This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Since its introduction more than 150 years ago, the thought-provoking idea of Maxwell's demon has profoundly shaped our understanding of the relationship between information and energy. Maxwell's demon is an imagined microscopic gatekeeper that exploits information at the microscopic scale to produce macroscopic work.
Initially controversial, the demon appeared to challenge a fundamental law of thermodynamics by suggesting that work could be extracted from a system in thermal equilibrium. Today, this apparent paradox is resolved by recognizing the thermodynamic value of information: Information itself is a physical resource that can be converted into work. This insight has inspired growing interest in information engines—microscopic machines that, unlike conventional heat engines, are powered by information rather than by temperature differences.
The work is published in Nature Physics. To understand how such a demon extracts work from information, consider a small door connecting two compartments filled with gas molecules. By monitoring the motion of individual molecules, the demon selectively opens the door for fast molecules moving in one direction and slow molecules moving in the other.
Over time, one compartment becomes hotter while the other becomes colder, creating a temperature difference that can be used to drive a machine and perform work. The key point is that the demon creates this energetic imbalance not by supplying energy itself, but solely by exploiting information about the microscopic particle motion. In realistic settings, however, a demon never has complete information.
Even for a single particle, its position and velocity cannot be measured with perfect accuracy. Moreover, microscopic machines are often expected to operate not in simple liquids such as water, but in far more complex surroundings—including polymer solutions, biological fluids and other structured materials—with an internal molecular microstructure that influences the particle's motion. Because such internal microstructures are not directly accessible to the demon, part of the relevant information remains hidden.
This missing information limits the efficiency of microscopic machines under such conditions. In a combined experimental and theoretical study, physicists at the University of Konstanz and the Max Planck Institute for Dynamics and Self-Organization in Göttingen have now shown that such hidden information can be exploited as a valuable thermodynamic resource. In the experiments, a microscopic particle is confined by a tightly focused laser beam inside a complex liquid.
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