Why Mirrors Flip Left and Right but Not Up and Down Explained

Many people think mirrors flip left and right. They actually do not. A mirror reflects light straight back from front to back.

If you raise your right hand, your reflection seems to raise its left hand. This happens because you imagine turning around to face yourself. During that mental turn, your left and right sides switch.

The mirror does not rotate your image. It simply sends light back in the opposite front-to-back direction. Up stays up, and down stays down because nothing changes along that direction.

An interesting detail is that a mirror reflects every tiny point of light exactly where it comes from. It follows the same simple law of reflection used in cameras, telescopes, and periscopes.

A practical way to test this is to hold up a page with writing. The letters look backward in the mirror, but if you face the page toward the mirror first, the reflection becomes easy to read.

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