Lessons in reversal

by Miriam English


"Time for school, honey"

"Awww, Mum. Can't I just talk with Juno for a bit longer."

"Sorry darling, you have to go to school, besides you learn all kinds of cool stuff don't you?"

"Not with Mister Grunt. He's a moron."

"Rebecca! Don't say that. His name is Mister Grant and he is a very smart man. You kids are lucky to have him guest-speaking for you this week."

"Well he is. Yesterday he was talking about light and he said the dumbest thing!"

"You are so lucky to be learning this stuff at seven years old, Becky. I didn't learn about the physics of light till I was almost twice your age. What did he say that you thought was so dumb?"

"Most of us in class had already talked about this stuff ages beforehand anyway, but when Mister Grant said light reflected in a mirror is laterally reversed, it was so stupid most of us just started laughing."

"Well, what's wrong with that? Isn't that what the textbooks say? It's what I learned in school."

"Don't you see Mum? It's a social statement. It's about the observer. It doesn't say anything about the light."

"Huh? But if I look in a mirror and I raise my right hand, my reflection raises its left hand."

"No. You're making the same mistake as Mister Grant made. There isn't anybody in the mirror. Your statement is about you — what it would look like to you if you could split in two and one of you walked around so you were facing each other."

"I don't see why that's wrong. You'd better not be delaying me to get out of going to class young lady."

"I'm not Mum. You remember Cherkik, my friend from Europa?"

"Yes honey, a very nice, polite kid."

"Well you know how their species live in the water in the ice cracks. They are disk-shaped; tall and long, but not very wide. If they want to turn around in the cracks they have to turn upside down. Their top and bottom are almost identical. They look like those fish... ummm..."

"Angelfish. Yes, I remember dear. Is this going anywhere?"

"What does it look like to them when they look in a mirror?"

"The same I expect. A mirror is a mirror. It just reflects light."

"Yes, but what do they say about the reversal?"

"Well I would have thought just the same we do, but you aren't going to say that are you."

"No. Can't you see Mum? They think the mirror reverses things vertically. It is because of how they think they see someone else in the mirror. In order to be facing them the figure would have to turn upside down in their environment."

"Ah. I see what you mean. But you shouldn't be too hard on Mister Grant. It doesn't really matter if the reversal is left-right or top-bottom, it is still just a simple symmetrical reversal."

"No Mum. You still don't get it. Neither did Mister Grant. It really has nothing to do with symmetry or reversal or even the mirror. The statement is just about us... or in the case of Cherkik's people about them."

"How can you say that, Honey? You can see the reversal right there in front of you."

"Hmmm, that's what Mister Grant said too. Did you know we have some smart clothing in our class?"

"Yes Sweetie. I think it is wonderful they are getting full rights now. It is about time."

"Well we had a couple of smart gloves in there and they just couldn't see why Mister Grant couldn't get it."

"Oh... Oh! I see what you're getting at. When a glove looks in the mirror it doesn't see a reflection of itself. It sees what looks like its other half of the pair. A left glove sees a right glove in the mirror and a right glove sees a left glove. No matter how a glove moves around, turning horizontally or vertically it can't be its reflection."

"You got it Mum... mostly. There is one way a glove can appear in the mirror — by turning inside out. So to intelligent gloves a mirror appears to show an inside-out version."

"Amazing! Did you kids think this all up yourselves, or did you read it somewhere?"

"Nope we realised it while we were chatting before school a few months ago. Cool huh?"

"Very, very cool. You kids are so smart these days. I'm so proud of you. Now off to school missie and get even smarter so you can amaze me even more."

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