The Cosmic Foam: Stochastic Geometry and Spatial Clustering Across the   Universe
  We stress the importance of stochastic geometry as a branch of mathematical statistics particularly suited to model and investigate nontrivial spatial patterns. One of its key concepts, Voronoi tessellations, represents a versatile and flexible mathematical model for foamlike patterns. Based on a seemingly simple definition, Voronoi tessellations define a wealthy stochastic network of interconnected anisotropic components, each of which can be identified with the various structural elements of the cosmic galaxy distribution. Here we describe results of an ongoing investigation of a variety of aspects of cosmologically relevant spatial distributions and statistics within the framework of Voronoi tessellations. Interesting is the recent finding of a profound scaling of both clustering strength and clustering extent for the distribution of tessellation nodes, representing galaxy clusters. It suggests a hitherto unexpected fundamental and profound property of foamlike geometries. In a sense, cellular networks may be the source of an intrinsic ``geometrically biased'' clustering. 
Rien van de Weygaert (Kapteyn Institute, University of Groningen)