Gluons are the fundamental force carriers underlying the strong force. W and Z bosons are the force carriers which mediate the weak force. Photons are the force carriers of the electromagnetic field. The observed elementary bosons are all gauge bosons: photons, W and Z bosons, gluons, and the Higgs boson. At low densities, both types of statistics are well approximated by Maxwell–Boltzmann statistics, which is described by classical mechanics.Īll observed elementary particles are either fermions or bosons. In large systems, the difference between bosonic and fermionic statistics is only apparent at large densities-when their wave functions overlap. However, in relativistic quantum field theory, the spin–statistics theorem shows that half-integer spin particles cannot be bosons and integer spin particles cannot be fermions. In the framework of nonrelativistic quantum mechanics, this is a purely empirical observation. The fundamental interactions of virtual bosons with real particles result in all forces we know.Īll known elementary and composite particles are bosons or fermions, depending on their spin: particles with half-integer spin are fermions particles with integer spin are bosons. Interactions between elementary particles are called fundamental interactions. Another result is that the spectrum of a photon gas in thermal equilibrium is a Planck spectrum, one example of which is black-body radiation another is the thermal radiation of the opaque early Universe seen today as microwave background radiation. The properties of lasers and masers, superfluid helium-4 and Bose–Einstein condensates are all consequences of statistics of bosons. The quantum fields of bosons are bosonic fields, obeying canonical commutation relations. Thus fermions are sometimes said to be the constituents of matter, while bosons are said to be the particles that transmit interactions (force carriers), or the constituents of radiation. Fermions, on the other hand, obey Fermi–Dirac statistics and the Pauli exclusion principle: two fermions cannot occupy the same quantum state, resulting in a "rigidity" or "stiffness" of matter which includes fermions. Fermions are usually associated with matter (although in quantum physics the distinction between the two concepts is not clear cut).īosons are particles which obey Bose–Einstein statistics: when one swaps two bosons (of the same species), the wavefunction of the system is unchanged. Since bosons with the same energy can occupy the same place in space, bosons are often force carrier particles. Two or more identical fermions cannot occupy the same quantum state (see Pauli exclusion principle). Symmetric wavefunction for a (bosonic) 2-particle state in an infinite square well potential.īosons differ from fermions, which obey Fermi–Dirac statistics. If it exists, a graviton must be a boson, and could conceivably be a gauge boson.Ĭomposite bosons are important in superfluidity and other applications of Bose–Einstein condensates. The only scalar boson (the Higgs boson (H0))Īdditionally, the graviton (G) is a hypothetical elementary particle not incorporated in the Standard Model. While most bosons are composite particles, in the Standard Model there are five bosons which are elementary: ![]() This property holds for all particles with integer spin (s = 0, 1, 2 etc.) as a consequence of the spin–statistics theorem.īosons may be either elementary, like photons, or composite, like mesons. leptons and quarks) are fermions, the elementary bosons are force carriers that function as the 'glue' holding matter together. Whereas the elementary particles that make up matter (i.e. Unlike bosons, two identical fermions cannot occupy the same quantum space. This property is exemplified by helium-4 when it is cooled to become a superfluid. Cooper pairs, plasmons, and phonons).:130Īn important characteristic of bosons is that their statistics do not restrict the number of them that occupy the same quantum state. mesons and stable nuclei of even mass number such as deuterium (with one proton and one neutron, mass number = 2), helium-4, or lead-208) and some quasiparticles (e.g. ![]() Examples of bosons include fundamental particles such as photons, gluons, and W and Z bosons (the four force-carrying gauge bosons of the Standard Model), the Higgs boson, and the still-theoretical graviton of quantum gravity composite particles (e.g. The name boson was coined by Paul Dirac to commemorate the contribution of the Indian physicist Satyendra Nath Bose in developing, with Einstein, Bose–Einstein statistics-which theorizes the characteristics of elementary particles. Bosons make up one of the two classes of particles, the other being fermions. In quantum mechanics, a boson (/ˈboʊsɒn/, /ˈboʊzɒn/) is a particle that follows Bose–Einstein statistics.
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