ar X iv : a st ro - p h / 98 10 34 0 v 1 2 1 O ct 1 99 8 The Cosmological Constant Λ , the Age of the Universe and Dark Matter

Evidence for a positive cosmological constant Λ, derived from the Lyα–forest in high–resolution spectra of quasars, leads to a closed, low–density, Λ-dominated universe. The analysis is based on the assumption of a universal shell structure expanding predominantly with the Hubble flow. Supporting evidence comes from two pairs of very wide absorption lines in the spectra of two quasars separated by 8 arcmin on the sky. These results contradict the higher values of the density parameter Ω M,0 derived, for example, from clusters of galaxies by the pure gravitational instability theory. Implications thereof and for the amount of non–baryonic dark matter in the universe are discussed with some Λ–dominated models, in particular with Ω M,0 = 0.2 and with pure baryonic models. The evidence points to low–density, closed models with spherical metric, expanding forever. When Albert Einstein in 1931 realized that the value of Λ could not be determined from the cosmological observations available at that time he recommended dropping the term " aus Gründen der logischen¨Okonomie " (for reasons of logical economy) until observations force us to reintroduce it again. His famous saying " Die Einführung von Lambda war vielleicht die größte Eselei in meinem Leben " (" Λ was perhaps the biggest blunder in 1