How can a mirror see hidden objects?
A mirror isn’t a flat picture, it works like a window into a mirrored copy of the room. Behind the glass there’s a copy of the book and the fox. Straight on, the copied book hides the fox. Step to the side and you look into that room at a new angle, so you can peek past the book, just as you could through a real window.
Straight on, the book is in the way
Stand in front of the mirror and the light from the fox heading toward the mirror hits the back of the book. Where the fox should appear, the mirror only shows the book.
Share this stepThe mirror is a window, not a picture
Think of the mirror as a window into a copy of the room. Behind the glass stands a mirrored book with the fox behind it. What you see depends on where you stand, exactly like looking out of a window.
Share this stepFrom the side, light slips past the book
Take a step to the side and the light from the fox can pass the edge of the book, hit the mirror and bounce off at the same angle straight into your eyes. You’re peeking around the book in the mirrored room.
Share this stepYou can look around things in a mirror, just like through a window.
Step asidenew anglethe fox appears
A photo of a mirror would never show the fox, because the photo has one fixed viewpoint. A real mirror gives everyone their own view, depending on where they stand. That’s why two people can see different things in the same mirror.
Common follow-up questions
How do I try the hidden-object trick?
Stand a book a short distance in front of a mirror, and place a small object on your side of the book, right in front of it. Look straight into the mirror: you only see the book, because it hides the object from the mirror. Now take a step to the side, and the object appears in the mirror, peeking out from behind the book.
Why is my reflection reversed?
It isn’t really flipped left to right. The mirror reverses front and back: the side of you facing the mirror is shown facing you.
Can a mirror see around corners?
Yes, that’s exactly what it does. Shops and roads use convex mirrors at blind corners so you can see what’s coming.
Why do mirrors look silver?
Most mirrors are glass with a thin metal layer behind it, usually silver or aluminum, which reflects almost all colors of light equally.
