Why helium can flow without ordinary drag
In liquid helium-4, cooling below about 2.17 kelvins produces a superfluid component: part of the liquid that can move without the usual internal friction. The transition is a collective quantum effect. Helium atoms, which normally behave as individual particles, begin sharing a coordinated quantum state, so the liquid’s motion no longer loses energy through ordinary viscous drag.
The change is not simply that every atom suddenly becomes frictionless. Near the transition, liquid helium is described as a mixture of two interwoven components: a superfluid one and a “normal” one that still has viscosity. As the liquid gets colder, the superfluid share grows. This distinction matters because viscosity is the resistance to flow within a liquid; electrical resistance applies to electric current and is not what makes helium climb a container.
How a film escapes the container
Helium is unusually good at wetting surfaces: its atoms are attracted to the container’s walls, so even a very thin layer spreads across them. In ordinary liquids, viscosity makes such a film sluggish. In superfluid helium, the frictionless component can move through the film with almost no energy loss, carrying liquid up and over the rim.
Once outside, the film continues down the container’s exterior under gravity. The visible motion is therefore not helium defying gravity; surface attraction draws it onto the wall, while gravity helps it flow back down. The film is only a few atoms thick, yet its movement reveals a change in the liquid’s underlying quantum behavior—one that is usually hidden in much larger collections of matter.
