Glass’s structure is disordered, but that doesn’t make it a liquid
In a crystal, atoms settle into a repeating pattern. Ordinary window glass lacks that long-range pattern: its atoms are arranged irregularly, more like those in a liquid. But appearance at the atomic scale is not the same as behavior in a room. Glass holds its shape and resists shear—the kind of force that would make a fluid keep deforming—so it behaves as a solid under everyday conditions.
Glass is often called an amorphous solid: “amorphous” means it has no repeating crystal structure. Its atoms can, in principle, rearrange, but at room temperature those rearrangements are so extraordinarily slow that they produce no measurable sag over the lifetime of a window. Heating glass changes the situation: it softens and can be shaped, which is why glassblowers and manufacturers work with it while hot.
Why old windows can look thicker at the bottom
The uneven panes sometimes cited as evidence of flowing glass were made by older methods that produced sheets of inconsistent thickness. When installers fitted them, they often placed the heavier, thicker edge at the bottom for stability. The variation was present when the pane was installed; it is not a record of glass slowly draining downward.
So glass can resemble a frozen liquid in its atomic arrangement without acting like a liquid in a window frame. Its structure explains why it can be transparent and brittle, while its rigidity explains why centuries-old panes remain where they were put.
