If you’ve heard that “glass is a liquid” - well, sort of. Glass is what scientists call an amorphous solid. It’s hard, brittle, and behaves like a solid for all practical purposes - but at the molecular level, its atoms are arranged in the messy, random pattern of a liquid rather than the neat repeating pattern of a true crystalline solid.
When most liquids cool down, they form crystals - molecules lining up in neat rows. Glass cools so quickly that the molecules get frozen in their disorderly liquid arrangement before they can crystallize. It’s basically a liquid that ran out of time to become a real solid.
A famous myth says that very old church windows are thicker at the bottom because glass slowly flows downward over centuries. The thicker bottoms are actually because medieval glassmakers couldn’t make perfectly uniform panes - they installed them with the thicker edge down for stability. Real glass flow is extraordinarily slow; even at room temperature, you’d need many millions of years to see it deform meaningfully. So while glass technically isn’t quite solid, it’s not running anywhere on human timescales.
