The ice cream that Erasto Mpemba made when he was a teenager in 1963 showed that a hot liquid can freeze faster than a cold liquid – throwing chaos into the world of physics for decades. After all, it was really a matter of… chaos.
The homemade ice cream was a popular dessert when Erasto Mpemba He was a student at Magamba Secondary School in Tanzania.
But no one hoped that the ice cream made by the Tanzanian student in 1963 would throw waves of shock into the world of physics – which spread to this day, recalls.
Reason: The method that MPEMBA used to make your homemade ice cream showed that a Hot liquid can freeze faster than a cold liquid.
“The school boys make it boil milk, mixing it with sugar and placing it in the freezer From the refrigerator, after having cooled almost at room temperature, ”wrote the Tanzanian in a published in the school newspaper in 1969.
But, says the then student, the Competition for the freezer space It was intense. One afternoon, MPEMBA and another boy followed two different paths while playing him.
Or mpemba colleague Mixed the milk with sugar and laid it directly on an ice board, without boiling it. In order not to be exceeded, MPEMBA boiled your milk – But it jumped the step to let it cool, to be able to catch the last ice board.
“An hour and a half later, my milk tray had turned into ice cream, while His was still just a thick liquid“Wrote MPEMBA.
A few years later, the student asked his science teacher why this happened – Because hot milk froze faster than cold milk, Contrary to Newton’s Law.
According to this law of the famous British physicist, the cooling rate of an object is proportional to the difference between the temperatures of the object and the environment.
At the time, the teacher’s ironic response was exhaustive: “All I can say is that this is MPEMBA PHYSICS AND NOT UNIVERSAL PHYSICS“.
The incident became a joke in the classroom. Whenever MPEMBA was mistaken in a math problem, the teacher and his colleagues called him “A MPEMBA Mathematics“.
One day, when the physical Denis Osborne He visited his secondary school, Mpemba also asked him to explain about the bizarre phenomenon. Intrigued, Osborne invited him to visit what is currently the University of Giving Es Salaam and discussing the most deep issue.
Osborne Is They then dedicated themselves to studying the mysterious behavior of ice cream and other liquids, and published one on the subject in the magazine Physics Education.
(dr) Ben Gurr / The Times
Erasto Mpemba E Denis Osborne
A known effect
In fact, the counter-intricate behavior of MPEMBA ice cream is a known phenomenon since antiquity, and it was, according to Aristotle“Of general knowledge”.
“Water previously heated cools faster. Many people, when they want to quickly cool hot water, start by putting it in the sun“The Greek philosopher about 340 BC.
Also the English philosopher and politician Francis Bacon knew this effect of thermodynamics: “water is a small amount of warm-up easily, which is completely cold“, In his work A new organof 1620. That is, “slightly warm water freezes more easily than completely cold water.”
Descartes was equally aware of the phenomenon: “water that was kept to the heat for a long time freezes faster than other waters,” the French philosopher, scientist and mathematician in his Speech about the method.
Despite the apparent knowledge that existed about this strange behavior of liquids, the article by Mpemba and Osborne launched decades of controversy in the world of physicssince it challenged a fundamental theory about the behavior of matter.
For years, numerous researchers have tried to recreate the results of Mpemba and Osborne, with a limited success.
In 2016, the physical Henry Burridgefrom the Imperial College of London, and the mathematician Paul Lindenfrom the University of Cambridge, published a study that had tried to confirm the phenomenon, reporting “sadly” that could not find any proof of the MPEMBA effect.
Worse, they concluded, all these studies – including the original MPEMBA experience – could have been easily distorted by small factors Experimental, such as the configuration of the isolation of the equipment or the placement of thermometers.
Cooling and chaos
From 2017, a new series of studies eventually confirmed the observation of MPEMBA, suggesting that the explanation lies in mysterious mechanics of chaos “And that water may have been a major obstacle to proving the widest theory.”
Water behaves differently of most other substances, especially when it changes statebetween solid, liquid and gaseous, so scientists who studied the MPEMBA effect sought to completely eliminate water from the equation.
In an abstract experience, the American physicist John Bechhoefer and their colleagues warmed microscopic glass spheres (designed to replace the water molecules) with lasers and observed the cooling speed.
Found that not only some Warm spheres cooled faster than their cold homologous, as they sometimes did exponentially faster.
“The simplicity of the study is part of its beauty,” said Bulgara theoretical physics Mary Vucelj to. “It’s one of these very simple settings and is already rich enough to show this effect.”
Shortly thereafter, another group of physicists published one that suggested a more abstract structure to understand the MPEMBA effectwhich involved the modeling of Random dynamics of particles.
The results of these studies suggest that the key to the mystery of MPEMBA is a dose of chaos: A liquid that moves quickly from hot to cold is “out of balance”, which means that It is a system that does not follow the rules Linear that we (or Newton) could expect them to follow.
Science News compares the cooling of a hot liquid under the MPEMBA effect with “the way a walker can reach a destination faster Starting furtherif this starting point allows you to avoid an arduous climb of a mountain. ”
Suggests it in turn that it is a bit like someone who uses Trampolines to cross a river: “If you have the right initial energy, you can jump directly from the first to the third without ever landing in the second” – that is, since a hot liquid is more unbalanced than a cold liquid, it can have the right energy to jump over the stones.
It is known that Chaos plays an important role in physics, mathematics and even human geography. The explanations found for the MPEMBA effect show us that it also intervenes in the technique of making a simple homemade ice cream.
