Maxwell's demon in the lab: hidden information yields extra work

Researchers at the University of Konstanz and the Max Planck Institute for Dynamics and Self-Organization (MPI-DS) in Göttingen have shown how usable work can be extracted from hidden processes in a particle's surroundings. The study by Muruga, Ginot, Loos and Bechinger was published on 16 October in the journal Nature Physics (DOI 10.1038/s41567-026-03442-w). It draws on the 19th-century thought experiment known as Maxwell's demon.

In the experiment, a silica sphere 2.7 micrometres in diameter, held by an optical trap, floats in a viscoelastic fluid made of wormlike micelles. This network relaxes only slowly after a disturbance and thus “remembers” earlier movements – but its exact state remains hidden. “We measured the particle twice with a defined temporal delay in between,” says Clemens Bechinger of the University of Konstanz. Depending on the result, the trap was shifted. In some states, the work extracted exceeded the energy stored in the directly observable particle – the rest came from the environment.

No energy is created in the process, and the second law of thermodynamics holds: the information only helps to find and use free energy that is already there. The MPI-DS sees the work as a step towards microscopic information engines that do not need macroscopic temperature differences – for example in polymer solutions or biological fluids.