  In this paper we address the problem of the arrow of time from a cosmological
point of view, rejecting the traditional entropic approach that defines the
future direction of time as the direction of the entropy increase: from our
perspective, the arrow of time has a global origin and it is an intrinsic,
geometrical feature of space-time. Time orientability and existence of a cosmic
time are necessary conditions for defining an arrow of time, which is
manifested globally as the time-asymmetry of the universe as a whole, and
locally as a time-asymmetric energy flux. We also consider arrows of time of
different origins (quantum, electromagnetic, thermodynamic, etc.) showing that
they can be non-conventionally defined only if the geometrical arrow is
previously defined.
