PlanetPhysics/Fermion

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Fermions are [[../Particle/|particles]] with a half-integer [[../QuarkAntiquarkPair/|spin]] value, and they are named after the famous Italian--American, Nobel Laureate physicist Enrico Fermi who built the first known operational [[../Cyclotron/|nuclear reactor]] in Chicago as part of the Manhattan project during WWII. Several particles like [[../Lepton/|leptons]], [[../ExtendedQuantumSymmetries/|quarks]] and [[../QuarkAntiquarkPair/|baryons]] are all fermions.

Since fermions have half-integer spin they obey a certain [[../Bijective/|type]] of quantum-mechanical statistics called the [[../FermiDiracDistribution/|Fermi-Dirac statistics]], which also includes the consequences of the [[../PauliExclusionPrinciple/|Pauli `exclusion principle';]] the latter principle states that no two fermions can occupy the same quantum mechanical state of a quantum mechanical [[../SimilarityAndAnalogousSystemsDynamicAdjointnessAndTopologicalEquivalence/|system]]. The exclusion principle is the main reason that fermions are the building blocks of the existing physical world, and for the stability of the [[../MolecularOrbitals/|electron orbitals]] in atoms and [[../Molecule/|molecules]].

All known `elementary particles': quarks, electrons, protons, etc are fermions with a spin value of 1/2-- and this suggests that the spin 1/2 elementary particle state is a unique, fundamental state of all stable matter in our [[../MultiVerses/|physical Universe]].

(One notes however that in superconducting systems that are usually macroscopically coherent quantum systems, the formation of phase-correlated `[[../LongRangeCoupling/|Cooper pairs]]' of electrons coupled to the ionic lattice of the superconducting metal does apparently run counter to the Pauli exclusion principle; furthermore, the transition to [[../WavePhenomena/|superconductivity]] involves necessarily a [[../LongRangeCoupling/|spontaneous symmetry breaking]] that gives rise to [[../LongRangeCoupling/|Goldstone bosons]] without which the superconductivity phenomenon/superconductivity phase transition would not be possible. Thus, in superconducting materials the electron pairs follow the [[../BoseEinsteinStatistics/|Bose-Einstein statistics]] of very low-temperature condensates and behave like coupled [[../BoseEinsteinStatistics/|boson]] chains, instead of the [[../LongRangeCoupling/|Fermi statistics]] of uncorrelated electrons which is most common to high [[../BoltzmannConstant/|temperature]] electrons; then, all such superconducting electron pairs are able to occupy the ground state with the lowest possible [[../CosmologicalConstant/|energy]] in certain superconducting materials for temperatures below approximately 110 degree K.)

Fermions at high temperatures act on each other by exchanging [[../BoseEinsteinStatistics/|field carrier]] bosons, just as, for example, in the case of quarks (that are fermions) and [[../ExtendedQuantumSymmetries/|gluons]] (that are bosons) inside a [[../QuarkAntiquarkPair/|nucleon]], such as a proton or a [[../Pions/|neutron]] of an atomic nucleus.