Fig. 5.2. Feedback diagrams in which the arrows indicate the actions of causality. (a) A simple loop. (b) A complex network unwanted emergent structures in amplifiers, but for systems that are intended to oscillate, positive feedback is an essential element of the design.
Journals of nonlinear science offer many examples of positive feedback and the subsequent emergence of coherent structures . In the physical sciences, structures emergent from positive feedback loops include tornadoes, tsunamis, optical solitons, and Jupiter's Great Red Spot, among many others. Biological examples include the nerve impulse, cellular reproduction, flocks of birds and schools of fishes, and the development of new species, in addition to the emergence of life itself. In the social sciences, there are lynch mobs, natural languages, and the founding of a new town or city . In hierarchical systems, downward causation (WDC, MDC, or both) leads to additional opportunities for more intricate closed causal loops (or networks), as is suggested in Fig. 5.2b. Here the network comprises the following closed loops of causation: ABCD, CDG, AEFD, and AEGCD, where the letters correspond to coherent entities at various levels of the biological and cognitive hierarchies. In the context of modern nonlinear science, each such diagram would correspond to the presence of an attractor in the phase space describing the system dynamics, and it could lead to the emergence of a new coherent entity of theoretically unbounded complexity.
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