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Superfluidity is one of the most amazing quantum phenomena, which we can sit and watch them happening before our eyes! Watch this video, it is only a couple of minutes long, which will bring you face-to-face with quantum mechanics in all its beauty. Then take a look at the questions below.


A superfluid has the amazing ability to climb up the walls of the glass container that it is in: Does it defy gravity?

A superfluid can get out through the walls of the glass container: Quantum tunnelling in action before our eyes?

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Liquids can rise up a narrow tube and the phenomenon is called capillary action. This is how plants have water (and other stuff) to rise up from the roots, through stems, to reach leaves. Gravity doesn't absolutely pull things down; it attaches an energy cost for things to go up. If that energy cost is met (for eg: helicopters, balloons) then things can go up else things go down. So this phenomenon is gravity-defying only to the extent that anything else that rises would be. So I suggest you remove that mention of defying gravity, from your question. It is otherwise a good question. – Siva Mar 21 '13 at 7:50
@Siva A capillay of 1-5 mm diameter cannot be compared with 5-10cm diameter beaker. Your response over this in your answer holds more weight than the one in your comment! – JKL Mar 21 '13 at 11:11
I didn't mean to suggest that capillary action is the explanation, in the case of superfluid helium. I simply mean to analogize (by referring to a different example) that it doesn't make sense to call it anti-gravity. – Siva Mar 21 '13 at 15:57

When the superfluid helium leaks out of the container, that's not tunnelling. A few drops of superfluid helium contain many many atoms and for all of them to tunnel through would be extremely improbably as to pretty much not happen. So what makes the helium flow out?

If you notice carefully, the container is not a normal glass mug, but it's bottom is made of some other material (I think it's some kind of ceramic with tiny pores). As the scientist in the video says, the only reason "normal" liquid helium (above the critical temperature) did not flow out through those pores, was that viscous drag kept it from dripping out. After the phase transition to a superfluid, the *super*fluid doesn't have any viscosity and no longer resists flow. So it flows out of the container.

As far as the wall-climbing goes: It should somehow be that (loosely) it is energetically/probabilistically preferable for the fluid to climb up the walls and then flow out rather than stay in. I don't really understand why exactly it climbs the walls of a container and a cursory search seems to indicate that though there are explanations based on viscosity for this too, there isn't any clear consensus which is perfectly validated by experiment.

I think this video (with annotations) is more informative:

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My QFT professor said it's something along the lines of the van Der Waals interactions being strong enough to pull it up the container. Normal fluids don't do this because of the energy penalty of viscous friction against the walls. – Nick Oct 6 '13 at 23:39

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