A diminished capacity for spontaneous change; the inability to translate psychic or physical energy into a new form.In its psychiatric use the term is roughly equivalent to rigidity or stodginess, and is sometimes applied by psychoanalysts to an incapacity to form new attachments or make any kind of change in life. This often occurs among aged persons, who insist on wearing the same clothes, eating the same food, or taking the same walks even though other opportunities are offered to them. They become set in their ways not only because they lack the physical energy to make a change, but because they have a profound emotional investment in their habitual way of life. Any change would therefore arouse feelings of uncertainty and put a strain on their reduced powers of adaptation. Entropy, however, varies greatly. Some people lose their “mental plasticity” at a relatively early age, others extremely late in life.In sociology, the term “social entropy” applies to the doctrine that every social change reduces the energy available for further progress, and therefore every society has a tendency to become static in time. This usage, like the first, is derived by analogy from thermodynamics, in which entropy is the measure of the amount of the energy in a system which cannot be taken out and is therefore not available for doing work. In this sense, the total available energy decreases in old age, and therefore the capacity for making changes is diminished.