The large numbers hypothesis considered by Dirac (1937) has led to the discussion of continuous creation by many authors and the proposal of various processes of creation. The present investigation is concerned with the validity of the Dirac relations on which these discussions and proposals are based. Dirac postulates that the observed approximate equality of three dimensionless numbers is not accidental but causal. Attention is given to the basic hypothesis of the theory of relativity, and questions regarding the invariability of some of the involved parameters. It is concluded that, within the Friedmann-Lemaitre model, which seems to give the best description of the evolution of the present universe, the Dirac hypothesis is logically self-consistent only if the curvature of the universe and the cosmological constant are equal to zero.