  The Big Bang predicted theoretically by Friedmann could not be discovered in
the 1920th, since global cosmological distances (more than 300-1000 Mpc) were
not available for observations at that time. In 1927-29, Lema\^itre and Hubble
studied receding motions of galaxies at local distances of less than 20-30 Mpc
and found that the motions followed the (nearly) linear velocity-distance
relation, known now as Hubble's law. For decades, the real nature of this
phenomenon has remained a mystery, in Sandage's words. After the discovery of
dark energy, it was suggested that the dynamics of local expansion flows is
dominated by omnipresent dark energy, and it is the dark energy antigravity
that is able to introduce the linear velocity-distance relation to the flows.
It implies that Hubble's law observed at local distances was in fact the first
observational manifestation of dark energy. If this is the case, the commonly
accepted criteria of scientific discovery lead to the conclusion: In 1927,
Lema\^itre discovered dark energy and Hubble confirmed this in 1929.
