  Systems with long-range persistence and memory are shown to exhibit different
precursory as well as recovery patterns in response to shocks of exogeneous
versus endogeneous origins. By endogeneous, we envision either fluctuations
resulting from an underlying chaotic dynamics or from a stochastic forcing
origin which may be external or be an effective coarse-grained description of
the microscopic fluctuations. In this scenario, endogeneous shocks result from
a kind of constructive interference of accumulated fluctuations whose impacts
survive longer than the large shocks themselves. As a consequence, the recovery
after an endogeneous shock is in general slower at early times and can be at
long times either slower or faster than after an exogeneous perturbation. This
offers the tantalizing possibility of distinguishing between an endogeneous
versus exogeneous cause of a given shock, even when there is no ``smoking
gun.'' This could help in investigating the exogeneous versus self-organized
origins in problems such as the causes of major biological extinctions, of
change of weather regimes and of the climate, in tracing the source of social
upheaval and wars, and so on. Sornette, Malevergne and Muzy have already shown
how this concept can be applied concretely to differentiate the effects on
financial markets of the Sept. 11, 2001 attack or of the coup against Gorbachev
on Aug., 19, 1991 (exogeneous) from financial crashes such as Oct. 1987
(endogeneous).
