Glass transition
What is the physical nature of the glass transition — why does a liquid cooled fast enough become a rigid amorphous solid with a huge (often 10+ orders of magnitude) slowdown in molecular motion, without any obvious change in structure or a sharp thermodynamic phase transition?
History and references
Still open in the literature as of 2026.
P. W. Anderson called the glass transition one of the deepest unsolved problems in condensed matter physics. Liquids like silica or many polymers, cooled quickly enough to avoid crystallizing, become amorphous rigid solids, and their viscosity rises by 10-17 orders of magnitude over a modest temperature range with no obvious structural signature. Numerous theories (mode-coupling theory, random first-order transition theory, dynamical facilitation) each capture part of the picture, but there is no consensus first-principles theory linking the dramatic dynamical slowdown to an underlying thermodynamic transition, or explaining whether one is hiding beneath experimentally inaccessible timescales.
Window glass and amber sitting quietly for centuries are secretly frozen liquids whose internal physics has resisted a complete explanation for over a century.
Explanations that circulated
- That the glass transition is a standard thermodynamic phase transition like freezing; it lacks a sharp discontinuity and the 'transition temperature' depends on cooling rate
References
- Supercooled liquids and the glass transition, Pablo G. Debenedetti, Frank H. Stillinger, Nature, 2001
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