Jun 30, 2022 11:47 PM
https://www.quantamagazine.org/does-hot-...-20220629/
EXCERPTS: It sounds like one of the easiest experiments possible: Take two cups of water, one hot, one cold. Place both in a freezer and note which one freezes first. Common sense suggests that the colder water will. But luminaries including Aristotle, Rene Descartes and Sir Francis Bacon have all observed that hot water may actually cool more quickly. Likewise, plumbers report hot water pipes bursting in subzero weather while cold ones remain intact. Yet for more than half a century, physicists have been arguing about whether something like this really occurs.
The modern term for hot water freezing faster than cold water is the Mpemba effect, named after Erasto Mpemba, a Tanzanian teenager who, along with the physicist Denis Osborne, conducted the first systematic, scientific studies of it in the 1960s. While they were able to observe the effect, follow-up experiments have failed to consistently replicate that result. Precision experiments to investigate freezing can be influenced by many subtle details, and researchers often have trouble determining if they have accounted for all confounding variables.
Over the past few years, as the controversy continues about whether the Mpemba effect occurs in water, the phenomenon has been spotted in other substances — crystalline polymers, icelike solids called clathrate hydrates, and manganite minerals cooling in a magnetic field. These new directions are helping researchers peek into the complicated dynamics of systems that are out of thermodynamic equilibrium. A contingent of physicists modeling out-of-equilibrium systems has predicted the Mpemba effect should occur in a wide variety of materials (along with its inverse, in which a cold substance heats up faster than a warm one). Recent experiments appear to confirm these ideas.
Yet the most familiar substance of all, water, is proving to be the slipperiest. “A glass of water stuck in a freezer seems simple,” said John Bechhoefer, a physicist at Simon Fraser University in Canada whose recent experiments are the most solid observations of the Mpemba effect to date. “But it’s actually not so simple once you start thinking about it.”
[...] Over the decades, scientists have offered a wide variety of theoretical explanations to explain the Mpemba effect. ... Those explanations all assume that the effect is real — that hot water really does freeze faster than cold. But not everyone is convinced... (MORE - missing details)
EXCERPTS: It sounds like one of the easiest experiments possible: Take two cups of water, one hot, one cold. Place both in a freezer and note which one freezes first. Common sense suggests that the colder water will. But luminaries including Aristotle, Rene Descartes and Sir Francis Bacon have all observed that hot water may actually cool more quickly. Likewise, plumbers report hot water pipes bursting in subzero weather while cold ones remain intact. Yet for more than half a century, physicists have been arguing about whether something like this really occurs.
The modern term for hot water freezing faster than cold water is the Mpemba effect, named after Erasto Mpemba, a Tanzanian teenager who, along with the physicist Denis Osborne, conducted the first systematic, scientific studies of it in the 1960s. While they were able to observe the effect, follow-up experiments have failed to consistently replicate that result. Precision experiments to investigate freezing can be influenced by many subtle details, and researchers often have trouble determining if they have accounted for all confounding variables.
Over the past few years, as the controversy continues about whether the Mpemba effect occurs in water, the phenomenon has been spotted in other substances — crystalline polymers, icelike solids called clathrate hydrates, and manganite minerals cooling in a magnetic field. These new directions are helping researchers peek into the complicated dynamics of systems that are out of thermodynamic equilibrium. A contingent of physicists modeling out-of-equilibrium systems has predicted the Mpemba effect should occur in a wide variety of materials (along with its inverse, in which a cold substance heats up faster than a warm one). Recent experiments appear to confirm these ideas.
Yet the most familiar substance of all, water, is proving to be the slipperiest. “A glass of water stuck in a freezer seems simple,” said John Bechhoefer, a physicist at Simon Fraser University in Canada whose recent experiments are the most solid observations of the Mpemba effect to date. “But it’s actually not so simple once you start thinking about it.”
[...] Over the decades, scientists have offered a wide variety of theoretical explanations to explain the Mpemba effect. ... Those explanations all assume that the effect is real — that hot water really does freeze faster than cold. But not everyone is convinced... (MORE - missing details)