Glass is not truly a solid but a slow-flowing liquid. Over many years, window glass will eventually flow like water, and old windows have thicker glass at the bottom because the glass flowed downward.
Glass is an amorphous solid with properties between crystalline solids and liquids, but it is not a liquid. It doesn't flow at room temperature. The thicker glass at the bottom of old windows is due to manufacturing methods of the time that produced uneven thickness, not flowing glass. Glass exhibits a glass transition temperature at which it softens, but this is around 1500 degrees Fahrenheit, not at room temperature.
Reception
Sources
- American Chemical Society: Glass is a Solid REFERENCE
- Physics Central: Glass Properties REFERENCE