If you place warm water and cold water in a freezer, which one will freeze faster? Since water freezes at 0°C, common sense tells us that the cold water should freeze first. However, in reality, the warm water freezes more quickly. This phenomenon is known as the “Mpemba Effect.”
The discovery of this effect began with a question from a teenage boy named Erasto Mpemba in Tanzania. During a lecture at his school, Mpemba asked a visiting physicist about something he had observed years earlier: when making ice cream, he had boiled milk mixed with sugar and put it into the freezer. Surprisingly, it froze faster than his friend’s milk, which had been cooled longer. Everyone laughed at the boy’s question, but the physicist took him seriously and ran experiments—confirming that what Mpemba had observed was indeed true. In 1969, the results were published in a scientific journal.
This phenomenon, which goes against conventional understanding in physics, attracted great interest in the academic community. Even today, many researchers are actively studying it, publishing various hypotheses and papers. Because one scientist paid attention to a young student’s question instead of dismissing it, a valuable and puzzling scientific challenge was discovered—contributing to the progress of science.