h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Hi, very nice and informative entry. One question (if you're still around): you say that Helium-II can flow without resistance and thus a flow will persist once established. However, the zero viscosity merely reflects the lack of INTERNAL friction between the helium molecules. Friction between the helium and its surroundings (air, the vessel containing the helium) is not absent however, so an everlasting flow would become impossible. Or am I overlooking something here ?

I think you are right. After all, helium in a spinning bucket (as discussed) develops vortexs due to the friction of the bucket on the liquid. Of course, the majority of the liquid is not supposed to move, just the edges and the vortexs, so it is quite clearly far too complex for this ex-physicist.

Thanks, well it's definitely over my head as well to get into the details. Actually this was the first thing I read on Helium-II.

I thought you probably wouldn't answer since I thought the writer (Michael He2) hadn't done anything in over a year. Or did you change your name/identity?

Nope, I'm just an interested bystander, so to speak, who had subscribed to this page. Hence your query popped up on my conversation list. I could be wrong on thi smind, I used Helium a lot, but never really studied it beyond the safety measures.

I have not been here for quite a long time. if you still are interested in an answer, here it is:

There is no interaction between the superfluid component of HeII and the walls of the container. Therefore it is quite difficult to set the fluid into rotation. Usually the experiment is performed by rotation the normal liquid and cooling the rotating liquid below the lambda point.

The rotating superfluid contains vortex lines. These vortex lines dissipate kinetic energy from the rotating superfluid when moving. To avoid this effect, the experiments are usually not performed in open buckets where the vortex lines are free to move. In order to trap the vortices the vessel is densely packed with some porous material (e.g. sintered silver powder). Even if it sounds weird: The liquid flows better now than within the open bucket.

Experiments performed within this setup showed no decrease of the rotation within days.