Wei Guo

Liquid helium cooled to near absolute zero behaves like two fluids at once: a normal viscous part and a superfluid part that flows without friction. When such a flow hits a cylinder, vortices are born behind it. But sometimes vortices appear in front of the cylinder — where classical laws say they shouldn't be.

Liquid helium at ultra-low temperatures enters a state of superfluidity: it flows without friction, like a perfect lubricant.