[andreapaiola]

a superfluid flows with zero viscosity, that means if we were to put it into some kind of centrifuge and spin it, it would not slow down due to friction. If it never slows down due to friction, in theory, that implies we should be able to accelerate a superfluid to the speed of light.

ah ah ah ah nope.

[fastball]

Could you explain why not?

It doesn't sound right to me either, but I have a hard time explaining to myself why it wouldn't maintain it's velocity.

[eesmith]

The first problem I thought of is that as the speed goes up, the centripetal force causes the pressure to increase. At some point there will be a transition from liquid to solid. Eg, for ⁴He, and if I read the phase diagram correctly, that's at 25 bar.

I searched for "rotating superfluid helium" and found http://physicsworld.com/cws/article/news/2018/feb/07/unexpec... , which is a summary of https://journals.aps.org/prb/abstract/10.1103/PhysRevB.97.01... . It says that there is friction, perhaps caused by "quasiparticles that become trapped within the cores of vortexes. As the vortexes accelerate, the quasiparticles gain energy, which they can then dissipate to their surroundings in the form of friction."