What is life?
Answer by Helier Robinson
The best definition that I know of was given by Erwin Schrodinger, the physicist of wave equation fame, who suggested that a living organism is a system of very high negative entropy in dynamic equilibrium. Entropy is a measure of disorder, and negative entropy is a measure of order. Dynamic equilibrium is equilibrium through change. For example, a car driving along a road is kept in dynamic equilibrium, relative to the legal side of the road to be driven on, by the driver; if the driver falls asleep then the equilibrium collapses. According to the second law of thermodynamics entropy can increase but not decrease, so that the opposite applies to negative entropy: it can decrease, but not increase. But living things manage to avoid this by feeding on negative entropy: sunlight, carbon dioxide, and oxygen for plants, and plants or other animals for animals. (The fate of every living thing is to live for a while and then be eaten by something else, with the exception of those that die in forest fires, volcanic eruptions, etc., and humans who do like the idea of being eaten and so get cremated or buried.) Your negative entropy is lower if you are tired or ill, and its dynamic equilibrium collapses when you die. See Schrodinger, What is Life? Cambridge University Press, 1948.