Why does hot water sometimes freeze faster than cold water?

The answer

The Mpemba effect - where hot water can freeze faster than cold water under certain conditions - was named after Erasto Mpemba, a Tanzanian student who observed it while making ice cream in 1963. Despite centuries of anecdotal evidence dating back to Aristotle, a complete physical explanation remains elusive. Proposed mechanisms include evaporation reducing the hot water's mass, dissolved gas differences affecting heat transfer, supercooling variations, and convection current differences. In 2020, researchers at Simon Fraser University proposed that the effect arises from specific initial conditions in the energy distribution of water molecules, not average temperature alone. A 2017 paper in Nature Communications suggested exponential distribution of heating histories explains the anomaly. The Royal Society of Chemistry held a competition in 2012 to explain the effect, receiving over 22,000 entries but finding no definitive answer.