum measurements always give definite outcomes, not a superposition of them as predicted by the Schrödinger equation, and more generally how the classical world emerges from quantum theory. The fundamental idea is that the unitary evolution of the wave function describing the state of a quantum system is approximate. It works well for microscopic systems, but progressively loses its validity when the mass / complexity of the system increases. In collapse theories, the Schrödinger equation is supplemented with additional nonlinear and stochastic terms (spontaneous collapses) which localize the wave function in space. The resulting dynamics is such that for microscopic isolated systems, the new terms have a neg ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
De Broglie–Bohm Theory
The de Broglie–Bohm theory is an interpretation of quantum mechanics which postulates that, in addition to the wavefunction, an actual configuration of particles exists, even when unobserved. The evolution over time of the configuration of all particles is defined by a guiding equation. The evolution of the wave function over time is given by the Schrödinger equation. The theory is named after Louis de Broglie (1892–1987) and David Bohm (1917–1992). The theory is deterministic and explicitly nonlocal: the velocity of any one particle depends on the value of the guiding equation, which depends on the configuration of all the particles under consideration. Measurements are a particular case of quantum processes described by the theory—for which it yields the same quantum predictions as other interpretations of quantum mechanics. The theory does not have a " measurement problem", due to the fact that the particles have a definite configuration at all times. The Born ru ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Oxford University Press
Oxford University Press (OUP) is the publishing house of the University of Oxford. It is the largest university press in the world. Its first book was printed in Oxford in 1478, with the Press officially granted the legal right to print books by decree in 1586. It is the second-oldest university press after Cambridge University Press, which was founded in 1534. It is a department of the University of Oxford. It is governed by a group of 15 academics, the Delegates of the Press, appointed by the Vice Chancellor, vice-chancellor of the University of Oxford. The Delegates of the Press are led by the Secretary to the Delegates, who serves as OUP's chief executive and as its major representative on other university bodies. Oxford University Press has had a similar governance structure since the 17th century. The press is located on Walton Street, Oxford, Walton Street, Oxford, opposite Somerville College, Oxford, Somerville College, in the inner suburb of Jericho, Oxford, Jericho. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Born Rule
The Born rule is a postulate of quantum mechanics that gives the probability that a measurement of a quantum system will yield a given result. In one commonly used application, it states that the probability density for finding a particle at a given position is proportional to the square of the amplitude of the system's wavefunction at that position. It was formulated and published by German physicist Max Born in July 1926. Details The Born rule states that an observable, measured in a system with normalized wave function , \psi\rang (see Bra–ket notation), corresponds to a self-adjoint operator A whose spectrum is discrete if: * the measured result will be one of the eigenvalues \lambda of A, and * the probability of measuring a given eigenvalue \lambda_i will equal \lang\psi, P_i, \psi\rang, where P_i is the projection onto the eigenspace of A corresponding to \lambda_i. : (In the case where the eigenspace of A corresponding to \lambda_i is one-dimensional and spanned by ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bryce DeWitt
Bryce Seligman DeWitt (born Carl Bryce Seligman; January 8, 1923 – September 23, 2004) was an American theoretical physicist noted for his work in gravitation and quantum field theory. Personal life He was born Carl Bryce Seligman, but he and his three brothers, including the noted ichthyologist, Hugh Hamilton DeWitt, added "DeWitt" from their mother's side of the family, at the urging of their father, in 1950. Several decades later, when Felix Bloch learned of this name-change, he was so upset that he blocked DeWitt's appointment to Stanford University; consequently, DeWitt and his wife Cecile DeWitt-Morette, a mathematical physicist, accepted faculty positions at the University of Texas at Austin. DeWitt trained in World War II as a naval aviator, but the war ended before he saw combat. He died September 23, 2004, from pancreatic cancer at the age of 81. He is buried in France, and was survived by his wife and four daughters. Academic life He received his bachelor' ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Many-worlds Interpretation
The many-worlds interpretation (MWI) is an interpretation of quantum mechanics that asserts that the universal wavefunction is Philosophical realism, objectively real, and that there is no wave function collapse. This implies that all Possible world, possible outcomes of quantum measurements are physically realized in different "worlds". The evolution of reality as a whole in MWI is rigidly Determinism, deterministic and principle of locality, local. Many-worlds is also called the relative state formulation or the Everett interpretation, after physicist Hugh Everett III, Hugh Everett, who first proposed it in 1957.Hugh Everett]Theory of the Universal Wavefunction Thesis, Princeton University, (1956, 1973), pp. 1–140. Bryce DeWitt popularized the formulation and named it ''many-worlds'' in the 1970s. See also Cécile DeWitt-Morette, Cecile M. DeWitt, John A. Wheeler (eds,) The Everett–Wheeler Interpretation of Quantum Mechanics, ''Battelle Rencontres: 1967 Lectures in Mathema ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hugh Everett
Hugh Everett III (; November 11, 1930 – July 19, 1982) was an American physicist who proposed the relative state interpretation of quantum mechanics. This influential approach later became the basis of the many-worlds interpretation (MWI). Everett's theory dropped the wave function collapse postulate of quantum measurement theory, incorporating the observer in the same quantum state as the observation result. The quantum statistic becomes a measure of the branching of the universal wave function. Everett also helped found small companies specializing in contracts with the US government. Although largely disregarded until near the end of his life, Everett's work received more credibility with the discovery of quantum decoherence in the 1970s and has received increased attention in recent decades, with MWI becoming one of the important interpretations of quantum mechanics. Early life and education Hugh Everett III was born in 1930 and raised in the Washington, D.C. area. Hi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Stanford Encyclopedia Of Philosophy
The ''Stanford Encyclopedia of Philosophy'' (''SEP'') is a freely available online philosophy resource published and maintained by Stanford University, encompassing both an online encyclopedia of philosophy and peer-reviewed original publication. Each entry is written and maintained by an expert in the field, including professors from many academic institutions worldwide. Authors contributing to the encyclopedia give Stanford University the permission to publish the articles, but retain the copyright to those articles. Approach and history As of August 5, 2022, the ''SEP'' has 1,774 published entries. Apart from its online status, the encyclopedia uses the traditional academic approach of most encyclopedias and academic journals to achieve quality by means of specialist authors selected by an editor or an editorial committee that is competent (although not necessarily considered specialists) in the field covered by the encyclopedia and peer review. The encyclopedia was created i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Physics World
''Physics World'' is the membership magazine of the Institute of Physics, one of the largest physical societies in the world. It is an international monthly magazine covering all areas of physics, pure and applied, and is aimed at physicists in research, industry, physics outreach, and education worldwide. Overview The magazine was launched in 1988 by IOP Publishing Ltd, under the founding editorship of Philip Campbell. The magazine is made available free of cost to members of the Institute of Physics, who can access a digital edition of the magazine; selected articles can be read by anyone for free online. It was redesigned in September 2005 and has an audited circulation of just under 35000. The current editor is Matin Durrani. Others on the team are Michael Banks (news editor) and Tushna Commissariat and Sarah Teah (features editors). Hamish Johnston, Margaret Harris and Tami Freeman are online editors. Alongside the print and online magazine, Physics World produces film ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
The European Physical Journal D
The ''European Physical Journal D: Atomic, Molecular, Optical and Plasma Physics'' is an academic journal recognized by the European Physical Society, presenting new and original research results. Scope The main areas covered are: *Atomic Physics *Molecular Physics and Chemical Physics *Atomic and Molecular Collisions *Clusters and Nanostructures *Cold Matter and Quantum Gases *Plasma Physics *Nonlinear Dynamics *Optical Phenomena and Photonics *Quantum Optics *Quantum Information *Ultraintense and Ultrashort Laser Fields The range of topics covered in these areas is extensive, from Molecular Interaction and Reactivity to Spectroscopy and Thermodynamics of Clusters, from Atomic Optics to Bose-Einstein Condensation to Femtochemistry. History The EPJ D arose from various predecessors: ''Il Nuovo Cimento (Section D)'', ''Journal de Physique'', and ''Zeitschrift für Physik D''. Prior to 1998, this journal was named ''Zeitschrift für Physik D: Atoms, Molecules and Clusters''. Unti ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
