If you put both warm water and cold water in the freezer, which do you think will freeze first? Since water freezes at 0°C, we naturally assume that cold water should freeze faster. But surprisingly, warm water freeze more quickly. This counterintuitive phenomenon is known as the Mpemba effect.
It all started with a question from a teenage boy in Tanzania named Erasto Mpemba. When a physicist visited his school for a lecture, Mpemba asked about something he had observed years earlier. While making ice cream, he had boiled milk mixed with sugar and placed it in the freezer—only to find that it froze faster than his friend’s milk, which had been cooler to begin with. Although others laughed at him, the physicist took his question seriously. He conducted experiments and confirmed the surprising result. In 1969, the findings were published in a scientific journal.
Because this phenomenon defies the basic assumptions of physics, it has attracted considerable interest from researchers. To this day, scientists are still exploring the Mpemba effect, offering new hypotheses and publishing their findings. One boy’s bold question—and one scientist’s open mind—led to the discovery of a scientific mystery that continues to challenge our understanding and expand the frontiers of science.
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