Is glass really a liquid?
Everyday window glass is an amorphous solid, despite a persistent story about old windows.
The difference between glass and crystal
In a crystal, atoms follow a repeating arrangement over long distances. Ordinary glass lacks that regular long-range pattern, which is why it is described as amorphous. At room temperature, however, the material is solid: it holds its shape and does not flow noticeably on human timescales.
Where the myth came from
Some older windows are thicker at the bottom than at the top. The popular explanation is that centuries of gravitational flow redistributed the glass. A more plausible explanation is historical manufacturing: older methods produced panes with uneven thickness, and installers often placed the thicker edge at the bottom.
What makes glass interesting anyway
Glass can soften when heated and has a transition region rather than the sharply defined melting behaviour of many pure crystals. Scientists study these properties in materials ranging from silica glass to metallic glasses and certain polymers. The real story is richer than the myth: a solid need not have an orderly crystal structure.
External references are provided for exploration; Curio Hour’s explanation is written separately.