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

Date

Oct 20, 2025

Time

4:30 PM - 5:30 PM

Speaker

Prof. John Bechhoefer

Affiliation

Simon Fraser University

Series

MPI-PKS Kolloquium

Language

en

Main Topic

Physik

Other Topics

Physik

Description

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.

Last modified: Oct 8, 2025, 7:37:45 AM