What is glass?
What is glass? Nobel Laureate Warren Anderson once said: "The deepest and most interesting of the unsolved problems in the theory of the solid state lies in the nature of glass." And although glass has been known to mankind for more than a millennium, scientists still do not understand what the reason for its unique mechanical properties is. We remember from school lessons that glass is a liquid, but is it? Scientists do not know exactly what the nature of the transition between liquid or solid and glassy phases is and what physical processes lead to the basic properties of glass.
The process of glass formation cannot be explained using any of the current tools of solid state physics, multiparticle theory, or fluid theory. In short, liquid molten glass, as it cools, gradually becomes more and more viscous until it becomes rigid. While in the formation of crystalline solids, such as graphite, atoms form the usual periodic structures at one moment.
Tarun Chitra, a molecular dynamics researcher, explains the organization of molecules in different substances using dance as an example:
The ideal rigid body is like a slow dance where two partners move around their starting position on the dance floor along with other couples.
The ideal fluid is like a dating party, where everyone tries to dance with everyone in the room (this property is called ergodicity), while the average pace at which everyone dances is about the same.
Glass, by this analogy, is like a dance when a group of people is divided into smaller subgroups and each is spinning in its own round dance. You can change partners from your circle, and this dance goes on forever.
Glass behaves in such a way that it cannot yet be described by equilibrium statistical mechanics. In particular, subexponential autocorrelations and the glass cross-correlation function can be obtained by an infinite number of random processes. Up to a certain point, the system "works" more or less clearly and predictably, but if you observe it long enough, you begin to see how some features are better described by the theory of probability and random processes.
