  We are at a specific period of modern cosmology, during which the large
increase of the amount of data leads to the idea that the determination of
cosmological parameters has been achieved with a rather good precision. There
is a large consensus around the so-called concordance model. Indeed this model
does fit an impressive set of independent data: CMB $C_l$ curve, most current
matter density estimations, Hubble constant estimation from HST, apparent
acceleration of the Universe, good matching of the power spectrum of matter
fluctuations. However, the necessary introduction of a non zero cosmological
constant is an extraordinary new mystery for physics, or more exactly the come
back of one of the ghost of modern physics since its introduction by Einstein.
Here, I would like to emphasize that some results are established beyond
reasonable doubt, like the (nearly) flatness of the universe and the existence
of a dark non-baryonic component of the Universe. But also that the evidence
for a cosmological constant may not be as strong as needed to be considered as
established beyond doubt. In this respect, I will argue that an Einstein-De
Sitter universe might still be a viable option. Three global tests: 1) the
evolution of the abundance of clusters with redshift 2) the baryon fraction
measured in local clusters 3) apparent evolution of the baryon fraction with
redshift might be consistent with a high matter density for the Universe in the
range $0.6-1.$. I therefore conclude that the dominance of vacuum to the
various density contributions to the Universe is presently an interesting and
fascinating possibility, but it is still premature to consider it as an
established scientific fact (abridged).
