Why is it that when you look up close in a mirror, you can see objects that are on the same plane as the mirror, but aren’t within the range of the mirror’s reflection?

Question

Title might be a bit messily worded here so allow me to elaborate:

Let’s say you have a mirror on the wall and a painting on the same wall that’s some distance away.

Why is it that if you press your face up close to it and look to the side, you can see the painting in the mirror despite the painting being far away and not even on the opposite wall, where it would normally be reflected? How does the mirror know that the painting, as well as everything else on the wall, is there?

In: 0

Answer 1

The same way that Captain America’s shield can deflect a grenade thrown at 45 degrees and have the grenade move in 45 degrees in the other direction. Neither the path of the grenade toward the shield nor leaving the shield is directly in front of the shield but it doesn’t matter.

Light can strike the mirror from basically any direction and its reflection always gets angled the same way but in the opposite direction. A planer mirror like that can basically “see” 180 degrees in all directions on that side of the plane. You just won’t always be in the position to see the reflected light.