Mpemba Effect Confirmed Near Ice Temperature, Reveals Freezer Condition Dependence

The seemingly impossible phenomenon known as the Mpemba effect, where hot water sometimes freezes faster than cold water, continues to challenge our understanding of fundamental physics, and researchers have long sought to explain this counterintuitive observation. Andrei Klimov and Alexei Finkelstein, at the Institute of Protein Research in Russia, alongside their colleagues, now demonstrate that this effect arises not from any unusual thermal properties of water, but from the random nature of ice formation. Their carefully controlled experiments reveal the Mpemba effect only occurs under specific freezer conditions, where the wide range of freezing times allows hot water to occasionally freeze first, despite starting at a higher temperature. This work establishes that the famous paradox is rooted in the stochastic processes typical of phase transitions, offering a new perspective on the Mpemba effect in water and potentially other systems undergoing similar changes of state.

An intuitive statement seems to breach fundamental thermodynamic and kinetic laws; however, numerous experiments with classical and quantum systems demonstrate the paradoxical Mpemba effect, leading to extensive discussions in prominent scientific journals. Despite this, the fundamental physical mechanisms remain elusive. Researchers performed water freezing experiments under carefully controlled conditions and found that the Mpemba effect only occurs when the freezer temperature is very close to the temperature of ice nucleation. In this case, the range of freezing times for both hot and cold water exceeds the delayed cooling of the hotter liquid, and therefore, sometimes the hot water freezes faster.

Hot and Cold Water Freezing Mechanisms

The central theme is the Mpemba effect, the counterintuitive observation that hot water can sometimes freeze faster than cold water. This research delves into the complex physics behind it, exploring related phenomena and proposing mechanisms to explain the observations. The Mpemba effect isn’t a simple, universally reproducible phenomenon; it’s highly dependent on specific conditions such as initial temperature, water purity, container shape, and cooling rate. The research argues against simplistic explanations and identifies several potential contributing factors, including evaporation, where hot water evaporates more quickly, reducing the mass of water to be frozen and potentially enhancing convection.

Temperature gradients drive convection currents, affecting heat transfer, and the removal of dissolved gases alters water’s properties and affects freezing. The degree of supercooling, where water remains liquid below its freezing point, can vary with initial temperature and affect ice nucleation, a crucial process influenced by impurities and dissolved gases. Understanding how antifreeze proteins inhibit ice nucleation can shed light on the factors that promote it.

Chance Explains Faster Freezing of Hot Water

Researchers have revisited the long-standing Mpemba effect and revealed the crucial role of chance in this phenomenon. This new work demonstrates that the effect isn’t a deterministic rule, but rather a probabilistic event governed by the inherent randomness of ice nucleation. The team’s carefully controlled experiments, with precise temperature monitoring, show that the Mpemba effect only occurs within a narrow temperature range, specifically when the freezer temperature is very close to the freezing point of water. They found a wide variation in the time it takes for ice to nucleate, even under identical conditions, typical of first-order phase transitions where the process begins with a single, random event: the formation of the first ice nucleus.

The results indicate that the observed Mpemba effect arises when the ranges of freezing times for both hot and cold water overlap, meaning that, purely by chance, a sample of hot water can sometimes freeze before a cold sample. The team quantified this randomness, demonstrating that the probability of observing the Mpemba effect is linked to the degree of variability in ice nucleation times. This research reframes our understanding of the Mpemba effect as a stochastic effect, driven by chance, that emerges from the inherent unpredictability of ice formation. The team suggests that similar stochastic effects may be at play in other first-order phase transitions, highlighting the importance of considering randomness when studying these processes.

Higher Temperatures Enable Faster Hot Water Freezing

This research clarifies the conditions under which the Mpemba effect, where hot water freezes faster than cold water, can occur. The team demonstrates that the effect is not a universal phenomenon, but rather emerges specifically when the freezer temperature is relatively high, close to the temperature at which ice nucleates. They found that at these temperatures, the range of possible freezing times for both hot and cold water overlaps, meaning the hot water can, by chance, freeze first. The study attributes this to the stochastic nature of ice nucleation, a fundamental process in first-order phase transitions.

Their analysis reveals that the broad range of freezing times at higher freezer temperatures exceeds the expected delay in cooling the initially hotter water, creating the possibility for the Mpemba effect to be observed. Importantly, the researchers acknowledge that at lower freezer temperatures, the variations in freezing times are minimal, and the effect does not occur. This work provides a physical explanation for a long-standing paradox, grounding it in the statistical mechanics of phase transitions, and encourages further investigation into the role of stochasticity in these processes.