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Fermi level physics (10^-15 m)
Particle physics descibes the world as built up from different classes of particles.
Bosons are force particles such as photons and gravitons that transmit
the electromagnetic and gravitational fields. Thera are also gluons that carry the strong
(nuclear) force together with the W and Z particles that carry the weak (nuclear) force.
Fermions are matter particles that come in two varities, "leptons" that are
observed as point-like particles such as the electron and "quarks" that combine to form
extended particles like the proton and the neutron.
Once seen as simple building blocks of nature the proton and neutron are really very
complex object. The 'u' and 'd' quarks that generates these "nucleons" each accounts
for only about one percent of the total mass. The main part of the proton and neutron
masses arises from a minute fireball of chromodynamic energy where 'sea' quarks exists in
a twilight zone between the 'virtual' quarks filling all of the vacuum and the 'real' quarks
that are created in high energy particle collisions. When one talks of the triplets of quarks
that generates the BARYONS or the doublettes of quarks and anti-quarks that generates
the MESONS the true meaning is that these particles are 'valence' quarks in analagoue
with chemistry where the properties of atoms are determined by the outermost shell of
electrons.
In recent years there has been successfull numerical simulations of baryons and
mesons (together known as HADRONS). These numerical calculations has also predicted
the masses of 'glueballs' a kind of particles that have no valence quarks but are defined
only by the chromodynamic energy of interacting gluons.