  After reviewing known results on sensitiveness and also on robustness of
attractors together with observations on their proofs, we show that for
attractors of three-dimensional flows, robust chaotic behavior meaning
sensitiveness to initial conditions for the past as well for the future for all
nearby flows) is equivalent to the existence of certain hyperbolic structures.
These structures, in turn, are associated to the existence of physical
measures. In short in low dimensions, robust chaotic behavior for smooth flows
ensures the existence of a physical measure.
