Quantum electrodynamics (QED)
Quantum electrodynamics (QED) is a scientific theory that is also known as the quantum theory of light. QED describes the quantum properties (properties that are conserved and that occur in discrete amounts called quanta) and mechanics associated with the interaction of light (i.e., electromagnetic radiation) with matter. The practical value of QED rests upon its ability, as a set of equations, to allow calculations related to the absorption and emission of light by atoms and to allow scientists to make very accurate predictions regarding the result of the interactions between photons and charged atomic particles such as electrons. QED is a fundamentally important scientific theory because it accounts for all observed physical phenomena except those associated with aspects of relativity theory and radioactive decay.
QED is a complex and highly mathematical theory that paints a picture of light that is counter-intuitive to everyday human experience. According to QED theory, light exists in a duality consisting of both particle and wave-like properties. More specifically, QED asserts that electromagnetism results from the quantum behavior of the photon, the fundamental "particle" responsible for the transmission electromagnetic radiation. According to QED theory, a seeming particle vacuum actually consists of electron-positron fields. An electron-positron pair (positrons are the positively charged antiparticle to electrons) comes into existence when photons interact with these fields. In turn, QED also accounts for the subsequent interactions of these electrons, positrons, and photons.
Photons, unlike other "solid" particles, are thought to be "virtual particles" constantly exchanged between charged particles such as electrons. Indeed, according to QED theory the forces of electricity and magnetism (i.e., the fundamental electromagnetic force) stem from the common exchange of virtual photons between particles and only under special circumstances do photons become observable as light.
According to QED theory, "virtual photons" are more like the wavelike disturbances on the surface of water after it is touched. The virtual photons are passed back and forth between the charged particles much like basketball players might pass a ball between them as they run down the court. As virtual particles, photons cannot be observed because they would violate the laws regarding the conservation of energy and momentum. Only in their veiled or hidden state do photons act as mediators of force between particles. The "force" caused by the exchange of virtual photons causes charged particles to change their velocity (speed and/or direction of travel) as they absorb or emit virtual photons.
Only under limited conditions do the photons escape the charged particles and thereby become observable as electro-magnetic radiation. Observable photons are created by perturbations (i.e., wave-like disruptions) of electrons and other charged particles. According to QED theory, the process also works in reverse as photons can create a particle and its antiparticle (e.g., an electron and its oppositely charged antiparticle, a positron).
In QED dynamics, the simplest interactions involve only two charged particles. The application of QED is, however, not limited to these simple systems; interactions involving an infinite number of photons are described by increasingly complex processes termed second-order (or higher) processes. Although QED can account for an infinite number of processes (i.e., an infinite number of interactions) the theory also dictates that more interactions also become increasingly rare as they become increasingly complex.
The genesis of QED was the need for physicists to reconcile theories initially advanced by British physicist James Clerk Maxwell regarding electromagnetism in the later half of the nineteenth century (i.e., that electricity and magnetism are two aspects of a single force) with quantum theory developed during the early decades of the twentieth century. Prior to WWII, British physicist Paul Dirac, German physicist Werner Heisenberg, and Austrian-born American physicist Wolfgang Pauli all made significant contributions to the mathematical foundations related to QED. Even for these experienced physicists, however, working with QED posed formidable obstacles because of the presence of "infinities" (infinite values) in the mathematical calculations (e.g., for emission rates or determinations of mass). It was often difficult to make predictions match observed phenomena and early attempts at using QED theory often gave physicists wrong or incomprehensible answers.
The calculations used to define QED were made more accessible and reliable by a process termed renormalization, independently developed by American physicist Richard Feynman (1918–1988), American physicist Julian Schwinger (1918–1994), and Japanese physicist Shin'ichiro Tomonaga (1906–1979). In essence the work of th
Quantum electrodynamics (QED)Quantum electrodynamics (QED) is a scientific theory that is also known as the quantum theory of light. QED describes the quantum properties (properties that are conserved and that occur in discrete amounts called quanta) and mechanics associated with the interaction of light (i.e., electromagnetic radiation) with matter. The practical value of QED rests upon its ability, as a set of equations, to allow calculations related to the absorption and emission of light by atoms and to allow scientists to make very accurate predictions regarding the result of the interactions between photons and charged atomic particles such as electrons. QED is a fundamentally important scientific theory because it accounts for all observed physical phenomena except those associated with aspects of relativity theory and radioactive decay.QED is a complex and highly mathematical theory that paints a picture of light that is counter-intuitive to everyday human experience. According to QED theory, light exists in a duality consisting of both particle and wave-like properties. More specifically, QED asserts that electromagnetism results from the quantum behavior of the photon, the fundamental "particle" responsible for the transmission electromagnetic radiation. According to QED theory, a seeming particle vacuum actually consists of electron-positron fields. An electron-positron pair (positrons are the positively charged antiparticle to electrons) comes into existence when photons interact with these fields. In turn, QED also accounts for the subsequent interactions of these electrons, positrons, and photons.
Photons, unlike other "solid" particles, are thought to be "virtual particles" constantly exchanged between charged particles such as electrons. Indeed, according to QED theory the forces of electricity and magnetism (i.e., the fundamental electromagnetic force) stem from the common exchange of virtual photons between particles and only under special circumstances do photons become observable as light.
According to QED theory, "virtual photons" are more like the wavelike disturbances on the surface of water after it is touched. The virtual photons are passed back and forth between the charged particles much like basketball players might pass a ball between them as they run down the court. As virtual particles, photons cannot be observed because they would violate the laws regarding the conservation of energy and momentum. Only in their veiled or hidden state do photons act as mediators of force between particles. The "force" caused by the exchange of virtual photons causes charged particles to change their velocity (speed and/or direction of travel) as they absorb or emit virtual photons.
Only under limited conditions do the photons escape the charged particles and thereby become observable as electro-magnetic radiation. Observable photons are created by perturbations (i.e., wave-like disruptions) of electrons and other charged particles. According to QED theory, the process also works in reverse as photons can create a particle and its antiparticle (e.g., an electron and its oppositely charged antiparticle, a positron).
In QED dynamics, the simplest interactions involve only two charged particles. The application of QED is, however, not limited to these simple systems; interactions involving an infinite number of photons are described by increasingly complex processes termed second-order (or higher) processes. Although QED can account for an infinite number of processes (i.e., an infinite number of interactions) the theory also dictates that more interactions also become increasingly rare as they become increasingly complex.
The genesis of QED was the need for physicists to reconcile theories initially advanced by British physicist James Clerk Maxwell regarding electromagnetism in the later half of the nineteenth century (i.e., that electricity and magnetism are two aspects of a single force) with quantum theory developed during the early decades of the twentieth century. Prior to WWII, British physicist Paul Dirac, German physicist Werner Heisenberg, and Austrian-born American physicist Wolfgang Pauli all made significant contributions to the mathematical foundations related to QED. Even for these experienced physicists, however, working with QED posed formidable obstacles because of the presence of "infinities" (infinite values) in the mathematical calculations (e.g., for emission rates or determinations of mass). It was often difficult to make predictions match observed phenomena and early attempts at using QED theory often gave physicists wrong or incomprehensible answers.
The calculations used to define QED were made more accessible and reliable by a process termed renormalization, independently developed by American physicist Richard Feynman (1918–1988), American physicist Julian Schwinger (1918–1994), and Japanese physicist Shin'ichiro Tomonaga (1906–1979). In essence the work of th
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