The basic idea is that the resting state of the universe is state which has the lowest amount of energy. We see this all the time, this is why crystal form — that arrangement of the mineral requires the least amount of energy. But, sometimes there’s a lower energy resting state available, but it requires a kick to get it over an energy hump before it can reconfigure to that lower energy state.
So the theory goes… what if vacuum isn’t the lowest energy state of our universe? What this means is that if we could provide that kick to get it over the bump and create a blob of space that’s lower energy than vacuum… the entire universe would essentially re-crystallize. Virtually instantly. You wouldn’t see it coming, and the laws of physics would change.
This is one theory on how the big bang could have happened.