v 2 2 1 O ct 1 99 6 Is the Universe Homogeneous on Large Scales ? Marc

This morning’s debate is focused on the question of the large-scale homogeneity of the Universe. I shall present the affirmative position, that there is overwhelming evidence for large scale homogeneity on scales in excess of approximately 50h Mpc, with a fractal distribution of matter on smaller scales. My worthy opponent, Dr. Luciano Pietronero, will present the counter-argument, that the fractal distribution observed on smaller scales continues to the largest observed scales, and that there is no evidence for homogeneity on any scale. This is an important question, since the Friedmann-Robertson-Walker metric presumes large scale homogeneity and isotropy for the Universe. This is the simplest cosmological model, and it is a fair question to ask the degree to which it is supported by the observational evidence. We know that the galaxy distribution is far from homogeneous on small scales, and large-scale structure in the form of long filaments and chains extends to lengths in excess of 100h Mpc [1]. Redshift surveys often show structures nearly as large as the entire survey size; how confident can we be that homogeneity is a valid concept for the large-scale universe?