THE FRACTAL NATURE OF THE UNIVERSE

We summarize a very recent, exhaustive review (Coleman and Pietronero, Pbys. Rep. 213 (1992) 311), which also presents some very exciting new analysis. In that review (and here), we reconsider the experimental data concerning the large scale structure of the universe utilizing the theoretical methods of modern statistical mechanics. This allows us to test the implicit assumptions of analyticity and homogeneity present in the usual analysis. The results are quite surprising: the usual methods of analysis are found to be mathematically inconsistent for all cases that can be explicitly tested. The reanalysis of galaxy and cluster distributions without any assumptions show long range (fractal) correlations up to the present observational limits without any tendency towards homogenization. These studies are then generalized by analysis of the whole distribution of visible matter (by including the galaxy masses), which shows well-defined multifractal features. This implies that the nature of the distribution is strongly non-analytic and no single average density can be defined, within the present limits set by the observations. This result should have important consequences for our knowledge of the properties of the universe as well as for the theoretical framework that one should use to describe it.