  It has been claimed that the observed magnitude of the vacuum energy density
is consistent with the distribution predicted in anthropic models, in which an
ensemble of universes is assumed. This calculation is revisited, without making
the assumption that the CMB temperature is known, and considering in detail the
possibility of a recollapsing universe. New accurate approximations for the
growth of perturbations and the mass function of dark haloes are presented.
Structure forms readily in the recollapsing phase of a model with negative
Lambda, so collapse fraction alone cannot forbid Lambda from being large and
negative. A negative Lambda is disfavoured only if we assume that formation of
observers can be neglected once the recollapsing universe has heated to T > 8
K. For the case of positive Lambda, however, the current universe does occupy a
extremely typical position compared to the predicted distribution on the
Lambda-T plane. Contrasting conclusions can be reached if anthropic arguments
are applied to the curvature of the universe, and we discuss the falsifiability
of this mode of anthropic reasoning.
