Why does the mirror image turn back from left to right, but not upside down?

You may immediately answer that this is the principle of light reflection. But that is not enough.

Stand in front of a mirror and you will see this immediately. The text on your T-shirt in the mirror is reverse. The turn of the part of your hair also moves to the other side. The mole on the left ear you are seeing is on the right side . In front of you is the image of yourself being inverted: what ever was on the left now on the right and vice versa. But what's above is still above, still below - as if the mirror moved left and right, but didn't turn from top to bottom.

Of course, the mirror does not "know " anything about your posture; it simply reflects light on it. So why does that reflected light come to the light sensor in your eyes, does the image in your mirror only reverse from left to right?

According to Gizmodo, the short answer is not reversed. In fact, the question of what makes the horizontal axis so special in the context of the mirror itself is flawed. That's because a mirror does not reverse the image from left to right or from top to bottom, but from front to back. In other words, the image in your mirror is not swapped but reversed in the third dimension , like a glove being turned inside out.

Your image has been reversed by the axis perpendicular to the mirror.

This is a thinking experiment to help illustrate the concept of reverse to backwards . Suppose, for a moment, you can straighten your body. Imagine that, your body can go through itself without damaging any other tissue of the body. When you stand in front of a mirror and press the tip of your nose into the mirror, it's easy to deduce that the image you see is looking back at you is your result (without a mirror) turning 180 degrees and stepping backwards, going through mirror, into the " territory" of the mirror. But this is not the case we are talking about.

In fact, the back half of your "no mirror" has been flattened in the direction of the mirror. When your shape starts flat like a pancake, the front half of your body (meaning all parts of your body are behind your nose, but still in front of the back half of your body), The back half of your body and the tip of your nose are all in the same plane (ie the plane is occupied by the mirror). But then your second half continues to push, continue the journey through the plane of the mirror and go straight through the front half of the body before regaining the "normal" shape on the other side of the mirror. This new, you are opposite symmetrically to you, but the two of you and your body in the mirror don't overlap. In chemistry, such entities are called "chiral" (asymmetric).

Here is another way to think about it, widely spread by physicist Richard Feynman (Massachusetts Institute of Technology): Stand in front of a mirror, and pay attention to the direction you're facing. For testing, let's say you're facing the north. Your right hand is pointing east and your reflection is also east. Likewise, pointing your left hand to the west indicates your reflexes in the same direction. That's because these directions are all along the plane parallel to the mirror. Similarly, just up or down and your reflexes will follow, moving in the same direction.

But deviating from that parallel plane even a little bit, things started shaking. Remember: your image has been reversed in a direction perpendicular to the mirror. Try pointing directly into the mirror, so that your finger is now directed to the north. Your reflection now points directly to you - not North, like your finger - but South.