Fluids can actually push particles along in a steady drift even if the water is just sloshing back and forth.
March 26, 2026
Original Paper
Geometric Memory Generates Irreversible Transport in Time-Periodic Irrotational Flows
arXiv · 2603.24455
The Takeaway
We usually assume that to push something permanently in one direction, you need a constant force or a turbulent current. This paper identifies 'geometric memory'—a phenomenon where the mere shape of a particle's path through a smooth, repeating flow causes it to drift forward forever.
From the abstract
Irreversible transport is generally attributed to vorticity, nonlinear forcing, or explicit symmetry breaking. We show that it can arise even in strictly time-periodic and locally irrotational flows through a purely geometric mechanism. By reconstructing the velocity gradient through causal self-transport over a finite memory time, deformation acquires the structure of a geometric connection whose holonomy generates a finite Lagrangian drift over one forcing cycle. The resulting contribution adm