The Number Illusion You Won’t Believe

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Sometimes math is so beautifully tricky, and presented in such a subtle way, that it’s virtually indistinguishable from magic. Welcome to The Kruskal Count.

David Copperfield is probably the most famous living magician/illusionist, and he’s made use of the Kruskal Count to convince millions of people worldwide that he harbors amazing predictive powers. Does he? Well… yes and no.

At the core of his mathematical mind reading is physicist Martin Kruskal’s discovery that certain counting games are really a sequence of chains that can intersect and eventually become one single chain. Using that knowledge of well-concealed probability, it’s easy to perform a mind-blowing demonstration that appears to be pure magic.

But it doesn’t *always* work, because that’s the way probability goes. Sometimes it’s perfect, sometimes it isn’t. By examining the Kruskal Count as a magic trick and also through its original card-based format, we’ll see that magic can be math… and math can be magic.

Play “The Kruskal Count Card Trick” simulator by Alex Frieden and Ravi Montenegro: http://faculty.uml.edu/rmontenegro/research/kruskal_count/kruskal.html

*** SOURCES ***

David Copperfield Vacation Destination Trick: https://youtu.be/RZmS_BTwPEU

“The Kruskal Count,” Lavarius, Rains, Vanderbei, October 2001. https://arxiv.org/pdf/math/0110143.pdf

Mathematical Card Tricks: “It’s probably magic,” American Mathematical Society: http://www.ams.org/publicoutreach/feature-column/fcarc-mulcahy6

“How Long Does It Take To Catch A Wild Kangaroo?” by Ravi Montenegro and Prasad Tetali:
https://arxiv.org/pdf/0812.0789.pdf

“Monte Carlo Methods for Index Computation,” by J.M. Pollard: https://www.jstor.org/stable/2006496?origin=crossref&seq=1

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