A general term for a wide range of scientific research in two key problematics: (i) the interconnectedness of the apparently unconnected (e.g., what effect does a butterfly flapping its wings in Beijing have on weather in London?); (ii) the emergence of change. Complexity in this context does not mean complicated because complex systems can in fact be relatively simple; rather it means that a particular phenomenon, such as air quality, cannot be considered in isolation from a diverse range of other factors, which in this case might include prevailing winds, the location of heavy industry, and so on. Research in this field aims to identify the critical causal agents in a particular system and separate out that which is accidental, or just background noise. In critical theory, complexity theory is utilized to engage cultural and social questions. For instance, it has been used by Manuel DeLanda to analyse the formation of cities. See also non-linear system.