A boiling cauldron with the occasional bubble of steam popping: that's what the early universe resembled. All of space was filled with a field in a false vacuum state, like water superheated above its boiling point. It would take just a tiny black hole to create a bubble of true vacuum: a region with new physics, capable of growing and engulfing everything around it.
Previously, it was thought that such bubbles, accelerated by the black hole's heat, would expand without any brakes, and trigger a chain reaction of vacuum decay. But the authors of the study, using two theoretical models (one with a simple field, the other with a periodic one), showed that the bubble loses energy to radiation. This is like a car whose brakes have failed, but a headwind still slows it down. As a result, the speed drops, and catastrophic growth does not occur.
So tiny black holes, capable of boiling the vacuum, turn out to be safe: radiation braking quenches their destructive potential. The universe will not explode because of a random bubble — physics has provided a self-regulating mechanism. Our world remains stable, like that same cauldron in which bubbles pop without destroying it.
If the false vacuum were to decay, fundamental constants would change, and atoms would cease to exist in their familiar form — the universe would become unrecognizable in a fraction of a second.
In Isaac Asimov's novel "The End of Eternity," reality changes instantaneously — roughly what vacuum decay triggered by a quantum fluctuation would look like.