Correct phrase for a 'forgetful' natural system? This is a rather general question: assume I have a system that has a certain 'forgetful' property, which means that while I can offset its current state for a moment, it will eventually return to its undisturbed state. An example would be a length of river (say, 100 m) from which I extract a certain amount of water: two days later it would not matter if I had removed the water or not. The system would not show any traces of my previous actions.
The opposite case would be a rock, a chunk of which I chisel away. Two days later the gap would still remain; the 'system' would never return to its original state.

What would you call a system that displays such 'forgetfulness'?
How would you call a system that displays such 'forgetfulness'?


In one word, dissipative. In multiple words, a system whose autocorrelation function tends to zero as time tends to infinity.

Note that the autocorrelation function may not exist; this concept implicitly assumes a linear (or approximately linear) system. Consider a river. Adding a small impulse of water upstream (e.g., a not-too-large downburst) results in the river flow increasing briefly but eventually stabilizing to some nominal value. Adding a slightly larger impulse results in a similar but slightly larger response. But adding a huge impulse of water upstream (e.g., a very large and rapid snowmelt) may cause the river to carve itself a new channel. With this huge impulse, the flow at some downstream point will increase initially but then drop to zero and stay that way because the river no longer flows past that point.