Vorlesen In small physical systems with dimensions in the nanometer range the entropy can decrease with periodic movements. They violate the second law of thermodynamics, which states that entropy always increases in cycle processes, or at best remains the same. An Australian team of researchers has now demonstrated for the first time an entropy decrease experimentally, thus confirming a ten years ago established theory. This is reported in the journal Physical Review Letters (Volume 89, reference number 050601). The experiment of Denis Evans researchers from the Australian National University examined the entropy changes that occur in the periodic motion of a latex ball only a few microns in size. For this purpose, the researchers caught a ball suspended in a liquid cell by means of the laser beam of a laser tweezers. The ball was thus bound by electrostatic forces to the focal point of the beam.

The researchers now moved the fluid cell forward and backward at a frequency of 54 Hertz, so that the latex ball floating in it moved at that frequency through the focal point of the laser beam. Using a high-speed camera, the team captured the location of the bullet a thousand times a second. This made it possible to determine the trajectories of the sphere, which in turn allowed us to determine the forces acting and the entropy changes associated with this movement.

Indeed, among the recorded trajectories, there were some where the system consumed entropy during one cycle and thus violated the second law of thermodynamics. However, this entropy decrease was only observed with very short observation times of a few fractions of a second. An entropy balance of this process carried out over a few tenths of a second could actually show an entropy decrease? however, when the balance was made over several seconds, entropy increased.

The researchers were able to confirm a theory they had established ten years ago. In their so-called fluctuation thesis, they predicted that small systems could consume entropy over short periods of time. display

The entropy decrease could be important for the functioning of nanomachines. If their entropy decreases, they would run "backwards". According to the researchers, fluctuation theory can also be applied to the study of biological protein engines.

Stefan Maier

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