I have some questions in regard to this paper. If I am not mistaken it is akin to Alexander Vilenkin's proposed cosmological model that has the Universe begin to exist from a quantum nucleation event.
What is a "small true vacuum bubble" and "metastable false vacuum"? I am having a hard time finding out and the closest I've came is that they are sectors of space. Does this mean they exist in spacetime or they require spacetime to exist?
What is created exactly in this paper? Is spacetime created? That is to say, the paper stars from a system of no space and no time and ends up with a system that has spacetime? The paper states that "once a small true vacuum bubble is created by quantum fluctuations of the metastable false vacuum" but if the false vacuum is a sector of space that means space (and time?) already exists in this paper.
What is meant by "spontaneous"? Are the quantum fluctuations really not caused ? I have heard someone say that either wave-function collapse (in collapse theories) or some hidden variable (in non-collapse theories) produces these fluctuations. The only thing there is debate about is whether the causation is deterministic or not.