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There are two possible kinds of 'thing...'


  1. There are two kinds of 'things' in the universe...

    1. Because quantum amplitudes are complex, there are two possible ways for something to satisfy the essential attribute of thingness: to be identical with itself. That is, for a given class of identical things we should be able to exchange any pair without altering the physical reality - and this requirement is two-fold degenerate with respect to the behavior of amplitudes...

    2. These two types of self-identical thing are called bosons and fermions. Every kind of elementary particle is either a boson or a fermion.
      some bosons are: photons, gluons, He4, ...
      fermions: electrons, quarks, He3, ...
      All bosons have either zero spin or an even integer spin; all fermions have half-integer multiple spins. (cf. spin and statistics)

    3. The scheme of Quantum Field Theory is that fermions interact by exchanging bosons.


  2. The two ontological classes have fundamentally different natures because they have special interactions which follow purely from their being identical particles: bosons are gregarious, and fermions are solitary.

    1. Bosons may occupy the exact same quantum state as other bosons,* as for example in the case of laser light which is formed of coherent, overlapping photons.

      * In fact, the more bosons there are in a state the more likely that another boson will join that state (and so on)...
    2. Only one fermion may occupy any quantum state - the fermionic solitariness of electrons is responsible for the structure of molecular matter (in fact for all 'structure' in the universe).


    Coherence
    Identical particles
    Bosons and Fermions