On the initial state of the universe and the time arrow

In this paper, we investigate an important issue addressed by several approaches to quantum cosmology, like that based on loop quantum gravity and string theory: the existence of an arrow of time driving the cosmological evolution according to the generalized second law of thermodynamics. In this way, by considering quantum corrections to the Friedmann equations, we find out that for such a cosmological arrow of time to exist, our universe must have occupied a state of negative entropy during its very early evolution. This opens a new, and interesting, perspective on the beginning of the cosmos: that our universe has emerged not from a Big Bang, but from a Dirac sea of negative entropy.