Editing Standard Model (section)

== Fundamental interactions ==
{{Main|Fundamental interaction}}
The Standard Model describes three of the four fundamental interactions in nature; only gravity remains unexplained. In the Standard Model, such an interaction is described as an exchange of [[boson]]s between the objects affected, such as a [[photon]] for the electromagnetic force and a [[gluon]] for the strong interaction. Those particles are called [[force carrier]]s or messenger [[particles]].<ref>{{Cite web|url=https://home.cern/science/physics/standard-model|title=The Standard Model|website=CERN|date=15 December 2023 }}</ref>

{| style="margin: 1em auto 1em auto;" class="wikitable floatcenter"
|+ The four fundamental interactions of nature<ref>{{cite web|url=http://www.pha.jhu.edu/~dfehling/particle.gif |title=Standard Model of Particles and Interactions |author=<!--Staff writer(s); no by-line.--> |website=jhu.edu |publisher=[[Johns Hopkins University]] |access-date=18 August 2016 |url-status=dead |archive-url=https://web.archive.org/web/20160304133522/https://www.pha.jhu.edu/~dfehling/particle.gif |archive-date=4 March 2016 }}</ref>
! style="" rowspan="2" | Property/Interaction
! style="background-color:#8080BF" rowspan="2" |Gravitation
! style="background-color:#BFA080" colspan="2" |Electroweak
! style="background-color:#80BF80" colspan="2" |Strong
|-
! style="background-color:#BFBF80" |Weak
! style="background-color:#BF8080" |Electromagnetic
! style="background-color:#AAD4AA" |<small>Fundamental</small>
! style="background-color:#D5EAD5" |<small>Residual</small>
|-
|Mediating particles
| align="center" {{Not yet}} observed<br /><small>([[Graviton]] hypothesised)</small>
| align="center" |[[W and Z bosons|W<sup>+</sup>, W<sup>−</sup> and Z<sup>0</sup>]]
| align="center" |[[Photon|γ]] (photon)
| align="center" |Gluons
| align="center" |[[Pion|π]], [[Rho meson|ρ]] and [[Omega meson|ω]] [[meson]]s
|-
|Affected particles
| align="center" |All particles
| align="center" |W<sup>+</sup>, W<sup>−</sup>: Left-handed [[fermions]]; Z<sup>0</sup>: All fermions 
| align="center" |Electrically charged
| align="center" |Quarks, [[gluon]]s
| align="center" |[[Hadron]]s
|-
|Acts on
| align="center" | [[Stress–energy tensor]]
| align="center" |[[Flavour (particle physics)|Flavor]]
| align="center" |Electric charge
| align="center" |[[Color charge]]
| align="center" |
|-
|Bound states formed
| align="center" |Planets, stars, galaxies, galaxy groups
| align="center" {{n/a}}
| align="center" |Atoms, molecules
| align="center" |Hadrons
| align="center" |Atomic nuclei
|-
|Strength at the scale of quarks<br /> (relative to electromagnetism)
| align="center" |{{val||e=-41}} <small>(predicted)</small>
| align="center" |{{val||e=-4}}
| align="center" |1
| align="center" |60
| align="center" {{No|Not applicable <br />to quarks}}
|-
|Strength at the scale of <br />protons/neutrons <br /> (relative to electromagnetism)
| align="center" |{{val||e=-36}} <small>(predicted)</small>
| align="center" |{{val||e=-7}}
| align="center" |1
| align="center" {{No|Not applicable <br />to hadrons}}
| align="center" |20
|}

{{Unreferenced section|date=June 2021}}

=== Gravity ===
{{See also|Quantum gravity|Gravity}}

[[File:Fundamental Interactions.png|thumb|Fundamental Interactions of the Standard Model including the hypothetical graviton]]

Despite being perhaps the most familiar fundamental interaction, gravity is not described by the Standard Model, due to contradictions that arise when combining general relativity, the modern theory of gravity, and quantum mechanics.<ref>{{Cite journal |last=Ashtekar |first=Abhay |date=2005-09-29 |title=Gravity and the quantum |url=https://iopscience.iop.org/article/10.1088/1367-2630/7/1/198 |journal=New Journal of Physics |volume=7 |pages=198–198 |doi=10.1088/1367-2630/7/1/198 |issn=1367-2630|arxiv=gr-qc/0410054 }}</ref><ref>{{Cite journal |last=Kuchař |first=Karel V. |date=2011-07-31 |title=TIME AND INTERPRETATIONS OF QUANTUM GRAVITY |url=https://www.worldscientific.com/doi/abs/10.1142/S0218271811019347 |journal=International Journal of Modern Physics D |language=en |volume=20 |issue=supp01 |pages=3–86 |doi=10.1142/S0218271811019347 |issn=0218-2718|url-access=subscription }}</ref> However, gravity is so weak at microscopic scales, that it is essentially unmeasurable. The [[graviton]] is postulated to be the mediating particle, but has not yet been proved to exist.<ref>{{Cite journal |last=Carney |first=Daniel |date=2024 |title=Graviton detection and the quantization of gravity |url=https://journals.aps.org/prd/abstract/10.1103/PhysRevD.109.044009 |journal=Physical Review D |volume=109 |issue=4 |doi=10.1103/PhysRevD.109.044009|arxiv=2308.12988 }}</ref>

=== Electromagnetism ===
{{See also|Electromagnetism|Quantum electrodynamics}}
Electromagnetism is the only long-range force in the Standard Model. It is mediated by photons and couples to electric charge.<ref>{{Cite web |date=2023-12-04 |title=The Standard Model |url=https://home.cern/science/physics/standard-model |access-date=2023-12-17 |website=CERN |language=en}}</ref> Electromagnetism is responsible for a wide range of phenomena including [[Electron shell|atomic electron shell structure]], [[chemical bonds]], [[electric circuit]]s and [[electronics]]. Electromagnetic interactions in the Standard Model are described by quantum electrodynamics.

=== Weak nuclear force ===
{{See also|Weak interaction|Electroweak interaction}}
The weak interaction is responsible for various forms of [[particle decay]], such as [[beta decay]]. It is weak and short-range, due to the fact that the weak mediating particles, W and Z bosons, have mass. W bosons have electric charge and mediate interactions that change the particle type (referred to as flavor) and charge. Interactions mediated by W bosons are [[charged current interaction]]s. Z bosons are neutral and mediate neutral current interactions, which do not change particle flavor. Thus Z bosons are similar to the photon, aside from them being massive and interacting with the neutrino. The weak interaction is also the only interaction to violate [[Parity violation|parity]] and [[CP violation|CP]]. Parity violation is maximal for charged current interactions, since the W boson interacts exclusively with left-handed fermions and right-handed antifermions.

In the Standard Model, the weak force is understood in terms of the electroweak theory, which states that the weak and electromagnetic interactions become united into a single ''electroweak'' interaction at high energies.

=== Strong nuclear force ===
{{See also|Strong interaction|Nuclear force|Quantum chromodynamics}}
The strong nuclear force is responsible for hadronic and [[Nuclear binding energy|nuclear binding]]. It is mediated by gluons, which couple to color charge. Since gluons themselves have color charge, the strong force exhibits [[Color confinement|confinement]] and [[asymptotic freedom]]. Confinement means that only color-neutral particles can exist in isolation, therefore quarks can only exist in hadrons and never in isolation, at low energies. Asymptotic freedom means that the strong force becomes weaker, as the energy scale increases. The strong force overpowers the [[electrostatic]] repulsion of protons and quarks in nuclei and hadrons respectively, at their respective scales.

While quarks are bound in hadrons by the fundamental strong interaction, which is mediated by gluons, nucleons are bound by an emergent phenomenon termed the ''residual strong force'' or ''[[nuclear force]]''. This interaction is mediated by mesons, such as the [[pion]]. The color charges inside the nucleon cancel out, meaning most of the gluon and quark fields cancel out outside of the nucleon. However, some residue is "leaked", which appears as the exchange of virtual mesons, that causes the attractive force between nucleons. The (fundamental) strong interaction is described by quantum chromodynamics, which is a component of the Standard Model.