Glass looks and feels solid, but it isn't entirely so.
Glass begins as a molten liquid substance that gets spun and blown into various shapes, and continues to flow long after it cools.
If you look at glass under a microscope, it appears as though glass never really stops flowing to settle into a truly solid crystalline structure. The molecules in glass flow very, very slowly--so slowly that it would take millions of years for a pane of glass to flow in any perceptible way.
But does glass eventually stop flowing, even if it may take millions of years? That's a surprisingly tricky question that's baffled scientists for years.
A team of researchers from England and Japan may have found an answer: Looking at glass molecules under very low temperatures, they found that the molecules do appear to eventually form into solid geometrical shapes. Glass becomes solid eventually--but at a pane-stakingly slow pace!
"Is Glass a True Solid?" (Phys.org)