Microscopic fluctuations disordered systems

Conventional kinematic notions are built around the idea that the system of interest can be characterized by a series of simple states without any reference to microscopic fluctuations or disorder. On the other hand, in the analysis of systems at finite temperature or in the presence of the effects of disorder, it is essential to build up measures that characterize the disposition of the system while at the same time acknowledging the possibility of an incomplete state of order within that system. Just as strain measures served as the primary kinematic engine used in our analysis of continua, the notion of a correlation function will serve to characterize the disposition of those systems that are better thought of statistically. Indeed, we will find that in problems ranging from the spins introduced earlier in conjunction... 

As it is known [5], the intensity of the scattered light gives us an information about the system s disorder, e.g., presence therein of pores, impurities etc. Since macroscopically liquid is homogeneous, critical opalescence arises due to local microscopic inhomogeneities - an appearance of small domains with different local densities. In other words, liquid is ordered inside these domains but still disorded on the whole since domains are randomly distributed in size and space, they appear and disappear by chance. Fluctuations of the order parameter have large amplitude and involve a wide spectrum of the wavelengths (which results in the milk colour of the scattered light). 

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