Scientists have realized on a macroscopic scale a device allowing to extract energy from disordered fluctuations. This type of experiment was imagined in the 19th century by the physicist Maxwell to show that, contrary to what thermodynamics asserts, entropy can decrease, giving rise to a long debate, famous in the history of physics.

Abstract

We present an experimental realization at macroscopic scale of the storied Brownian ratchet, which is an illustration of the Maxwell’s demon. In our mechanism, the rotation of a centimeter-scale 1D Brownian object in a granular gas is detected by an electromechanical converter (dynamo), generating a voltage proportional to its angular velocity. The current generated by this random rotation is rectified by an electronic device (demon), such that only positive current passes. Eventually, work can be produced. The advantage of such a macroscopic setup is to allow measurement of all the observables with time: useful power (work), heat taken from the bath, and finally the efficiency of the equivalent heat engine. The feedback allowing the conversion from heat into work expresses as a bias on the Brownian motion.

Reference: Human-Scale Brownian Ratchet: A Historical Thought Experiment. M. Lagoin, C. Crauste-Thibierge et A. Naert. Phys. Rev. Lett., September 15, 2022.
DOI: 10.1103/PhysRevLett.129.120606
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