Riddle/puzzle

[armb]

There is some writing on the back of my car. It isn't symmetrical. A passing pedestrian looks at it and it reads normally. A passing driver looks at it in their mirror and sees the single reflected writing reversed. I look at it in my mirror, and the singly reflected writing reads normally. Why?

Comments

[rdmaughan.livejournal.com]

It is written on your rear window.

The pedestrian reads it directly
The motorist read it reversed once
You read it reversed twice and so back to the right way around.

[armb.livejournal.com]

Yes. (Using the same wires as the demister.)

[ffutures.livejournal.com]

It's a transfer on your rear window. You see the reversed writing when you look at it, since you're inside the car, so a reflection will be unreversed. Anyone looking straigt at it from outside sees it the right way round, or mirror reversed if they're seeing it in a mirror.

[zanda-myrande.livejournal.com]

Very chuffed I actually got this before reading the answer...

[(Anonymous)]

Gosh, you folks are so smart!

Why does the motorist see the writing reversed left-to-right and not top-to-bottom?

[armb.livejournal.com]

Actually when I first noticed this (while adjusting my mirror) I thought it was a good demonstation of the fact that mirrors don't really reverse left to right, they reverse front to back. We think of them as reversing left to right because we are superficially symmetrical left to right, and used to turning around on our feet and not used to doing headstands. So, when we see ourselves in a mirror, at first glance it looks like we could turn ourselves to that position by turning around. Looking more closely, we see that wouldn't work, because left and right end up in the wrong places. the mirror hasn't swapped left and right, our "if I turned around" has.
If you turn a book to face a mirror, it reads backwards because you turned it that way - if you turn about a horizontal axis instead (the top moving away from you, the bottom towards you), it reads upside down instead. But we don't normally turn books that way, because if you want someone else to read it, they have to turn upside down. But they are reading it facing the opposite direction to you looking at the mirror.
If you write on glass, you can hold it up to a mirror without turning it, and then you can read the original and reflection facing the same way. If you cut out letters from card and colour them on one side and stick them on glass, you can see that it reads the same way, but you see the other side.
Another way to think about it is to imagine standing in front of a mirror facing north. Your left hand is west, your right hand is east. Imagine putting a glove on your left hand and waving it. The reflection waves its gloved west hand too, so left and right aren't reversed, but it is facing south, so front and back are. (You can even try it for real - the glove helps break the "superficially symmetrical" bit of the appearance, so you think of the "left gloved hand" being on the same side of the reflection, rather than "the hand which would be my left hand if I turned round to face that way".)