Is hot water freezing faster than cold? Scientists finally solve the 2,000-year-old physics puzzle

The counterintuitive physical phenomena have plagued scientists for thousands of years and may eventually reach their mathematical match. Researchers at Kyoto University have developed a universal framework to explain the mysterious MPEMBA effect—and under the same conditions, thermal systems are sometimes faster than cold ones.

Aristotle first observed two thousand years ago that later rediscovered this particular heat behavior while making ice cream in cooking classes at Tanzanian student Erasto Mpemba, which has not been consistently explained despite decades of research.

The challenge is one of the measurements – how do you prove certainly that something will be “faster” when the concept of “faster” depends on your measurement technique?

“Our study demonstrates that the use of thermotumors is equivalent to taking into account all monotonic measures at the same time,” explained Tan Fan Wo, corresponding author of Kyoto University, whose team’s findings were published in a physical review letter on March 10.

This mathematical breakthrough provides the first general criterion for determining when the mpemba effect actually occurs, thus removing the ambiguity that plagued previous studies. Until now, researchers have to choose specific methods to measure cooling rates, resulting in inconsistent results – using one measure when using another seems to be the MPEMBA effect that may disappear.

This phenomenon was scientifically identified in 1963, when Mpemba noticed that hot ice cream mixes freeze faster than cold mixes. He collaborated with British physicist Denis Osborne to document this behavior, triggering decades of scientific research. Although initially observed in water, the researchers have since found effects in various systems including microscopic systems.

What is particularly important for the work of Kyoto researchers is their application to thermotumor theory – a mathematical framework that unifies different measurement methods. By adopting this view, they set a strict basis for evaluating the rate of thermal relaxation effective in all possible measurement techniques.

Perhaps most surprisingly, their work shows that this effect is not limited to a specific temperature range previously thought.

“This surprising result suggests that the MPEMBA effect reflects a more general underlying mechanism than previously thought,” VU noted in the study announcement.

From a practical point of view, understanding this phenomenon may lead to improvements in cooling technology and thermal engines. This study may also have an impact on quantum computing and biophysics, where thermal relaxation plays an important role.

Although this work represents a significant theoretical advancement, problems remain. The researchers noted that determining the “minimum time scale for the MPEMBA effect that may occur in thermotumors” is a crucial next step to establish a basic restrictive system, i.e. how the system can quickly relax to balance.

For those who debate every day whether hot water is actually frozen on ice cube trays, research provides mathematical verification that, in some cases, seems not only impossible, but predictable. Sometimes in physics, like in life, the faster the counterintuitive path is.