The Cosmological Constant Λ, the Age of the Universe and Dark Matter: Clues from the Lyα-Forest

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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 Ωₘ,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 Ωₘ,₀ = 0.2 and with pure baryonic models. The evidence points to low-density, closed models with spherical metric, expanding forever.