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Topic: Quantum electrodynamics


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In the News (Sat 20 Jul 19)

  
  Quantum Electrodynamics (QED)   (Site not responding. Last check: 2007-10-26)
Quantum electrodynamics, commonly referred to as QED, is a quantum field theory of the electromagnetic force.
The quantum field theory approach visualizes the force between the electrons as an exchange force arising from the exchange of virtual photons.
QED was the first successful quantum field theory, incorporating such ideas as particle creation and annihilation into a self-consistent framework.
hyperphysics.phy-astr.gsu.edu /hbase/forces/qed.html   (199 words)

  
 Quantum electrodynamics Summary
Quantum theory began in 1900, when Max Planck assumed that energy is quantized in order to derive a formula predicting the observed frequency dependence of the energy emitted by a fl body.
Modern quantum mechanics was born in 1925 with Werner Heisenberg's matrix mechanics and Erwin Schrödinger's wave mechanics and the Schrödinger equation.
QED, a quantum theory of electrons, positrons, and the electromagnetic field, was the first satisfactory quantum description of a physical field and of the creation and annihilation of quantum particles.
www.bookrags.com /Quantum_electrodynamics   (6252 words)

  
 Quantum Physics
The reason the EPR paradox is so severe is that the predictions of quantum mechanics fly in flat contradiction to the laws of relativity, which are so solidly established and so successfully built into the deepest form of quantum mechanics, quantum electrodynamics.
Quantum mechanics predicts that the choice of the axis for the first measurement of spin will alter the results of measurement of spin of the second particle, in a manner which is not consistent with the notion that the two particles have separated and become independent.
Quantum mechanics seems to contradict the idea that, prior to measurement, a particle is a point-like object with an unknown position, and appears to say that the particle is actually a wave spread over space.
www.kheper.net /cosmos/quantum_physics/quantum_physics.htm   (3060 words)

  
 Theory of Everything
Quantum electrodynamics, or QED, is a quantum theory of the interactions of charged particles with the electromagnetic field.
Quantum chromodynamics is the subfield of physics that describes the strong or ``color'' force that binds quarks together to form baryons and mesons, and results in the complicated the force that binds atomic nuclei together.
Quantum gravity is a type of quantum theory of elementary particles and their interactions that is based on the particle symmetry known as supersymmetry and that naturally includes gravity along with the other fundamental forces (the electromagnetic force, the weak nuclear force, and the strong nuclear force).
zebu.uoregon.edu /~js/21st_century_science/lectures/lec17.html   (3325 words)

  
 Quantum mechanics - Wikipedia, the free encyclopedia
Quantum mechanics is a more fundamental theory than Newtonian mechanics and classical electromagnetism, in the sense that it provides accurate and precise descriptions for many phenomena that these "classical" theories simply cannot explain on the atomic and subatomic level.
For instance, the well-known model of the quantum harmonic oscillator uses an explicitly non-relativistic expression for the kinetic energy of the oscillator, and is thus a quantum version of the classical harmonic oscillator.
The quantum field theory of the strong nuclear force is called quantum chromodynamics, and describes the interactions of the subnuclear particles: quarks and gluons.
en.wikipedia.org /wiki/Quantum_mechanics   (5586 words)

  
 Quantum Field Theory (Stanford Encyclopedia of Philosophy)
Quantum Field Theory (QFT) is the mathematical and conceptual framework for contemporary elementary particle physics.
First, quantum fields which one expects to be somehow physically concrete like classical fields are on the side of observables although, as far as the development of theories is concerned, they are the successors of states (in their position representation, namely wave functions), e.g., in the Klein-Gordon equation of relativistic QM as described above.
A relativistic quantum theory of a fixed number of particles, satisfying in particular the localizability and the locality condition, has to assume a world devoid of particles (or at least a world in which particles can never be detected) in order not to contradict itself.
plato.stanford.edu /entries/quantum-field-theory   (16460 words)

  
 Two concepts about quantum electrodynamics and quantum field theory
Quantum field theory is the general theory resulting from attempts to put quantum mechanics and special relativity together.
Quantum electrodynamics is the resulting quantum field theory when applied to electromagnetic phenomena.
Other quantum field theories that are studied are the Electroweak theory, which is the unification of electromagnetism with the weak force, and QCD, the field theory of the strong force.
www.physicsforums.com /showthread.php?p=279904   (1368 words)

  
 Quantum Electrodynamics - Search Results - MSN Encarta
Quantum Electrodynamics (QED), in physics, a theory that describes how electrically charged particles and electromagnetic fields interact.
- quantum mechanics dealing with electromagnetic interactions: a quantum field theory that describes the properties of electromagnetic radiation and its interaction with electrically charged particles
physical science, astrophysics, nuclear physics, quantum mechanics, quantum electrodynamics, astronomy, dynamics, forces, physical processes,...
encarta.msn.com /Quantum_Electrodynamics.html   (139 words)

  
 Highbeam Encyclopedia - Search Results for quantum   (Site not responding. Last check: 2007-10-26)
Quantum field theory applied to the understanding of electromagnetism is called quantum electrodynamics (QED), and it has proved spectacularly successful in describing the interaction of light with matter.
quantum evolution (quantum speciation) Traditionally, the rapid speciation that can occur in small populations isolated from the large, ancestral population, and that are therefore subject to the founder effect and to genetic drift.
Quantum introduces two high-capacity drive families with MR heads and advanced read channels; technological strength is the foundation for new levels of performance, reliability and disk capacity for 3.5-inch drives.
www.encyclopedia.com /SearchResults.aspx?Q=quantum   (1000 words)

  
 quantum electrodynamics. The Columbia Encyclopedia, Sixth Edition. 2001-05
(QED), quantum field theory that describes the properties of electromagnetic radiation and its interaction with electrically charged matter in the framework of quantum theory.
Charged particles interact by emitting and absorbing photons, the particles of light that transmit electromagnetic forces.
See R. Feynman, QED (1985); P. Milonni, The Quantum Vacuum: An Introduction to Quantum Electrodynamics (1994); S. Schweber, QED and the Men Who Made It: Dyson, Feynman, Schwinger, and Tomonaga (1994); G. Scharf, Finite Quantum Electrodynamics: The Causal Approach (1995).
www.bartleby.com /65/qu/quantumel.html   (447 words)

  
 [No title]
This intrinsic lower certainty of neo-Darwinism than (for example) that of quantum electrodynamics means that there is legitimate room for disputation concerning the history of biology on Earth.
The Casimir Effect is relevant to FTL considerations because it has been predicted from quantum electrodynamics that the speed of light is greater in the energy-depleted vacuum between the Casimir plates than in free space.
Matter and radiation in the laboratory appear to be extraordinarily well described by the laws of quantum mechanics, electromagnetism, and their unification as quantum electrodynamics.
www.lycos.com /info/quantum-electrodynamics--miscellaneous.html?page=2   (412 words)

  
 QUANTUM COMPUTATION WITH QUANTUM DOTS AND TERAHERTZ CAVITY QUANTUM ELECTRODYNAMICS   (Site not responding. Last check: 2007-10-26)
This quantum computer will use electrons in "quantum dots" and cavity quantum electrodynamics at Terahertz frequencies to effect quantum logic operations.
A universal quantum logic operation involving any pair of QDs can be effected by a sequence of gate-voltage pulses that tune the QD energy levels into resonance with frequencies of the cavity or a laser.
Functionally, this proposal differs in the important respect that quantum logic operations can be performed that couple arbitrary pairs of qubits in the computer, whereas the other proposals are limited to coupling qubits that are nearest neighbors.
research.ucsb.edu /tech_transfer/technologies/1999-114/1999-114.HTM   (296 words)

  
 Quantum electrodynamics
The field of quantum chemistry was pioneered by Walter Heitler and Fritz London, who published a quantum account of the covalent bond of the hydrogen molecule in 1927.
Quantum electrodynamics is a quantum theory of electrons, positrons, and the electromagnetic field, and serves as a role model for subsequent quantum field theories.
QED was the first quantum field theory in which the difficulties of building a consistent, fully quantum description of fields and of the creation and annihilation of quantum particles were satisfactorily resolved.
www.zamandayolculuk.com /cetinbal/quantumelectrodinamics.htm   (1179 words)

  
 Historical Notes: Quantum gravity
That there should be quantum effects in gravity was already noted in the 1910s, and when quantum field theory began to develop in the 1930s, there were immediately attempts to apply it to gravity.
The first idea was to represent gravity as a field that exists in flat spacetime, and by analogy with photons in quantum electrodynamics to introduce gravitons (at one point identified with neutrinos).
Starting in the 1950s a rather different approach to quantum gravity involved trying to find a representation of the structure of spacetime in which a quantum analog of the Einstein equations could be obtained by the formal procedure of canonical quantization (see page 1062).
www.wolframscience.com /reference/notes/1054a   (1043 words)

  
 What is Quantum Electrodynamics (QED)?
Quantum electrodynamics (QED) is the quantum field theory explaining how electrically charged particles interact with each other through the exchange of photons (light \"quanta\", or little packets of light).
QED is referred to as a gauge theory, with a mathematically specified gauge field representing the electromagnetic force.
The theory of QED is one of the most well-verified theories on Earth, sometimes giving precise results to ten decimal places, and was the first quantum field theory to be called consistent and complete.
www.wisegeek.com /what-is-quantum-electrodynamics.htm   (457 words)

  
 [13.0] Quantum Electrodynamics
This was an application of what quantum physicists now call the "totalitarian theorem": whatever is not forbidden is compulsory, or in other terms, anything that can possibly happen, will happen, at its appropriate level of probability.
Instead of a photon or electron or other quantum entity represented as a probabilistic wavefunction and not existing until it is measured, sum over histories says that it exists over all possible paths and the measured value is simply a sum of all those paths.
The Lamb shift that led to the development of modern QED is due to the ZPE, as is the unavoidable "quantum noise" that becomes a fundamental barrier to sensitivity in electronic and optical equipment.
www.vectorsite.net /tpqm_13.html   (4335 words)

  
 Quantum Reality
Because quantum mechanics cannot predict which outcome will occur when any quantum choice is made, several physicists have suggested that there may be a deeper theory which expalins the principle of choice.
Quantum reality is a superposition of all the possible states in a single wave function, so if we can arrange a wave function to represent all the states in such a computation, collapse of the wave packet might give us the answer by a form of parallel quantum computation.
Quantum computing takes a step in from the cold PHYSICISTS have found a relatively easy way to make a BoseEinstein condensate, the bizarre state of ultra-cold atoms that is helping to shed light on the quantum world.
www.dhushara.com /book/quantcos/quant1/quant.htm   (5971 words)

  
 THE SYNTHESIS OF QUANTUM ELECTRODYNAMICS, SPECIAL RELATIVITY AND CLASSICAL MECHANICS
Both argue strongly for the view that radiation is due solely to the quantum excitation of orbital electrons and collisions rather than the continuous spectrum of uniform oscillations whose wavelength varies with impulse and relative speed.
The potential source is understood to be magnetic and the mechanical angular momentum vector of the electron is guaranteed to be the same magnitude by the Bohr equivalence.
The intrinsic magnetic moment of the electron is greater than the proton by their mass ratio and would serve as the nucleus of the inverse configuration.
www.wbabin.net /babin/wd6.htm   (4029 words)

  
 Bulk Spin Resonance Quantum Computation   (Site not responding. Last check: 2007-10-26)
Quantum computation is an exciting prospect, because a quantum computer (if it could be built) would be exponentially faster than a classical computer on some problems.
The problem with building a quantum computer is that the quantum bits (called qubits) simultaneously need to be protected from the environment so that they retain their quantum phase, but they need to be coupled to the environment so that initial conditions can be loaded, the calculation applied, and the results read out.
This has been done in systems such as trapped ions, or cavity quantum electrodynamics, that carefully isolate the qubits and cool them to their ground state.
www.media.mit.edu /physics/projects/spins/home.html   (530 words)

  
 FeynmanQED.nb
In addition, a relation is established between the amplitude for a given process in an arbitrary unquantized potential and in a quantum electrodynamical field.
This separation is especially useful in quantum electrodynamics which represents the interaction of matter with the electromagnetic field.
To show that this same picture may be used in quantum electrodynamics when the potentials are not fixed, a special argument is made based on a study of the relationship of quantum electrodynamics to motion in a fixed potential.
www.wolfram.com /products/publicon/samples/feynman/FeynmanQED.html   (6339 words)

  
 Wiley::Cavity Quantum Electrodynamics: The Strange Theory of Light in a Box
Cavity Quantum Electrodynamics addresses a fascinating question in physics: what happens to light, and in particular to its interaction with matter, when it is trapped inside a box?
Despite being one of many specialties within physics, cavity quantum electrodynamics serves as a window to many of the fundamental issues of physics.
Cavity Quantum Electrodynamics will serve as an excellent resource for advanced undergraduate quantum mechanics courses as well as for graduate students, researchers, and scientists who need a comprehensive introduction to the field.
www.wiley.com /WileyCDA/WileyTitle/productCd-0471443387.html   (396 words)

  
 electrodynamics — FactMonster.com
This area of electrodynamics, often known as classical electrodynamics, was first systematically explained by the physicist James Clerk Maxwell.
A more recent development is quantum electrodynamics, which was formulated to explain the interaction of electromagnetic radiation with matter, to which the laws of the
The physicists P. Dirac, W. Heisenberg, and W. Pauli were the pioneers in the formulation of quantum electrodynamics.
www.factmonster.com /ce6/sci/A0816993.html   (196 words)

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