In the microworld, noise usually disrupts fragile states, like ripples shattering a reflection in a puddle. But sometimes the coordinated noise of many particles does the opposite — a stable unidirectional flow emerges.
The direction is set by geometry, akin to spacetime curvature. The paradox is that trying to clean the system of noise (as in spectroscopy, where you filter the signal) destroys this pattern — motion grinds to a halt. This is a phenomenon of open systems, where entropy not only grows but also builds structures. The ideas trace back to the work of von Neumann and Wigner on chaos and measurements.
Remove the noise, and the wave freezes: the particles stop moving. Order demands disorder.