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Feynman
Richard Phillips Feynman (; May 11, 1918 – February 15, 1988) was an American theoretical physicist. He is best known for his work in the path integral formulation of quantum mechanics, the theory of quantum electrodynamics, the physics of the superfluidity of supercooled liquid helium, and in particle physics, for which he proposed the parton model. For his contributions to the development of quantum electrodynamics, Feynman received the Nobel Prize in Physics in 1965 jointly with Julian Schwinger and Shin'ichirō Tomonaga. Feynman developed a pictorial representation scheme for the mathematical expressions describing the behavior of subatomic particles, which later became known as Feynman diagrams and is widely used. During his lifetime, Feynman became one of the best-known scientists in the world. In a 1999 poll of 130 leading physicists worldwide by the British journal ''Physics World'', he was ranked the seventh-greatest physicist of all time. He assisted in the dev ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Feynman Diagram
In theoretical physics, a Feynman diagram is a pictorial representation of the mathematical expressions describing the behavior and interaction of subatomic particles. The scheme is named after American physicist Richard Feynman, who introduced the diagrams in 1948. The calculation of probability amplitudes in theoretical particle physics requires the use of large, complicated integrals over a large number of variables. Feynman diagrams instead represent these integrals graphically. Feynman diagrams give a simple visualization of what would otherwise be an arcane and abstract formula. According to David Kaiser, "Since the middle of the 20th century, theoretical physicists have increasingly turned to this tool to help them undertake critical calculations. Feynman diagrams have revolutionized nearly every aspect of theoretical physics." While the diagrams apply primarily to quantum field theory, they can be used in other areas of physics, such as solid-state theory. Frank Wi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Feynman Sprinkler
A Feynman sprinkler, also referred to as a Feynman inverse sprinkler or reverse sprinkler, is a sprinkler-like device which is submerged in a tank and made to suck in the surrounding fluid. The question of how such a device would turn was the subject of an intense and remarkably long-lived debate. The device generally remains steady with no rotation, though with sufficiently low friction and high rate of inflow, it has been seen to turn weakly in the opposite direction of a conventional sprinkler. A regular sprinkler has nozzles arranged at angles on a freely rotating wheel such that when water is pumped out of them, the resulting jets cause the wheel to rotate; a Catherine wheel and the aeolipile ("Hero's engine") work on the same principle. A "reverse" or "inverse" sprinkler would operate by aspirating the surrounding fluid instead. The problem is commonly associated with theoretical physicist Richard Feynman, who mentions it in his bestselling memoirs '' Surely You're Joking, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Feynman Propagator
In quantum mechanics and quantum field theory, the propagator is a function that specifies the probability amplitude for a particle to travel from one place to another in a given period of time, or to travel with a certain energy and momentum. In Feynman diagrams, which serve to calculate the rate of collisions in quantum field theory, virtual particles contribute their propagator to the rate of the scattering event described by the respective diagram. Propagators may also be viewed as the inverse of the wave operator appropriate to the particle, and are, therefore, often called ''(causal) Green's functions'' (called "''causal''" to distinguish it from the elliptic Laplacian Green's function). Non-relativistic propagators In non-relativistic quantum mechanics, the propagator gives the probability amplitude for a particle to travel from one spatial point (x') at one time (t') to another spatial point (x) at a later time (t). The Green's function G for the Schrödinger equation ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hellmann–Feynman Theorem
In quantum mechanics, the Hellmann–Feynman theorem relates the derivative of the total energy with respect to a parameter to the expectation value of the derivative of the Hamiltonian with respect to that same parameter. According to the theorem, once the spatial distribution of the electrons has been determined by solving the Schrödinger equation, all the forces in the system can be calculated using classical electrostatics. The theorem has been proven independently by many authors, including Paul Güttinger (1932), Wolfgang Pauli (1933), Hans Hellmann (1937) and Richard Feynman (1939). The theorem states where *\hat_ is a Hermitian operator depending upon a continuous parameter \lambda\,, *, \psi_\lambda\rangle, is an eigenstate (eigenfunction) of the Hamiltonian, depending implicitly upon \lambda, *E_\, is the energy (eigenvalue) of the state , \psi_\lambda\rangle, i.e. \hat_, \psi_\lambda\rangle = E_, \psi_\lambda\rangle. Note that there is a breakdown of the Hellma ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Feynman–Kac Formula
The Feynman–Kac formula, named after Richard Feynman and Mark Kac, establishes a link between parabolic partial differential equations and stochastic processes. In 1947, when Kac and Feynman were both faculty members at Cornell University, Kac attended a presentation of Feynman's and remarked that the two of them were working on the same thing from different directions. The Feynman–Kac formula resulted, which proves rigorously the real-valued case of Feynman's path integrals. The complex case, which occurs when a particle's spin is included, is still an open question. It offers a method of solving certain partial differential equations by simulating random paths of a stochastic process. Conversely, an important class of expectations of random processes can be computed by deterministic methods. Theorem Consider the partial differential equation \fracu(x,t) + \mu(x,t) \fracu(x,t) + \tfrac \sigma^2(x,t) \fracu(x,t) -V(x,t) u(x,t) + f(x,t) = 0, defined for all x \in \mathbb ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Feynman Checkerboard
The Feynman checkerboard, or relativistic chessboard model, was Richard Feynman's sum-over-paths formulation of the kernel for a free spin- particle moving in one spatial dimension. It provides a representation of solutions of the Dirac equation in (1+1)-dimensional spacetime as discrete sums. The model can be visualised by considering relativistic random walks on a two-dimensional spacetime checkerboard. At each discrete timestep \epsilon the particle of mass m moves a distance \epsilon c to the left or right (c being the speed of light). For such a discrete motion, the Feynman path integral reduces to a sum over the possible paths. Feynman demonstrated that if each "turn" (change of moving from left to right or conversely) of the space–time path is weighted by -i \epsilon mc^2/\hbar (with \hbar denoting the reduced Planck constant), in the limit of infinitely small checkerboard squares the sum of all weighted paths yields a propagator that satisfies the one-dimensional Dira ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Feynman Parametrization
Feynman parametrization is a technique for evaluating loop integrals which arise from Feynman diagrams with one or more loops. However, it is sometimes useful in integration in areas of pure mathematics as well. It was introduced by Julian Schwinger and Richard Feynman in 1949 to perform calculations in quantum electrodynamics. Formulas Richard Feynman observed that :\frac=\int^1_0 \frac which is valid for any complex numbers ''A'' and ''B'' as long as 0 is not contained in the line segment connecting ''A'' and ''B.'' The formula helps to evaluate integrals like: :\begin \int \frac &= \int dp \int^1_0 \frac \\ &= \int^1_0 du \int \frac. \end If ''A''(''p'') and ''B''(''p'') are linear functions of ''p'', then the last integral can be evaluated using substitution. More generally, using the Dirac delta function \delta: :\begin \frac&= (n-1)! \int^1_0 du_1 \cdots \int^1_0 du_n \frac \\ &=(n-1)! \int^1_0 du_1 \int^_0 du_2 \cdots \int^_0 du_ \frac. \end This formula is valid fo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Laurie Brown (physicist)
Laurie Mark Brown (April 10, 1923 – October 25, 2019) was an American theoretical physicist and historian of quantum field theory and elementary particle physics. Life and career Laurie Mark Brown was born in Kings, New York on April 10, 1923. He studied at Cornell University, where in 1951 he received his Ph.D. under Richard Feynman. Since 1950 he has been on the faculty of the physics department of Northwestern University, where he became a tenured professor and eventually retired as professor emeritus. For the academic year 1952–1953 he was at the Institute for Advanced Study. For the academic years 1958–1959 and 1959–1960 he was a Fulbright Scholar in Italy. In 1966 he was an IEA professor at the University of Vienna. From 1960 to 1970 he served as a consultant for Argonne National Laboratory and the Laboratory's Accelerator Committee. Brown is one of the leading science historians for the development of quantum field theory and elementary particle physics, especially ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Albert Hibbs
Albert Roach Hibbs (October 19, 1924 – February 24, 2003) was an American mathematician and physicist affiliated with the Jet Propulsion Laboratory (JPL). He was known as "The Voice of JPL" due to his gift for explaining advanced science in simple terms. He helped establish JPL's Space Science Division in 1960 and later served as its first chief. He was the systems designer for Explorer 1, the USA's first satellite, and helped establish the framework for exploration of the Solar System through the 1960s. Hibbs qualified as an astronaut in 1967 and was slated to be a crew member of Apollo 25, but he ultimately did not go to the Moon due to the Apollo program ending after the Apollo 17 mission in 1972. Education Hibbs earned bachelor's degree in physics from the California Institute of Technology (Caltech) in 1945, having attended Caltech under the sponsorship of the US Navy's V-12 program. He then obtained a master's degree in mathematics from the University of Chicago ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Feynman Point
A sequence of six consecutive nines occurs in the decimal representation of the number pi (), starting at the 762nd decimal place.. It has become famous because of the mathematical coincidence, and because of the idea that one could memorize the digits of up to that point, and then suggest that is rational. The earliest known mention of this idea occurs in Douglas Hofstadter's 1985 book '' Metamagical Themas'', where Hofstadter states This sequence of six nines is colloquially known as the "Feynman point", after physicist Richard Feynman, who allegedly stated this same idea in a lecture.. However it is not clear when, or even if, Feynman ever made such a statement. It is not mentioned in his memoirs and unknown to his biographer James Gleick. Related statistics is conjectured, but not known, to be a normal number. For a normal number sampled uniformly at random, the probability of a specific sequence of six digits occurring this early in the decimal representation is about ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
John Archibald Wheeler
John Archibald Wheeler (July 9, 1911April 13, 2008) was an American theoretical physicist. He was largely responsible for reviving interest in general relativity in the United States after World War II. Wheeler also worked with Niels Bohr to explain the basic principles of nuclear fission. Together with Gregory Breit, Wheeler developed the concept of the Breit–Wheeler process. He is best known for popularizing the term "black hole" for objects with gravitational collapse already predicted during the early 20th century, for inventing the terms "quantum foam", "neutron moderator", "wormhole" and "it from bit", and for hypothesizing the "one-electron universe". Stephen Hawking called Wheeler the "hero of the black hole story". At 21, Wheeler earned his doctorate at Johns Hopkins University under the supervision of Karl Herzfeld. He studied under Breit and Bohr on a National Research Council (United States), National Research Council fellowship. In 1939 he collaborated with Bohr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Feynman Gauge
In the physics of gauge theory, gauge theories, gauge fixing (also called choosing a gauge) denotes a mathematical procedure for coping with redundant Degrees of freedom (physics and chemistry), degrees of freedom in field (physics), field variables. By definition, a gauge theory represents each physically distinct configuration of the system as an equivalence class of detailed local field configurations. Any two detailed configurations in the same equivalence class are related by a certain transformation, equivalent to a symmetry transformation, shear along unphysical axes in configuration space. Most of the quantitative physical predictions of a gauge theory can only be obtained under a coherent prescription for suppressing or ignoring these unphysical degrees of freedom. Although the unphysical axes in the space of detailed configurations are a fundamental property of the physical model, there is no special set of directions "perpendicular" to them. Hence there is an enormo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
