Superfluid helium can come out of a container along its walls

A container can empty without a hole or tilt. At very low temperatures, liquid helium offers a confusing demonstration: a thin layer runs along the inner wall, crosses the edge and then descends to the outside. Drops can then join the helium bath located lower.

David Lee describes this behavior in his Nobel Lecture. It concerns in particular helium 4 under its transition point, close to 2.17 kelvins under the described conditions. This temperature is only a few degrees from absolute zero. The liquid then has superfluid properties, including flows without the usual internal resistance and exceptional heat transport.

The phenomenon does not correspond to an entire cup that would leap against gravity. It is a moving film that connects the different surfaces. The necessary thermal conditions must be maintained. A wall can therefore seem to close a container while offering, to a particular fluid, a continuous path that our daily experience makes us easily forget.