We develop a general framework for the discussion of detailed balance and
analyse its microscopic background. We find that there should be two additions
to the well-known T- or PT-invariance of the microscopic laws of motion:
- Equilibrium should not spontaneously break the relevant T- or
PT-symmetry.
- The macroscopic processes should be microscopically distinguishable to
guarantee persistence of detailed balance in the model reduction from micro- to
macrokinetics.
We briefly discuss examples of the violation of these rules and the
corresponding violation of detailed balance.