I'd say this sounds like a science fiction story, but it's already been several science fiction stories. Star Trek has already had one episode (DS9: "Playing God") and at least two novels (The Wounded Sky and The Three-Minute Universe) about proto-universes threatening to expand into and eradicate our universe. And I'm sure I've heard of other SF works about the idea too.
Wasn't the mostly execrable film Supernova
(2000) based on a similar premise, where the state change was triggered by an alien artifact and a supernova?
Anyway, that the vacuum isn't in its lowest possible energy state has been mooted since at least the 70s.