This is rephrased from a previous question and expanding on it. Considering the model of an "inflating" universe which extends infinitely in past (and possibly future) time, constantly creating new space within itself: within that inflating universe, at any point with some low probability per unit of time, a phase transition (like water freezing to ice) can start to happen, fundamentally changing the nature of space and time at one point. That effect propagates out (again like supercooled water freezing) creating a growing bubble of this changed space-time, which in an abuse of language, we call "a bubble universe".
Assuming the rate of expansion during inflation is known (rate of expansion of 10^26 every 10^-32 second to achieve a flat universe), the size of our visible universe is known (17Gly), is it possible to calculate the unit probability per unit of time a phase transition occurs during inflation that would be necessary for another universe to collide with ours with likelihood 95%. If we hypothesize that the inflation field is a scalar field of known value consistent with quantum field theory, would this probability of transition be consistent with quantum fluctuation in that field?