4.7 Chemical oscillation; coupling and networks.

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Communication = ferrying information. A sender, it can be a cell or a system or a person, usually gets a response from the receiver, which in turn prompts it to send the next message. In the life of a cell, a change in a physical or chemical variable counts as a stimulus. Any such change pulls along a train of effects, usually aimed at counteracting the change or at compensating for it. Change and counterchange establish a dynamic equilibrium: a pull in one direction is redressed by a push in the opposite direction. Thus any event in the environment may give rise to a series of fluctuations such as growth and decline in a population of molecules, cells or synapses. Put in another way: an oscillation of chemical and physical variables in it's state of balance, is temporarily changed when the system receives a signal or stimulus from outside.

On quite another level, that of human institutions, we recognise analogical events. If we look at the equilibrium between political parties, it is typically a fluctuating one. When the right wing has a majority and has been in control for some time, people tend to favour the left, and the government is changed. After a while a reaction sets in, and voters incline again to the right. These oscillations within parties and between parties stabilise the course of politics in the long run. When unpalatable opinions are suppressed by a powerful majority, this may seem to promote stability in the short term, but it may prove to provoke a revolutionary movement in the long term.

Nearly all components of nature are part of one or more cyclical processes, which means that they continuously receive signals from contingent components in their immediate environment. Meaningful information is transmitted from one system to another by oscillation. In this way interactions between tissue components are sustained. The frequency in which systems oscillate are an indication of their readiness for communication. Systems with more or less similar response times are in continuous interaction with each other. The oscillations are the very substance of coherence. Interactions between a large number of oscillating systems amount to a network. A stimulus imparted to one of the components spreads like a wave over the other parts of the network. This has been clarified in Chapter 3 by an example from embryogenesis.

4.8 Biological clocks.