"To assert that there exists an order parameter in essence says: ‘‘I may not understand the microscopic phenomena at all’’ (as was historically, the case for superfluid helium), ‘‘but I recognize that there is a microscopic level and I believe it should have certain general, overall properties especially as regards locality and symmetry: those then serve to govern the most characteristic behavior on scales greater than atomic.’’ ... Know the nature of the order parameter—suppose, for example, it is a complex number and like a wave function—then one knows much about the macroscopic nature of a physical system! ... Landau's introduction of the order parameter exposed a novel and unexpected foliation or level in our understanding of the physical world. Traditionally, one characterizes statistical mechanics as directly linking the microscopic world of nuclei and atoms (on length scales of 10-13 to 10-8 cm) to the macroscopic world of say, millimeters to meters. But the order parameter, as a dynamic, fluctuating object in many cases intervenes on an intermediate or mesoscopic level characterized by scales of tens or hundreds of angstroms up to microns (say, 10-6.5 to 10-3.5 cm)."