For centuries, observant scientists from Aristotle to Descartes have harbored a suspicion that — contrary to all conventional wisdom — hot water can somehow freeze faster than cold water. But there was no scientific consensus that this conjecture was actually true.
In 1963, a Tanzanian physics student named Erasto B. Mpemba (pronounced em-pem-ba) rekindled the idea via a fluke accident that occurred when he was making ice cream at his school. He seemed to prove what Aristotle and Descartes had suspected: Hot water reaches a freezing point faster than cold water does. He wrote about his observations in a 1969 paper, titled simply "Cool?" which gave rise to the term "Mpemba effect." But was Erasto Mpemba correct? Does hot water really freeze faster than cold water?