Physics:Quantum fermion: Difference between revisions

From ScholarlyWiki
Jump to navigation Jump to search
← Older edit
Remove duplicate Quantum backlink template
Update quantum article navigation for Majorana fermion
 
(15 intermediate revisions by 2 users not shown)
Line 1: Line 1:
{{Short description|Type of subatomic particle}}
{{Short description|Half-integer-spin quantum particle obeying Fermi-Dirac statistics}}
 
{{Quantum matter backlink|Particles}}
{{Quantum matter backlink|Particles}}
 
{{Quantum article nav|previous=Physics:Quantum elementary particle|previous label=Elementary particle|next=Physics:Quantum Majorana fermion|next label=Majorana fermion}}
<div style="display:flex; gap:24px; align-items:flex-start; max-width:1200px;">
<div style="display:flex; gap:24px; align-items:flex-start; max-width:1200px;">


Line 10: Line 9:


<div style="flex:1; line-height:1.45; color:#006b45; column-count:2; column-gap:32px; column-rule:1px solid #b8d8c8;">
<div style="flex:1; line-height:1.45; color:#006b45; column-count:2; column-gap:32px; column-rule:1px solid #b8d8c8;">
A '''fermion''' is a [[Physics:Quantum particle|subatomic particle]] that follows [[Fermi–Dirac statistics]]. Fermions have [[half-integer]] [[Physics:Quantum spin|spin]] and obey the [[Physics:Quantum Pauli exclusion principle|Pauli exclusion principle]]. These particles include all [[Physics:Quantum quark|quarks]], [[Physics:Quantum lepton|leptons]], and composite particles made from an odd number of fermions, such as [[Physics:Quantum proton|protons]], [[Physics:Quantum neutron|neutrons]], many nuclei, and many atoms.
'''fermion''' is a Book II topic in the Quantum Collection. A quantum fermion is a particle with half-integer spin that obeys Fermi-Dirac statistics. Fermions have antisymmetric many-particle wavefunctions, so identical fermions cannot occupy the same one-particle quantum state. This rule gives matter much of its structure, from atomic shells to degenerate stars. A quantum fermion is a particle with half-integer spin that obeys Fermi-Dirac statistics. Fermions have antisymmetric many-particle wavefunctions, so identical fermions cannot occupy the same one-particle quantum state. This rule gives matter much of its structure, from atomic shells to degenerate stars. The spin-statistics connection links half-integer spin with fermionic exchange behavior in relativistic quantum theory. Exchanging two identical fermions changes the sign of the many-body wavefunction.
 
Fermions differ from [[Physics:Quantum boson|bosons]], which obey Bose–Einstein statistics. In relativistic [[Physics:Quantum field theory|quantum field theory]], particles with integer spin behave as bosons, while particles with half-integer spin behave as fermions.
 
<div style="float:right; border:1px solid #e0d890; background:#fff8cc; padding:6px; margin:0 0 1em 1em; width:460px;">
<div style="font-size:90%;">Elementary Fermions one of the basic building blocks of matter in the Standard Model.</div>
</div>
</div>
</div>


<div style="width:300px;">
<div style="width:300px;">
[[File:Elementary Fermions.png|thumb|280px|Quantum fermion.]]
[[File:Quantum fermion complex yellow.png|thumb|300px|Complex yellow illustration of fermions with half-integer spin, excluded quantum states, and Pauli-structure cues.]]
</div>
</div>


</div>
</div>


== Description ==
== Spin and statistics ==
Fermions possess conserved baryon or lepton quantum numbers in addition to their spin properties. Because of the Pauli exclusion principle, no two identical fermions can occupy exactly the same quantum state at the same time.<ref>{{cite journal |last=Weiner |first=Richard M. |date=4 March 2013 |title=Spin-statistics-quantum number connection and supersymmetry |url=https://journals.aps.org/prd/abstract/10.1103/PhysRevD.87.055003 |journal=Physical Review D |volume=87 |issue=5 |pages=055003–05 |arxiv=1302.0969 |bibcode=2013PhRvD..87e5003W |doi=10.1103/physrevd.87.055003 |issn=1550-7998 |access-date=28 March 2022 |s2cid=118571314}}</ref>
The spin-statistics connection links half-integer spin with fermionic exchange behavior in relativistic quantum theory. Exchanging two identical fermions changes the sign of the many-body wavefunction. The resulting Pauli exclusion principle is not an ordinary force; it is a constraint on the allowed quantum states.<ref name="peskin">{{cite book |last1=Peskin |first1=Michael E. |last2=Schroeder |first2=Daniel V. |title=An Introduction to Quantum Field Theory |publisher=Addison-Wesley |year=1995 |isbn=978-0-201-50397-5}}</ref>


If several fermions occupy the same spatial region, at least one quantum property, such as spin orientation, must differ between them. This exclusion principle is responsible for much of the structure and stability of ordinary matter, including electron shells in atoms.
== Elementary and composite fermions ==
Elementary fermions include [[Physics:Quantum quark|quarks]] and [[Physics:Quantum lepton|leptons]]. Composite systems can also behave as fermions when their total spin is half-integer, as in protons, neutrons, many nuclei, atoms, and quasiparticle excitations in condensed matter.


Fermions are generally associated with matter, while bosons are usually associated with force mediation. However, under special conditions fermions can collectively display bosonic behaviour. Examples include superconductivity and superfluidity.
== Physical consequences ==
Fermion statistics explain the periodic structure of atoms, electron degeneracy pressure, band filling in solids, and the stability of ordinary matter. In particle physics, fermion flavor, chirality, and mass mixing are central to weak interactions, neutrino oscillations, and matter-antimatter studies.<ref name="griffiths">{{cite book |last=Griffiths |first=David J. |title=Introduction to Elementary Particles |edition=2nd |publisher=Wiley-VCH |year=2008 |isbn=978-3-527-40601-2}}</ref>


Composite fermions such as protons and neutrons are the primary building blocks of ordinary baryonic matter.
== Description ==
 
'''fermion''' is a matter-scale concept used to organize how quantum theory describes atoms, particles, fields, condensed matter, plasma, or spacetime-related systems. In the Quantum Collection it is placed by scale so the reader can move from materials and molecules down to subatomic degrees of freedom.
The term ''fermion'' was introduced by English physicist [[Biography:Paul Dirac|Paul Dirac]] in honour of Italian physicist [[Biography:Enrico Fermi|Enrico Fermi]].<ref>Notes on Dirac's lecture ''Developments in Atomic Theory'' at Le Palais de la Découverte, 6 December 1945, UKNATARCHI Dirac Papers BW83/2/257889. See note 64 on page 331 in "The Strangest Man: The Hidden Life of Paul Dirac, Mystic of the Atom" by Graham Farmelo</ref>
 
== Elementary fermions ==
{{Standard model of particle physics|cTopic=[[Elementary particle]]s}}
 
The [[Physics:Quantum Standard Model|Standard Model]] recognizes two families of elementary fermions:


* [[Physics:Quantum quark|quarks]]
== Quantum context ==
* [[Physics:Quantum lepton|leptons]]
At this scale, the relevant behavior is controlled by quantized states, interactions, conservation laws, and the way excitations or particles are observed. The concept is normally linked to measurable properties such as energy, momentum, charge, spin, spectra, scattering rates, or collective modes.


In total there are 24 elementary fermions when antiparticles are included.
== Role in the collection ==
 
This page provides a compact reference point for related pages in Book II. It should be read together with nearby matter-scale topics and the corresponding foundations in [[Physics:Quantum mechanics|quantum mechanics]].<ref name="matter-wiki">{{cite web |url=https://en.wikipedia.org/wiki/Quantum_mechanics |title=Quantum mechanics |website=Wikipedia |access-date=2026-05-20}}</ref>
=== Quarks ===
The six known quarks are:
 
* [[Physics:Quantum up quark|up quark]]
* [[Physics:Quantum down quark|down quark]]
* [[Physics:Quantum strange quark|strange quark]]
* [[Physics:Quantum charm quark|charm quark]]
* [[Physics:Quantum bottom quark|bottom quark]]
* [[Physics:Quantum top quark|top quark]]
 
Quarks carry color charge and participate in the strong interaction. They combine to form hadrons such as protons and neutrons.
 
=== Leptons ===
The six leptons are:
 
* [[Physics:Quantum atoms/electron|electron]]
* [[Physics:Quantum electron neutrino|electron neutrino]]
* [[Physics:Quantum muon|muon]]
* [[Physics:Quantum muon neutrino|muon neutrino]]
* [[Physics:Quantum tau|tau]]
* [[Physics:Quantum tau neutrino|tau neutrino]]
 
Leptons do not participate in the strong interaction. Neutrinos interact only weakly and gravitationally.
 
=== Types of fermions ===
Mathematically, several forms of fermions are known:
 
* [[Physics:Quantum Weyl fermion|Weyl fermions]] (massless)
* [[Physics:Quantum Dirac fermion|Dirac fermions]] (massive)
* [[Physics:Quantum Majorana fermion|Majorana fermions]] (their own antiparticles)
 
Most Standard Model fermions are believed to behave as Dirac fermions, although the exact nature of neutrinos remains uncertain.<ref name="MoriiLim2004">{{cite book |last1=Morii |first1=T. |title=The Physics of the Standard Model and Beyond |last2=Lim |first2=C. S. |last3=Mukherjee |first3=S. N. |date=1 January 2004 |publisher=[[World Scientific]] |isbn=978-981-279-560-1}}</ref>{{rp|106}}
 
In 2015, Weyl fermions were experimentally realized in [[Physics:Quantum Weyl semimetal|Weyl semimetals]].
 
== Composite fermions ==
Composite particles can behave as fermions or bosons depending on the number of constituent fermions.
 
Examples include:
 
* a proton, containing three quarks
* a neutron, containing three quarks
* the nucleus of carbon-13
* helium-3 atoms
* deuterium atoms
 
A composite particle containing an odd number of fermions behaves overall as a fermion and has half-integer spin.
 
The fermionic or bosonic behaviour of composite systems is most evident when their constituents remain spatially separated. At shorter distances, the internal structure becomes important.
 
== Fermion pairing ==
Under certain conditions, fermions can pair together and collectively behave like bosons.
 
=== Superconductivity ===
In superconductors, electrons form [[Physics:Quantum Cooper pair|Cooper pairs]] through interactions mediated by phonons. These paired electrons can move collectively without electrical resistance.
 
=== Superfluidity ===
In helium-3, fermionic helium atoms pair through spin interactions and form a superfluid state at extremely low temperatures.
 
=== Composite fermions ==
Quasiparticles observed in the [[Physics:Quantum fractional quantum Hall effect|fractional quantum Hall effect]] are called composite fermions. They consist of electrons bound to quantized vortices.
 
== Physical interpretation ==
Fermions are responsible for the structure of matter because the Pauli exclusion principle prevents identical fermions from collapsing into the same state. This principle explains:
 
* atomic shell structure
* chemical behaviour
* stability of white dwarfs and neutron stars
* degeneracy pressure
* the organization of matter at microscopic scales
 
== Properties ==
 
* half-integer spin
* obey Fermi–Dirac statistics
* follow the Pauli exclusion principle
* include quarks and leptons
* form ordinary matter
* can combine into composite fermions
* may form paired bosonic states in superconductors and superfluids


=See also=
=See also=
{{#invoke:PhysicsQC|tocHeadingAndList|Physics:Quantum basics/See also/Matter}}
{{#invoke:PhysicsQC|tocHeadingAndList|Physics:Quantum basics/See also/Matter}}
== Notes ==
{{reflist|3}}


=References=
=References=
Line 138: Line 44:
{{Author|Harold Foppele}}
{{Author|Harold Foppele}}


{{Sourceattribution|Fermion|1}}
{{Sourceattribution|Physics:Quantum fermion|1}}

Latest revision as of 17:44, 22 May 2026

← Back to Particles Book II
← Previous : Elementary particle
Next : Majorana fermion →

fermion is a Book II topic in the Quantum Collection. A quantum fermion is a particle with half-integer spin that obeys Fermi-Dirac statistics. Fermions have antisymmetric many-particle wavefunctions, so identical fermions cannot occupy the same one-particle quantum state. This rule gives matter much of its structure, from atomic shells to degenerate stars. A quantum fermion is a particle with half-integer spin that obeys Fermi-Dirac statistics. Fermions have antisymmetric many-particle wavefunctions, so identical fermions cannot occupy the same one-particle quantum state. This rule gives matter much of its structure, from atomic shells to degenerate stars. The spin-statistics connection links half-integer spin with fermionic exchange behavior in relativistic quantum theory. Exchanging two identical fermions changes the sign of the many-body wavefunction.

Complex yellow illustration of fermions with half-integer spin, excluded quantum states, and Pauli-structure cues.

Spin and statistics

The spin-statistics connection links half-integer spin with fermionic exchange behavior in relativistic quantum theory. Exchanging two identical fermions changes the sign of the many-body wavefunction. The resulting Pauli exclusion principle is not an ordinary force; it is a constraint on the allowed quantum states.[1]

Elementary and composite fermions

Elementary fermions include quarks and leptons. Composite systems can also behave as fermions when their total spin is half-integer, as in protons, neutrons, many nuclei, atoms, and quasiparticle excitations in condensed matter.

Physical consequences

Fermion statistics explain the periodic structure of atoms, electron degeneracy pressure, band filling in solids, and the stability of ordinary matter. In particle physics, fermion flavor, chirality, and mass mixing are central to weak interactions, neutrino oscillations, and matter-antimatter studies.[2]

Description

fermion is a matter-scale concept used to organize how quantum theory describes atoms, particles, fields, condensed matter, plasma, or spacetime-related systems. In the Quantum Collection it is placed by scale so the reader can move from materials and molecules down to subatomic degrees of freedom.

Quantum context

At this scale, the relevant behavior is controlled by quantized states, interactions, conservation laws, and the way excitations or particles are observed. The concept is normally linked to measurable properties such as energy, momentum, charge, spin, spectra, scattering rates, or collective modes.

Role in the collection

This page provides a compact reference point for related pages in Book II. It should be read together with nearby matter-scale topics and the corresponding foundations in quantum mechanics.[3]

See also

Table of contents (84 articles)

Index

Full contents

References

  1. ↑ Peskin, Michael E.; Schroeder, Daniel V. (1995). An Introduction to Quantum Field Theory. Addison-Wesley. ISBN 978-0-201-50397-5. 
  2. ↑ Griffiths, David J. (2008). Introduction to Elementary Particles (2nd ed.). Wiley-VCH. ISBN 978-3-527-40601-2. 
  3. ↑ "Quantum mechanics". https://en.wikipedia.org/wiki/Quantum_mechanics. 


Author: Harold Foppele


Source attribution: Physics:Quantum fermion

Retrieved from "https://scholarlywiki.org/index.php?title=Physics:Quantum_fermion&oldid=8894"