The Mpemba effect: Anomalous thermal relaxation from Aristotle to colloids and beyond

Datum

20.10.2025

Zeit

16:30 - 17:30

Sprecher

Prof. John Bechhoefer

Zugehörigkeit

Simon Fraser University

Serie

MPI-PKS Kolloquium

Sprache

en

Hauptthema

Physik

Andere Themen

Physik

Beschreibung

Naively, an object that is hot should take longer to cool than when it is warm. Yet, some 2300 years ago, Aristotle remarked that “to cool hot water quickly, begin by putting it in the sun.” In the 1960s, Tanzanian teenager Erasto Mpemba similarly found that hot water can freeze more quickly than cold water, but such experiments have been hard to reproduce. Recently, we have observed this Mpemba effect in a more controlled setting, the thermal quench of a colloidal system immersed in water, which serves as a heat bath. The results are reproducible and agree quantitatively with calculations based on a recently proposed theoretical framework. Under the right conditions, we even find an exponential speed-up of cooling. Surprisingly, we also find that heating can be anomalous, the first observations of an inverse Mpemba effect. Our experiments give a physical picture of the generic conditions needed to accelerate relaxation to thermal equilibrium. The idea that the Mpemba effect is a prototype for a wide range of anomalous relaxation phenomena has inspired an enormous amount of current research and may have significant technological application.

Letztmalig verändert: 20.10.2025, 07:37:41