Yes, you read that right. It seems impossible unless you grew up in a very cold climate. The story of the theory of freezing is an example of science marching backwards, of a case when folklore was correct instead of establishment science.

The fact that hot water freezes faster than cold has been known for many centuries.  The earliest reference to this phenomenon dates back to Aristotle in 300 B.C.  The phenomenon was later discussed in the medieval era, as European physicists struggled to come up with a theory of heat.  But by the 20th century the phenomenon was only known as common folklore, until it was reintroduced to the scientific community in 1969 by Mpemba, a Tanzanian high school student.  Since then, numerous experiments have confirmed the existence of the “Mpemba effect”, but have not settled on any single explanation.

Later, in the 1600’s, it was apparently common knowledge that hot water would freeze faster than cold.  In 1620 [Francis] Bacon wrote “Water slightly warm is more easily frozen than quite cold” [2], while a little later Descartes claimed “Experience shows that water that has been kept for a long time on the fire freezes sooner than other water” [3].

In time, a modern theory of heat was developed, and the earlier observations of Aristotle, Marliani, and others were forgotten, perhaps because they seemed so contradictory to modern concepts of heat.  However, it was still known as folklore among many non-scientists in Canada [11], England [15-21], the food processing industry [23], and elsewhere.

It was not reintroduced to the scientific community until 1969, 500 years after Marliani’s experiment, and more than two millennia after Aristotle’s “Meteorologica I” [1].  The story of its rediscovery by a Tanzanian high school student named Mpemba is written up in the New Scientist [4].  The story provides a dramatic parable cautioning scientists and teachers against dismissing the observations of non-scientists and against making quick judgements about what is impossible.

If you’re still skeptical that warm water can freeze faster than cold water under some conditions, hear this logic and tremble with misgivings.

Remember that a mole of water has ~10²³ particles moving in 3 dimensions, i.e. the full mathematical description has ~10²⁴  parameters for 3-position and 3-momentum of each particle.  If you treat Temperature as uniform, that’s just one parameters — not the whole story. Ice is a crystal structure so if the heat allows the molecules to bump into place, they could solidify faster than slow-moving molecules.

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  1. isomorphismes posted this