AGE CRISES, SCALAR FIELDS, AND THE APOCALYPSE

Recent observations suggest that Hubble's constant is large, to the ex tent that the oldest stars appear to have ages which are greater than the Hubble time, and that the Hubble expansion is slowing down, so tha t according to conventional cosmology the age of the Universe is less than the Hubble time. The concepts of weak and strong age crises (resp ectively to < 1/H-0 but longer than the age inferred from some lower l imit on q(0), and t(0) > 1/H-0 and q(0) > 0) are introduced. These obs ervations are reconciled in models which are dynamically dominated by a homogeneous scalar field, corresponding to an ultra-light boson whos e Compton wavelength is of the same order as the Hubble radius. Two su ch models are considered, an open one with vacuum energy comprising a conventional cosmological term and a scalar field component, and a hat one with a scalar component only, aimed respectively at weak and stro ng age crises. Both models suggest that anti-gravity plays a significa nt role in the evolution of the Universe.