Superfluidity

Taken from a Polish science programme, this video is a fascinating demonstration of superfluid helium.
(The translation is a little dubious in places, but it’s understandable enough).

Note the moment at around 1:07 in the video where the helium goes superfluid, bubbles, and then goes eerily still. This is when it’s cooled to it’s lambda point at 2.17K, barely above absolute zero and colder than the cosmic microwave background.

A superfluid is a kind of Bose-Einstein condensate. Superfluids have no friction, no viscosity, zero entropy and infinite thermal conductivity (in a similar way to superconductors having infinite electrical conductivity). They flow without any resistance up the walls of any container they’re placed in. Give superfluid helium a large enough container which is all at a low enough temperature, and it will form a thin layer of liquid helium one atom thick across the entire inside surface of the container.

Sometimes known as a quantum liquid, it’s effectively a macroscopic manifestation of quantum mechanics. It’s hard to explain exactly what that means, but you can think of it this way: If you pour superfluid helium into a container and rotate the container slowly, the liquid inside will not rotate with the container because it has no viscosity. However, if you rotate the container at the correct speed, all of the superfluid will suddenly start to rotate along with the container. In other words, its rotation is quantised (the same way a single molecule works in spectroscopy); it can only rotate at a specific set of speeds. This bizarre effect is known as a quantum vortex.

The lack of viscosity also means that in slow motion, superfluid droplets look really cool.

One final interesting thing that superfluids do. Because superfluids have infinite thermal conductivity, they follow temperature gradients. Put a pipette into some superfluid helium and warm it — even if you only warm it by a fraction of a degree by shining a light on it — and it’ll chase the temperature, creating a fountain effect like this next video shows.

Yet another reason why helium is cool.
(No pun intended).

About Invader Xan

Molecular astrophysicist, usually found writing frenziedly, staring at the sky, or drinking mojitos.
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