Jay Lake (jaylake) wrote,
Jay Lake

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[child] The true nature of magic

This past weekend the_child wanted to rent and watch Twitches imdb ]. As always, I watched it with her the first time through.

She likes to mess around with DVD extras. If there's a "making of" disc, she'll often watch that first, and spend more time with that than the actual movie. DVDs are a highly immersive experience for this kid.

The Twitches release we rented has one of those little DVD games you sometimes find. It supposedly tells your fortune, by making you select a secret number, asking you some leading questions, then identifying the secret number you picked and giving you a prediction associated with that number.

the_child was quite astonished her first time through this, and demanded to know how they did that. She was amazed by the magic trick the DVD had pulled on her.

We went through it carefully together, and I helped her analyze it. Here's the algorithm involved:

  • Pick a number between 1 and 55

  • If it's a two digit number, add the digits together

  • If it's a one digit number, simply use the number itself

  • Subtract your second, calculated value from the original number

The solution set falls within the series {0,9,18,27,36,45}. ie, a zero or a multiple of nine. I don't know the name of this function, but it's kind of cute. The leading questions were nothing but smokescreens ("What flavor of ice cream do you like best?") to obscure the math going on in the fortune telling process.

When the game reached its culmination, it presented a screen of numbers from 0 to 55, with a mix of symbols. The solution set always has the same symbol next to each member of the set. All the other symbols are there, again, as a smokescreen. It told her to note the symbol next to her number, then presented it on a following screen along with a generic prediction ("You will soon meet a person with a dog," that sort of thing).

Once the_child understood that this was how the DVD "knew" what number she'd guessed, she was disappointed. "I thought it was real magic," she told me.

I explained that everything that looks like magic has an explanation, and the "real magic" is in knowing how the trick was done. She decided this was pretty cool, after all.

I do believe I'm raising a thoughtful skeptic.
Tags: child, funny
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