10 - Nonlinear galaxy clustering

Summary

… we seek a theory which describes all that actually happens, and nothing that does not, a theory in which everything that is not forbidden is compulsory.

The Unity of the Universe D. W. Sciama (Faber & Faber, 1959)

The clustering of galaxies on scales < 5h^-1Mpc¹ shows some remarkable scaling properties which somehow arise out of nonlinear gravitational self-organisation. This scaling is characteristic of structures that are referred to as multifractals. There are several ways of looking at these structures each providing their own special insights into the nature of the clustering. Multifractal scaling can be shown to be closely associated with the fact that galaxy counts-in-cells are approximately Lognormally distributed and with hierarchical fragmentation processes. Moreover, the statistical moments of the galaxy distribution scale in a way that is reminiscent of the renormalization group. This may throw light on the nature of the underlying dynamics of the nonlinear gravitational clustering process.

INTRODUCTION

When Dennis Sciama published his book “The Unity of the Universe” in 1959, the great debate was which theory of the Universe was the correct one: the “Big Bang” or the “Steady State”? Dennis had been a member of a group of Steady-State enthusiasts at Cambridge in the early 1950's.