Silly Putty, when you stretch it, remembers its shape for a few seconds. Water in a glass forgets the motion of a spoon right away. But some liquids combine the flow of water with the memory of Silly Putty. Dissolved in such a liquid are micelles, tiny clusters of molecules that look like a sponge made of spaghetti. When a bacterium-sized particle enters, the micelle network wraps around it and remembers every movement.
Scientists placed a particle in such a liquid and held it with a laser beam, like tweezers. The particle was constantly jiggling due to the thermal motion of molecules. This jiggling was recorded 100 times per second. Then they measured the particle's position twice, one second apart. It turned out that for one of the states, the particle's energy first rises and then falls. The micelle network, having contracted around the particle, releases stored energy to it, like a spring that was first compressed and then let go.
This effect made it possible to extract work that exceeds the particle's own energy. Previously, it was thought that the environment instantly forgets the past. Now it is clear: the liquid's memory can be turned into useful work. This opens the way to microscopic engines that use the memory of biological fluids or polymer solutions as fuel. Silly Putty, which remembers its shape, can now not only amaze but also work.
The micellar network in which the particle floated has a relaxation time of about 6 seconds. It is as if the water in a glass remembered the motion of a spoon for several seconds after the spoon was taken out.
The idea of extracting work from hidden memory echoes the plot of Stanisław Lem's short story "The Fourteenth Voyage," in which the protagonist tries to use information about the past to obtain energy, though in the story this leads to paradoxes rather than practical gain.