Abstract
The cosmological constant Λ is a measure of the energy density of the vacuum. Therefore properties of the energy of the system in the metastable vacuum state reflect properties of Λ = Λ(t). We analyze properties of the energy, E(t), of a general quantum system in the metastable state in various phases of the decay process: In the exponential phase, in the transition phase between the exponential decay and the later phase, where decay law as a function of time t is in the form of powers of 1/t, and also in this last phase. We found that this energy having an approximate value resulting from the Weisskopf--Wigner theory in the exponential decay phase is reduced very fast in the transition phase to its asymptotic value E(t) ≃ E_min + α₂/t²+… in the late last phase of the decay process. (Here E_min is the minimal energy of the system). This quantum mechanism reduces the energy of the system in the unstable state by a dozen or even several dozen orders or more. We show that if to assume that a universe was born in metastable false vacuum state then according to this quantum mechanism the cosmological constant Λ can have a very great value resulting from the quantum field theory calculations in the early universe in the inflationary era, Λ ≃ Λ_qft, and then it can later be quickly reduced to the very, very small values.