Although lines on the diagram can represent virtual particles, all line entering or leaving a Feynman diagram must represent real particles with observable values of energy, momentum and mass (which may be zero). Lastly, the diagrams can depict the collisions of electrons with positrons that results in their mutual annihilation and the production of a photon.įeynman diagrams presuppose that energy and momentum are conserved during every interaction and hence at every vertex. In addition, is possible to depict the photon production of an electron-positron pair. Accordingly, the diagram can depict the emission and absorption of photons by either electrons or positrons. The representation regarding motion is highly schematic and does not usually reflect the velocity of a particle.įeynman diagrams depict electromagnetic interactions as intersections (vertices) of three lines and are able to describe the six possible reactions of the three fundamental QED particles (i.e., the electron, positron, and the photon). Vertical y axis displacement in Feynman diagrams represents particle motion. Positrons are depicted by a straight line with the arrow oriented to the left. Electrons are denoted by straight lines with arrows oriented to the right. Photons, for example, are represented by wavy lines. All of the lines comprising the diagram represent particular particles. In Feynman time-ordered diagrams, time is represented on the x axis and a depicted process begins on the left side of the diagram and ends on the right side of the diagram. Accordingly, only in their veiled or hidden state do photons act as mediators of force between particles and only under special circumstances do photons become observable as light. QED theory therefore specifies that the electromagnetic force results from the constant exchange of virtual photons between charged particles that cause the charged particles to constantly change their velocity (speed and/or direction of travel) as they absorb or emit virtual photons. As virtual particles, photons cannot be observed because they would violate the laws regarding the conservation of energy and momentum. Photons, unlike the particles of everyday experience, are virtual particles constantly exchanged between charged particles. QED accounts for the subsequent interactions of these electrons, positrons, and photons. According to QED theory, particle vacuums actually consist of electron-positron fields and electron-positron pairs (positrons are the positively charged antiparticle to electrons) are created when photons interact with these fields. QED, as quantum field theory, asserts that the electromagnetic force results from the quantum behavior of the photon, the fundamental particle responsible for the transmission electromagnetic radiation. The practical value of QED rests upon its ability, as set of equations, to allow calculations related to the absorption and emission of light by atoms and thereby allow scientists to make very accurate predictions regarding the result of the interactions between photons and charged atomic particles (e.g., electrons).įeynman diagrams are form of shorthand representations that outline the calculations necessary to depict electromagnetic and weak interaction particle QED describes the quantum properties (properties that are conserved and that occur in discrete amounts called quanta) and mechanics associated with the interaction of electromagnetic radiation (of which visible light is but one part of an electromagnetic spectrum) with matter. Quantum electrodynamics (QED), is a fundamental scientific theory that is also known as the quantum theory of light. Because Feynman diagrams allow physicists to depict subatomic processes and develop theories regarding particle interactions, the diagrams have become an indispensable and widely used tool in particle physics.įeynman diagrams derive from QED theory. Moreover, Feynman diagrams allow visual representation and calculation of the ways in which particles can interact through the exchange of virtual photons and thereby provide a tangible picture of processes outside the human capacity for observation. With regard to QED theory, Feynman is perhaps best remembered for his invention of what are now known as Feynman diagrams, to portray the complex interactions of atomic particles. American physicist Richard Feynman ’s (1918 –1988), work and writings were fundamental to the development of quantum electrodynamic theory (QED theory).
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