When one looks into a mirror, one see an image of himself....

When raising one's right hand, the image raises its left. When raising one's left, the image raises its right.

So, why is it that the mirror reverses left and right, but not top and bottom? Why does a mirror appear to invert the left-right directions, but not up-down?

The guy in the mirror is holding up the hand on the same side of the mirror as I am, on my right. If I was to stand in his position and do the same thing, I would be raising my left hand, but to do so, I first have to turn around.

On the other hand (npi), to say that I am looking up when the other guy is looking up is also true. Up and down are defined in the same way no matter which way you turn around.

We think the mirror reverses right and left because those directions are relative to our bodies, and change as we move around. Up and down are also relative, I suppose, but relative to the earth (in general), and is not dependent on whether you are looking at the mirror or inside it.

Here is another interesting discussion of the same topic ..

Posted by DJ on 2004-01-29 15:40:43