  It is shown that the de Sitter state is invariant with respect to Wick
rotation. In imaginary time, super- horizon quantum and classical metric
fluctuations of the empty FLRW space (with no matter fields) form a
self-consistent de Sitter state. The invariance with respect to Wick rotation
suggests that this de Sitter state is formed also in the empty space of real
time. At the start and by the end of its cosmological evolution the Universe is
empty, so that the de Sitter expansion of the empty space can be the cause of
inflation and dark energy. This scenario is consistent with the existing
observational data
