Good clocks, which are naturally subject to fluctuations, 
can be characterized in statistical terms and the 
evolution of quantum systems according to these clocks 
obey  a master equation. This master equation is 
diffusive and produces loss of coherence. Moreover, real 
clocks can be described in terms of effective interactions 
that are non-local in time. Alternatively, they can be 
modeled by an effective thermal bath coupled to the 
system. This may give interesting hints in the  study of 
some aspects concerning the evolution of quantum 
low-energy fields in a foamlike  spacetime, with involved 
topology at the Planck scale but with a smooth metric 
structure at large length scales, which also introduces 
nonlocal interactions that can be modeled by a quantum 
bath, and low-energy fields evolve according to a master 
equation.