In 1963, a 13-year-old student in Tanzania named Erasto Mpemba was making ice cream in cookery class. He noticed something his teacher said was impossible: when he started with hot milk and put it straight into the freezer, it froze faster than the cold milk his classmates were using.
His teacher told him he was confused. But Mpemba kept testing the effect at home, and a few years later, when a physics professor visited his school, he asked the question again. The professor decided to do real experiments - and confirmed it. Sometimes hot water genuinely does freeze faster than cold water.
The effect is now called the Mpemba effect. Even 60 years later, scientists don’t fully agree on why it happens. Possible explanations include: hot water evaporates more, leaving less water to freeze; hot water sets up stronger convection currents that cool more efficiently; or differences in dissolved gases. Probably all of these matter in different conditions. It’s one of the only “kitchen physics” mysteries still unsolved.
