The Global Cosmological Parameters

In these lectures I shall discuss the status of the determination of the three cosmological parameters which enter the Einstein equation and govern geometry and evolution of space-time of the Universe: the Hubble constant H0, the mass density parameter Ω and the cosmological constant λ. Among the three parameters, the Hubble constant is the dimensionfull quantity which sets the basic size and age of the Universe. The perennial effort to determineH0 dates back to Hubble (1925) and has a long history of disconcordance. Recent progress has done much to resolve the long-standing discrepancy concerning the extragalactic distance scale, but there are some newly revealed uncertainties in the distance scale within the Milky Way. The emphasis in this lecture is on discussion of these uncertainties. The mass density parameter directly determines the formation of cosmic structure. So, as our understanding of the cosmic structure formation is tightened, we should have a convergence of the Ω parameter. An important test is to examine whether the Ω parameter extracted from cosmic structure formation agrees with the value estimated in more direct ways. This gives an essential verification for the theory of structure formation. The third important parameter in the Friedmann universe is the cosmological constant Λ. We now have some evidence for a non-zero Λ which, if confirmed, would have most profound implications for fundamental physics. This lecture will focus on the strength of this ‘evidence’. We take the normalisation