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at and above $T_G$ glass temperature

Perspective: The glass transition Biroli, 2013

Theoretical perspective on the glass transition and amorphous materials Rev Mod Phys 2011

Ludovic Berthier, Giulio Biroli

As long as the nucleation time is much larger than the structural relaxation time, τα, they can be considered as bona fide equilibrium states, at least using Feynman’s definition: “When all fast things have happened and all slow things have not, then the system is in equilibrium” (Feynman, 1972). After all, the people who value diamonds do not worry that they will turn into graphite anytime soon. A more serious
concern is that the relaxation time of the supercooled liquid cannot really diverge at a finite temperature if the thermodynamically stable state is a crystal

The glass transition 1998, C Austen Angell

Angell The glass transition

https://www.nytimes.com/2008/07/29/science/29glass.html