"Color force" redirects here. For the company, seeColor Force.
An animation ofcolor confinement, a property of the strong interaction. If energy is supplied to the quarks as shown, thegluon tube connectingquarks elongates until it reaches a point where it "snaps" and the energy added to the system results in the formation of a quark–antiquark pair. Thus single quarks are never seen in isolation.An animation of the strong interaction between a proton and a neutron, mediated bypions. The colored small double circles inside aregluons.
Most of themass of aproton orneutron is the result of the strong interaction energy; the individual quarks provide only about 1% of the mass of a proton. At the range of 10−15 m (1femtometer, slightly more than the radius of anucleon), the strong force is approximately 100 times as strong aselectromagnetism, 106 times as strong as theweak interaction, and 1038 times as strong asgravitation.[1]
In the context of atomic nuclei, the force binds protons and neutrons together to form a nucleus and is called thenuclear force (orresidual strong force).[2] Because the force is mediated by massive, short livedmesons on this scale, the residual strong interaction obeys a distance-dependent behavior between nucleons that is quite different from when it is acting to bind quarks within hadrons. There are also differences in thebinding energies of the nuclear force with regard tonuclear fusion versusnuclear fission. Nuclear fusion accounts for most energy production in theSun and otherstars. Nuclear fission allows for decay of radioactive elements andisotopes, although it is often mediated by the weak interaction. Artificially, the energy associated with the nuclear force is partially released innuclear power andnuclear weapons, both inuranium orplutonium-based fission weapons and in fusion weapons like thehydrogen bomb.[3][4]
Before 1971, physicists were uncertain as to how the atomic nucleus was bound together. It was known that the nucleus was composed ofprotons andneutrons and that protons possessed positiveelectric charge, while neutrons were electrically neutral. Based on established principles of electromagnetism, positive charges would be expected to repel one another and the positively charged protons would be expected to cause the nucleus to fly apart. However, this was never observed. New discoveries in physics were needed to explain this phenomenon.
A stronger attractive force was postulated to explain how the atomic nucleus was bound despite the protons' mutualelectromagnetic repulsion. This hypothesized force was called thestrong force, which was believed to be a fundamental force that acted on theprotons and neutrons that make up the nucleus.
In 1964,Murray Gell-Mann, and separatelyGeorge Zweig, proposed thatbaryons, which include protons and neutrons, andmesons were composed of elementary particles. Zweig called the elementary particles "aces" while Gell-Mann called them "quarks"; the theory came to be called thequark model.[5] The strong attraction between nucleons was the side-effect of a more fundamental force that bound the quarks together into protons and neutrons. The theory ofquantum chromodynamics explains that quarks carry what is called acolor charge, although it has no relation to visible color.[6] Quarks with unlike color charge attract one another as a result of the strong interaction, and the particle that mediates this was called thegluon.
The strong interaction is observable at two ranges, and mediated by different force carriers in each one. On a scale less than about 0.8 fm (roughly the radius of a nucleon), the force is carried bygluons and holdsquarks together to form protons, neutrons, and other hadrons. On a larger scale, up to about 3 fm, the force is carried bymesons and binds nucleons (protons andneutrons) together to form thenucleus of anatom.[2] In the former context, it is often known as thecolor force, and is so strong that if hadrons are struck by high-energy particles, they producejets of massive particles instead of emitting their constituents (quarks and gluons) as freely moving particles. This property of the strong force is calledcolor confinement.
The fundamentalcouplings of the strong interaction, from left to right: (a) gluon radiation, (b) gluon splitting and (c,d) gluon self-coupling.
The wordstrong is used since the strong interaction is the "strongest" of the four fundamental forces. At a distance of 10−15 m, its strength is around 100 times that of theelectromagnetic force, some 106 times as great as that of the weak force, and about 1038 times that ofgravitation.
The force carrier particle of the strong interaction is the gluon, a masslessgauge boson. Gluons are thought to interact with quarks and other gluons by way of a type of charge calledcolor charge. Color charge is analogous to electromagnetic charge, but it comes in three types (±red, ±green, and ±blue) rather than one, which results in different rules of behavior. These rules are described byquantum chromodynamics (QCD), the theory of quark–gluon interactions.Unlike thephoton in electromagnetism, which is neutral, the gluon carries a color charge. Quarks and gluons are the only fundamental particles that carry non-vanishing color charge, and hence they participate in strong interactions only with each other. The strong force is the expression of the gluon interaction with other quark and gluon particles.
All quarks and gluons in QCD interact with each other through the strong force. The strength of interaction is parameterized by the strongcoupling constant. This strength is modified by the gauge color charge of the particle, agroup-theoretical property.
The strong force acts between quarks. Unlike all other forces (electromagnetic, weak, and gravitational), the strong force does not diminish in strength with increasing distance between pairs of quarks. After a limiting distance (about the size of ahadron) has been reached, it remains at a strength of about10000N, no matter how much farther the distance between the quarks.[7]: 164 As the separation between the quarks grows, the energy added to the pair creates new pairs of matching quarks between the original two; hence it is impossible to isolate quarks. The explanation is that the amount of work done against a force of10000 N is enough to create particle–antiparticle pairs within a very short distance. The energy added to the system by pulling two quarks apart would create a pair of new quarks that will pair up with the original ones. In QCD, this phenomenon is calledcolor confinement; as a result, only hadrons, not individual free quarks, can be observed. The failure of all experiments that have searched forfree quarks is considered to be evidence of this phenomenon.
The elementary quark and gluon particles involved in a high energy collision are not directly observable. The interaction produces jets of newly created hadrons that are observable. Those hadrons are created, as a manifestation of mass–energy equivalence, when sufficient energy is deposited into a quark–quark bond, as when a quark in one proton is struck by a very fast quark of another impacting proton during aparticle accelerator experiment. However,quark–gluon plasmas have been observed.[8]
AFeynman diagram (shown by the animation in the lead) with the individualquark constituents shown, to illustrate how the fundamental strong interaction gives rise to thenuclear force. Straight lines are quarks, while multi-colored loops aregluons (the carriers of the fundamental force).
While color confinement implies that the strong force acts without distance-diminishment between pairs of quarks in compact collections of bound quarks (hadrons), at distances approaching or greater than the radius of a proton, a residual force (described below) remains. It manifests as a force between the "colorless" hadrons, and is known as thenuclear force orresidual strong force (and historically as thestrong nuclear force).
The nuclear force acts between hadrons, known asmesons andbaryons. This "residual strong force", acting indirectly, transmits gluons that form part of the virtualπ andρmesons, which, in turn, transmit the force between nucleons that holds the nucleus (beyondhydrogen-1 nucleus) together.[9]
The residual strong force is thus a minor residuum of the strong force that binds quarks together into protons and neutrons. This same force is much weakerbetween neutrons and protons, because it is mostly neutralizedwithin them, in the same way that electromagnetic forces between neutral atoms (van der Waals forces) are much weaker than the electromagnetic forces that hold electrons in association with the nucleus, forming the atoms.[7]
Unlike the strong force, the residual strong force diminishes with distance, and does so rapidly. The decrease is approximately as a negative exponential power of distance, though there is no simple expression known for this; seeYukawa potential. The rapid decrease with distance of the attractive residual force and the less rapid decrease of the repulsive electromagnetic force acting between protons within a nucleus, causes the instability of larger atomic nuclei, such as all those withatomic numbers larger than 82 (the element lead).
Although the nuclear force is weaker than the strong interaction itself, it is still highly energetic: transitions producegamma rays.[clarification needed] The mass of a nucleus is significantly different from the summed masses of the individual nucleons. Thismass defect is due to the potential energy associated with the nuclear force. Differences between mass defects powernuclear fusion andnuclear fission.
The so-calledGrand Unified Theories (GUT) aim to describe the strong interaction and the electroweak interaction as aspects of a single force, similarly to how the electromagnetic and weak interactions were unified by the Glashow–Weinberg–Salam model intoelectroweak interaction. The strong interaction has a property calledasymptotic freedom, wherein the strength of the strong force diminishes at higher energies (or temperatures). The theorized energy where its strength becomes equal to the electroweak interaction is thegrand unification energy. However, no Grand Unified Theory has yet been successfully formulated to describe this process, and Grand Unification remains anunsolved problem in physics.
^Feynman, R.P. (1985).QED: The Strange Theory of Light and Matter. Princeton University Press. p. 136.ISBN978-0-691-08388-9.The idiot physicists, unable to come up with any wonderful Greek words anymore, call this type of polarization by the unfortunate name of 'color', which has nothing to do with color in the normal sense.
^"3. The Strong Force"(PDF). Department of Applied Mathematics and Theoretical Physics, University of Cambridge. Archived fromthe original(PDF) on 22 October 2021. Retrieved10 January 2023.
