A hydrodynamic analog of critical phenomena: an uncountably infinite number of universality classes

Shoko Ii, Ko Okumura

Published 2024-05-05Version 1

The concept of universality class has emerged from our understanding of critical phenomena widely observed in nature and has guided the recent development of physics. Accordingly, identifying a rich variety of universality class is a major issue in modern physics. Here, we report that a daily phenomenon, similar to a drop falling from a faucet, possesses a strikingly close analogy with critical phenomena, but this version remarkably reveals the existence of an uncountably infinite number of universality classes. The key for our present findings is the confinement of a system into a thin cell, in which we observe the dynamics of air-liquid interface formed by entrained air into viscous liquid by a solid disk, to find critical exponents that define a universality class depend on continuous numbers characterizing the confinement.