Erasto B. Mpemba

Erasto Bartholomeo Mpemba (1950–2023)[note 1] was a Tanzanian game warden who, as a schoolboy, discovered the eponymously named Mpemba effect, a paradoxical phenomenon in which hot water freezes faster than cold water under certain conditions; this effect had been observed previously by Aristotle, Francis Bacon, and René Descartes.

He discovered the phenomenon at Magamba Secondary School in 1963 while preparing ice cream to earn pocket-money.[3] Due to lack of time, he skipped the cooling phase when preparing the ice cream and immediately put it into the freezer; unexpectedly, his milk mixture froze faster than that of his classmates.[2] His physics teacher at the time told him that his observation was clearly not possible.[2] A few years later, the head of Mpemba's school invited British physicist Denis Osborne (1932-2014) from the University of Dar es Salaam to give a guest lecture on his work.[4] At the end of the presentation, Mpemba asked the question that had been bothering him for so long: “If you take two beakers with equal volumes of water, one at 35°C and the other at 100°C, and put them into a refrigerator, the one that started at 100°C freezes first. Why?”[2] Teachers and classmates present thought the claim absurd and mocked Mpemba for the question. Osborne was also caught off guard, but was later able to prove experimentally the correctness of Mpemba's observations.[2][4] In 1969, during Mpemba's studies at the College of African Wildlife Management near Moshi, a paper that he and Osborne had written on the phenomenon was published.[5]

Mpemba later studied in Australia and the USA[6] and became Principal Game Officer for the Tanzanian Ministry of Natural Resources and Tourism and a member of the African Forestry and Wildlife Commission's working party on the management of wildlife and protected areas circa 2002.[7] He has since retired.[8]