Quantum Pendulum Trick Explained - Science News: "So he was intrigued when, in the early 2000s, researchers in Helsinki reported experiments in which a pendulum sped up when dunked in a Fermi liquid mixture. He decided to see if he could figure out why. In a series of calculations, Thuneberg and his student Virtanen worked out the mathematics of how the pendulum interacts with the fluid.
When chilled down into a Fermi liquid, particles no longer interact strongly with one another as they do at higher temperatures. Instead there appear quasiparticles, which are the combination of a particle itself along with how it affects the environment around it. Like the original particle, each quasiparticle carries spin, charge and momentum.
The researchers calculated that the quasiparticles ricochet around in the liquid like bullets, increasing the force on the pendulum."