Talk:Mirror image

What causes "mirroring"?

This is not a question we usually ask ourselves, somehow we imagine that the answer is obvious. The mirror causes the mirroring, or at least the reflection does. But it's a rather subtle and elusive problem (at least to me).

First of all, it is clear that that which we call a "mirror image" depends on how we rotate an object toward the mirror. If we turn it around its vertical axis, as we tend to do, we get the "backward" mirror image. But if we instead turn it toward the mirror by rotating it 180 degrees around its horisontal axis, what we see is not a mirror image at all, but one that is upside down. Left is still left, right is right.

Someone told me when I asked them about this that looking through a mirror is like looking from the position of the mirror, at the object. But this is not the case. If I put myself in the place of the mirror, I don't see things mirrored, I see them normally. So there is clearly a difference. But why is it so? After all, if I imagine the light rays that bounce off the reflective surface, it would seem to me as if they behave exactly as if they had continued beyond and "behind" the mirror surface, for an equal distance. But If I had been standing back there, behind the mirror, and the mirror had not been in place, I would not have seen things mirrored, but normally. The reason would seem to be that in that case I would have been rotated 180 degrees (or something like that) compared to when I'm standing in front of the mirror.

Yet another indication that it is our turning the object that inverts the image, and not the mirror, is the fact that the same thing happens with rubber stamps. When you press a rubber stamp against a paper or other surface, there is nothing magical about that surface that mirrors the image. To the contrary, the text of the stamp is transfered to the paper just the way it is. If you then take a look at the text on the stamp, you notice that it is in fact in mirror writing. But that's just because you just turned the stamp 180 degrees toward you! This assumes that you turned it around its vertical axis. If you instead turn it around its horisontal axis, the text will be upside down instead. This seems to indicate that there is no absolute relationship between the mirrored text on the stamp and the unmirrored text of the stamped paper. The relationship is completely dependent on how you turn the stamp toward you.

But these are all questions. I'm still waiting for someone to explain why it is this way.