LIMITS on the way fluids can behave have emerged from a theoretical study of black holes in 10-dimensional space.
Dam Thanh Son of the University of California, Santa Barbara, and his colleagues used string theory to model a 10-dimensional black hole 鈥� a mathematical entity rather than a real astrophysical object 鈥� as a liquid. They focused on two properties of the fluid: viscosity and entropy density, which is a measure of its internal disorder. Son鈥檚 team found that the ratio of these two values is a constant that can be expressed as a combination of fundamental constants from the quantum world.
The researchers suggest that this constant might represent a universal lower limit for the ratio of viscosity to entropy in real fluids. This tallies with their calculations based on the famed Heisenberg uncertainty principle, which suggest that such a limit should exist.
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鈥淭hat is what we hypothesise,鈥� says Son. 鈥淲e couldn鈥檛 prove that it is the case, but we couldn鈥檛 find anything that is less viscous.鈥� For example, the value of this ratio for water is 400 times greater than for black-hole fluid. Even for liquid helium it is nine times as great.
Fluids that could approach the limit include super-cold clouds of atoms, or the plasmas created in particle colliders, Son suggests.
