Fluctuations in an aging system: absence of effective temperature in the sol-gel transition of a quenched gelatin sample

TL;DR

This study investigates fluctuations in a quenched gelatin system and finds no evidence of an effective temperature, highlighting the importance of careful data analysis in aging, non-ergodic systems.

Contribution

The paper demonstrates that, contrary to previous reports, no effective temperature emerges during gelatin's sol-gel transition, emphasizing the need for rigorous analysis in non-ergodic systems.

Findings

No anomalous fluctuations observed in particle position

Fluctuations exhibit equilibrium-like properties

Careful analysis rules out artifacts like drift or mixing

Abstract

We study the fluctuations of a Brownian micro particle trapped with optical tweezers in a gelatin solution undergoing a fast local temperature quench below the sol-gel transition. Contrary to what was previously reported, we observe no anomalous fluctuations in the particle's position that could be interpreted in terms of an effective temperature. A careful analysis with ensemble averages shows only equilibrium-like properties for the fluctuations, even though the system is clearly aging. We also provide a detailed discussion on possible artifacts that could have been interpreted as an effective temperature, such as the presence of a drift or a mixing in time and ensemble averages in data analysis. These considerations are of general interest when dealing with non-ergodic or non-stationary systems.