I’ve heard that mirrors have something behind them to make the glass reflective but how does that work?
In: Engineering
To answer your second question, all materials are technically reflective. But most materials reflect light diffusely, meaning that light rays get scattered in random directions. This makes the reflecting object visible to the eye, but that’s all it does.
The reason for diffuse reflection is that most objects are made of a bunch of smaller things, like the tiny crystallites that make up rocks, or the fibers that make up organic matter. When light hits one of these objects, the light rays get bounced around inside of those miniature building blocks like pinballs, until they finally find a path back out of the surface and back to your eye. And by the time this happens, the exact direction any given light ray came from no longer matters.
Mirrors, however, are made of glass and metal, which are different. Glass is not made of a bunch of smaller objects. It’s basically just a random cluster of atoms, with no structure to it whatsoever. So any light rays that don’t bounce right off the surface just pass straight through. And metals have a very precise, uniform crystal structure, with atoms bound so tightly together in such a perfect arrangement that light rays simply have nowhere to bounce to but off the surface.
So as long as you can get the surfaces smooth enough that there are no bumps or valleys to bounce around, the light rays will all keep moving in the same direction, even when they bounce off. And because the light rays are all moving in the same direction relative to each other as they were when they hit the mirror, we see almost the exact same thing in the mirror that we would see if we were looking at the source of those light rays. This is called specular reflection.
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