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Fermions and bosons
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Half-integer vs integer spin particles.
Fermions (electrons, quarks, spin ½) obey exclusion and antisymmetric wavefunctions; bosons (photons, gluons, Higgs, spin 0 or 1) can occupy the same state.
Lasers (photons) and superfluid helium (bosons).
Composite particles are bosons if they contain an even number of fermions.
In more detail
Fermions have half-integer spin and obey the Pauli exclusion principle, while bosons have integer spin and can share states. Electrons are fermions, and photons are bosons.
Real-world uses
- Metals conduct because of Fermi-Dirac behaviour of electrons.
- Lasers exploit boson behaviour of photons.
- Engineers and physicists separate fermions and bosons, since they follow different statistics and behave very differently in bulk.
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Frequently asked questions
What are examples of bosons?
Photons, gluons, the Higgs boson and helium-4 atoms.
What about composite particles?
A composite particle is a fermion or boson depending on the number of fermions it contains.
Which particles are fermions?
Electrons, protons and neutrons, which all have half-integer spin.
Related topics in Quantum Mechanics
Electron spin · Stern–Gerlach experiment · Pauli exclusion principle · Identical particles · Angular momentum in QM · Addition of angular momenta