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Glass is often called a solid, but at the molecular level it behaves oddly. When most liquids cool, their atoms snap into the neat, repeating grid of a crystal. Molten glass, however, is cooled so quickly that its atoms freeze in place before they can organise, locking into the same disordered tangle they had as a liquid. Because of this jumbled structure, scientists classify glass as an amorphous solid rather than a true crystal. A persistent myth claims that old windows are thicker at the bottom because glass slowly flows downward, but the real cause is simply the uneven way panes were once manufactured.