Microscopic parameters of a stochastic system and variance of physical quantity (ideal gas, electric current, thermal radiation of a black body)

It is shown that the variance of a random physical quantity F can be expressed and directly calculated with the help of a microscopic parameter which, under certain conditions, may be called the invariable intrinsic microquantity of chaos (MQC). MQC is a self-sufficient concept that characterizes a physical system or a stochastic process. The following statement is proposed: if a random physical quantity F is additive and its fluctuations are statistically independent, then its variance can be expressed as the product of the mean value and the corresponding value of the MQC. Physical situations are considered in the frame of which this statement has been substantiated. The MQC concept is demonstrated for fluctuations in the ideal gas. Expressions of MQC are proposed for fluctuations of black body radiation, electrical and photocurrents. Arguments for the usefulness of the MQC concept are presented. (Author)