Time reversal breaking of colloidal particles in cells

Area of Science:

• Physics
• Biophysics
• Statistical Mechanics

Background:

• Time reversal symmetry is a fundamental concept in physics.
• Stochastic processes in biological systems often exhibit complex dynamics.
• Quantifying deviations from equilibrium is crucial for understanding active matter.

Purpose of the Study:

• To investigate signatures of broken time reversal symmetry in stochastic trajectory data.
• To apply the mean back relaxation (MBR) method to both model systems and biological cell data.
• To identify the cellular components responsible for time reversal symmetry breaking.

Main Methods:

• Utilizing a three-point correlation function known as mean back relaxation (MBR).
• Analyzing stochastic trajectory data from a simple driven model.
• Examining data from colloidal particles within living and passivated biological cells.
• Employing drug treatments to probe the role of cellular structures.

Main Results:

• MBR successfully detected broken time reversal symmetry in both model and cell data.
• The method allowed determination of relevant time and length scales of activity.
• Microtubules were identified as predominantly necessary for time reversal symmetry breaking in cells.
• A bound for entropy production showed qualitative agreement with active energies quantifying fluctuation-dissipation theorem violation.

Conclusions:

• Mean back relaxation is a robust tool for detecting broken time reversal symmetry in complex systems.
• Cellular activity, particularly involving microtubules, actively breaks time reversal symmetry.
• The findings provide insights into the physics of active biological matter and non-equilibrium thermodynamics.