Abstract

A Test-experiment based on the Spontaneous Emission (SE) from optically excited Cr atoms in a ruby crystal is proposed. The system, to be carried into the skyes by a mission spacecraft, provides a unique and most direct measurement apparatus of the density ρ_vac of the inhomogeneous QED vacuum-field in the Universe. As such it may contribute to enlighten several puzzling cosmological processes as, for instance, the ones related to the very nature of QED vacuum, of dark-energy and of dark-matter. A measured large
inhomogeneity of ρvac is expected to resolve the enigma of the cosmological constant and several aspects of the Hubble constant tension.

Keywords

Spontaneous Emission, QED, Dark energy, Dark matter, Hubble tension