Devaraj van der Meer, Ko van der Weele, and Detlef Lohse Department of Applied Physics and J.M. Burgers
Centre for Fluid Dynamics, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands

Granular gases spontaneously separate into dense and dilute regions. Here it is experimentally and
theoretically demonstrated that the cluster formation and its breakdown are fundamentally different due to
the lack of time reversibility: For a vibro-fluidized granular gas in N connected compartments the cluster
formation takes place gradually, via several metastable states, whereas the collapse of the cluster is very
abrupt. The observed cluster lifetime (as a function of the driving intensity) is analytically calculated
within a flux model, making use of the self-similarity of the process. After collapse, the cluster diffuses
out into the uniform distribution with an anomalous diffusion exponent 1/3.