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Related Experiment Video

Updated: Jan 8, 2026

Forming, Confining, and Observing Microtubule-Based Active Nematics

Forming, Confining, and Observing Microtubule-Based Active Nematics

Published on: January 13, 2023

Discontinuous transition to active nematic turbulence.

Malcolm Hillebrand^1,2,3, Ricard Alert^4,5,6,7,8,9

¹Max Planck Institute for the Physics of Complex Systems, Dresden, Germany.

Nature Communications

|December 15, 2025

Summary

This summary is machine-generated.

The transition to active turbulence in active fluids is discontinuous, featuring a sudden jump in velocity and bistability between laminar and chaotic flow states. This contrasts with continuous transitions observed in confined systems.

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Area of Science:

Physics
Fluid Dynamics
Soft Matter Physics

Background:

Active fluids exhibit chaotic flows at low Reynolds numbers, termed active turbulence.
Statistical properties of active turbulence are understood, but the transition from laminar to turbulent flow remains unclear.

Purpose of the Study:

Investigate the transition from laminar to turbulent flow in unbounded, defect-free active nematics.
Characterize the nature of this transition, whether continuous or discontinuous.

Main Methods:

Simulations of a minimal model for active nematics.
Analysis of mean-squared velocity, bistability, hysteresis, and finite-time Lyapunov exponents.

Main Results:

The transition to active turbulence is discontinuous, marked by a jump in mean-squared velocity.
Bistability and hysteresis between laminar and chaotic flows were observed.
A critical activity number (A* ≈ 4900) was identified for the transition.
Subcritical bifurcations leading to oscillations and long chaotic transients occur below the transition.

Conclusions:

The transition to active turbulence in unbounded active nematics is discontinuous.
Long-range hydrodynamic interactions in Stokes flow likely suppress spatial coexistence of flow states, leading to the discontinuous transition.
Findings contrast with continuous transitions in confined systems.