Indian Simulation Explains the Mpemba Effect — Why Hot Water Can Freeze Faster
Indian researchers have created the first supercomputer-based simulation that successfully reproduces the Mpemba effect, offering clarity on a puzzle that has intrigued scientists for centuries — situations in which hot water freezes sooner than cold water.
The Mpemba effect describes this counter-intuitive outcome under particular conditions of cooling and evaporation. It is named after Erasto Mpemba, a Tanzanian student who documented the observation scientifically in 1969, though thinkers such as Aristotle, Francis Bacon and René Descartes had recorded similar ideas much earlier.
The phenomenon forgotten over time was rediscovered in the last century by Erasto Mpemba after whom it is now named. Since then, there has been considerable interest in understanding it and identifying whether the effect is specific only to phase transitions in water. Even though it is recently shown that the effect appears during phase transitions in several other systems, the understanding remains largely elusive. Furthermore, quite interestingly, the case of water has recently become controversial, even at the experimental level. Due to the demanding nature of water simulations, there exists no computational study to resolve the debate.
Researchers from Jawaharlal Nehru Centre for Advanced Scientific Research (JNCASR), an autonomous institute of the Department of Science and Technology (DST) has used supercomputers to develop the first simulation of ice formation proving the Mpemba effect of water and also demonstrating that it can appear during fluid-to-solid transitions in systems other than water.
They have explained that when water cools, it can get stuck in intermediate states of short-lived molecular arrangements before true ice begins to grow. Different starting temperatures get stuck for varied lengths of time.
Hotter water can sometimes “choose” a quicker path to nucleation, the birth of ice, bypassing the delays that colder water suffers.
The best explanation yet of why “hot can freeze faster than cold” is one major step into the world of nonequilibrium physics.