A thermodynamic description of the time evolution of a stock market index

The scope of this paper is to present a phenomenological analysis for the time evolution of a Stock Index. The model which is introduced represents a new methodology for the description of the up and down trends of a stock index and also an example is presented referring to the Athens Stock Index (ASI). The day-by-day closing prizes of the ASI exhibit exponential laws. This behavior supports an alternative formalism based on the thermodynamic concepts of Physics in order to study the macroscopic properties of stock markets. Hence, the Newton's law of cooling is introduced as a pattern for up and down trends of the ASI. The results encourage us to construct a more complete thermodynamic model in order to understand the time evolution and the behavior of the ASI.