Measurements on the time variation of the fine structure constant and of
the proton-electron mass ratio suggest that basic quantities of the
Standard Model, such as the QCD scale parameter, may not be conserved
in the course of the cosmological evolution. The masses of the nucleons
and of the atomic nuclei would also be affected. These measurements can
be interpreted as a leakage of matter into vacuum or vice versa. The dark
energy in our universe could be the dynamical vacuum energy in
interaction with ordinary baryonic matter as well as with dark matter.