A phase of matter is characterized by its organization of atoms. The atoms in a solid arrange themselves in uniform patterns.
Contrastingly, atoms behave disorderly in gases and liquids. At one moment atoms may be locally packed, then disperse an instant later.
Gases and liquids are fluid, as both flow when under stress. Unlike gases, liquids can form a free surface: a coherent interface layer.
The interface between gases and liquids at the atomic level can only be explained by incorporating a hierarchy of resonances (wave synchronies) during the spontaneous symmetry breaking (Goldstone mode) that naturally occurs between atoms during van der Waals interactions (distant-dependent interactivity). There is a subtle, hidden, atomic order in the seeming chaos of fluids converging.
A microscopic theory of correlations in the interfacial region between gases and liquids originates from recognizing that the correlation function displays, in addition to a Goldstone mode, an unexpected hierarchy of resonances that severely constrain structural properties. ~ English physicist Andrew Parry & Spanish mathematician Carlos Rascón