Super-selection rules modulating complexity: an overview

Complex systems comprising a large number of elements are potentially capable of finding themselves in a huge variety of states arising by combining the states of their parts. If such a combinatorial explosion were indeed materializing, the observed behavior would resemble to random noise. It is therefore essential that physically relevant complex systems be capable of developing mechanisms for selecting a meaningful subset of states out of the large set of a priori available states. In this communication some generic mechanisms for reducing complexity are analyzed and illustrated on case studies.