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"The strong interaction is observable in two areas: on a larger scale (about 1 to 3 femtometers (fm)), it is the force that binds protons and neutrons (nucleons) together to form the nucleus of an atom. On the smaller scale (less than about 0.8 fm, the radius of a nucleon), it is also the force ... that [forms and holds together] protons, neutrons and other hadron particles."[1]

"In the context of binding protons and neutrons together to form atoms, the strong interaction is called the nuclear force (or residual strong force). [T]he strong interaction ... obeys a quite different distance-dependent behavior between nucleons ... ."[1]

Theoretical strong interactions[edit]

"In field theory it is known that coupling constants “run”. This means that the values of the coupling constants that one measures depend on the energy at which the measurement is performed. [...] the three different coupling constants [one each for the strong force, electromagnetic force, and the weak force] of the standard model seem to converge to the same value at an energy scale of about 1016 GeV [...] This suggests that there is only one coupling constant at high energies and most likely only one symmetry group. [...] The current belief [is] that the electromagnetic, weak and strong forces [are] unified at about 1016 GeV [as such] one has to rely on [the] particle physics interactions which can lead to electromagnetic radiation and cosmic rays".[2]

Behavior of the strong force[edit]

"Unlike [the] electromagnetic [and] weak [interactions], the strong force does not diminish in strength with increasing distance. After a limiting distance (about the size of a hadron) has been reached, it remains at a strength of about 10,000 newtons, no matter how much farther the distance between [hadrons].[3] The ... force between [hadrons] remains constant at any distance after [the hadrons] travel only a tiny distance from each other, and is equal to that need to raise one ton, which is 1000 kg x 9.8 N = ~ 10,000 N.[3]"[1]

"[T]he amount of work done against a force of 10,000 newtons (about the weight of a one-metric ton mass on the surface of the Earth) is enough to create particle-antiparticle pairs within a very short distance of an interaction."[1]

"The strong force is ... nearly absent between such hadrons (i.e., between baryons or mesons). In this case, only a residual force (described below) called the residual strong force acts between [these] hadrons, and this residual force diminishes rapidly with distance, and is thus very short-range (effectively a few femtometers)."[1]

Residual strong force[edit]

"The residual effect of the strong force is called the nuclear force. The nuclear force acts between hadrons, such as mesons or the nucleons in atomic nuclei. This "residual strong force", acting indirectly, transmits ... pi and rho mesons, which, in turn, transmit the nuclear force between nucleons."[1]

"The residual strong force is thus a minor residuum of the strong force which binds ... together ... protons and neutrons. This same force is much weaker between neutrons and protons, because it is mostly neutralized within them, in the same way that electromagnetic forces between neutral atoms (van der Waals forces) are much weaker than the electromagnetic forces that hold the atoms internally together.[3] Unlike the strong force itself, the nuclear force, or residual strong force, does diminish in strength, and in fact diminishes rapidly with distance. The decrease is approximately as a negative exponential power of distance, though there is no simple expression known for this; see Yukawa potential. This fact, together with the less-rapid decrease of the disruptive electromagnetic force between protons with distance, causes the instability of larger atomic nuclei, such as all those with atomic numbers larger than 82 (the element lead)."[1]


A hadron, like an atomic nucleus, is "a composite particle ... held together by the strong force ... Hadrons are categorized into two families: baryons (such as protons and neutrons[)] ... and mesons".[4]


"A baryon is a composite subatomic particle [bound together by] the strong interaction, whereas leptons [are] not. The most familiar baryons are the protons and neutrons that make up most of the mass of the visible matter in the universe. Electrons (the other major component of the atom) are leptons. Each baryon has a corresponding antiparticle (antibaryon)".[5]

"Baryonic matter is matter composed mostly of baryons (by mass), which includes atoms of any sort (and thus includes nearly all matter that may be encountered or experienced in everyday life)."[5]


A meson is a composite subatomic particle "bound together by the strong interaction."[6]

"Because mesons are composed of sub-particles, they have a physical size, with a radius roughly one femtometre, which is about 2/3 the size of a proton or neutron. All mesons are unstable, with the longest-lived lasting for only a few hundredths of a microsecond. Charged mesons decay (sometimes through intermediate particles) to form electrons and neutrinos. Uncharged mesons may decay to photons."[6]

"Mesons are not produced by radioactive decay, but appear in nature only as short-lived products of very high-energy interactions in matter ... In cosmic ray interactions, for example, such particles are ordinary protons and neutrons. Mesons are also frequently produced artificially in high-energy particle accelerators that collide protons, anti-protons, or other particles."[6]

"In nature, the importance of lighter mesons is that they are the associated quantum-field particles that transmit the nuclear force, in the same way that photons are the particles that transmit the electromagnetic force."[6]

"Each type of meson has a corresponding antiparticle (antimeson) in which quarks are replaced by their corresponding antiquarks and vice-versa."[6]

Mesons are subject to "both the weak and strong interactions. Mesons with net electric charge also participate in the electromagnetic interaction."[6]

"While no meson is stable, those of lower mass are nonetheless more stable than the most massive mesons, and are easier to observe and study in particle accelerators or in cosmic ray experiments. They are also typically less massive than baryons, meaning that they are more easily produced in experiments, and thus exhibit certain higher energy phenomena more readily than baryons composed of the same quarks would."[6]


"Sources of electromagnetic fields consist of two types of charge – positive and negative."[7]

The relative strengths and ranges of the charge interactions:

Interaction Mediator Relative Magnitude Behavior Range
Strong interaction gluon 1038 1 10−15 m
Electromagnetic interaction photon 1036 1/r2 universal
Weak interaction W and Z bosons 1025 1/r5 to 1/r7 10−16 m
Gravity interaction photon 10 1/r2 universal


"Due to the very low energy of the colliding protons in the Sun, only states with no angular momentum (s-waves) contribute significantly. One can consider it as a head-on collision, so that angular momentum plays no role. Consequently, the total angular momentum is the sum of the spins, and the spins alone control the reaction. Because of Pauli's exclusion principle, the incoming protons must have opposite spins. On the other hand, in the only bound state of deuterium, the spins of the neutron and proton are aligned. Hence a spin flip must take place [...] The strength of the nuclear force which holds the neutron and the proton together depends on the spin of the particles. The force between an aligned proton and neutron is sufficient to give a bound state, but the interaction between two protons does not yield a bound state under any circumstances. Deuterium has only one bound state."[8]

The "force acting between the protons and the neutrons [is] the strong force".[8]

"A potential of 36 MeV is needed to get just one energy state."[8]

The width of a bound proton and neutron is "2.02 x 10-13 cm".[8]

"Another possibility [regarding neutron stars, called "baryon matter",] is that in the absence of gravity high-density baryonic matter is bound by purely strong forces. [...] nongravitationally bound bulk hadronic matter is consistent with nuclear physics data [...] and low-energy strong interaction data [...] The effective field theory approach has many successes in nuclear physics [...] suggesting that bulk hadronic matter is just as likely to be a correct description of matter at high densities as conventional, unbound hadronic matter."[9]

"The idea behind baryon matter is that a macroscopic state may exist in which a smaller effective baryon mass inside some region makes the state energetically favored over free particles. [...] This state will appear in the limit of large baryon number as an electrically neutral coherent bound state of neutrons, protons, and electrons in β-decay equilibrium."[9]


A "new type of neutron star model (Q stars) [is such that] high-density, electrically neutral baryonic matter is a coherent classical solution to an effective field theory of strong forces and is bound in the absence of gravity. [...] allows massive compact objects, [...] and has no macroscopic minimum mass."[9]

"Compact objects in astronomy are usually analyzed in terms of theoretical characteristics of neutron stars or black holes that are based upon calculations of equations of state for matter at very high densities. At such high densities, the effects of strong forces cannot be neglected. There are several conventional approaches to describing nuclear forces, all of which find that for a baryon number greater than ~250, a nucleus will become energetically unbound. High-density hadronic matter is not stable in these theories until there are enough baryons for gravitational binding to form a neutron star, typically with a minimum mass ≳ 0.1 M and maximum mass ≲ 3 M."[9]

where m means mass, p refers to a proton, and e refers to an electron. This suggests 917 electrons, 918 positrons, and 1 or more neutrinos.


"The molecular cloud Cepheus B is subject to strong forces both trying to compress and to disrupt it simultaneously."[10]

Intergalactic medium[edit]

The "scaling of the acceleration efficiency with IGM temperature derived assuming a collisionless IGM may also extend to the case of a weakly-collisionless IGM implying that the conclusion that stochastic acceleration is stronger in the hottest clusters holds for a wide range of (micro-)physical conditions."[11]

The "turbulent magnetic compressions on the scale of the mean free path and less are the most effective for inducing the instability*. As the scattering happens on magnetic perturbations induced by the instability, the mean free path of particles decreases as a result of the operation of the instability. This results in the process being self-regulating, i.e. the stronger the turbulence at the scale of injection, the smaller is the mean free path of plasma particles and the larger is the span of scales over which the fluid behaves as essentially collisional."[11]

"*MHD turbulence theory has a long history (see Biskamp 2003) and its details are still a subject of hot debates. However, recent numerical calculations are roughly consistent with the model of strong Alfvenic turbulence in Goldreich & Sridhar (1995) (see Beresnyak & Lazarian 2009) and cofirm scaling of compressible modes reported in Cho & Lazarian (2003) (see Kowal & Lazarian 2010)."[11]

Recent history[edit]

Main sources: History/Recent and Recent history

The recent history period dates from around 1,000 b2k to present.

"Before the 1970s ... it was known that the nucleus was composed of protons and neutrons and that the protons possessed positive electric charge while neutrons were electrically neutral."[1]

"A stronger attractive force was postulated to explain how the atomic nucleus was bound together despite the protons' mutual electromagnetic repulsion. This hypothesized force was called the strong force, which was believed to be a fundamental force that acted on the nucleons (the protons and neutrons that make up the nucleus). Experiments suggested that this force bound protons and neutrons together with equal strength."[1]


Main source: Hypotheses
  1. The strong interaction is relateable to the electromagnetic interaction and the weak interaction by distance and charge (electromagnetic, the number).

See also[edit]


  1. 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 "Strong interaction, In: Wikipedia". San Francisco, California: Wikimedia Foundation, Inc. May 27, 2012. Retrieved 2012-06-30. 
  2. Tanmay Vachaspati (1998). "Topological defects in the cosmos and lab". Contemporary Physics 39 (4): 225-37. doi:10.1080/001075198181928. Retrieved 2013-11-05. 
  3. 3.0 3.1 3.2 H. Fritzsch (1983). Quarks: The Stuff of Matter. Basic Books. pp. 167–168. ISBN 978-0-465-06781-7. 
  4. "Hadron, In: Wikipedia". San Francisco, California: Wikimedia Foundation, Inc. July 11, 2013. Retrieved 2013-07-12. 
  5. 5.0 5.1 "Baryon, In: Wikipedia". San Francisco, California: Wikimedia Foundation, Inc. May 3, 2013. Retrieved 2013-07-12. 
  6. 6.0 6.1 6.2 6.3 6.4 6.5 6.6 "Meson, In: Wikipedia". San Francisco, California: Wikimedia Foundation, Inc. June 16, 2013. Retrieved 2013-07-12. 
  7. "Electromagnetic field, In: Wikipedia". San Francisco, California: Wikimedia Foundation, Inc. July 1, 2013. Retrieved 2013-07-12. 
  8. 8.0 8.1 8.2 8.3 Giora Shaviv (2013). Giora Shaviv. ed. Towards the Bottom of the Nuclear Binding Energy, In: The Synthesis of the Elements. Berlin: Springer-Verlag. pp. 169-94. doi:10.1007/978-3-642-28385-7_5. ISBN 978-3-642-28384-0. Retrieved 2013-12-19. 
  9. 9.0 9.1 9.2 9.3 Safi Bahcall, Bryan W. Lynn, and Stephen B. Selipsky (October 10, 1990). "New Models for Neutron Stars". The Astrophysical Journal 362 (10): 251-5. doi:10.1086/169261. Retrieved 2014-01-11. 
  10. M.A. Moreno-Corral, C. Chavarria-K., E de Lara, and S. Wagner (June 1993). "Hα Interferometric Optical and Near IR Photometric Studies of Star Forming Regions I. The Cepheus-B/Sh2-155/Cepheus OB3 association complex". Astronomy and Astrophysics 273 (06): 619-32. Retrieved 2013-12-11. 
  11. 11.0 11.1 11.2 G. Brunetti, A. Lazarian (April 2011). "Particle reacceleration by compressible turbulence in galaxy clusters: effects of a reduced mean free path". Monthly Notices of the Royal Astronomical Society 412 (2): 817-24. doi:10.1111/j.1365-2966.2010.17937.x. Retrieved 2014-02-09. 

Further reading[edit]

  • D.J. Griffiths (1987). Introduction to Elementary Particles. John Wiley & Sons. ISBN 0-471-60386-4. 
  • F. Halzen, A.D. Martin (1984). Quarks and Leptons: An Introductory Course in Modern Particle Physics. John Wiley & Sons. ISBN 0-471-88741-2. 
  • G.L. Kane (1987). Modern Elementary Particle Physics. Perseus Books. ISBN 0-201-11749-5. 
  • R. Morris (2003). The Last Sorcerers: The Path from Alchemy to the Periodic Table. Joseph Henry Press. ISBN 0-309-50593-3. 

External links[edit]

{{Astronomy resources}}{{Charge ontology}}{{Physics resources}}{{Repellor vehicle}}