In reading “Genius”, James Glieck’s biography of physicist Richard Feynman, I came across a discussion of superfluids, including supercooled liquid helium, which apparently exhibits the characterisitcs of a superfliud, most notably “frictionless” behavior.
Here’s a passage referring to a superfluid experiment. The “mixture” referred to here is a mixture of a superfluid and a normal liquid:
Apparently this flow continues indefinitely. Glieck notes it will “persist as long as the universe itself”. So here’s my question. If the superfluid “ignores” the powder and the container from a frictional standpoint, as it must to continue flowing indefinitely, how is it induced to flow in the first place? Anyone familiar with this experiment or superfluids in particular would be a saint if they would deign to scratch this mental itch a bit.
A while ago I helped edit the English translation of a memoir by the Russian physicist Andronikashvili. AIP called it Reflections on Liquid Helium*. It’s actually a very nice book describing his personal interactions with Landau et al.
First, let me admit I’m not the expert you requested, but I’ll give it a shot. I don’t see the delima. The superfluid obviously lacks the normal surface tension of a conventional fluid. This allows the individual molecules to flow between the individual powder molecules, which also lack surface tension. Seems like there’s nothing to keep you from pushing the superfluid along with a metal (or other solid material) piston whose molecules are bound together fairly tightly so that the superfluid cannot pass between. Does this answer the question you were asking?
The really freaky part is the fact that the counter flow between the superfluid and the powder is apparently, completely frictionless… I’m finding this a bit hard to swallow.
This may be a dumb question, but I’ll forge ahead anyway:
If the superfluid is indeed completely frictionless, how could you really set it spinning within the tube as described? It seems that you would have to wobble the tube in order to let gravity take over and move the helium in the proper direction. Spinning would only seem to work on “normal” fluids which would be affected by such things as surface tension and friction. Maybe they had the superfluid isolated in a compartment within the tube and were able to remove the compartment walls once the proper rotational speed was reached.
Maybe I’m just nitpicking, or maybe I’m just overlooking the obvious. Wouldn’t be the first time…
It’s even dumber still that I posted a redundant follow-up question in this thread. I should have stopped to scan the other responses a bit more carefully. That’s what I get for sneaking peeks at the MB while I’m at work.
Thanks for the effort, but there is no mention of a piston. The tube apparatus is “set spinning”, as I quoted in the OP. The implication is that spinning the tube somehow induces the contents of the tube to spin. When the tube is stopped, the powder stops flowing eventually but the superfluid does not. This is a sealed system, in fact the determination that the superfluid is still spinning is made by observing the system’s resistance to cross-axial torque, in the manner of a spinning gyroscope. So my question still stands. How did the superfluid start moving in the first place? I had trouble sleeping last night because of this. I know, I need to get a grip.
Well, here’s an idea. Set the temperature
just slightly above the point where the helium goes superfluid. Spin the sucker up.
Everything spins. Drop the temperature and put on the brakes. The wheel stops. The powder stops. The superfluid just keeps on going…
Why, Finagle, I think you just may have it. There’s no mention of that action but it fits the constraints described for the experiment. I’ve been looking for another cite of the procedure in question but Glieck gives no names, dates, or locations. I gather that it was fairly common (by superfluid experimentation standards, I suppose) and repeatable, which may be why there are few details. Thanks, all, for the contributions so far.
It’s pretty thick going and I wouldn’t be surprised if Gleick got some of the details wrong. For instance, it looks like they spin up the device and the superfluid component of the Helium III (there’s also a normal component but don’t ask me what that is)remains stationary in the laboratory frame of reference. The net effect being the same as if you had spun the Helium III up and then stopped the wheel.
Apparently the HeIII is not totally immune to friction – nucleating sites on the cylinder cause vortices to form. The team referenced above studies the vortices.
They make a brief mention of spinning up the system and dropping it through the critical temperature (score one for the home team), but they also mention an experiment where the device is spun up below the critical temperature. Different types of vortices form depending on which method is used.
Anyway, the answer to the OP may depend on what it means for He III to have a normal and superfluid component. The normal component does accelerate with the container due to viscous coupling with the sides. I suppose you could always send email and ask…
The superfluidity of liquid Helium has fascinated me since I first heard about it. It has been a long time since I read this but supposedly it can also “climb” out of a container to reach a lower level. The anthropomorphic principle states that we are here because certain physical constants and processes are what they are. (Read John Gribben’s book.) A minor but unusual physical process, enormously handy here on earth, is that water expands when it freezes. If it did not, and bodies of water froze from the bottom up, life would have taken a different path. There is probably some entity somewhere, existing at a few degrees above absolute zero, commenting on the fact that Helium has superfluid properties, otherwise its entire biosphere could not exist.