Pauli exclusion principle

The Pauli exclusion principle is a quantum mechanical principle formulated by Wolfgang Pauli in 1925, which states that no two identical fermions may occupy the same quantum state simultaneously. It is one of the most important principles in physics, primarily because the three types of particle from which ordinary matter is made - electrons, protons, and neutrons - are all subject to it. The Pauli exclusion principle underlies many of the characteristic properties of matter, from the large-scale stability of matter to the existence of the periodic table of the elements.

Related Topics:
Quantum mechanical - Wolfgang Pauli - 1925 - Identical - Fermions - Quantum state - Physics - Matter - Electron - Proton - Neutron - Periodic table of the elements

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Particles obeying the Pauli exclusion principle are called fermions. Apart from the familiar electron, proton and neutron, these include the neutrinos, the quarks (from which protons and neutrons are made), as well as some atoms like helium-3. All fermions possess "half-integer spin", meaning that they possess an intrinsic angular momentum whose value is hbar = h/2pi (Planck's constant divided by 2π) times a half-integer (1/2, 3/2, 5/2, etc.). In the theory of quantum mechanics, fermions are described by "antisymmetric states", which are explained in greater detail in the article on identical particles.

Related Topics:
Particle - Fermion - Neutrino - Quark - Atom - Helium-3 - Spin - Angular momentum - Planck's constant - Half-integer - Identical particles

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Particles that are not fermions can only be bosons, which are particles described using "symmetric states" in quantum theory. Bosons are allowed to share quantum states, and possess integer spin. Examples of bosons include the photon and the W and Z bosons.

Related Topics:
Boson - Photon - W and Z bosons

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