  A non-Abelian gauge theory describes the strong interactions among particles
with the commutator of generators are non-zero. An $SU(3)$ gauge theory
describes the interactions that lead to nuclear forces among particles. The
Lagrangian density refers to fermions with colour and flavour and the gauge
field quanta implying gluons. The gauge theory is treated at finite temperature
using the Thermo Field Dynamics (TFD). Using self interaction of gluons the
Stefan-Boltzmann law and the Casimir effect are calculated at finite
temperature. An appendix is attached to give a response of a massless quarks in
gauge theory.
