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Fermions And Bosons

  To discuss the similarities and difference between fermion and boson particles, the concept of intrinsic spin, or angular momentum, must be introduced. In current understanding, all particles possess intrinsic angular momentum, which is a fundamental property of the particle. This angular momentum is quantized in units of h/2, where h is a physical constant with the value 1.054 × 10-34.

The Standard Model, the currently accepted description of how particles interact, leads us to believe that there are two types of particle: particles which constitute matter, and particles which are used as intermediaries of forces. The first type are fermions, and have half-integral values of h for intrinsic spin; the second are bosons, with integral values.

These particles interact very differently. Fundamental requirements of symmetry lead to the Pauli Exclusion Principle, which states that no two fermions in a system may have the same set of Quantum numbers. This is identical to the statement that no two fermions may occupy the same place at the same time. For bosons, these symmetry requirements have more subtle consequences, which lead to macroscopic quantum phenomena such as superfluidity and superconductivity.

Bosons behave differently, and have no exclusion principle. This difference in behaviour may be seen when two fermions interact together to form an effective boson, which occurs in superconducting metals. Electrons are fermions, which is why they form ordered shells around the nucleus of an atom. If they were bosons, they would be at liberty to all fall down to the lowest energy level, and if this were the case, chemistry and therefore life would never have existed. JJ

See also quantization.



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