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Why does the bowl of a spoon turn my reflection upside down?

Dear Cecil:

It's 2:30 AM. It's Friday morning. There's a bluesy tune on KNON. And I'm finally making the big move. Why does my reflection turn upside down in my entire stock of spoons? I have a feeling you're the man with the straight dope.

Monica, Dallas

Cecil replies:

Nice opening, Monica; somewhat disorienting segue. But if you want to talk about spoons, fine, we’ll talk about spoons. Much as I appreciate the thought, it wasn’t necessary for you to enclose a sample spoon. I too have spoons. They all work the same way — the bowl acts as a “parabolic reflector.” (It’s not a perfect parabola, and it’s not a perfect reflection, either.) Light coming from above is reflected down, light coming from below is reflected up, and the result is an inverted image. We thus have a remarkable thing: a mirror that, in contrast to standard mirrors, reverses up and down but not left and right.

The business of curved reflecting surfaces is fascinating, and not just to people in the fun-house mirror business. I’m told that somebody has designed a mirror that uses a complex combination of concave and convex surfaces (although presumably still basically spoonlike) to produce a “right-reading” image — a mirror, in other words, that shows us not a “mirror image” of ourselves, but rather the appearance we present to the rest of the world. Remember that famous poem by Robert Burns? “O wad some Power the giftie gie us / To see oursels as ithers see us!” Were Burns still around today, we’d have an answer for him: Here, Bob, have a spoon.

Cecil Adams

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