Why does a mirror reflect an image with only left/right reversal, but not top/bottom reversal or any other reversal?
Jim Barnard, Bolton UK
- Left and right are the only directions which are described relative to the observer. Up and down (and north, south etc) are independent of whichever way you're facing. When you look in the mirror, up, down, east and west are still in the same place. But you read printed text from left to right - not east to west - hence the problem with 'mirror writing'.
Benet, London
- The mirror does not reverse images from left to right, it reverses them from front to back relative to the front of the mirror. Stand facing a mirror. Point to one side. You and your mirror image are pointing in the same direction. Point to the front. Your mirror image is pointing in the opposite direction to you. Point upwards. You both point in the same direction. Now stand sideways on to the mirror and repeat. You are now pointing in opposite directions when you point sideways. Place the mirror on the floor and stand on it. This time you point in opposite directions when you point upwards and your upside down image points downwards. In all cases the direction reverses only when you point towards or away from the mirror. The answer stems from the fact that a reflection is not the same as a rotation. Our bodies have a strong left-right symmetry, and we try to interpret the reflection as a rotation about a central vertical axis. We imagine the world in front of the mirror has been rotated through 180¡ about the mirror's vertical axis, and it has arrived behind the mirror where we see the image. Such a rotation would put the head and feet where we expect them, but leaves the left and right sides of the body on opposite sides to where they appear in the reflection. But if instead we imagine the world to have been rotated about a horizontal axis running across the mirror, this would leave you standing on your head, but would keep the left and right sides of your body in the expected positions. The image would then appear top/bottom inverted, but not left-right. So whether you see the image as left-right inverted or top-bottom inverted, or for that matter inverted about any other axis, depends upon which axis you unconsciously (and erroneously) imagine the world has been rotated about. If you lie on the floor in front of a mirror you can observe both effects at once. The room appears left-right reflected about its vertical axis, while you interpret your body as being left-right reflected about a horizontal axis running from head to foot.
matthew payne, london
- You must have some strange mirrors. My mirrors don't reverse anything, each section of mirror simply reflects what is directly in front of it. Hence whatever is on my right as I look into the mirror will be on the right in the mirror. Nothing's been reversed it's just a reflection, that's all.
Seth, Edinburgh UK
- actually it does. Follow these steps, spread your arms horizontally in front of a mirror. now bend your body 90 degrees from your waist so that left hand touches ground & right hand indicates the sky. Now observe in the mirror, your image is touching the ground with right hand.the image is reversing vertically also.
prashant, bhopal india
- A New Approach to an Old Problem
MikeO, San Diego USA
- You guys are making it too complicated. The text reverses left-to-right because when you turn the paper towards the mirror, YOU'VE reversed the writing left-to-right. Then you just see a mirror image of it. Try writing on a transparency, and hold it up so you can read it correctly. Then hold it in front of the mirror. NO REVERSAL.
Alan P, Hudson, OH US
- It is an enigma that just occurred to me in depth. It is a mirror image or what you see if you were looking from the mirror but still gazing forward. No, wait. If you look at a mountain in a lake it is upsidedown. But not left to right. The image depends on the plane of the reflec tive surface as to what we see from where we are. It is something one could puzzle over for many hours. Kinda like an Escher picture with its impossible planes or a Moebus strip, one sided piece of paper puzzle. Impossible, yet there it is, in the flesh before you. Or is it behind you. Hang on. Which way am I facing here, I mean there.
Kerry, Sonoma, USA
