The Universe as revealed in state of the art surveys appears organized with large scale clustering of galaxies in filaments bounding large scale voids, as shown in Fig. 1.1. This distribution was discovered by the Center for Astrophysics (CfA) Redshift Survey [364], and has now been mapped in great detail by the Two-Micron All Sky Survey (2MASS) [542] and the Sloan Digital Sky Survey (SDSS) [541].

The large scale structure emerged out of embryonic inhomogeneities in the early evolution of the Universe [263] as imprinted, in pattern and amplitude, in the cosmic microwave background (CMB). These fluctuations in the CMB can be seen as tiny temperature variations with an amplitude of about 10 microkelvin, roughly 10−5 of the average CMB temperature, 2.724 K [308]. The present day low CMB temperature results from adiabatic cooling in the cosmological expansion over 13.75 Gyr [308], since radiation decoupled from matter, when the Universe was a mere 400 kyr of age and about one thousand times smaller in linear size. By Newtonian attraction, the associated local inhomogeneities in the (dark) matter distribution gave rise to the large scale structure of the Universe, as presently observed. The evolution of this structure is accompanied by violent processes and entropy creation on scales of ~1 Mpc and less [558, 263, 644], in addition to entropy of possibly cosmological origin (e.g., [238, 190]).