'In an environment where the ambient temperature is well below the melting point of ice, as it is in most of the universe far from the highly localized effects of stellar heating, any water vapor would readily crystallize into complex, asymmetric structures. Snowflakes would be eternal, or at least would remain intact until cosmic rays tore them apart.

This example illustrates that many simple systems of particles are unstable, that is, have limited lifetimes as they undergo spontaneous phase transition to more complex structures of lower energy. Since "nothing" is as simple as it gets, we cannot expect it to be very stable. It would likely undergo a spontaneous phase transition to something more complicated, like a universe containing matter. The transition of nothing-to-something is a natural one, not requiring any agent. As Nobel laureate physicist Frank Wilczek has put it, "The answer to the ancient question 'Why is there something rather than nothing?' would then be that 'nothing' is unstable."'

-- God: The Failed Hypothesis, Victor J Stenger, p 133.