Natural processes can have a distinct recurrent behaviour, e.g. periodicities (as [[Seasonality|seasonal]] or [[Milankovich cycle]]s), but also irregular cyclicities (as [[El Niño]] Southern Oscillation, heart beat intervallsintervals). Moreover, the recurrence of states, in the meaning that states are again arbitrarily close after some time of [[divergence]], is a fundamental property of [[deterministic]] [[dynamical systems]] and is typical for [[nonlinear]] or [[chaotic system]]s (cf. [[Poincaré recurrence theorem]]). The recurrence of states in nature has been known for a long time and has also been discussed in early work (e.g. [[Henri Poincaré]] 1890).
