RT Journal Article SR 00 ID 10.1088/1361-6404/aa5a87 A1 Holovatch, Y. A1 Kenna, R. A1 Thurner, S. T1 Complex systems: physics beyond physics JF European Journal of Physics YR 2017 FD 2017-02-15 VO 38 IS 2 SP 023002 AB Complex systems are characterised by specific time-dependent interactions among their many constituents. As a consequence they often manifest rich, non-trivial and unexpected behaviour. Examples arise both in the physical and non-physical worlds. The study of complex systems forms a new interdisciplinary research area that cuts across physics, biology, ecology, economics, sociology, and the humanities. In this paper we review the essence of complex systems from a physicists' point of view, and try to clarify what makes them conceptually different from systems that are traditionally studied in physics. Our goal is to demonstrate how the dynamics of such systems may be conceptualised in quantitative and predictive terms by extending notions from statistical physics and how they can often be captured in a framework of co-evolving multiplex network structures. We mention three areas of complex-systems science that are currently studied extensively, the science of cities, dynamics of societies, and the representation of texts as evolutionary objects. We discuss why these areas form complex systems in the above sense. We argue that there exists plenty of new ground for physicists to explore and that methodical and conceptual progress is needed most. PB IOP Publishing SN 0143-0807 LK https://pure.iiasa.ac.at/id/eprint/14386/