What is the least viscous fluid? If you said water, you’re wrong. If you said a gas, like light and buoyant helium, you’re clever — but still wrong. Quantum physicists predicted a theoretical lower limit for the viscosity of fluids, a value represented by ħ/4π, (π being our good friend pi, 3.14, and ħ being the Planck constant, an extremely small number). Helium, even though it is a super-fluid, does not even closely approach this limit. However, a complicated plasma of quarks and gluons does, and it has CERN physicists questioning whether the limit could be pushed even further. Also known as “quark soup,” a quark-gluon plasma is not quite like traditional plasma, but is an extremely hot fluid composed of some of the smallest building blocks of matter. It is difficult to take readings from this quantum state of matter but physicists think that quark-gluon plasma’s viscosity could be even less than what was thought to be the theoretical limit.
