Observership in Cosmology: the Anthropic Principle

Abstract

The Anthropic Principle is that if the universe around us were hostile to Life then we could not be observing it. Today's cosmologists often see this as helping to explain why the observed universe has life-producing characteristics. Are they right? My aim here is to speed in new directions over territory already surveyed in two earlier papers.1 In B. Carter's classic formulation of it2 the Principle has 'weak' and 'strong' forms. The weak is 'that our location in the universe is necessarily privileged to the extent of being compatible with our existence as observers'; the strong, that our universe 'must be such as to admit the creation of observers within it at some stage'. Carter sees the strong form as offering 'an explanation' when we think 'in terms of a world ensemble of universes characterised by all conceivable combinations of initial conditions and fundamental constants', observers existing only in 'an exceptional cognizable subset' of the Ensemble. Care is needed in interpreting all this. (i) When the weak principle speaks of our being appropriately 'located', temporal as well as spatial location is in question. Carter points out that our universe must now be old enough for heavy elements (needed to build our bodies) to have been formed inside stars. (ii) In 'our existence as observers' it is observership and not our being us which is important. While our universe may well contain many trillion little green men they will be men thanks to their intelligence, not to their having human form: 'anthropic' considerations would give no excuse for a belief in an Ensemble of universes if they dealt with our human observership alone. Still, they can support such a belief only if we can assume such things as that observers must be like us in having bodies, and even bodies which could not exist in such places as the sun's centre or the surfaces of neutron stars-habitats taken seriously by a scientifically ingenious minority and particularly by G. Feinberg and R. Shapiro.3 (iii) When the strong principle says that our universe 'must be such as to admit the presence of observers' it is not meant that this universe's basic character