  The problem of relating microscopic chaos to macroscopic behavior in a
many-degrees-of-freedom system is numerically investigated by analyzing
statistical properties associated to the position and momentum of a heavy
impurity embedded in a chain of nearest-neighbor anharmonic Fermi-Pasta-Ulam
oscillators. For this model we have found that the behavior of the relaxation
time of the momentum autocorrelation function of the impurity is different
depending on the dynamical regime (either regular or chaotic) of the lattice.
