CWL

Physicists have explained yet another quirk of the quantum world: why, if you swing a pendulum through a quantum fluid, it speeds up rather than slowing down. Tiny “quasiparticles” ricocheting around in the fluid are to blame, Finnish researchers report in an upcoming issue of Physical Review Letters.

The effect is the opposite of that experienced in the ordinary world. Immerse the pendulum of a grandfather clock in water, for instance, and it will slow down.

It takes a special kind of fluid to pull off this quantum trick. Physicists Timo Virtanen and Erkki Thuneberg of the University of Oulu have been studying helium-3 atoms, which at very low temperatures form a substance known as a Fermi liquid. In such a liquid, the atoms stop interacting with each other as they ordinarily do and instead start behaving in strange quantum ways.

Researchers have studied Fermi liquids for decades to better understand phenomena that kick in at cold temperatures, such as superconductivity. “It’s a very profound theory — one of the most basic things to understand,” says Thuneberg.