Editing Virtual particle (section)

{{Short description|Transient quantum fluctuation (physics)}}
{{distinguish|Antiparticle}}
{{For|related articles|Quantum vacuum (disambiguation)}}
{{Use American English|date = February 2019}}
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A '''virtual particle''' is a theoretical transient [[particle]] that exhibits some of the characteristics of an ordinary particle, while having its existence limited by the [[uncertainty principle]], which allows the virtual particles to spontaneously emerge from vacuum at short time and space ranges.<ref>{{cite book |author=Griffiths, D.J. |title=[[Introduction to Elementary Particles (book)|Introduction to Elementary Particles]]|publisher=[[John Wiley & Sons]] |year=2008 |isbn=978-3-527-40601-2 |edition=2nd |page=65 |author-link=David J. Griffiths}}</ref> The concept of virtual particles arises in the [[perturbation theory (quantum mechanics)|perturbation theory]] of [[quantum field theory]] (QFT) where interactions between ordinary particles are described in terms of exchanges of virtual particles. A process involving virtual particles can be described by a schematic representation known as a [[Feynman diagram]], in which virtual particles are represented by internal lines.<ref>Peskin, M.E., Schroeder, D.V. (1995). ''An Introduction to Quantum Field Theory'', Westview Press, {{ISBN|0-201-50397-2}}, p. 80.</ref><ref>Mandl, F., Shaw, G. (1984/2002). ''Quantum Field Theory'', John Wiley & Sons, Chichester UK, revised edition, {{ISBN|0-471-94186-7}}, pp. 56, 176.</ref>

Virtual particles do not necessarily carry the same [[mass]] as the corresponding ordinary particle, although they always conserve [[energy]] and [[momentum]]. The closer its characteristics come to those of ordinary particles, the longer the virtual particle exists.  They are important in the physics of many processes, including particle scattering and [[Casimir force]]s.   In quantum field theory, forces—such as the [[electromagnetic repulsion]] or attraction between two charges—can be thought of as resulting from the exchange of [[virtual photon]]s between the charges. Virtual photons are the [[exchange particle]]s for the [[Electromagnetism|electromagnetic interaction]].

The term is somewhat loose and vaguely defined,<ref>{{Cite journal |last=Martinez |first=Jean-Philippe |date=2024-06-01 |title=Virtuality in Modern Physics in the 1920s and 1930s: Meaning(s) of an Emerging Notion |url=https://direct.mit.edu/posc/article-abstract/32/3/350/116521/Virtuality-in-Modern-Physics-in-the-1920s-and?redirectedFrom=fulltext |journal=Perspectives on Science |volume=32 |issue=3 |pages=350–371 |doi=10.1162/posc_a_00610 |issn=1063-6145}}</ref> in that it refers to the view that the world is made up of "real particles". "Real particles" are better understood to be excitations of the underlying quantum fields. Virtual particles are also excitations of the underlying fields, but are "temporary" in the sense that they appear in calculations of interactions, but never as asymptotic states or indices to the [[scattering matrix]]. The accuracy and use of virtual particles in calculations is firmly established, but as they cannot be detected in experiments, deciding how to precisely describe them is a topic of debate.<ref>{{cite journal|last1=Jaeger|first1=Gregg|title=Are virtual particles less real?|journal=Entropy |volume=21 |issue=2|page=141|date=2019|doi=10.3390/e21020141|pmid=33266857 |pmc=7514619|bibcode=2019Entrp..21..141J|url=http://philsci-archive.pitt.edu/15858/1/Jaeger%20Are%20Virtual%20Particles%20Less%20Real_%20entropy-21-00141-v3.pdf|doi-access=free}}</ref> Although widely used, they are by no means a necessary feature of QFT, but rather are mathematical conveniences — as demonstrated by [[lattice field theory]], which avoids using the concept altogether.{{cn|date=May 2025}}