  The spread of the time arrows from the environment to an observed subsystem
is followed within a harmonic model. A similarity is pointed out between
irreversibility and a phase with spontaneously broken symmetry. The causal
structure of interaction might be lost in the irreversible case, as well. The
Closed Time Path formalism is developed for classical systems and shown to
handle the time arrow problem in a clear and flexible manner. The quantum case
is considered, as well, and the common origin of irreversibility and
decoherence is pointed out.
