illuminating science

As I’ve mentioned several times, in addition to physics I also dabble in magic. (When I first wrote that sentence I had them swapped around! Hmm!) I imagine everyone’s done the good old “three piles of seven” trick? Just in case you haven’t:

• Take 21 cards from a deck
• Deal them face up into three rows of 7
• Ask someone to pick a card, and tell you which pile it’s in. Then pick up the piles, turning them face down, and putting the selected pile in the middle
• Deal them into 3 piles again (alternating piles), and get them to tell you which pile it’s in. Pick up in the same way and redeal.
• When they select their pile this time, the middle card is their card! Either remember it and reveal it appropriately, or pick up the piles in the same way, and the 11th card from either end is their card.

Well, I just watched a video on YouTube with what has got to be the most convoluted card trick ever. Seriously. Assuming it really does work, it would be fun to follow the maths through and explain why! (I haven’t yet, and my head still hurts from following the video through, so someone should feel free to jump in!)

I must confess that although as a kid I liked the mathematical magic tricks, it was more because I enjoyed following the maths through! As a general rule, any time the magician starts doing a vaguely convoluted procedure of counting, knocking out cards and counting again, or anything like that - think maths. I saw a trick the other day which screamed maths to me, and a little time with pencil and paper meant I could reproduce the trick. Sure I needed to know how to do a little bit of set up first, but any half intelligent audience member could follow it through and get to a reasonable approximation. (Maybe his audiences aren’t usually that intelligent - or just tipsy!)