Eli5: What’s the difference between a mirror and a white surface if both reflect all light?


Eli5: What’s the difference between a mirror and a white surface if both reflect all light?

In: Physics

Think about bouncing a rubber bouncy ball. If you bounce it on a smooth gymnasium floor, it is easy to bounce and catch because it bounces predictably. Now think about bouncing it on a parking lot. When it hits a small stone or a crack it bounce in an unpredictable way but it still bounces.

A mirror bounce the light back in the same way it comes in – this is the smooth predictable bounce. White things bounce the light like a rough parking lot – the scattered light is out of order and no longer looks like an image.

When light reflects off of the white object it’s not reflecting in the exact same “shape” that it was when it hit it you’re seeing the result of all of that light mixing together to form the color white. When it reflects off of the mirror or other metallic object it is bouncing off of it in the exact same wavelength and pattern that hit it allowing it to preserve the image exactly. This is why if you take any object and polish it it will still have some reflective quality to it just tinted in whatever color, think paint on a shiny car for instance. It’s really just a matter of how smooth the surface is at a molecular level. If you take anything and you polish it* down to the most flat it can possibly be then it will be reflective as long as it doesn’t inherently absorb light like some materials do. Even those little dirt ball things that people make are shiny even though it’s just dirt. The polished surface allows the light to reflect properly rather than diffuse and be scrambled.

Edit: continuation

The material on the back of the mirror that provides the reflectiveness is a color as well as is the glass, but the impurities in the glass are so few that its inherent green tint does not show through unless the glass is really really thick.