Push a particle to the right. It moves to the left.
This is absolute negative mobility — a transport phenomenon where the average drift is opposite to the applied force. Not a transient. Not a fluctuation. On average, over many realizations, the particle goes the wrong way.
Previous demonstrations of absolute negative mobility required either inertia (so the particle could overshoot barriers and get caught in the wrong well) or asymmetric potentials (which bias the available pathways). The phenomenon was real but appeared to demand specific, somewhat contrived conditions.
Białas, Hänggi, and Spiechowicz (arXiv:2603.06070, March 2026) show it in a much simpler system: an overdamped particle — no inertia at all — in a piecewise linear, symmetric periodic potential. The potential has no bias. The particle has no momentum to exploit. The only unusual ingredient is the noise: Poisson shot noise instead of Gaussian thermal noise.
Gaussian noise is symmetric — positive and negative kicks are equally probable and equally sized. Poisson shot noise is asymmetric — the kicks come at random times with random amplitudes drawn from an exponential distribution. Most kicks are small; rare kicks are large. This asymmetry interacts with the symmetric potential barriers in a way that thermal noise cannot. A rare, large kick can push the particle over a barrier in one direction. A sequence of small kicks moves it back partway but not over the next barrier. The asymmetry of the noise creates a directional bias within the symmetric landscape.
When a small external force is applied, the bias from the noise asymmetry can exceed the bias from the force — producing net motion against the force. The particle responds to the noise geometry, not to the force. The force is there. The particle feels it. It goes the other way.
The simplicity of the system is the point. No inertia, no asymmetric potential, no external driving. Just a symmetric landscape and asymmetric fluctuations. The authors suggest this mechanism may operate in biological cells, where molecular motors and active processes generate non-Gaussian noise. If intracellular transport exhibits absolute negative mobility, it would mean that cellular components can be directed against chemical gradients without any molecular motor specifically pulling them — the fluctuation statistics do the work.
Białas, Hänggi, and Spiechowicz, "Absolute negative mobility in a one-dimensional overdamped system driven by active fluctuations," arXiv:2603.06070 (March 2026).