Why does a mirror reverse right to left but not top to bottom?
If you look into a mirror, you “see” an image of yourself facing towards you as if you had stepped forward and turned around. If you actually stepped forward and turned around, your left and right would be reversed, so you see the image as having its right hand across from your left hand and its left hand across from your right hand.
But…you aren’t upside down.
Of course you aren’t. That’s ridiculous!
But what about left and right?
It’s not hard to realize that the left/right shift is an illusion, a false assumption in your mind from our primitive instincts. Looking in the mirror, if you raise your right hand, the image’s “left” hand raises. Obviously, the image is directly across from your right hand and is, in fact, the reflection of your right hand. Nothing has been reversed.
The reason the mind so persistently interprets the image as left/right reversed must be because if you see another person coming towards you, friend or enemy, their right and left are opposite to yours. That is important for you to know, whether you are about to shake hands or engage in combat. Our minds have developed with this assumption for thousands of years.
The question “Why does a mirror reverse right to left but not top to bottom?” has no answer, because it’s based on a false premise. This false premise is that a mirror reverses right to left. It doesn’t. A mirror doesn’t reverse anything. It just reflects what is directly across from it. It’s our minds that interpret (incorrectly) the left/right reversal.
I think it’s important to realize that some questions have no answer. We don’t know the answer, not because we aren’t smart enough, or don’t have enough information, or because someone is lying to us. It’s because there is literally no answer. Any attempt to directly answer the question “Why…” will not answer the question. It isn’t right or wrong, it’s just irrelevant.
These kinds of questions are traps, and they sometimes come up in personal and political relationships. Watch out for them!