quantamagazine.orgIn 1992, mathematicians famously proved that seven "riffle shuffles" - the kind where a player splits a deck of cards into two piles, then uses their thumbs to interleave them back together in a zipperlike motion - are enough to mix up the deck. When Dave Bayer and Persi Diaconis came up with this proof, they also revealed something surprising about what happens along the way: At first…