Unifying themes of complex systems

Taken from Introduction to Complex Systems lecture by Tomaso Aste:

Complex systems

• exhibit emergence (some properties present at system level are not present at lower level — e.g. a cell is alive but is made of inanimate elements)
• are open (energy and information are constntly being imported and exported acoss system boundaries)
• have a history (the history cannot be ignored, even a small change in circumstances can lead to large deviations in the future)
• can adapt (in response to external or internal changes, the system can reorganize itself without breaking — self organizing)
• are not completely predictable (when a system is adaptive, unexpected behaviours can emerge — prediction becomes expectation)
• are multi-scale and hierarchical (system size and structure scale are over several orders of magnitude and distinct properties and functions are associated with different scales; dynamics can propagate through scales — avalanches, cascade effects)
• are disordered (there is no compact and concise way to encode the whole information contained in the system)
• have multiple (meta) (stable) states (small perturbations lead to recovery, larger ones can lead to radical changes of properties; dynamics do not average simply).