Enhanced diffusion by reciprocal swimming

TL;DR

This paper demonstrates that reciprocal swimmers in fluctuating environments experience significantly enhanced diffusion, providing a potential advantage for small organisms like marine bacteria, despite the constraints of Purcell's scallop theorem.

Contribution

The study combines numerical simulations and theoretical analysis to show that reciprocal motion can lead to enhanced diffusion in fluctuating environments, challenging traditional views.

Findings

Reciprocal swimmers exhibit increased diffusivity in fluctuating environments.

Enhanced diffusion can be orders of magnitude higher than normal diffusion.

Reciprocal motion offers advantages for small organisms like bacteria.

Abstract

Purcell's scallop theorem states that swimmers deforming their shapes in a time-reversible manner ("reciprocal" motion) cannot swim. Using numerical simulations and theoretical calculations we show here that in a fluctuating environment, reciprocal swimmers undergo, on time scales larger than that of their rotational diffusion, diffusive dynamics with enhanced diffusivities, possibly by orders of magnitude, above normal translational diffusion. Reciprocal actuation does therefore lead to a significant advantage over non-motile behavior for small organisms such as marine bacteria.