Pauli Exclusion Principle

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Pauli exclusion principle follows mathematically from definition of Wave Function for a system of identical particles - it can be either Symmetric or Antisymmetric (depending on particles' Spin ). Particle s with Antisymmetric Wave Function s are called Fermion s - they have to obey the Pauli exclusion principle. Apart from the familiar electron, proton and neutron, these include the Neutrino s, the Quark s (from which protons and neutrons are made), as well as some Atom s like Helium-3 . All fermions possess "half-integer Spin ", meaning that they possess an intrinsic Angular Momentum whose value is $\backslash hbar\; =\; h/2\backslash pi$ ( 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 . Particles with integer spin have Symmetric Wave Function and are called Boson s, in contrast to fermions they share same quantum states. Examples of bosons include the Photon and the W And Z Bosons . CONNECTION TO QUANTUM STATE SYMMETRY The Pauli exclusion principle was originally formulated as an Empirical Principle . It was invented by Pauli in 1924 to explain experimental results in the Zeeman Effect in Atomic Spectroscopy , Ferromagnetism , and how the Periodic Table is regulated by the Electron structure of atoms, well before the 1925 formulation of the modern theory of quantum mechanics by Werner Heisenberg and Erwin Schrödinger . However, this does not mean that the principle is in any way approximate or unreliable; in fact, it is one of the most well-tested and commonly-accepted results in physics. The Pauli exclusion principle can be derived starting from the assumption that a system of particles occupy antisymmetric quantum states. According to the Spin-statistics Theorem , particles with integer spin occupy symmetric quantum states, and particles with half-integer spin occupy antisymmetric states; furthermore, only integer or half-integer values of spin are allowed by the principles of quantum mechanics.

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