Appendix 1: Feedback Loops

Feedback loops, both positive and negative, are common in our everyday lives. A negative feedback involves one variable affecting a second variable, which in turn affects the first. A common example of this is an oven thermostat. When the oven reaches a preset temperature, the thermostat turns the oven off, causing the oven to cool. When the oven cools beyond a certain point, the thermostat turns the oven on again and the temperature rises. In this system, the thermostat and temperature influence each other to maintain a stable temperature. An example of a positive feedback loop is the feedback noise made when a microphone is placed too close to a speaker. The sound of the speaker is picked up by the microphone, amplified, and re-emitted out through the speaker, where it is, once again, fed back into the microphone.

"The chaotic sound is the result of an amplifying process in which the output of one stage becomes the input of another." The ideas of positive feedback and sensitivity on initial conditions are not unique to modern science. The writer J.B. Priestly examined the idea in a play called "Dangerous Corner", which has two entirely different outcomes, both wholly dependant on whether a simply question regarding a cigarette box is asked. The notion also has a place in folklore: For want of a nail, the shoe was lost;

For want of a shoe, the horse was lost;

For want of a horse, the rider was lost;

For want of a rider, the battle was lost;

For want of a battle, the kingdom was lost!

And all for the sake of a horse shoe nail.