Is Dark Energy due to an excited quantum state of the Universe?
One of the mysteries of modern cosmology is the origin of dark energy. The current cosmological model, that is in agreement with the experimental data, predicts that the expansion of the galaxies is accelerated. In order to take this acceleration into account, an additional term is introduced in the Einstein equations invoking the existence of a cosmological constant. The origin of this additional term is still unknown. The aim of this paper is to explain dark energy as the energy of the quantum state of the universe that, instead of being in a fundamental state with zero energy, is in an excited state with a non-vanishing value of energy. The experimental value found for the cosmological constant is shown to be compatible with the model, taking, in our equations, the only free parameter of the order of Planck length.