  The decay of 2-gluon colour singlets in quarks: 2g --> q-qbar +2q-2qbar has
been simulated with the Monte-Carlo method, taking into account an effective
1-gluon exchange interaction between the emitted quarks, which was folded with
a 2-gluon density determined self-consistently. 2-gluon densities were found
with different radii, which correspond to 0^{++} glueballs of the size of light
q-qbar, s-sbar, c-cbar, b-bbar, and heavier q-qbar systems. Binding potentials
between the two gluons have been deduced, which are consistent with the
confinement potential from lattice results. However, self-consistency for the
deduction of 2-gluon densities requires massless (or very light) quarks for all
flavours. The masses are given by the binding energies of quarks and gluons,
yielding excitation spectra of 0^{++} glueballs and Phi, J/Psi, and Upsilon
states consistent with observation. The sum of q-q potentials yields a strong
coupling alpha_s consistent with the available data up to large momenta. The
nucleon is described by a gluonium state coupled to 3 valence quarks, yielding
ground state and radial excitations consistent with experiment. Finally, we
discuss the compressibility of the nucleon and relate it to that of nuclear
matter.
