Every fluid -- from Earth's atmosphere to blood pumping through the human body -- has viscosity, a quantifiable characteristic describing how the fluid will deform when it encounters some other matter. If the viscosity is higher, the fluid flows calmly, a state known as laminar. If the viscosity decreases, the fluid undergoes the transition from laminar to turbulent flow. The degree of laminar or turbulent flow is referred to as the Reynolds number, which is inversely proportional to the viscosity. However, this Reynolds similitude does not apply to quantum superfluids. A researcher has theorized a way to examine the Reynolds similitude in superfluids, which could demonstrate the existence of quantum viscosity in superfluids.
