Treebeard's Stumper 24 October 2003

Looking-glass World

Ordinary things can be remarkable! Look at yourself in a mirror, like the beginning of Alice's second adventure: "That's just the same... only things go the other way." Sure, it's a mirror image. If I raise my right arm, my mirror-twin raises his left arm. But he's not upside-down. Why do ordinary mirrors reverse left and right but not up and down? Mirrors are the same on all sides, but rotating a mirror does not rotate the image. Why is there a preference for left and right? There's nothing hidden in a mirror. Can you explain what we see?

I took the photo on the left shooting straight into our bathroom mirror. I was holding the camera with my right hand up to my right eye and the word "mirror" on the card is normal. But the photo shows my mirror-twin in the looking-glass world where "things go the other way". He is holding his camera in his left hand, and the card looks very different, and he definitely has less hair than me!

The mirror-image photo above-right is what you would see standing "behind the mirror" and looking right at me as I took the picture. Right is now right, left is left, and you can read the sign. Remember the famous mirror scene in the Marx Brothers' Duck Soup? This is the photo that Harpo (in the "mirror" on the right) would take of Groucho on the left. (There is a 21 MB QuickTime movie file here.)

Here are more looking-glass stumpers:

• What looking-glass words and numbers could I write on my sign that would look the same in both photos?
• How should I focus my camera when shooting photos in a mirror?
• What if you stand on your head or stand on the mirror?
• Can you make a "true mirror" that shows you as others see you? Can you photograph the image?
• Is there any reason other than local convention to prefer driving on the left or right?
• If everything in the universe suddenly switched to its mirror-image, could we tell that something had changed?
• Why do photographers (and people applying cosmetics) open their mouths like this?!

Answer

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