6.2. A conservative view
As a caution against the view that radical evolutionary changes in the look-back time are needed to explain the excess in the counts, and therefore that we have strong direct evidence for a radically different universe at large redshifts, we quote from the quiet voices of Koo and Kron (1992) where they write:
"To account for part of these data, different groups have proposed modifications to the conventional picture of mild luminosity evolution for z < 1. Examples include adoption of a large cosmological constant; substantial merging at low redshifts; a vast increase in bursting activity at moderate look-back times; or entirely new populations of galaxies that were present at high redshift but absent today. We have instead taken a more conservative stance and asked whether all the data might be found to be consistent with a simpler picture in which the cosmological constant is zero, the number of galaxies is conserved over time, and the shape of the luminosity function for each galaxy class is constant. Notwithstanding the new redshift data, we have argued that the combined uncertainties in the models and in the data so far preclude the necessity of more exotic assumptions."