Genmiao M. Wang of the Australian National University and colleagues discovered the anomaly when they dragged a micron-sized bead through a container of water using optical tweezers. The team found that, on occasion, the water molecules interacted with the bead in such a way that energy was transferred from the liquid to the bead. These additional kicks used the random thermal motion of the water to do the work of moving the bead, in effect yielding something for nothing. For periods of movement lasting less than two seconds, the bead was almost as likely to gain energy from the water as it was to add energy to the reservoir, the investigators say. No useful amounts of energy could be extracted from the set-up, however, because the effect disappeared if the bead was moved for time intervals greater than two seconds.
The findings suggest that the miniaturization of machines may have inherent limitations. Noting that nanomachines are not simply "rescaled versions of their larger counterparts," the researchers conclude that "as they become smaller, the probability that they will run in reverse inescapably becomes greater."