Stuff Matters: Exploring the Marvelous Materials That Shape Our Man-Made World

by Mark Miodownik

Even if light is not absorbed by glass, moving through the interior of an atom still affects it, slowing it down until it emerges from the other side of the glass, when it speeds up again. If the light strikes the glass at an angle, different parts of the light will enter it and emerge from it at different instants, forcing them to travel momentarily at slightly different speeds. This momentary difference is what causes the light to bend, or refract, and this is what makes an optical lens possible, with the curvature of the glass resulting in different angles of refraction at different points along its surface. Controlling the curvature of the glass means we can magnify images, which allows us to make telescopes and microscopes, and, for those of us who wear glasses, to see.