Feynman diagram | physics - Encyclopedia Britannica

A Feynman diagram is a two-dimensional representation in which one axis, usually the horizontal axis, is chosen to represent space, while the ... Feynmandiagram TableofContents Feynmandiagram Introduction FastFacts 2-MinSummary RelatedContent Quizzes Media Images More MoreArticlesOnThisTopic Contributors ArticleHistory Home Science Physics Feynmandiagram physics Actions Cite verifiedCite Whileeveryefforthasbeenmadetofollowcitationstylerules,theremaybesomediscrepancies. Pleaserefertotheappropriatestylemanualorothersourcesifyouhaveanyquestions. SelectCitationStyle MLA APA ChicagoManualofStyle CopyCitation Share Share Sharetosocialmedia Facebook Twitter URL https://www.britannica.com/science/Feynman-diagram GiveFeedback ExternalWebsites Feedback Corrections?Updates?Omissions?Letusknowifyouhavesuggestionstoimprovethisarticle(requireslogin). 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ExternalWebsites InstituteforAdvancedStudy-FeynmanDiagramsandtheEvolutionofParticlePhysics MassachusettsInstituteofTechnology-FeynmanDiagramsinQuantumMechanics By ChristineSutton • EditHistory TableofContents Feynmandiagram Seeallmedia KeyPeople: RichardFeynman ...(Showmore) RelatedTopics: quantumelectrodynamics ...(Showmore) Seeallrelatedcontent→ Summary Readabriefsummaryofthistopic Feynmandiagram,agraphicalmethodofrepresentingtheinteractionsofelementaryparticles,inventedinthe1940sand’50sbytheAmericantheoreticalphysicistRichardP.Feynman.Introducedduringthedevelopmentofthetheoryofquantumelectrodynamicsasanaidforvisualizingandcalculatingtheeffectsofelectromagneticinteractionsamongelectronsandphotons,Feynmandiagramsarenowusedtodepictalltypesofparticleinteractions.AFeynmandiagramisatwo-dimensionalrepresentationinwhichoneaxis,usuallythehorizontalaxis,ischosentorepresentspace,whilethesecond(vertical)axisrepresentstime.Straightlinesareusedtodepictfermions—fundamentalparticleswithhalf-integervaluesofintrinsicangularmomentum(spin),suchaselectrons(e−)—andwavylinesareusedforbosons—particleswithintegervaluesofspin,suchasphotons(γ).Onaconceptuallevelfermionsmayberegardedas“matter”particles,whichexperiencetheeffectofaforcearisingfromtheexchangeofbosons,so-called“force-carrier,”orfield,particles. BritannicaQuiz AllAboutPhysicsQuiz Whowasthefirstscientisttoconductacontrollednuclearchainreactionexperiment?Whatistheunitofmeasureforcyclespersecond?Testyourphysicsacumenwiththisquiz. Atthequantumleveltheinteractionsoffermionsoccurthroughtheemissionandabsorptionofthefieldparticlesassociatedwiththefundamentalinteractionsofmatter,inparticulartheelectromagneticforce,thestrongforce,andtheweakforce.ThebasicinteractionthereforeappearsonaFeynmandiagramasa“vertex”—i.e.,ajunctionofthreelines.Inthiswaythepathofanelectron,forexample,appearsastwostraightlinesconnectedtoathird,wavy,linewheretheelectronemitsorabsorbsaphoton.(Seethefigure.)Feynmandiagramsareusedbyphysiciststomakeveryprecisecalculationsoftheprobabilityofanygivenprocess,suchaselectron-electronscattering,forexample,inquantumelectrodynamics.Thecalculationsmustincludetermsequivalenttoallthelines(representingpropagatingparticles)andallthevertices(representinginteractions)showninthediagram.Inaddition,sinceagivenprocesscanberepresentedbymanypossibleFeynmandiagrams,thecontributionsofeverypossiblediagrammustbeenteredintothecalculationofthetotalprobabilitythataparticularprocesswilloccur.Comparisonoftheresultsofthesecalculationswithexperimentalmeasurementshaverevealedanextraordinarylevelofaccuracy,withagreementtoninesignificantdigitsinsomecases.ThesimplestFeynmandiagramsinvolveonlytwovertices,representingtheemissionandabsorptionofafieldparticle.(Seethefigure.)Inthisdiagramanelectron(e−)emitsaphotonatV1,andthisphotonisthenabsorbedslightlylaterbyanotherelectronatV2.Theemissionofthephotoncausesthefirstelectrontorecoilinspace,whiletheabsorptionofthephoton’senergyandmomentumcausesacomparabledeflectioninthesecondelectron’spath.Theresultofthisinteractionisthattheparticlesmoveawayfromeachotherinspace.OneintriguingfeatureofFeynmandiagramsisthatantiparticlesarerepresentedasordinarymatterparticlesmovingbackwardintime—thatis,withthearrowheadreversedonthelinesthatdepictthem.Forexample,inanothertypicalinteraction(showninthefigure),anelectroncollideswithitsantiparticle,apositron(e+),andbothareannihilated.Aphotoniscreatedbythecollision,anditsubsequentlyformstwonewparticlesinspace:amuon(μ−)anditsantiparticle,anantimuon(μ+).Inthediagramofthisinteraction,bothantiparticles(e+andμ+)arerepresentedastheircorrespondingparticlesmovingbackwardintime(towardthepast). GetaBritannicaPremiumsubscriptionandgainaccesstoexclusivecontent. SubscribeNow More-complexFeynmandiagrams,involvingtheemissionandabsorptionofmanyparticles,arealsopossible,asshowninthefigure.Inthisdiagramtwoelectronsexchangetwoseparatephotons,producingfourdifferentinteractionsatV1,V2,V3,andV4,respectively. ChristineSutton