  An unexpected Minkowskian solution of the equation of General Relativity
(Einstein-1915) is trivial because it simply means that both members of the
equation are equal to zero. However, if alternatively, one considers the
complete equation with a non-zero (cosmological constant (Einstein-1917), a
Minkowskian solution is no longer trivial because it amounts to impose a
constraint on the right hand side of the equation (i.e. a non-null
stress-energy tensor). If furthermore one identifies (as usual) this tensor to
the one of a perfect fluid, one finds that this fluid has a positive energy
density and a negative pressure. We discover finally an expanding Universal
Minkowskian fluid (Flat Universe) that has not only dynamical properties
(acceleration) but also optical properties that are connected with Doppler
Redshift. Einstein special relativity in 1905 consisted in dissolving a ghost:
the old electromagnetic ether; our relativistic approach involves also the
dissolution of a ghost: the Dark Dnergy. This new cosmological ether becomes a
pure relativistic effect of Minkowskian solution with CC.
